eia for the proposed additional exploratory drilling in

EIA for the Proposed Additional Exploratory Drilling in NELP-I Block

KG-DW N-98/2, KG Offshore, Andhra Prade sh



Environmental Impact Assessment Report for

Development drilling of 45 wells at Block KG-DWN-

98/2,KG offshore, Tehsil Allavaram, District East

Godavari, Andhra Pradesh by MIs ONGC Ltd

2015

Project Leader &QCI Accredited EIA Coordinator

Dr. J.S.Sharma

General Manager(Chem)

Corporate HSE, Delhi

Project Team

B.Phaneendra Babu Dr Sajid Jamal Debashis Chakravorty Deputy General Manager (Chem) Deputy General Manager Deputy General M a n a g e r

HSE, KG Basin Corporate HSE, Delhi MBA Basin, Kolkata

S.K.Lijhara J V H Prasad

Chief Chemist, Corporate HSE, Delhi I/c HSE, EOA, Kakinada

Other Associated Members in the project

Mrs Vartika Roy, Sh. Ashish Bhuwan , Sh Setu Goel

2015 Corporate Health Safety and Environment,

Oil and Natural Gas Corporation Ltd.

(A Govt. of India Enterprise),

8th

Floor, Scope Minar, South Tower, Laxmi Nagar, Delhi-110092



Team from Project Proponent

EIA Sector Number as per NABET 2

Name of Sector

Offshore & On land oil & gas exploration, development &

production

EIA Coordinator

Name Dr. J.S.Sharma

Signature & Date

Period of Involvement October, 2014 onwards

Contact Information ONGC, CHSE, SCOPE Minar, 8th Floor, Laxmi Nagar, New Delhi. Mobile:9868282230

Functional Area Experts

Sl.No. Name Functional Area

1. Dr. J.S.Sharma i. Air Pollution Control ii. Water Pollution iii. Solid and Hazardous Waste

2. Dr. ArchanaYadav Ecology and biodiversity

3. Vineeta Kumari Sattawan Ecology and biodiversity as Associate

4. Ram Raj Dwivedi Soil Conservation

5. S.K. Lijhara Soil Conservation

6. Devendra Kumar Trivedi Noise and Vibration

7. Sushanta Kumar Mohapatra Socio-Economy

8. Nilay Meshram i. Solid and Hazardous Waste ii. Land Use

9. B.C.Kapale Land Use

10. Vineeta Mehata Pandit Land Use

11. Hemendra Jagdish Godbole i. Water Pollution Control ii. Solid and Hazardous Waste

12. Ravi Mishra i. Hydrology and Ground Water ii. Geology

13. Amlan Chakraborty Risks and Hazard



FOREWORD

The operational area in KG Basin Rajahmundry covers an area

of 28000 sq. km. onland and 1,45,000 sq. km. of offshore,

including deep waters. This is a unique basin in the sense that

hydrocarbons have been discovered in the geologically oldest

(250 Million years) to the youngest (5 million years) sediments

and from both onland and offshore parts of the basin. Till date

more than 600 onland wells and 200 offshore wells have been

drilled overcoming the challenges of high pressure, high

temperature and other drilling problems.

The " Environmental Impact Assessment Report for Development

drilling of 45 wells at Block KG-DWN-98/2,KG offshore, Tehsil

Allavaram, District East Godavari, Andhra Pradesh by MIs

ONGC Ltd" has been prepared by the team of Dr. JS Sharma,

General Manager(Chemistry), Corporate Health Safety &

Environment (CHSE), ONGC, New Delhi & QCI approved EIA

Coordinator and Functional Area Expert, & his team based on

various field studies and data collected from various

Government agencies.

ONGC is committed to operate responsibly by implementing

environmentally sound technologies and practical solutions

for energy security of India in a sustainable way. The point

wise compliance o f the TOR has been given in the report.

This report is being submitted for grant of Environmental

Clearance.

M C DAS ED Chief HSE, ONGC



TABLE OF CONTENTS

EXECUTIVE SUMM ARY i-vii

1.0 PROJECT DESCRIPTION AND BENEFITS 1.1. Introduction 1 1.2. Purpose and Basis of the Environmental Impact

Assessment 4

1.3 Geological setting 5 1.4 Legal and other requirem ents 6 1.5 Project Benefits 8 2. DRILLING TECHNOLOGY SUBSEA C OMPLET ION AND PROCESS

DESCRIPTION

2.1. Drilling Process 9 2.2. General Requirement of Drilling 11 2.3 Deep W ater Drilling Technology 20 2.4 Deep W ater W ell Abandonment 25 2.5 Subsea Equipment, Pipelines and Architecture

2.6 Offshore Processing Facilities

3 BASELINE ENVIRONMENTAL STATUS 3.1 Introduction 28 3.2. Climate 29 3.3 Physical Environment 30 3.4 Marine water quality 37 3.5 Biological characteristics 46 4. IDENTIFICATION, PREDICTION AND EVALUATION

OF ENVIRONMENTAL IMPACTS

4.1 Identification and Assessment of Impact 62 4.2 Impact prediction 63 4.3 Impact Evaluation 68 4.4 Impact Significance 71

4.5 Impact Mitigation Measures 73 4.6 Response of Marine Ecosystems to oil spills 78 4.7 Summary of Environmental Impacts 80 5.0 ADDITIONAL STUDIES (RISKS AND HAZARDS) 5.1 Identification of Risks Hazardous in Exploratory Drilling Operations 84 5.2 Major Hazards 89 5.3 Control Measures for Major Hazards 93 5.4 Fire Fighting Facility 106 6.0 ENVIRONMENT MANAGEMENT PLAN 6.1 Physical Presence Movement of Vessels 122 6.2 Emissions and Discharges from Drilling Operations 123 6.3 Oil Spill Contingency Plan 127

6.4 Occupational Health 131 6.5 H2S Protection in Drilling Operations 134 6.6 Summary of Environment Management Plan 138 7.0 ENVIRONMENTAL MONITORING PLAN 140



List of Tables

Table-1.1 Project details Table-1.2 Block details Table-1.3 Coordinates of the Proposed Locations Table-1.4 Applicable acts & guidelines Table-2.1 Approximate quantity of drill cuttings Table-2.2 Typical chemical requirement for drilling the deep water well Table-2.3 Composition of synthetic oil base mud Table-3.1 Resources for Oceanographic and Meteorological

data measurement techniques Table-3.2 Bathymetry of the block KG-DW N-98/2

Table-3.3 Significant W ave Height (SW H) in meters of the block (averaged over each area and month)

Table-3.4 Current speed (cm/s) and direction (deg.) at the block. Table-3.5 Wind speed (m/s) and direction (deg.) at the block.

Table-3.6 Area Averaged Salinity at standard depths at Block Table-3.7 Area averaged temperature at standard depths at Block Table-3.8 W ater Quality Data

Table-3.9 Average concentrations of dissolved phosphorus and

nitrogen compounds Table-3.10 Concentration of Chlorophyll (µg/L) from 2002 to 2011

Table-3.11 Seasonal differences in productivity and chl-a. Table-3.12 Observed Values of Chlorophyl-a Table-3.13(a,b) Observed values of Phyto-plankton

Table-3.14(a,b) Observed values of Zooplankton

Table-3.15 Observed values of Benthos in S1-S5

Table-3.16 Marine Fish Species in KG Basin Coastal Stretch

Table-4.1 Identification of Potential Impacts: Activities –Impacts/Risks

Interaction Table-4.2 Emission Characteristics

Table-4.3 Impact Significance Criteria Table-4.4

Potential Environmental Impacts of Proposed Project activity (W ithout Mitigation Measures)

Table-4.5 Potential Environmental Impacts of Proposed Project activity

(W ith Mitigation Measures) Table-4.6 Summary of Environmental Impacts due to exploratory

drilling and environment management plan Table-5.1 Major hazards and risks of Oil/Gas well drilling Table-5.2 Criteria for the Risk Ranking Table-5.3 Risk Categories and Significance of Criteria Table-5.4 Location of the firefighting gadgets at drilling rig



Table-5.5 Identification of various hazards, its consequences and

prevention and mitigations measures of exploratory drilling Table-6.1 Occupational Health hazards and mitigating measures Table-6.2 Periodicity of PME Table-7.1 Environmental Monitoring

List of Figures

Fig-1.1 Oil & Gas fields of KG Basin Fig-1.2 Map showing the proposed drilling locations and distance of the

blocks from the coast Fig- 2.1 Typical offshore Drill Ship Fig-2.2 Mud Circulation system

Fig-3.1 Significant wave height in the block Fig:3.2 Current speed and direction at the block

Fig-3.3 Wind rose diagram showing wind directions in the block KG-DW N-

98/2.

Fig:3.4 Sampling Locations of the block KG-DWN-98/2

Fig-3.5 Surface distribution of salinity

Fig-3.6 Sea surface temperature

Fig-3.7 Sea water collection at different sampling points

Fig-5.1 Risk Ranking Matrix

Fig-5.2 Sub Surface Oil S pill Plume

Fig-5.3 Oil / Gas W ell Blow-out Communication Flow Chart

LIST OF ANNEXURES

I Blowout Control Equipment and Case study of Deep water Horizon

Rig II Oil Spill Contingency Plan III TORs issued by MoEF vide EAC Agenda No.10.2.33 IV Form-1 NELP- I Offshore block KG-DW N-98/2 V Copy of the Existing EC VI Six monthly Compliance report for the existing EC VII Google map showing the nearest drilling locations of the block from

the coast VIII Emission calculations

EIA for Development Drilling of 45 wells at Block KG-DWN-98/2, KG Offshore in NELP-I Block

KG-DWN-98/2, KG Offshore, Andhra Pradesh

1

TOR COMPLIANCE

TO R No.F.No. J-11011/316/2014-IA II (I) Dated 6th

January, 2015 for “Development

Drilling of 45 wells at Block KG-DWN-98/2,KG offshore”

Sl.No. TOR point Compli ance 1. Details of sensitive areas such as coral

reef, marine water park, sanctuary and any other eco-sensitive area

There are no coral reefs, marine water park, sanctuary and eco sensitive areas within 10 km radius of drilling

locations (Annex-vii) 2. Project Description and Project Benefits

3. Distance from coast line 22 – 45 Kms 4. Climatology and meteorology including

wind speed, wave and currents, rainfall etc.

5. Base line status for surface water

within 1 km for drilling and coring

site, particularly in respect of oil

content

6. Noise abatement measures and

measures to minimize disturbance due

to light and visual intrusions in case

coastally located

7. Procedure for handling oily water

discharges from deck washing, drainage

systems, bilges etc.

8. Procedure for preventing spills and spill contingency plans

9. Procedure for treatment and disposal of

produced water

10. Procedure for sewage treatment and

disposal and also for kitchen waste

disposal

11. Procedure for handling solid waste and

any waste segregation at source for

organic, inorganic and industrial waste

12. Storage of chemicals on site 13.

Safety issues, Risk assessment and mitigation measures including whether any independent reviews of well deSign, construction and proper cementing and casing practices have been followed

14. Handling of spent oils and lubes

15. Handling of oil from well test operations

16. H2S emissions control plans

17. Details of all environment and safety related documentation within the company in the form of guidelines, manuals, monitoring programmes including Occupational Health Surveillance Programme etc.



2

18. Restoration plans and measures to be

taken for decommissioning of the rig

19. A note on identification and

implementation of Carbon Credit project if

any should be included

20. CRZ clearance, if any, may be obtained wherever applicable for offshore to onshore

activities

21. A tabular chart with index for point-wise

compliance of above TORs



3

EXECUTIVE SUMMARY

This EIA report is prepared in line with Ministry of Environment and Forests

(MoEF) approved Terms of Reference (TOR) vide F.No. J-11011/316/2014-IA II (I)

Dated 6th January, 2015 for “Development Drilling of 45 wells at Block KG-

DWN-98/2, KG offshore” during their meeting of 26th Reconstituted Expert

Appraisal Committee (Industry) held during 29th - 30th October, 2014 against agenda

point 26.4.10, for preparation of EIA/EMP report. The NELP-I offshore block KG-DW

N-98/2 is located off the coast of Godavari Delta in the east coast of India.

The present report is being submitted for Environment Clearance to the

development drilling of 45 wells, Floating, Production, Storage and Offloading

(FPSO), Offshore Platform, Subsea Equipment and Pipelines in NELP-I block KG-

DWN-98/2 in the KG Basin, Andhra Pradesh. The project details are as follows:

The purpose of this study is to assess the environmental impacts arising due to

development drilling of proposed 45 wells, Floating, Production, Storage and

Offloading (FPSO), Offshore Platform, Subsea Equipment and Pipelines in this

block. ONGC has instituted following studies for baseline as per prescribed TOR.

I. Collection for surface water for one season leaving the monsoon

season within 1km of each exploratory well, particularly in respect of oil content.

II. Meteorological and climatological data has been finalized based on primary

& secondary data from the Indian National Centre for Ocean Information

Services (INCOIS). (ONGC has institutionalized relationship with INCOIS)

III. There are no sensitive areas located near the block.

In addition to above, TOR’s related to procedures on Waste management, Oil

Spill and Blow Out prevention etc. have also been prescribed.



4

1.0 Project Description

Offshore part of the Krishna Godavari Basin categorized as shallow and deep

waters, covers the area of Srikakulam coast in the north to off Nellore in the

south and is considered as highly prospective for Hydrocarbon exploration.

Exploration efforts carried out so far in this block has led to discovery of

hydrocarbons in the entire block and established Northern Discovery Area

(NDA) with significant discoveries like Annapurna (R-1), Kanakadurga (G2P1),

Padmavati (M1) etc. and Southern Discovery Area (SDA) with UD-1. Present

proposal is for deve lopment drilling of 45 wells for r e a l i s i n g t h e

re se r ve s of the block. The water depth in this area of the block ranges from

320 m to 3100m. However, there are no eco-sensitive areas or forest or wild life

sanctuaries within the 10 km study area.

1.1 Project at a Glance



5

1.2 Existing facility & Development Plan

There is an existing terminal at Odalarevu, and coordinates for the existing G-1 10”

export flow line shore crossing.

Cluster-1 Development Plan: The produced Gas from this cluster is proposed to be

taken to a Fixed Platform (located at 16o 31’27.1”N 82o 22’39.74”E +/- 3 kms) in

shallow water depths, through 18” – 16.1 Kms Dual Pipeline and treated as per the

process plan (as detailed in following text), compressed and subsequently evacuated

to Odalarevu onshore terminal through 20” – 35.5 Kms Pipeline for sales to GAIL

(Gas Authority of India Limited) custody transfer point.

Cluster-2 Development Plan

The produced Oil from Cluster-2 is proposed to be taken on to an FPSO (Floating

Production Storage and Offloading) anchored/moored (Located at 16 o 20’ 46’’ N, 82

o 18’ 55’’E +/- 3 Km), through 18” – 21.5 Kms Dual Pipeline. The Oil with associated

Gas is treated for separation of Oil, Gas and Water on FPSO as detailed in Process

plan given below and the stabilized crude oil is transported through sea tankers

and dehydrated Gas is evacuated on to Fixed platform, through 18” – 21.4 Kms

Dual Pipeline with an option of evacuating from FPSO to Odalarevu Onshore

Terminal through 22” – 34.3 Kms Pipeline for sales to GAIL custody Transfer point.

Process Description:

Well Fluid will be transported to the GAIL custody transfer meter point for sales

through subsea pipelines (20” pipeline from Fixed Platform and 22” Pipe line from

FPSO) up to landfall point and from landfall to MEG (Methyl Ethylene Glycol)

recovery plant located in the existing Vashishta & S1 Plant at Odalarevu Onshore

plant.

2.0 Drilling Technology

As this proposed block is located in deep and ultra-deep water, drill ship with

Dynamic Positioning (DP) and specialized deep water technology tools will be used

for drilling. Presence of extreme temperature and pressures at these depths,

special drilling muds are used to prevent formation of hydrates at the sea bed level



6

and to combat dual gradients. Glycol based drilling mud to be used for the

prevention of hydrate formation in these wells. Initially the well was drilled with

water based mud system and Synthetic Oil Based Mud (SOBM) with low toxicity

LC>50,000 (mysid toxicity) is also used in sections having specific borehole

problems. Drilling mud circulated in the system is continuously treated at the

surface after removal of drilled solids with sophisticated solids removal

equipment and re-circulated back in to the system. SOBM is completely

recovered and transported to another site and is not disposed into sea. Thoroughly

washed cuttings are discharged into the sea.

3.0 Baseline Environment

In this report, the baseline environment description includes collection of primary

and secondary data through field investigations, environmental monitoring,

scientific literature, reports and maps etc. The collected data/information has been

analysed for identification of impacts and arrives at mitigation measures for

minimizing the any adverse environmental impacts due to the proposed

exploratory drilling activities.

W ith this view, baseline physico-chemical parameters of sea water such as

pH, Salinity, dissolved oxygen, inorganic nutrients (nitrates and

phosphates), trace elements, petroleum hydrocarbons etc. are studied. The

occurrence of marine species - both flora and fauna has largely been controlled by

the physico-chemical properties of sea water. In view of wide variations in

biological production in a marine ecosystem, the biological parameters considered

for the present evaluation are phytoplankton (pigments, population and dominant

genera), zooplankton (biomass, population and faunal groups), macro benthos

(biomass, population and faunal groups) and status of fishery.

Climate Over this block which is located at the distance of 28-250 km from the coast, the

northeast monsoon is from November through April as continental high

pressure system in north of the bay produces northeast winds characteristic



7

of the winter season. During the northern summer (June–September) the rain-

bearing southwest monsoon prevails, as intense heat produces a low-pressure

system over the continent and a subsequent air flow from the ocean. North

east monsoon and cyclonic storms over the Bay of Bengal along South East

coast of Peninsular India bring heavy rainfall associated with major physical

changes.

3.1 Physical Environment

ONGC has shared information& knowledge about Oceanographic and

Meteorological data for the block area with premier national institute INCOIS,

Hyderabad. The data for Bathymetry, Significant Wave Height, Surface Ocean

Currents, W ind speeds, Salinity and Temperature is real time data monitored

by satellites.The most important processes that control the dynamics of the sea

which are directly linked with the transport of the pollutants are tides, waves,

winds and currents. The average significant wave height ranges from 0.4 m to

1.5 m in the block area. The wind speeds has a maximum value of 5.4 m/s

during south west monsoon. The currents are oriented in the northerly direction

most of the time (avg. speed). The currents are intense during the southwest

monsoon and post monsoon months has a maximum speed of 47.7 cm/s. The

currents in the Bay of Bengal are intense close to the coast mainly because of

the eddies – “warm” core and “cold” core as well as the alongshore intense

gradients in the thermo-haline characteristics because of the substantial river

discharge of major river systems.

3.2 Marine Water Quality

The area of the block KG-DWN-98/2 is largely oceanic and therefore not

expected to undergo significant changes in water quality, temporarily as well

as spatially. Parameters like pH, Salinity and dissolved oxygen are in the range

of typical Bay values due to farther-ness from the coast and subject to less coastal

influences. The surface salinity in the open part of the Bay oscillates from 32 ppt

to 34 ppt (i.e parts per thousand). The observed values of the pH, salinity and

dissolved oxygen are in the range of 7.6-7.9, 32.9 to 33.9 ppt. and 6.0 to 6.3 mg/l



8

respectively. There is a considerable variation in the observed values of

NO3-2 (9.96-12.02 µmol/l) and PO4

-3 (2.34 – 2.98 µmol/l) nutrient levels with

that of reported for the near-shore coastal waters. Most of the heavy metals

analysed are below their detection limits. The concentrations of dissolved and

dispersed Petroleum hydrocarbons (PHC) in the study area are low and

uniformly distributed (2.6 to 3.9 µg/l).

3.3 Biological Environment The occurrence of marine species - both flora and fauna has largely been

controlled by the physico-chemical properties of sea water. In view of wide

variations in biological production in a marine ecosystem, the biological

parameters considered for the present evaluation are phytoplankton (pigments,

population and dominant genera), zooplankton (biomass, population and faunal

groups), macro benthos (biomass, population and faunal groups) and also

status of fishery. The phyto pigment concentration, diversity index and density

in the study area shows marked variation in the block. Sampling locations S1-S5

which are relatively near to the coast and shows high pigment concentration

(6.57-7.88 µgl-1). Whereas, at points S6-S8, which are far from the coast and has

low pigment concentration (0.31-0.89). The dominant fish species in the

area are Elasmobrabches, Clupedis, Peachis, Flast Fishes, Drift Fishes,

Carangids, Seerfishes Oceanic Tunas, Neritic Tunas, Mackerals Pomfrets ,

Deepsea Fishes, Lobosters, Cephalopods and other marine mammals- Shrimp

(Littoral), Other Crustaceans and Shrimp (Deep sea).

4.0 Identification, Prediction and Evaluation of I m pa c ts Presence of the rig in the deep sea environment has an overall positive impact

as it can be used as a fish aggregating device. Impacts of air emissions and other

routine activities are expected to be below prescribed levels. Available

information in this area does not indicate the presence of any protected habitat or

endangered species. Impacts on marine water quality has been envisaged to be

insignificant as the wastewater and drill cuttings from the drilling & other activities



9

shall be treated to meet requirements of stipulated standards prior to its disposal.

Based on the baseline data of this area and other studies carried out

for aforementioned parameters, it can be concluded that under the normal operating

conditions there will not be any significant marine environmental impact due

to proposed development drilling

5.0 Risk Assessment & Mitigations Measures Major risks associated with the deep water drilling are blowout, oil spill,

hydrate formation due to low temperature/high pressure, loss of hydrostatic head

due to riser disconnect and passing vessel hitting the rig. To prevent hydrate

formation glycol based muds are used for deep water drilling. For containment of oil

spill, the contingency plan has been developed. There is a full-fledged Crisis

Management Team (CMT) for blow out and dedicated contingency plan for H2S

em iss ion .

6.0 Environmental Management Plan Offshore drilling operations may interact with marine environment and may result in

physical, chemical and biological changes. Impacts of these changes, if any are

to be mitigated by adopting standards as suggested in TOR, CPCB Standards, as

per provisions of Merchant Sipping Act and MARPOL. The offshore drilling

operation generates two major and three minor waste streams. The major waste

streams are drilling fluids and drill cuttings. The minor waste streams are of deck

drainage, sanitary waste and domestic waste etc. Water based muds will be

recycled to maximum possible extent and non-usable portion will be discharged

intermittently (50 bbl/hr) in sea with proper dilution. SOBM will be completely

recycled and reused. Sanitary waste is treated in the sewage treatment plants

of the drilling rig and disposed to sea after maintaining the required disposal

parameters. W aste water generated during drilling operations will be 30-35

m 3/day. Kitchen waste is separated into bio-degradable and non-biodegradable

components. Non- biodegradable waste is packed, labelled and sent to land

base for further safe disposal.



10

CHAPTER-1

Project Description and Benefits

1.0 Introduction

Krishna Godavari Basin, offshore categorized as shallow and deep waters, covers the area

of Sriakulam coast in the north to off Nellore in the south and is considered highly

prospective for Hydrocarbon exploration point of view. It is a unique basin as hydrocarbon

occurrences are in the entire geological sedimentary sequence. Exploration effort carried out

in the block has enabled converting the area into discovery area by successful discovery of

hydrocarbons in the entire block.

Present proposal is being submitted for obtaining Environmental Clearance (EC):

To drill 45 development wells

Floating Production Storage and Offloading (FPSO)

Offshore Fixed Platform

Subsea Production Systems (SPS) and Subsea Pipelines connecting to Landfall

point to existing onshore terminal for custody transfer to GAIL.

This EIA report is prepared in line with Ministry of Environment and Forests (MoEF)

approved Terms of Reference (TOR) vide F.No. J-11011/316/2014-IA II (I) Dated 6th

January, 2015 for “Development Drilling of 45 wells at Block KG-DWN-98/2, KG

offshore” during their meeting of 26th Reconstituted Expert Appraisal Committee (Industry)

held during 29th - 30th October, 2014 against agenda point 26.4.10, for preparation of

EIA/EMP report. The NELP-I offshore block KG-DW N-98/2 located off the coast of

Godavari Delta in the east coast of India.



11

Earlier Environmental Clearance Status of the Block

As per the Environmental Clearances, initially the permission was granted for

exploratory drilling of twenty wells (nine + eleven) in two trenches to M/s Cairn

Energy (India) Limited (CEIL) vide EC No.J-11011/18/2004-IA II (I) dated 8th

December’2004.

CEIL has initially drilled six exploratory wells. After acquiring the operatorship,

ONGC has drilled the remaining fourteen exploratory wells. Subsequently, ONGC

was granted Environmental Clearances vide EC Nos.J-11011/474/2010-IA II (I)

dated11th May’2011 and J-11011/70/2011-IA II (I) dated 4thSeptember’ 2012 for

drilling three and seven exploratory wells respectively.

Recently ONGC has obtained EC for drilling of 10 exploratory/appraisal wells

through vide EC No. J-11011/189/2013-IA II (I) dated 24th January’ 2014 , during the

13th re-constituted EAC (MoEF) agenda meeting held on 19th November’2013 for

the total 39 wells.



12

1.1 Project Description

The KG-DWN-98/2 Block

covers area of 7294.6 sq.

km. ONGC intends to

develop the NELP-I Block

KG-DWN-98/2 in deep

waters off east coast of

India. The KG-DWN-98/2

block is located within 25-

80 km from the nearest

coastline. The discovery

area of the block has been

categorized as Northern

Discovery Area (NDA-

3800.6 Sq km) and

Southern Discovery

Area (SDA-3494 Sq km)

Fig: 1. The water depth in

this block varies between

300 metres to 3200

metres. A location map

identifying the KG-DWN-

98/2 development area is

is given in Fig:2.

Fig:1 Location map of the block



13

1.2 Northern Discovery Area (NDA)

NDA is divided into two primary production

areas:

Cluster 1

o Predominantly gas, located in

the north of NDA, includes fields D, E

and G4.

o Within Cluster 1 lies the G4 field

(Nominated Godavari PML Block)

Cluster 2

o Mix of oil and gas, located in the

south of NDA, includes the following

fields :

o Oil fields (Cluster 2A) – A2, P1,

M3, M1 and G-2-2.

o Gas fields (Cluster 2B) – R1,

U3, U1, and A1.

Fig: 2 Location map of Northern & Southern discovery area

1.3 Southern Discovery Area (SDA)

SDA has Ultra Deep (UD) reservoirs, which demand state-of-Art technologies in

completion and evacuation methodologies/designs and hence, realisation of SDA

hydrocarbon reserves is proposed to be taken up in future.



14

Table: 1.1

PROJECT AT A GLANCE



15

Table 1.2 Block Coordinates

1.4.2 Tentative coordinates of proposed locations are given in Table:1.3

Project Region: Offshore area in KG Basin, AP

Block Title: NELP-I Block KG-DWN-98/2

Block Area (Sq. Km.): 7294.6

Block Coordinates:

POOINT LATITUDE (N) LONGITUDE (E)

J 15 30 00 82 07 00

I 16 10 00 82 07 00

H 16 10 00 82 15 00

G 16 19 50 82 15 13

F1 16 26 03 82 20 20

F 16 26 03 82 24 59

E 16 28 42 82 25 00

D 16 31 42 82 29 58

L 15 30 00 82 30 00

M 15 30 00 82 21 00

N 15 12 00 82 21 00

O 15 12 00 82 26 30

P 14 54 00 82 26 30

Q 14 43 00 82 10 00

R 14 43 00 82 00 00

A 15 29 00 82 00 00



16

Table: 1.3 Tentative Coordinates of the proposed locations

Coordinates of locations, KG-DWN-98/2 and G-4

Gas Field Well Latitude Longitude

DWN-A A-1-A 16° 20' 7.517" N 82° 21' 38.576" E

DWN-D D-1-A 16° 29' 55.227" N 82° 29' 14.848" E

D-1-B 16° 30' 34.011" N 82° 28' 58.613" E

DWN-E DWN-E-1 16° 28' 13.214" N 82° 28' 38.136" E

DWN-R-1 R-1-A 16° 16' 3.938'N 82° 23' 9.944'E

R-1-B 16° 15' 51.321" N 82° 23' 28.623' E

R-1-C 16 ° 17' 44.450" N 82° 22' 44.112" E

DWN-U-1 U-1-A 16° 7' 51.015" N 82° 18' 57.143" E

U-1-B 16° 8' 5.105" N 82° 18' 29.714" E

DWN-U-3 DWN-U-3 16° 8' 14.190" N 82° 16' 59.708" E

U-3-A 16° 7' 42.329" N 82° 15' 52.336" E

G-4 G-4-A 16° 31' 53.116" N 82° 29' 31.204" E

G-4-B 16° 32' 10.589" N 82° 30' 17.666" E

G-4-C 16° 32' 51.717" N 82° 30' 35.975" E

G-4-D 16° 33' 18.330" N 82° 28' 28.822" E

Oil Field Well Latitude Longitude

DWN-A-2 DWN-A-2 16° 19' 37.557" N 82° 21' 0.997" E

A-2-A 16° 19' 20.798" N 82° 21' 3.590" E

A-2-B 16° 18' 31.924" N 82° 21' 46.561" E

A-2-C 16° 18' 43.880" N 82° 22' 8.171" E

A-2-D 16° 19' 18.594" N 82° 20' 29.044" E

A-2-E 16° 20' 27.104" N 82° 19' 34.920" E

A2-WI-A 16° 20' 0.204" N 82° 21' 2.612" E

A2-WI-B 16° 19' 15.226" N 82° 21' 42.344" E

A2-WI-C 16° 19' 27.764" N 82° 19' 54.801" E



17

A2-WI-D 16° 19' 47.021" N 82° 20' 1.070" E

Kanakadurga P-1-A 16° 18' 15.829" N 82° 17' 46.643" E

P-1-B 16° 18' 15.850" N 82° 17' 8.301" E

P-1-C 16° 18' 50.411" N 82° 18' 39.429" E

P-1-D 16° 19' 9.378" N 82° 16' 10.360" E

DWN-P-1 16° 18' 31.422" N 82° 17' 23.280" E

P1-WI-A 16° 17' 53.483" N 82° 18' 2.493" E

P1-WI-B 16° 19' 8.427" N 82° 16' 53.348" E

P1-WI-C 16° 19' 28.282" N 82° 15' 47.956" E

DWN-M-1 M-1 16° 23' 4.481" N 82° 21' 39.312" E

M-1-WI-A 16° 23' 34.105" N 82° 21' 55.371" E

DWN-M-3 M-3-A 16° 25' 30.982" N 82° 23' 48.095" E

M-3-B 16° 25' 6.492" N 82° 23' 43.695" E

M3-WI-A 16° 25' 11.314" N 82° 24' 9.223" E

M3-WI-B 16° 25' 49.361" N 82° 23' 54.496" E

G-2-2 G-2-2-A 16° 18' 58.778" N 82° 17' 52.474"E

G-2-2-WI-A 16° 18' 40.367" N 82° 18' 25.834"E

Locations are about 22 to 45 km from reference point Odalarevu and are oriented towards NE & SE.

1.4 Cluster-1 Development Plan

The produced Gas from this cluster is proposed to be taken to a Fixed Platform (located at

16o 31’27.1”N 82o 22’39.74”E +/- 3 kms) in shallow water depths, through 18” – 16.1 Kms

Dual Pipeline and treated as per the process plan (as detailed in following text), compressed

and subsequently evacuated to Odalarevu onshore terminal through 20” – 35.5 Kms

Pipeline for sales to GAIL (Gas Authority of India Limited) custody transfer point.



18

Fig: 4 Pipeline Layout Map for cluster 1 development

1.4.1 Cluster-2 Development Plan

The produced Oil from Cluster-2 is proposed to be taken on to an FPSO (Floating

Production Storage and Offloading) anchored/moored (Located at 16 o 20’ 46’’ N, 82 o 18’

55’’E +/- 3 Km), through 18” – 21.5 Kms Dual Pipeline. The Oil with associated Gas is

treated for separation of Oil, Gas and Water on FPSO as detailed in Process plan given

below and the stabilized crude oil is transported through sea tankers and dehydrated

Gas is evacuated on to Fixed platform, through 18” – 21.4 Kms Dual Pipeline with an

option of evacuating from FPSO to Odalarevu Onshore Terminal through 22” – 34.3

Kms Pipeline for sales to GAIL custody Transfer point.



19

Fig: 5 Pipeline Layout Map for cluster 2 development



20

Integrated development scheme of Cluster-1 and Cluster-2 is illustrated in Fig: 6.

Fig: 6.Integrated development scheme of Cluster-1 and Cluster-2

1.5 On land Facilities at Odalarevu Onshore Terminal

There is an existing terminal at Odalarevu, for processing of hydrocarbons received from offshore

fields: G-1, Vasishta and S-I through the existing 10” & 14” export flow line crossing shore at

land fall point as shown in Fig:3. The 20” & 22” gas export flow lines from KG-DWN-98/2

fields will also be crossing the shore at same land fall point, passing in the same corridor

parallel to the existing 10” & 14” export flow line, where in the production from KG-DWN-

98/2 field will be processed at the facilities to be created in the existing on shore terminal.



21

Figure 7: Odalarevu Terminal and 10” Pipeline Shore Crossing

1.6 COASTAL REGULATION ZONE

The earlier project consisting of the onshore facility and sub-sea pipeline is located in the

Coastal Regulation Zone (CRZ) as per the CRZ Notification, 2011. The project was

appraised and recommended for CRZ clearance by the Andhra Pradesh Coastal Zone

Management Authority (APCZMA) in the meeting held on 21st September 2013. Proposal

for CRZ clearance was presented in 144th meeting held on 28-30th January’2015. CRZ

Clearance was agreed to the project vide File No: 11-2/2015 –IA-III.



22

The High Tide Line (HTL) and Low Tide Line (LTL) was demarcated for the proposed project

area by the Institute of Remote Sensing (IRS), Anna University, Chennai, which is one of the

authorized agency to do t Report for the same. The HTL-LTL map is provided in Figure 7.

The total area of proposed onshore facility is 2, 22, 577 m2 (55 acre) of which only about

2,671 m2 (1.2% of the total area) falls in the region of 200 m – 500 m from the HTL, which is

designated as CRZ III (Areas that are relatively undisturbed and those do not belong to

either CRZ-I or II, which include coastal zone in the rural areas (developed and

undeveloped) and also areas within municipal limits or in other legally designated urban

areas, which are not substantially built up).

The proposed pipeline from the proposed expansion is coming under CRZ III. As per Section

8, III (A, iii, f and B, iii) of the CRZ Notification 2011, “facilities for regasification of liquefied

natural gas” is permissible in CRZ III.

The existing pipe lines carrying hydrocarbons from G-1& Vasishta and S-I offshore fields

passing from land fall points to the existing Odalarevu onshore terminal passes through

forest land for which stage-1 clearance is being obtained vide RC. No: 6907/2012-D1, Dated

31.12.2014.

1.6 Process Description

Well Fluid will be transported to the GAIL custody transfer meter point for sales through

subsea pipelines (20” pipeline from Fixed Platform and 22” Pipe line from FPSO) up to

Terminal for proposed facilities

Existing Terminal



23

landfall point and from landfall to MEG (Methyl Ethylene Glycol) recovery plant located in the

existing Vashishta & S1 Plant at Odalarevu Onshore plant.

Brief description of the processing facilities as well as utilities at Fixed Offshore Platform

(for processing of Gas) and FPSO (for processing of Oil and Associated Gas):

1. Receiver Facilities: Production fluid will be received at fixed offshore platform

(Free Gas from Cluster-1 fields)/FPSO (Oil with associated Gas from Cluster-2 (a) &

(b) fields). The produced hydrocarbon fluids are passed through Vertical separator

for first stage of separation. The vertical separator will separate the well fluid in to HC

gas and water streams while flowing through the separator. The separated gas will

be further treated, compressed and conditioned to meet desired sales gas

specifications. Separated produced water will flow into the treatment facilities for

treatment and disposal. Vertical 2-phase separator is installed to separate full well

stream into gas and liquid phase. The production separator operates at pressure of

30 kg/cm2 (Early Life) and 15 kg/cm2 (Late Life)

Gas Compression System: Produced gas is compressed from 30 k/cm2 to 150

k/cm2 on offshore facilities before sending back to onshore via export pipelines (22”

or 20”) for metering and sale through GAIL custody transfer meter

Booster Compression System: At late field life, booster compression system is

required to boost the pressure from 15 kg/cm2 to 30 kg/cm2 for offshore facilities

Chemical Injection Skids-Wellhead: Chemical Injection skids like PPD (Pour Point

Depressant), CI (Corrosion Inhibitor) and Scale inhibitor

Flare System/Flare Stacks: Flare stacks are primarily used for burning off

flammable gas released by pressure relief valves during unplanned over-pressuring

of plant equipment. During total plant or partial plant start-ups and shutdowns, flare

stacks are also often used for the planned combustion of gases over relatively short

periods.

Instrument Air Package: To Supply IA (Instrumentation Air) to Flare and Process

consumption

2. Gas Treatment, Compression, Dehydration: Separated gas from separator will

receive further treatment in inlet scrubbers for removal of 99.9% liquid and solid

particles over 10 microns. This will ensure that small particles of liquid do not go into



24

the compressors. All compressor units will be equipped with auxiliary systems such

as inter-stage and outlet gas coolers and inlet, inter-stage and outlet liquid

separators. Compressed stream from the gas compressors shall be considered for

dehydration. The Gas dehydration package shall be designed to dehydrate the gas

down to the water level of 7 lb/mmscf. Finally, the conditioned gas will be transported

to onshore for metering and sale through GAIL custody transfer meter.

3. Produced Water Treatment: Produced water separated from the separator will be

treated in water treating package and stored in to produced water tank which will be

further pumped to the disposal wells through existing transfer lines. Since MEG

(Mono-Ethylene-Glycol) will be injected as hydrate inhibitor at upstream, produced

water treating facilities shall include necessary arrangement for MEG recovery.

Recovered MEG along with produced water shall be pumped to onshore facility for

regeneration and recycled back to the chemical injection package for injection.

4. Utilities / Off-sites & Miscellaneous Systems: Utilities as needed to be generated

within the terminal. Following utility systems are envisaged for the terminal:

a. Plant and Instrument Air System

b. Nitrogen System

c. Water System

d. Circulating Hot Oil System

e. Fuel Gas System

f. Power Generation System

g. Chemical Injection system

h. Diesel system

i. Flare and Drain System

j. Fire Water System

5. Gas Dehydration Package: TEG (Tri-Ethylene-Glycol) based vendor designed &

supplied gas dehydration package to be guaranteed for water content in outlet gas as

7 lb/MMSCF.

6. Produced Water Treating: The produced water (PW) treating package shall perform

PW degassing, HC condensate separation, filtration and MEG recovery.

7. Air & Nitrogen System: Compressed dry air will be used for instrumentation. The

system shall be designed to suppress the water dew point to -40°C at atmospheric

pressure. Instrument air receiver shall be designed for hold-up time of 30 minutes



25

minimum. Separate utility air receiver shall be provided for service air requirements.

Nitrogen will be used for inert gas blanketing and miscellaneous purging purposes.

Nitrogen generator shall be membrane type producing 98.5% (by vol.) pure nitrogen.

8. Circulating Hot Oil System: Circulating hot oil system shall be designed to suffice

heating needs at gas dehydration and TEG regeneration package. Hot oil heating will

be through waste heat recovery system at power generator exhaust.

9. Diesel: Diesel storage and transfer pumps shall be provided to cater diesel needs at

the terminal. Diesel tanks to be provided for fire water pumps and emergency DG

set.

10. Power: In-house gas based power generation to be considered for total power needs

at the terminal.

11. Flare: Flare is used to dispose of waste gases and relief gases resulting from

treatment process upsets. The process involved will dictate flare system design

requirements. For disposal of blow down gases during a plant emergency shutdown,

a dedicated flare system will normally be needed to handle the large quantity

and varied composition of the gas.

1.6.1 Oil Processing System Functionality:

Crude Stabilization System: Crude oil is stabilized in 2-stage stabilization system

Stabilization Heater: Heating the oil to achieve TVP of 10 psia @1000C

Vapour Recovery System: 3-stage Vapour Recovery Unit (VRU) is applied to compressed

the associated gas from crude stabilization from 0.5 kg/cm2 to 30 kg/cm2 before sending the

recovered gas stream into Export Gas Compression system

Gas Lift Compression System (Late Field Life): 80 MMscfd (Million Standard Cubic Feet

per Day) gas lift is compressed from 150 kg/cm2 to 260 kg/cm2

Produced Water Treatment Package: Consist of hydro-cyclone and degasser for achieving

the OIW spec of 40ppm



26

Chemical Injection Skids: Chemical Injection skids like Biocides, demulsifies, Clarifier and

Corrosion inhibitor

Product Quality & Specifications to be maintained as per PNGRB

Product Quality / Specification

Gas

Inerts (CO2 + N2): 5 mol% (max)

H2S : 5 ppmv (max)

Dewpoint : 0 deC

Oil

RVP : 10 psia

BS&W: 0.2 wt% (max) Salt

NaCl: 5 ppm (max)

Block Diagram of the Process on Fixed Platform is given Fig: 7 & Process on FPSO is given

in Fig: 8



27

Fig: 7 Block Diagram of the Process on Fixed Platform



28

Fig: 8 Block Diagram of the Process on FPSO



29

1.7 SUBSEA PIPELINES AND EQUIPMENT

1.7.1 Pipeline and Subsea Structures

The proposed project of KG-DWN-98/2 development comprises of 31 production wells and

10 water injection wells as detailed elsewhere in the document. Production fluids shall be

evacuated to the offshore processing facilities at the offshore platform and FPSO (Floating

Production, Storage and Offloading) facilities via dual 20 inch nominal bore (NB) production

pipelines manifold and the offshore processing facilities. The infield pipelines that tie-in the

wellheads to the manifolds shall be 8 inch pipelines. The Gas export pipelines to the onland

facilities for custody transfer shall be 20 inch pipelines one each from the offshore platform

and 22 inch from the FPSO.

The approximate length of the pipeline between the offshore platform and onshore custody

transfer point is 35 km and from the FPSO to the onshore custody transfer point will be 35

Km. The onshore section of pipeline between landfall and the terminal ESDVs is

approximately 4km. The network of pipelines between various subsea components and

wellheads to the offshore processing facilities is as shown in the figures. The landfall section

of pipe has higher integrity requirements and therefore higher wall thickness. Constant bore

has been maintained through the pipeline to allow pigging.

1.7.2 Subsea Structures and their Arrangement

The major subsea equipment/facilities, other than the pipeline include: Subsea tees, On tree

flow meters (multiphase), Subsea Controls (comprising of Subsea Distribution Unit (SDU’s),

Umbilical Termination Assemblies (UTA’s), HDU, Master Control System (MCS)/Electric

Power Unit (EPU) and Topside Umbilical Termination Unit (TUTU), Main and infield umbilical

and Diver less connectors

Inline tees shall be installed as part of the pipeline, at the all the well locations and shall

facilitate tie-in of the wells. Spare inline tees and slots in the various manifolds will be

provided to allow future expansion. The tie-back distance between landfall and the FPSO

location is approximately 30km. The tie-back distance from landfall point to offshore platform

approximately 30 km. There is also an approximately 4km onshore section of pipeline

between landfall and ESDVs.

All tees and PLEM shall allow for the production fluids from the associated well to be

diverted to either, or both of the dual pipelines. All infield jumper spools between PLETs,

PLEM, tees and wells shall be rigid 6 inch pipe. All connections shall be via vertical

diverless connectors.



30

Master control system (MCS), Hydraulic Power Units (HPU), Electrical Power Unit

(EPU) and Chemical Injection System shall be provided at the FPSO and offshore

platform. These components shall be connected to the subsea system via a static

umbilical, which run along with the pipelines and terminated in an Umbilical Termination

Distribution Assembly (UTDA) at Vashishta well cluster.

Infield umbilicals (each approximately 3km) shall connect the Xmas trees.

All subsea umbilical and flying lead connections will be driverless make-up.

1.7.3 Design Details of Production pipelines

All the well fluid from the Gas field shall will be produced via 20 inch and 22 inch NB

pipelines routed from offshore platform and FPSO to terminal respectively.

Pipeline Design Conditions- The pipelines shall be designed according the following

parameters:

Parameter KG - DWN - 98/2

Water Depth Max (m) 1500

Water Depth Min (m) 0

Pipeline Length (m) 28,000 to 35,000

Maximum Design Temperature

( C)

65

Minimum Design Temperature ( C) -75

Design Pressure (barg) 255

Pre-trenching; burial along with concrete weight coating for protection of pipeline

shall be done as follows:

- 2.5 metres burial for the onshore section.

- 2.5 metres burial and 50mm concrete coating up to 27 metres water depth. This

will be approximately up to two thirds of the way along the first leg of the

pipeline.

- 1.0 metre burial and 50mm concrete coating up to 79 metres water depth.



31

- 30mm concrete coating up to 200 metres water depth.

- Three layer polypropylene (3LPP) coating and surfaced laid for the remainder

of the development.

The pipelines shall be protected from external corrosion by a combination of

coatings and cathodic protection via bracelet anodes, fitted along the length of the

pipeline. A 3LPP/ 3LPE is the recommended anti-corrosion coating for the gas

production pipeline.

The corrosion inhibitor selected shall achieve a minimum of 95% inhibitor

efficiency for the basic process condition of KG-DWN-98/2 produced fluids and

compatibility with MEG injection shall be ensured.

The pipelines shall be designed to permit the use of pigs, with due consideration

to be taken of transitions in bore between the flow line, pipelines and manifold

piping. Any tees within the main production flow line system shall be piggable with

the inclusion of pigging bars and any bends shall have a minimum radius of 5D.

1.8 Pipeline Material Details

Item Material

Gas

Production

Flowline

Linepipe- Seamless carbon steel line pipe API 5L X65 with 3.0

mm corrosion allowance.

Tie-in spools Linepipe/Bends- UNS S32760 or BETTER super dulex with 1.0

mm corrosion allowance.

PLEM Piping System- Seamless carbon steel line pipe API 5L X65 with

6.0 mm corrosion allowance or corrosion resistance alloy

(duplex/super duplex stainless steel) if any uncertainties over

inhibitor efficiency in the PLEM System.

PLET Piping- Seamless carbon steel line pipe API 5L X65 with 6.0 mm

corrosion allowance or corrosion resistance alloy (CRA)

(duplex/super duplex stainless steel) if any uncertainties over

inhibitor efficiency in the PLET System.



32

Item Material

Valve The valve body system shall match the piping material: 25% Cr

Duplex/ Carbon Steel body with UNS N06625 overlay. The valves

internals from all valves shall be manufactured from CRA ad

comply with BS EN ISO 15156. Seat and ball/gate faces shall be

hard faced with tungsten carbide

Connectors The connector hubs shall match the piping material

Structural

Steel

Primary Members- BS EN 10225 grade 355 minimum or

equivalent

Secondary Steel- BS EN 10025 grade 275 minimum or

equivalent.

1.9 Resource requirement

i) Construction Material

All the structures will be prefabricated at Yards, likely to be outside India

and transported by Material barges. The structures will be piled and

productions systems shall be installed on the piled structures.

ii) Fuel

Fuel requirements will be mainly for the purpose of electricity generation during

construction and operational activities of the pipeline shall be met from the

generators on the construction barges. Approximately 4-6 months will be required

for installation of the pipeline.

iii) Water

Water requirement during construction activities shall be met through water

makers installed on the offshore processing facilities and sea vessels used for

construction and through supply vessels.

iv) Chemicals

Chemicals such as Corrosion inhibitors, scale inhibitors and degreasing agents

shall be required during pre-commissioning phase of the pipeline and shall be

stored at existing onshore Odalarevu Terminal.



33

1.10 Noise, Air Emissions, Effluents, and Solid Waste Generation

i) Noise

Noise is likely to be generated from the operation of generator sets, construction

machinery, earthing equipment etc during construction and installation of onshore

and offshore pipeline. Underwater sound is likely to be generated due to usage of

equipments (such as flowlines, subsea valves etc) during pipeline installation.

Transportation activities may also contribute to onshore and offshore noise levels.

ii) Air

Emission of air pollutants is likely to occur due to usage of construction vehicles

and equipment during construction, commissioning and operation of the

pipelines.

iii) Effluent and Solid Waste

Water generated from hydraulic testing of pipelines shall be reused for

multiple tests. In case of discharged into sea, discharge of water shall be

ensured at a suitable location to minimise adverse impacts.

Sewage- Sewage generated shall be treated in the Effluent Treatment Plant

(ETP). The treated effluent after treating to the desired levels shall be

discharged into sea.

Construction waste- Solid waste consisting of recyclable waste and non-

recyclable generated from construction activities, shall be segregated in

appropriated bins and will be disposed off to approved contractors for their

final disposal.

Solid waste including domestic waste (from kitchen, gallery, laundries etc),

combustible and recyclable waste generated shall be collected, segregated

and stored in specified containers and shall be transferred to authorized

contractors for its disposal.

Hazardous wastes such as waste lube/system oil from machinery, used oil

from D.G set (in case of operation) are likely to be generated. The waste shall

be handled as per Hazardous Wastes (Management, Handling and Trans-

boundary Movement) Rules, 2008. The waste will be carefully stored in drums

and transported to MoEF approved recyclers for its final disposal. All

precautions will be taken to avoid spillage from the storage.



34

1.10.1 Field wise Hydrocarbon Reserve Breakup:

Free Gas Volume Estimate:

Fields U1 U3 A1 R1

(Annapurna)

D1 E1 UD

(SDA)

Total

(BCM)**

Gas Production

(2018-2034) in BCM**

9.32 7.27 6.21 15.26 10.39 2.88 --

GIIP* 12.38 9.44 9.166 21 13.95 3.64 80.33 149.9

*Gas Initial In-Place **Billion Cubic Meter

Oil Volume Estimate:

Discovery/

Find

Padmavathi

(M1)

Kanakadurga

(G2P1)

G-2-2-A A-2 M-3 Total

(OIIP) Oil Production (2019-2031) in MMM3

1.79 7.08 0.78 13.5 3.65 ---N/A---

OIIP*

in MMM3

7.49 23.13 4.7 55.819 15.25 106.389

* Oil Initial In Place

1.11 Geological setting

The NELP block KG-DWN-98/2 falls in the offshore part of the Krishna-Godavari Basin (KG

Basin). Krishna-Godavari (KG) Basin, a peri-cratonic rift basin along the East Coast of India,

is located between 15 to 17.50 N and 80 to 89.50 E. It covers an area of 41,000 Km2 both

onshore and offshore and includes the deltas of Krishna and Godavari rivers (Fig 1.1). The

basin comprises of the sediments ranging in age from Lower Permian to Recent. The on

land part of the basin is under alluvial cover. However, Permo-Triassic, Late Jurassic-



35

Cretaceous and Tertiary rocks outcrop along the western margin of the basin. The basement

is of Achaean and Proterozoic rocks of the Eastern Ghats.

The basin evolution shows remarkable correlation with various tectonic episodes of opening

of East Coast of India. Four stages of tectono-stratigraphic evolution represented by four

major units such as: early rift, rift, early thermal subsidence, and late thermal subsidence.

The subsurface information obtained so far through drilling has indicated that mixed sand-

mud system may be used to interpret the depositional process in the deep water KG

offshore basin.

The area where the block KG-DWN-98/2 is located, the stratigraphy consists of slope

depositional systems and deep water depositional systems. The Pliocene section is

generally clay dominated with few deep water channel and fan deposits. Miocene to Eocene

consists of deep water clays and sand deposits in the form of basin floor fans and channels.

These form exploration targets over basement highs.

1.12 Legal and other requirements

ONGC activities will conform to all National and International legislations, regulations,

conventions, etc., relating to aspects of hydrocarbon operations in India. The project shall

abide by the Oil Industry Safety Directorate (OISD) guidelines and standards.

Recognizing the need of environmental safety, operator has established an HSE Policy

towards environmental protection. A list of applicable Acts and Rules is described in Table

1.4.

Table: 1.4 Applicable Acts and Guidelines

Issues Applicable Legislation

Hazardous

Substances &

Wastes

1) The Environment (Protection) Act, 1986 and Rules there under -

a) Hazardous Wastes (Management, Handling and Trans-boundary

Movement) Rules, 2008 and amendments thereafter;

b) Guidelines for disposal of solid wastes by Oil Drilling and Gas

Extraction industry as notified, vide notification dated GSR 546

(E) August 2005

2) The Public Liability Insurance Act, 1991 and Rules 1991

Water 3) The Environment Protection Act, 1986 - Standards for liquid

discharge by Oil Drilling and Gas Extraction industry as notified

vide notification dated GSR 176 (E) April 1996 and subsequent

amendments .

Safety and 4) Oil Mines Regulations, 1984.



36

Issues Applicable Legislation

Protection

against Pollution

of Environment

5) Oil Field (Regulation and Development) Act 1948 and The

Petroleum & Natural Gas Rules, 1959 and amendments thereafter.

6) Coast Guard Act, 1950 for combating marine pollution and security

of the maritime zones of India-NOSDCP

7) Territorial water, continental shelf, exclusive economic zone and

other maritime zones act, 1976 for certain matters relating to the

territorial water, continental shelf, exclusive economic zone and

other maritime zones of India.

8) MARPOL Convention, 1973/78 for preventing and minimizing

pollution from ships-both accidental pollution and that from routine

operations.

9) International convention for the Safety of Life at Sea (SOLAS),

1973, as amended for safety of vessels

1.13 Project benefits

It is expected that the proposed development drilling and subsequent development of

fields would lead to production of 51.33 BCM (Billion Cubic Meters) of Gas over a period

of 16 years and 26.71 MMM3 (Million Cubic Meters) of Oil over a period of 12 years, in

the present scenario of growing demand of Oil and Gas in the country. Floating

Production Storage and Offloading (FPSO), Offshore Fixed Platform, Subsea Production

Systems (SPS) and Subsea Pipelines connecting to Landfall point to existing onshore

terminal for custody transfer to GAIL would further enhance the energy security.

This will help in moving toward achieving self-sufficiency in energy sector and also saving a

huge foreign exchange reserves of the country. This will also help in propelling the growth of

local Industry thus improving the local population wellbeing and significantly contributing to

the economy of society by creating indirect employment.



37

CHAPTER-2

Drilling Technology

2.1 Drilling Process

Drilling in deep waters is done by using drill ships which is a self-propelled,

dynamically Positioned vessel (Fig 2.1) with drilling facilities on board. The well is

drilled using rotary drilling system that consists of a derrick mounted on the drill floor,

at the top of which is mounted a crown block and a hoisting block with a hook. From

the swivel is suspended a Kelly stem which passes through a square or hexagonal

Kelly bush which fits into the rotary table. The rotary table receives the power to

drive it from an electric motor. The electric motor rotates the rotary table which

passes through the Kelly bush and the rotations are transmitted to the bit. As the

drilling progresses, the drill pipe in singles is added to continue the drilling process.

At the end of the bit life, the drill pipes are pulled out in stands and stacked on the

derrick platform. After changing the bit, the drill string is run back into the hole and

further drilling is continued. This process continues till the target depth is reached.

Initially well is drilled with water based mud systems. Synthetic Oil Based Mud

(SOBM) is used as drilling fluid in the target sections(12-1/4” and 8-1/2” hole). The

quantity of drill cuttings generated is around 300-500 m3 and quantity of wastewater

will be around 20 m3/day. The rig will be provided with solids handling system

comprising Shale shakers, De-sander and De-silter.

transports them to the surface through the annular space between the drill string and

the hole. The mud not only transports crushed rock cuttings from the bottom of the

hole, but it also cools the bit as it gets heated due to friction with formation while

rotating. The mud also helps in balancing subsurface formation pressures, and

diminishes the possibility of crumbling or caving of the well bore.by forming a cake

on the walls of the well.



38

Approximate quantities of cuttings

Table: 2.1 (a) At water depth of 600 m, Drilling Depth: 4500 m

Hole size(in) 26” 171/2” 12¼” 8½” Total vol. of

cuttings (M3)

Depth (m) 600-700 700-1600 1600-3000 3000-

4500

--

Cuttings(m³) 35 105 110 55 305 +20%

caving

Approx. ~ 370

M3

Recipient

environment

Sea

Bed

Sea Bed Sea Sea

Table: 2.1 (b) At water depth of 2500 m Drilling depth 6000 m

Hole size(in) 26” 171/2” 12¼” 8½” Total vol. of cuttings

(M3)

Depth (m) 2500-

2600

2600-

3500

3500-

5000

5000-

6000

--

Cuttings(m³) 35 105 115 38 293 +20% caving

Approx. ~ 350 M3

Recipient

environment

Sea

Bed

Sea Bed Sea Sea

Cuttings generated due to the crushing action of the bit, are removed by flushing the

well with duplex/triplex mud pumps. The mud from the pump discharge through the

rotary hose connected to stationary part of the swivel, the drill string and bit nozzles

(Fig 2.2). The mud coming out of the bit nozzles lift the cuttings up hole and At the

surface, the mud coming out from well along with the cuttings falls in a trough,

passes through the solids control equipment i.e. shale shaker, de-sander and de-

silter. These equipment remove the solids of different sizes which get mixed with the

mud during the course of drilling. The cleaned mud flows back to the suction tanks to

be re-circulated into the well. The drilling mud/fluid circulation is thus a continuous



39

cyclic operation. The mud is continuously tested for its properties (density, viscosity,

yield point, water loss, pH value etc). to ensure that the drilling operations can be

sustained without any down hole complications. Sufficient hydrostatic head (mud

density) is maintained to prevent any influx of formation fluid.

2.2 General Requirements of Drilling

Drilling is a temporary activity which will continue for about 45-60 days for a well in

the block. The rig is self-contained for all routine jobs. Once the drilling operations

are completed, if sufficient indications of hydrocarbons are observed while drilling

and in logs recorded, the well will be tested by straddle packer Drill Stem Testing

(DST), which normally takes one day. If the well is found to be successful &

hydrocarbon bearing, it is sealed off for future development. Exploratory drilling

programme requires the following common facilities:

2.2.1 Drilling muds

Drilling of wells requires specially formulated drilling fluids, to give mud weight

(density), fluidity and filter cake characteristics. The drilling muds have several

functions like lubrication and cooling of the drill bit, balancing subsurface formation,

bringing out the drill cuttings from the well bore, thixotropic property to hold cuttings

during non-operations, formation of thin cake to prevent liquid loss along well bore

etc. Several additives are mixed into the mud system to give the required properties.

Water based mud is initially used. Subsequently Synthetic Oil Base (SOBM) mud is

used in the target sections to avoid hole complications associated with the geological

formations, temperature and associated hole stability problems. SOBM provides flat

rheology profile in temperature range of 40o -250o F, which better manages the

Effective Circulating Density (ECD) and hydraulics, thereby allowing good hole

cleaning. The essential constituents of Synthetic Oil Base Mud are base oil, lime and

CaCl2, brine, along with Emulsifier and Wetting agents. Viscosifier used to control

fluid loss.

The development of deep water and ultra deep water operations brings new and

more complex technical challenges due to extreme pressures and temperature



40

encountered at these depths (Temperatures of up to 2o C and pressures up to 400

bars are common at the mud line).



41

Fig: 2.1 Typical Offshore Drillship



42

Fig: 2.2 Mud circulation system

The drilling fluid while flowing through well and riser length will experience

temperatures ranging from 0oC to 150o C and must keep its properties for this whole

range. The mud rheological properties will strongly depend on temperature and

pressure variation and these variation will be different for different mud formulations.

These temperature and pressure ranges are also favourable conditions for the

formation of gas hydrates in drilling mud. Hydrates are solid structures formed from

water and gas. Water content in drilling mud form under certain temperature and

pressure conditions, a solid structure with gas molecules. Hydrate formation requires

four factors to be present:



43

Gas ,

Temperature lower than the calculated freezing point,

Pressure (hydrostatic at BOP),

Time. Formations of these solid gas hydrates is likely to plug, kill and choke lines as well

as annular spaces, and may cause interruption of drilling operation and even

destruction of rig equipment. Use of thermodynamic inhibitor additives (mainly salt

and glycol additives), displaces the equilibrium point of hydrate formation.

In this block, water depth ranges from 320-2840 m. Drilling in these extreme water

depths may require the use of riser less drilling technique which is not constrained by

the length limitations of a riser system. Riser less mud recovery (RMR) provides a

dual gradient drilling setup of the well while capturing the drilling fluids and returning

it to the drill ship. The term dual gradient implies two hydrostatic gradients-

The sea water gradient that begins at sea surface

The drilling mud gradient that begins at the sea floor

Conventional drilling has only one pressure gradient for both sea water and mud

that originates at sea surface. Because dual gradient drilling has much less

hydrostatic head associated with the drilling mud in the borehole, drilling fluids can

be properly weighted allowing drilling to be more easily within the formation pore

pressure and fracture pressure there by avoiding well bore instability.

Initially a 12¼” investigative hole will be drilled to check any shallow water flows. Any

flow will be killed with Heavy Mud. The 36” conductor casing will be jetted up to 90m

below mud line and further drilling with 26” bit will be carried out with Pump and

Dump method after pumping High viscous Sweep displaced with Inhibitive Glycol

mud. Casing 20” will be lowered and cemented. Low seabed temperatures and

water depths may lead to the formation of gas hydrates inside the BOP. In principle,

the freezing point is suppressed by using the salts up to the density limits, and then

with Mono-ethylene glycol (MEG) and Poly-Alkylene Glycol (PAG). Achievement of

adequate cuttings transport in the long riser section at the relatively low annular

velocity is the critical factor. The mud’s carrying capacity must be maintained. And



44

the riser flow rate should be boosted wherever possible. Good shear thinning

characteristics are therefore required to minimize the PV. The ECD should be

closely monitored to avoid exceeding the expected low fracture gradients.

GLYDRIL is a water based polymer fluid, which consists of the following chemicals:

Sodium and/or Potassium salts.

GLYDRIL MC – Mid Salinity range clouding Poly alkylene Glycol.

PAC-R/UL – (Poly anionic Cellulose) – Primary filtration control.

POLYPLUS RD (PHPA) – Provide solids encapsulation, well bore stability

and filtration control. IDCAP-D, a low molecular weight poly-acyrlamide

can be substituted for Polyplus-RD.

DUOVIS (Xanthan Gum) – Provide low-end rheology.

KLASTOP – Polyamine for supplemental inhibition.

For new mud additions, seawater can be used, properly treated with Bactericide and

softened with Soda Ash and Caustic Soda to remove the unwanted divalent ions,

Ca++ and Mg++. However later, if chloride levels have to be controlled, drill water

treated in the same way should be used. The potassium ions will exchange with

sodium ions on the clay platelets. Subsequent additions of KCl will have the effect of

increasing the chlorides, mud weight and hydrate suppression.

Table:2.2 Typical chemical requirement for drilling the deep water well.

PRODUCT Concentration(lb) Purpose

ASPHASOL 5.0 Inhibitor

BARITE As required Weighting Agent

BENTONITE As required Clay

CALCIUM

CARBONATE

As required Loss control Additive

CAUSTIC

SODA

0.5 pH

CITRIC ACID As required pH control

CONQUOR

303A

As required Corrosion Inhibitor

KLASTOP 10.5 Emulsifier

Duovis 1.5 Viscosifier



45

Glydrill-MC 17.5 Hydrate inhibitor

Guar GUM As required viscosifier

KCL 23.5 Inhibitor

MEG 28.0 Hydrate inhibitor

MI-cide 0.3 Biocide

Nacl 56.0 Hydrate inhibitor

PacUL 3.5 Fluid loss control

Polyplus RD 1.5 Encapsulating Polymer

In case of any Borehole problem environment friendly Low toxic Synthetic Oil Base

Mud will be used. After lowering Riser and BOP, further drilling will be resumed with

RHELIANT Synthetic Oil Base Mud up to target depth. The following chemicals are

generally be used.

Table:2.3 Composition of Synthetic Oil Base Mud

Additive Trade Name Concentration in Drilling Mud Pounds/Barrel

Emulsifier SUREMUL 6-10

Rheological Modifier

RHETHIK,RHEFLAT 0.1-0.25

Fluid Loss Additive ECOTROL 0.25-0.75

Lime -- 8.0

Calcium Chloride -- 23.6

Wetting Agent SUREWET 1.0-2.0

Base Oil EDC Diamond 60%

2.2.2 Power Generation

The drilling process requires movement of drill bit through the draw works which

require power. The power requirement of the drilling rig will be met by using the

Diesel Generator sets of 1430 kVA capacity 4 nos. with a diesel consumption of

about 8-12 Kl / day. The exhaust stacks of the DG sets are likely to vent off the

emissions at the height of approximately 30 m above mean sea level.



46

2.2.3 Water requirements

The water requirement in a drilling rig is meant for preparation of drilling mud apart

from washings and domestic use. The water requirement for domestic and wash use

is very less. The daily water consumption will be 30 m3/d will be used. The operating

personnel in the drilling rigs will operate from on board accommodation. Sanitary

water is passed through sewage treatment plant on board and discharged to sea

after treatment and meeting the requirement of standards i.e Residual chlorine 1

ppm.

2.2.4 Solids removal

During drilling operations, approx.. 300-500 m3 of wet drill cuttings are expected to

be generated for one well depending on the depth of the well. The rock cuttings and

fragments of shale, sand and silt associated with the return drilling fluid during well

drilling will be separated using shale shakers and other solids removal equipment

like de-sander and de-silter. The recovered mud will be reused while the separated

solids will be discharged to sea after proper washing and dilution as per GSR 546(E)

2005. Residual waste mud if remained will be discharged into sea after proper

dilution as per guidelines.

2.2.5 Chemical storage

The drilling rig will have normal storage facilities for fuel oil, required chemicals and

the necessary tubular and equipment. The drilling rig have general deck storage

system. All the chemicals are clearly labelled the storage places will be clearly

marked.

The Deep water drilling requires storage of the following chemicals

Hydrate inhibitors (Mono ethylene Glycol, Poly alkene Glycol, NaCl etc)

Polymeric viscosifiers

Polymeric Fluid loss control agents

Barite(Weighting Agents)

KCl (Ionic inhibition of shales)

PHPA (Partially Hydrolysed Poly Acrylamide)



47

Sulphonated Asphalt (Shale Stabilisers)

Caustic Soda (for pH control)

Cement additives

Completion Chemicals

The Bulk chemicals like Barite and Cement are stored in Silos. The corrosive

chemicals like Caustic Soda is kept in a separate enclosure with lock and key

available with the Mud Engineer.

The Chemical ware house is equipped with fire extinguisher, smoke detector, and

Fire alarm system. Material Safety data sheets of all the chemicals are kept at the

warehouse to be used in case of emergency. The Hydrate inhibitors are stored in

sealed drums. In the case of spillage, the remedial action is taken in line with the

MSDS. Drilling Detergent and EP lube is stored in seal tight barrels so that the

spillage of these chemicals during transit is avoided.

2.2.6 Manpower

The drilling rig will be having approx. 50-60 persons on the rig at any time.

Accommodation provided on board. The manpower operates in two shifts (12 hrs)

with continuous operations on the rig. The rig personnel operates on 14/28 days

ON/OFF duty pattern.

2.2.7 Logistics

Crew transfers to and from the drilling rig is through helicopter from

Rajahmundry/Visakhapatnam. The drilling materials, diesel and chemicals will be

transported through supply vessel from Kakinada base..

2.3 Deep water drilling Technology

Wells drilled in deep water have a different casing scheme than wells drilled in

shallow water. Fracture gradients are very low in deep water. This results in mud

weights very close to fracture gradients and requires more casing strings.

The casing-drill technique of setting the structural casing has been used in water

depths of 200-7500 feet. It eliminates the risk of losing the hole when the drilling



48

assembly is pulled from the unconsolidated formation to run the structural pipe. The

procedure utilizes a hydraulically actuated Dyna-Drill motor and slightly under guage

bit suspended in the casing to drill/jet the structural pipe to the pre-determined depth.

The “pilot hole” is drilled/jetted by the bit with power supplied by the motor. The

weight of the casing at the bottom wedges additional formation into the hole where it

is drilled by the bit. The cuttings are carried up the annulus and ejected through ports

in the top of the running tool. The most commonly used assembly is a Dyna Drill (9-

5/8”, high-speed, low-torque) with attached 26” stabilizer blades and a 26” bit. The

low-torque motor minimizes turning of the casing string. A jet-sub allows the required

annular fluid volume to be achieved by diverting the fluid prior to its entry into the

motor.

The weight of the casing assembly applied to the formation varies from an initial 10-

20% to a maximum of 80% at the total setting depth of the casing. The controlled,

lighter weights at the start aid in keeping the casing at or near vertical, while the 80%

maximum provides a safety margin, keeping the neutral weight point below the

running tool.

As the casing penetrates the formation, the side frictional forces increase, absorbing

much of the applied weight. This friction is controlled by reciprocation (working) the

casing string until the drag (over pull) is reduced, allowing an effective rate of

penetration with the proper weight applied to the bottom.

Proper execution of these guidelines result in the least soil disturbance, which

minimizes the time for the soil to heal. The soil’s ability to “hold” must not be

seriously damaged by staying at one depth while washing.

After reaching the setting depth, the casing is allowed to “soak” or sit in a stationary

position allowing the soil that was penetrated to “heal” around the casing and regain

most of its holding capacity. The average is approximately 1-2 hours, with some

allowing 6 hours to soak. A trip is made for the drilling assembly while the casing

soaks. Some operators use a drill-ahead tool (Cam Actuated Drilling Assembly –



49

CADA) that eliminates the need for a trip to pick up the drilling assembly to begin

drilling.

2.3.1 Permanent Guide Base and Temporary Guide Base The permanent guide-base and a

temporary guide-base are run on the

same assembly with the structural pipe.

The guide-base matches-up with the

blow-out preventers and provides a base

to hang off subsequent casing strings as the well is drilled.

2.3.2 Cam Actuated Drilling Assembly Tool (CADA)

The Cam Actuated Drilling Assembly (CADA) is run in the casing drill/jetting

assembly. It is activated by the following procedures:

1. The motion compensator is activated to support the weight of the drill pipe

running string, the jetting string, and a 10,000 lb over-pull to the CADA Tool.

2. The mud pumps are used to agitate the cuttings left inside the structural

pipe.

3. The remote operated vehicle (ROV) is positioned to assist with the process.

4. The drill pipe is rotated to the right approximately 5 turns to retract the split-

ring on the CADA Tool and unlocks the tool from the Wellhead Housing.

5. The center stem is released by applying right-hand torque in excess of

13000 ft-lbs.

6. The mud motor is picked up and tested.

7. Picking up the center stem shears the shear pins (75,000 lbs. over pull).

This shears it out of the 30” housing. Re-landing the assembly into the

housing allows the drilling process to begin.

The 26” hole is drilled below the structural pipe to a predetermined depth.

The CADA tool is then retrieved prior to running 20” casing.



50

2.3.3 Down-Hole Equipment

A variety of equipment and tools are used to assist riser less drilling. They include

Logging While Drilling (LWD), Measurement While Drilling (MWD), Pressure

While Drilling (PWD), Mud Motors and Remote Operating Vehicles (ROV).

The LWD tool allows the operator to view a real-time log of the formation as it is

drilled. This is very important when drilling shallow hazards. The LWD tool is usually

located in the drill string about 30 feet above the bit. Therefore, information from the

tool is from the depth of the tool – not the depth of the bit. However, this information

is valuable to the operator while drilling.

The MWD tool allows the operator to monitor the angle and azimuth of the hole while

drilling and make necessary steering changes. This is important since the 20” casing

should be set in a near vertical position.

The PWD tool provides a constant read-out of the actual pressures in the hole while

drilling. PWD tools also measure the Equivalent Circulating Density (ECD) of the

fluid in the annulus. This knowledge allows the operator to avoid exceeding the

estimated formation fracture pressure. The mud must be circulating for the pulse of

the tool to be recorded at the surface. The tool is being used more often in the riser

less section, especially when shallow hazards are expected. Although the tool reads

directly, it is still not precisely on bottom. There are instances where the PWD tool

missed the pressure increase (when the pumps were shut off). Therefore, the PWD

tool can’t be totally relied on detecting a shallow flow. The R.O.V. will help when the

pump is shut off.

The typical rate of penetration for the riser less sections are 25’-50’ hour with pump

rates of 1000-1500 GPM. Higher penetration rates or lower pump rates could

overload the annulus with cuttings and result in loss circulation or ballooning

problems.



51

The use of Mud Motors to drill the riser less sections of the hole minimizes hole

deviation and doglegs. Rotating the entire drill string at >100 rpm is not the preferred

way to drill the riser less section. With the running tools, CADA tool, etc in the drill

string, the mud motor is the most efficient way to drill the hole.

The Remote Operating Vehicle (ROV) plays a crucial role in deep water drilling especially

when when operating in the riser less section. The vehicle performs numerous functions.

One very important function is to monitor the hole to be sure the well is not flowing while a

connection or a trip is made.

2.3.4 Hole Cleaning

Back-reaming: Back-ream to the shoe after drilling the 24” or 26” open hole. After

back-reaming, a viscous sweep is pumped and the well checked for a flow before

going in the hole.

Short Trips: Short trips ensures the hole cleaning & stability. A viscous sweep is

pumped at the casing point to help clean the casing and riser of any cuttings left in

the annulus.

Sweeps: Sweeps are usually pumped on a periodic basis to help clean the hole.

1. Volume: Typically a volume of 100-200 bbls is used every 45’-200’.

2. Formulation: Freshwater with 25-30 ppb of M-I GEL and ½ ppb Lime, caustic soda

and/or soda ash. The normal procedure for preparing a sweep is to adjust the

yield point of the pre-hydrated gel slurry to >50 by adding seawater prior to

pumping it down the hole. This usually requires a 50% ± dilution with seawater.

2.3.5 Spotting fluid (Kill Mud):

Prior to pulling the pipe out of the hole to run 26” or 20” casing, the hole should be

filled with weighted mud. Usually, 1.5-2.0 times the calculated hole volume is

pumped. The extra volume brings cuttings left in the hole to the sea floor and

compensates for hole enlargement. The mud density can vary from 9.5 – 12.0 ppg,

depending on the water depth. Reduce the API fluid loss to the 10 ml –25 ml range



52

to minimize the build-up of filter cake across the sands and improve chances of

getting the casing to bottom.

The kill mud weight must be sufficient to compensate for riser margin or hydrostatic

head pressure attributed to a column of seawater equivalent in length to riser and

airspace. One guideline suggests that the kill mud can be established by multiplying

the overburden pressure at the depth of interest by 0.85-0.88 divided by RKB-

TVD(Rig Kelly Bush-True vertical depth) times 0.052.

2.3.6 Drilling / Jetting 26” & 20” casing sections

One of the keys to drilling deep water wells successfully is setting the 20” casing in

the right place and having a good cement job. Some areas have a combination of

gas hydrate layers and/or shallow hazard zones to drill through. One option used is

to drill a pilot hole (8.5” or 12.5”) to total depth to determine the extent of the hazard

and minimize the effects of the hazard initially. The pilot hole mud system is typically

seawater with sweeps and returns to the seafloor. In some areas that have known

shallow hazards, the common practice is not to drill a pilot hole and to drill 24”, 26”

hole using seawater with sweeps with the larger bit sizes.

2.4 Deep water abandonment

The main requirements for any well abandonment programme are:

1. To leave the well in a safe down hole condition such that the well will retain

pressure integrity and there is no possibility of the well flowing when the BOP

or well head is removed.

2. To leave the seabed around the wellhead clear of drilling related debris.

2.4.1 Suspension requirements

The main requirements of the well suspension programme are:



53

To leave the well in a safe condition down hole such that, if the well head

is accidentally damaged or removed, the well will retain pressure integrity

and there is no possibility of the well flowing.

To allow the well to be re-entered at a subsequent date and a BOP

installed without recourse to repair work. To cover this requirement, a

corrosion cap will be run to protect the well head and its sealing areas.

To ensure that any sea floor obstruction is minimized.

2.4.2 Well Abandonment on decommissioning

The following steps followed for well abandonment:-

All casing strings will be cut off a minimum of 5m below the seabed.

Plugs will be set no more than 50m below the seabed.

When cut intermediate casing, production casing, and liners are plugged,

it shall be verified by weight testing with 22klbs (10 tons), and pressure

tested to 1030 psi (70bar) above the formation strength that potential flow

paths are isolated and sealed.

There shall be no non-isolated route behind a string of casing from an

open hole section to surface. If the casing/casing overlap has not been

isolated with cement then the casing string will be cut deep and isolated in

the same manner as in step 1 of “Abandonment Only” above.

If the annular top of cement has not been identified on a log, then the top

of cement will be assumed by calculation.

Cutting or perforating of non-cemented casing must be performed under

full pressure control.

When cutting casing, the shoe strength at the previous casing shoe must

be high enough to with stand the mud weight in the hole. If it is not, then

the mud weight will have to be reduced. After retrieving the well head’s

and guide base, a ROV seabed survey (or equivalent) must be carried out

to confirm that the seabed is clear of drilling related debris with in a 70m

radius of the well head. This plug will be pressure tested to 1030psi (70

bar) over the formation leak-off pressure at the casing shoe behind the

liner.



54

For permanent abandonment a 200m surface cement plug is required with

the top of the plug verified no more than 50 m below the sea bed

suspension only. In addition to common requirements the following apply

to well suspensions. A corrosion cap will be run and the well head filled

with hydraulic oil.

A planned inspection routine for the suspended well head must be

established.

The operator must also evaluate and document Buoy marking and

identification of the well head.

CHAPTER-3

Baseline Environmental Status

3.1 Introduction

In order to carry out an Environment Impact Study, it is necessary to delineate and

define the existing status of recipient environment in and around operational area of

the proposed project. Environment baseline study will record the existing quality of

environmental status within the area of influence before implementation of the

project. The existing baseline data is considered to adjudge the prevailing

environmental condition which are monitored, studied and described with respect to

climate and meteorology, oceanography, atmospheric conditions, offshore water

quality and marine ecology. Knowledge of the characteristics of the local chemical

and biological environment allows an understanding of the potential of the operations

to interact with the flora and fauna so that appropriate controls can be adopted to



55

mitigate negative impacts. This data will then be analyzed in the chapter-4 entitled

“Identification, Prediction and Evaluation of Impacts.”

The Environment Appraisal Committee EAC-Industry of Ministry of Environment and

Forest after due consideration about utility of data has recommended following

parameters to study. Copy of prescribed TOR is appended at Annexure-1.

Climatology and meteorological data including wind speed, wave

currents and rainfall etc.

Baseline data collection for surface water for one season leaving the

monsoon season within 1km of each exploratory well, particularly in

respect of oil content.

Details of sensitive areas such as coral reef, marine water park,

sanctuary and any other eco sensitive areas.

Procedure for handling solid waste and

Procedure for preventing spills and spill contingency plan

The offshore block KG-DWN-98/2 is located off the eastern coast of India in the Bay

of Bengal, approximately at a distance of 28 Km in the north to 250 Km in the west

from the nearest shore. The approximate mean water depth of the block is 2085 m

(Water depth varies from 300m to maximum of 3000 m).

The baseline description includes collection of primary and secondary data through

field investigations, environmental monitoring and secondary sources viz. maps,

reports, scientific literatures, etc. The obtained data has been analysed for

identification of impacts and arrive at mitigation measures for minimizing any

environmental impact due to the project activities. The activities that are likely to be

studied for each environmental component are described in subsequent sections.

The study area is oceanic. There is no land within the 10 km study area. No eco

sensitive zones and national parks in the study area.



56

3.2 Climate

According to the Indian Meteorological Organization (IMD), various seasons over

India are:

•Winter Season : January – February

•Pre Monsoon Season : March – May

•Southwest Monsoon Season : June -- September

•Post Monsoon Season : October -- December

In this block which is located at the distance of 28-250 km from the coast, the

northeast monsoon is from November through April as continental high pressure

system in north of the bay produces northeast winds characteristic of the winter

season (Fig 3.1). During the period June–September the rain-bearing southwest

monsoon prevails, as intense heat produces a low-pressure system over the

continent and a subsequent air flow from the ocean. North east monsoon and

cyclonic storms over the Bay of Bengal along South East coast of Peninsular India

bring heavy rainfall associated with major physical changes. From January to

October, the current is northward flowing, and the clockwise circulation pattern is

called the "East Indian Current". The Bay of Bengal monsoon moves in a northwest

direction striking the Nicobar Islands, and the Andaman Islands first, by end of May

and then the north eastern coast of India by end of June. The remainder of the year,

the counter-clockwise current is south west ward flowing, and the circulation pattern

is called the East Indian Winter Jet. September and December see very active

weather in the Bay of Bengal producing severe cyclones which affect the east coast

of India. Strong winds produce storm surges in many parts of the coast. Changes in

the frequency of tropical cyclones developing over the Arabian Sea and the Bay of

Bengal have been studied utilizing 122 years (1877-1998) data of tropical cyclone

frequency. Significant increasing trends in the cyclone frequency over the Bay of

Bengal have been observed during November and May which are main cyclone

months. During transitional months, June and September, however, the frequency

has decreased. The climate of the area is hot during summer season and the

temperature varies from 26o to 39oC at the surface, but the temperature decreases

to as low as 4oC at water depths of 1500m. The annual mean temperature variation

at standard depths is given in the Table: 3.7.



57

3.3 Physical Environment

The block KG-DWN-98/2 is at the distance of 28 Km to 250 Km from the coast and

bathymetry varies from 320 m to 3100 m. Logistically, it is very difficult to get the

vessel for sampling at higher depths. ONGC has contacted premier national institute

INCOIS for the Meteorological data of the block. ONGC & INCOIS has shared

knowledge & data on following parameters for the Oceanographic and

Table:3.1 Resources for Oceanographic and Meteorological data

Measurement techniques

Parameter Data source/Monitored by Remarks

Bathym etry ETOPO1 data available at a

resolution of 1 arc-minute X 1

arc minute global relief model of

Earth’s surface

Land topography and

ocean bathymetry, built

from numerous global and

regional data sets has

been integrated.

Significant Wave

Height (SW H) CNES, France, (AVISO)

generated data on a daily basis

globally at a 1 deg. X 1 deg.

resolution.

Sea Surface

Currents OSCAR (Ocean Surface

Currents Analyses Real time)

monthly mean data on currents

at 0.33 deg. x 0.33 deg.

Resolution.

--

Ocean Surface

W inds Satellite based active (radar) and

passive (radiometer) microwave

sensors. ASCAT aboard

EUMETSAT METOP satellite.

--

Salinity &

Temperature The W orld Ocean Database

2009. Data available at high

resolution of 1 deg. X 1deg.

These databases include

cruise data, satellite

altimeter data as well as

moored and floating buoy

data, etc. This data is

available from the surface

to 1500m, at the "standard

oceanographic depths".



58

Meteorology for the block area. The data for Bathymetry, Significant Wave Height,

Surface Ocean Currents, Wind speeds, Salinity and Temperature is real time data

monitored by satellites

3.3.1 Significant Wave Height

The significant wave height is obtained by analysing the shape and intensity of the

altimeter radar beam reflected from the sea surface (the radar echo). A long time

delay in the return signal indicates that waves are high and a short delay indicates

that the sea surface is calm. In the Table-3.3, the monthly average for the SWH (m)

based on daily data for the block location clearly shows that the maximum height

(around 2.0m) is observed during the southwest monsoon season (June-September)

associated with the sustained high winds during June-September, followed by the

northeast monsoon. During cyclones, associated with strong winds, very high

waves can form over the sea, even close to the coast. Since it is a critical

parameter, we have further examined the highest daily averaged value (averaged

over the block) during the year – 2010 (fig 3.5). It was seen that the SWH values

(averaged over the area) varied up to 3.5 m, associated with the Laila and JAL

cyclones.

Table:3.2 Bathymetry of the block KG-DWN-98/2.

Location Mean depth over

the region (m)

minimum depth in

the area (m)

maximum depth in

the area (m)

KG-DWN-98/2 2085 300 3100



59

Table: 3.3 Significant Wave Height in meters ( Monthly average).

Month KG-DWN-98/2 Jan 1.0 Feb 0.4 Mar 0.7 Apr 1.1 May 1.7 Jun 2.0 Jul 1.9 Aug 1.5 Sep 1.5 Oct 1.4 Nov 1.3 Dec 1.4

Maximum 3.5

Fig: 3.1 Wave Height in the Block area.

0

0.5

1

1.5

2

2.5

3

3.5

4

KG-DWN-98/2



60

3.3.2 Sea Surface Current

The most important processes that control the dynamics of the sea which are directly

linked with the transport of the pollutants are tides, waves and currents. The currents

are oriented in the northerly direction most of the time. The currents are intense

during the southwest monsoon and post monsoon months. The current speed (area

averaged over the block) has a maximum of nearly 47.7 cm/s (Table-3.4). The

currents are oriented in the northerly direction most of the time. The currents are

intense during the southwest monsoon and post monsoon months. The currents in

the Bay of Bengal are intense close to the coast mainly because of the eddies –

“warm” core and “cold” core as well as the alongshore intense gradients in the

thermo-haline characteristics because of the substantial river discharge of major

river systems.

Table: 3.4 Current speed (cm/s) and direction (deg.) at the block.

Month KG-DWN-98/2 KG-DWN-98/2

speed direction

Jan 7.2 123.7

Feb 11.2 79.7

Mar 46.1 49.4

Apr 47.7 57.0

May 39.1 50.2

Jun 11.2 10.3

Jul 26.4 37.3

Aug 13.0 22.6

Sep 12.0 311.6

Oct 41.6 207.2

Nov 36.8 247.6

Dec 15.6 320.2



61

Fig-3.2: Current speed and direction at the block

3.3.3 Ocean Surface Winds

The average wind speed and direction over the block area are given in the Table-3.5

and has a maximum wind speed value of 6.0 m/s in the month of June. The

southwest monsoon winds are maximum as compared to the northeast monsoon or

post monsoon period. Further, during cyclones, which occur more frequently in the

Bay of Bengal as compared to the Arabian Sea, the winds can have very high

magnitudes, with varying directions.



62

Table:3.5 Wind speed (m/s) and direction (deg.) at the block.

Month KG-DWN-98/2 KG-DWN-98/2

speed direction

Jan 4.5 253.0

Feb 2.5 295.2

Mar 3.4 357.3

Apr 5.2 1.7

May 5.3 13.1

Jun 5.4 45.6

Jul 6.0 54.2

Aug 2.7 47.6

Sep 3.5 64.4

Oct 0.7 64.5

Nov 5.1 259.5

Dec 4.6 239.8

Maximum 14.7 216.2

Fig: 3.3 Wind rose diagram showing the Pre dominant wind directions during the year in the block.



63

3.4 Marine Water Quality

The area of the block KG-DWN-98/2 is largely oceanic and therefore not expected to

undergo significant changes in water quality, temporarily as well as spatially.

Samples were collected keeping in view, where maximum drilling of exploratory wells

are expected to come. Therefore, most of the samples were collected in the

northern part of the block which is in close proximity to the coast where most of the

drilling prospects are located to study the environmental impacts in the area due to

proposed drilling activities (Fig 3.7). The water quality data for block is given in the

Table-8

Salinity and Temperature

The principal natural processes which lead to changes in the salinity of sea water

are those which bring about removal or addition of fresh water. In the coastal areas

of Bay of Bengal, increase in salinity is caused by evaporation and decrease in

salinity results from atmospheric precipitation and run-off from land. The surface

salinity in the open part of the Bay oscillates from 32 ppt to 34 ppt (i.e parts per

thousand) and in the coastal region it varies from 10‰ to 25‰. Figure 3.6 shows the

Surface Distribution of Salinity in the Study area and Bay of Bengal. The observed

values of the salinity are in the range of 32.9 ppt to 33.9 ppt (Table:3.8).



64

.

Fig: 3.5 Sampling Locations of the block KG-DWN-98/2

Sample location



65

Table:3.6 Area averaged salinity (ppt) at standard depths at Block at KG-DWN-

98/2

KG-0098-2-SALDepth Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

0.0 32.9 32.8 33.5 34.0 34.0 33.8 33.5 33.1 32.4 30.2 31.4 31.0

10.0 32.8 32.8 33.5 33.9 34.0 33.8 33.5 32.9 32.5 30.7 31.6 31.1

20.0 33.1 33.0 33.6 33.9 33.9 33.7 33.5 33.5 33.0 32.5 32.4 32.5

30.0 33.2 33.2 33.7 33.9 34.0 33.7 33.6 33.7 33.6 33.3 33.4 33.5

50.0 33.6 33.7 33.9 33.9 34.2 33.8 33.9 34.2 34.3 34.4 34.2 34.0

75.0 34.4 34.7 34.3 34.5 34.5 34.3 34.3 34.6 34.7 34.7 34.7 34.7

100.0 34.8 34.8 34.8 34.7 34.8 34.6 34.6 34.8 35.0 35.0 34.8 35.0

125.0 35.0 35.0 34.8 34.8 34.8 34.8 34.8 34.8 35.0 35.0 34.8 35.0

150.0 35.0 35.0 35.0 35.0 35.0 35.0 34.8 35.0 35.0 35.0 35.0 35.0

200.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0

250.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.1 35.0 35.0

300.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.1 35.0 35.0

400.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.1 35.0 35.0

500.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0

600.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0

700.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0

800.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0

900.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0

1000.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0

1100.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0

1200.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0

1300.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0

1400.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 34.8 35.0 35.0 35.0

1500.0 35.0 34.8 34.8 34.8 34.8 34.8 35.0 34.8 34.8 35.0 35.0 35.0



66

Fig: 3.5 Surface Distribution of Salinity in the Bay of Bengal



67

Table: 3.7 Area averaged temperature (0C) at standard depths at KG-DWN-98/2

KG-0098-2.tempr Depth Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

0.0 26.3 26.4 27.9 29.0 30.2 29.6 28.9 28.6 29.5 28.3 27.1 26.7

10.0 26.1 26.4 27.8 28.8 30.1 29.4 28.8 28.2 29.1 28.4 27.2 26.8

20.0 26.3 26.3 27.7 28.5 30.0 29.2 28.8 28.0 28.9 28.3 27.7 27.5

30.0 26.4 26.2 27.6 28.2 29.7 28.9 28.8 27.8 28.8 28.1 27.4 27.7

50.0 26.7 25.8 26.6 27.0 28.1 28.2 28.1 27.3 26.7 26.5 26.1 26.5

75.0 25.2 24.4 24.8 24.6 25.9 26.6 25.9 26.1 24.5 23.0 22.3 23.8

100.0 22.8 21.3 23.5 22.1 23.8 23.5 22.8 22.9 21.9 19.8 19.0 20.3

125.0 19.6 19.0 21.1 19.8 20.9 21.1 20.4 19.8 19.4 17.6 16.8 18.1

150.0 17.7 17.0 18.4 17.5 18.5 18.4 17.6 17.3 17.4 15.8 15.1 16.5

200.0 14.7 14.1 14.8 14.7 14.7 14.6 14.1 14.2 14.4 13.6 13.3 13.8

250.0 12.9 12.5 12.8 12.6 13.0 12.8 12.6 12.6 12.7 12.2 12.1 12.4

300.0 11.4 11.6 11.6 11.6 11.7 11.6 11.7 11.7 12.0 11.3 11.3 11.5

400.0 10.6 10.4 10.4 10.3 10.4 10.3 10.5 10.7 10.7 10.5 10.3 10.6

500.0 9.8 9.6 9.6 9.5 9.4 9.8 9.7 9.8 9.7 9.9 9.7 9.9

600.0 9.2 8.8 8.8 8.6 8.6 9.0 8.9 9.0 9.2 8.9 9.0 9.4

700.0 8.5 8.2 8.1 8.1 7.9 8.0 8.2 8.3 8.5 8.4 8.4 8.7

800.0 8.0 7.4 7.5 7.5 7.3 7.3 7.5 7.6 7.6 7.7 7.9 7.9

900.0 7.3 6.9 7.0 7.0 6.8 6.9 7.0 7.1 7.1 7.1 7.3 7.2

1000.0 6.6 6.7 6.6 6.5 6.5 6.6 6.5 6.6 6.5 6.6 6.7 6.6

1100.0 6.2 6.1 6.0 6.0 6.0 6.1 6.0 6.1 5.9 6.1 6.3 6.1

1200.0 5.5 5.6 5.6 5.3 5.3 5.4 5.4 5.6 5.5 5.7 5.8 5.7

1300.0 5.2 5.2 5.1 5.2 5.2 5.2 4.9 5.2 5.1 5.3 5.3 5.3

1400.0 4.7 4.7 4.7 4.7 4.7 4.6 4.5 4.8 4.7 4.8 4.7 4.9

1500.0 4.2 4.3 4.3 4.1 4.0 4.0 4.4 4.3 4.3 4.5 4.5 4.5



68

Fig:3.6 Sea Surface Temperature



69

Fig: 3.7 Sea water collections at different sampling point



70

Table: 3.8 Water Quality Data

Method of analysis: Cd, Iron, Ni, Zn, Pb, Cr, by AAS (IS3025):

PAH by GC (APHA 6440B) COD, DO, pH Oil & Grease, Alk, Hardness by

IS3025, BOD by APHA 4500C.

Minimum Detection Limits : Iron 0.1 mg/l, Copper 0.05 mg/l, Lead 0.05 mg/l, Zinc 0.5 mg/l,

Chromium 0.05 mg/l, Aluminium 0.03 mg/l, Nickel 1.0 mg/l,

Cadmium 0.01 mg/l, Mercury 0.001 mg/l, PAH 0.1 µg/l

Sl.

No

Parameter Unit S1 S2 S3 S4 S5 S6 S7 S8 S9

1 pH mg/l 7.6 7.9 7.9 7.7 7.8 7.76 7.69 7.83 7.86

2 Salinity ppt 33.1 33.3 32.9 33.3 33.7 33.8 33.7 33.9 33.9

3 Turbidity NTU 3.1 3.0 4.0 3.6 4.0 3.5 3.2 3.1 3.4

4 DO mg/l 6.0 6.0 6.3 6.2 6.2 6.0 6.1 6.3 6.2

5 BOD mg/l 7.1 8.4 6.2 7.2 6.4 4.1 3.7 4.8 4.6

6 COD mg/l 25.5 28.0 20.5 22.5 20.2 11.9 13.2 12.5 9.9

7 PAH µg/l BDL BDL BDL BDL BDL BDL BDL BDL BDL

8 Oil content µg/l 3.9 3.2 3.3 2.9 3.6 2.6 2.9 3.0 3.1

9 Alkalinity mg/l 214 210 208 196 188 311 361 377 383

10 Total

Hardness

mg/l 6065 6800 6066 6265 6380 6316 6076 5921 5883

11 Chloride g/l 16.23 15.02 16.03 15.17 16.25 16.19 12.39 10.59 11.64

12 Fluoride mg/l 5.5 5.6 5.2 5.0 4.8 2.31 2.74 2.68 2.38

13 Cadmium mg/l BDL BDL BDL BDL BDL BDL BDL BDL BDL

14 Iron mg/l 1.62 1.4 1.62 1.58 1.3 0.23 0.25 0.19 0.22

15 Nickel mg/l BDL BDL BDL BDL BDL BDL BDL BDL BDL

16 Zinc mg/l 0.74 0.72 0.75 0.67 0.62 0.71 0.68 0.73 0.72

17 Lead mg/l BDL BDL BDL BDL BDL BDL BDL BDL BDL

18 Chromium mg/l BDL BDL BDL BDL BDL BDL BDL BDL BDL



71

Under the influence of the buffering action of CO32-/HCO3

2-/CO2 system, the pH of

oxygenated seawater at the surface is fairly constant and varies in a narrow range.

The variation in the pH value near the study area is 7.6-7.9.

It is observed that the Dissolved Oxygen (DO) content shows high seasonal

variation. Lowest oxygen concentrations are observed in winter while higher oxygen

levels in the monsoon season. The intensity of the incident solar radiation is very

high in the pre monsoon, which causes maximum primary production to occur a few

metres below the sea surface thus, a DO maximum occasionally occurs in this layer.

The DO concentrations in the surface mixed layer in the Bay of Bengal are generally

uniform and close to the saturation value. Lowest oxygen concentrations are

observed in winter due to enhanced surface productivity in winter, the large amounts

of organic matter should be oxidized in intermediate layers, thus leading to oxygen-

deficient conditions. Surface DO concentrations could be considerably lower than the

saturation value in some areas and during the periods of upwelling when DO

deficient sub-surface water reaches the surface.

It is evident that the average DO is 6.1 mg/l in the studied are of this block and is

generally close to saturation indicating prevailing good oxidising conditions. The

observed DO values in KG-DWN-98/2 block are in the range of 6.0 mg/l to 6.3 mg.

Heavy metals namely mercury, chromium, lead, cadmium, aluminium, copper and

chromium were below the detectable range in all the sampling locations. The

concentration of iron was detectable in all the sampling locations, which was in the

range of 0.13 to 1.62 mg/L.

The concentrations of dissolved and dispersed Petroleum hydrocarbons (PHC) in

the study area are low and uniformly distributed. The observed values of Petroleum

hydrocarbons at different sampling locations in this block are in the range of 2.6 to

3.9 μg/L.

The literature data obtained from the published paper PHC varies in range of 1.6 to

14.8 μg/ l (Source: Sharma , V.V (1996) Petroleum hydrocarbons and trace metals in

Viskhapatnam harbor and Kakinada bay , eastcoast of India , Indian Journal of

Marine Species, Vol.-25, pp-, 148-150. )



72

In common with land plants, marine phytoplankton requires certain trace elements

for their healthy growth. The most important of these are nitrogen and phosphorus,

which may be taken-up by them from the water to such an extent that their further

growth is inhibited. The average concentrations of dissolved phosphorus and

nitrogen compounds vary considerably in the study area and their variation in

concentration is presented below in Table: 3.9

Table: 3.9 Average concentrations of dissolved phosphorus and nitrogen compounds

Source: * TripathyS.C. et al., 2001, Water quality assessment of Gautami Godavari

mangrove estuarine ecosystem of Andhra Pradesh, India. # Raman A.V. et al, 2005,

Macrobenthof of Kakinada Bay in the Godavari Delta, East Coast of India: comparing

decadal changes, Estuaraine Coastal and Shelf Science, Vol. 62, page 609 – 620

The average concentration of PO43--P and NO3

--N in the northern part of this block

was observed between 2.34 – 2.98 µmol/l and 9.96-12.02 µmol/l respectively. The

levels of NO2-N and NH4+N are low as expected for oxic coastal waters. The average

N: P ratio in the upper 100 m of the Bay of Bengal has been reported to be also low

and has been attributed to the reduction of NO3--N as a result of de-nitrification

associated with the advective transport of P from deeper layers.

3.5 Biological Environment

The occurrence of marine species - both flora and fauna has largely been controlled

by the physico-chemical properties of sea water. Water discharges from the

surrounding river catchments carry huge influx of sediments full of nutrients to the

Parameter 2001 *

2005 #

S1 S2 S3 S4 S5 S6 S7 S8 S9

PO4-3

(µmol/l)

1.76-

4.53

0.92-

6.9

2.98 2.85 2.78 2.59 2.62 2.64 2.29 2.46 2.34

NO3- -

(µmol/l)

7.4-

16.2

13.9-

21.4

12.02 11.39 11.52 11.65 10.36 10.78 10.01 9.92 9.86

NO2- -

(µmol/l)

0.98-

1.72

0.50-

2.24

1.42 1.02 1.62 1.69 0.85 0.82 1.02 0.94 0.92

NH4+

(µmol/l)

0.79-

14.2

0.33-

2.25

2.51 1.55 2.01 1.96 0.76 0.68 0.94 0.60 0.58



73

Bay, particularly along the near shore region. This has turned the Bay into a fertile

marine fishing ground of the region. The near-shore up-welling zone not only has a

high yield of nutrients, but also is a high primary production area for the

phytoplankton and related zooplankton zones. The Bay of Bengal, harbour a variety

of ecosystems and habitats, such as estuaries; intertidal foreshore-rocky, sandy and

muddy areas; coastal lagoons and backwaters; coral reefs and patchy corals; sea

grass beds; continental and deltaic islands; neritic and oceanic regions extending

through bathyal, abyssal and hadal depths. However, there are no eco-sensitive

areas or forest or wild life sanctuaries within the 10 km study area.

In view of wide variations in biological production in a marine ecosystem, the

biological parameters considered for the present evaluation are phytoplankton

(pigments, population and dominant genera), zooplankton (biomass, population and

faunal groups), macro benthos (biomass, population and faunal groups), status of

mangroves, fishery, marine reptiles, mammals and birds.

Table: 3.10 Concentration of Chlorophyll (µg/L)from 2002 to 2011

Chlorophyll Content (µg/L)

Sampling

locations

Year

2002

Year

2003

Year

2004

Year

2005

Year

2006

Year

2007

Year

2008

Year

2009

Year

2010

Year

2011

S6 0.629 1.005 0.430 0.761 0.944 0.961 0.524 0.735 1.255 0.496

S7 0.534 0.793 0.411 0.749 0.785 0.896 0.512 0.534 1.029 0.484

S8 0.426 0.673 0.413 0.564 1.115 0.464 0.408 0.437 0.644 0.361

S9 0.389 0.642 0.405 0.459 0.766 0.443 0.408 0.417 0.492 0.251

Primary productivity, which involves conversion of inorganic materials into living

biomass, is the foundation block of all the processes in the biosphere. The eastern

part of the Bay of Bengal including the study area is one of the high productive

zones. The higher chlorophyll concentration in the Bay of Bengal is attributed to the

vertical mixing of its water, higher nutrient concentration. Annual average of

Chlorophyll content from 2002 to 2011 in the study area is given in Table 3.10.

The surface productivity in terms of carbon is estimated to be 3.9 t/km2 in the Bay of

Bengal while, the corresponding integrated column productivity is computed to be

3.8 – 8.7 gcm-2d-1 which is less than 300 gcm-2yr-1. The seasonal variation in the



74

‘chlorophyll-a’ content in the Bay of Bengal is given in Table: 3.11. This is attributed

to the monsoons.

Table: 3.11 Seasonal differences in productivity and chl-a.

Season Chl a (µgl-1)

Pre-monsoon 0.62-25.9

Monsoon 0.86-15.9

Post-monsoon 2.36-16.2

Annual average 1.28- 19.33

(Source:Soo ria,P.M et al (2011) Influence of the river influx on Phytoplankton

community during fall inter – monsoon in the coastal waters off Kakinada , east

coast of India, Indian Journal of Geo-Marine Sciences, 40(4) pp- 550-558

Table: 3.12 Observed Values of Chlorophyll-a

Biological

Parameters

Observed Values

S1 S2 S3 S4 S5 S6 S7 S8 S9

Chl a(µgl-1) 6.57 7.25 7.88 7.23 7.56 0.89 0.67 0.31 0.49

The phytopigment concentration (Table 3.12), diversity index and density in the

study area shows marked variation in the block. Sampling locations S1-S5 which are

relatively near to the coast and shows high pigment concentration (6.57-7.88 µgl-1).

Whereas, at points S6-S8, which are far from the coast and has low pigment

concentration (0.31-0.89). Observed Phytoplankton diversity index and

phytoplankton density varies from 2.91 to 4.70 and 14-41 respectively. Details of

Diversity Index and Density for the observed Phytoplankton in the study area are

given the Tables: 3.13 (a) and 3.13 (b) below.

Diplonet and Nizschia closterium was the dominant genera in the surface samples

while Triceratium favus in midwater and Chaetoceros in the bottom samples were

dominant.

EIA for Development Drilling of 45 wells at Block KG-DWN-98/2, KG Offshore in NELP-I Block KG-DWN-98/2, KG

Offshore, Andhra Pradesh

62

Table: 3.13 (a) Observed values of Phyto-planktons in S1-S5.

S. No.

Name of Phyto-plankton

S1

S2

S3

S4

S5

Diversity Index Density

(Individual/Litre)

S1 S2 S3 S4 S5

S1

S2

S3

S4

S5

1 Rhodophyta y y y Y y

4.

6

4.

55

4.

30

2.

91

4.

7

1

6

1

4

1

7

2

3

1

8

2 Phaeophyta y y y Y y

3 Achnanthes

stromii

x y y y x

4 Aulacodiscus

orbiculatus

x y x y x

5 Ceratium belone x x x y x

6 Coscinodiscus

lineatus

x y y x x

7 Nitzschia

forcipata

x y x y x

8 Triceratium

favus

y y y y y

9 Diplonets sp. y y y y y

1

0

Amphidinium

curcubita

y y y y y

1

1

Ornithocercus

heteroporus

y y y x y

1

2

Lyngpyamajuscu

la

x y x y x

1

3

Oscillatoria

acutillsima

x x x y x

1

4

Cyclotella striata y y y y y

1

5

Amphidium

klabsie

x y y y y

1

6

Bacillariaparatox

a

x y x y x

1

7

Gymnodinium

falcatum

y y x y x



63

S. No.

Name of Phyto-plankton

S1

S2

S3

S4

S5


(Individual/Litre)

S1 S2 S3 S4 S5

S1

S2

S3

S4

S5

1

8

Dinophysis

hastata

x y y y y

1

9

Eucampia

cornuta

x y y y x

2

0

Bacteriastrum

pavillardii

y y y y y

2

1

Amphora

decussata

y y y y y

2

2

Ceratium

longirostrum

y y X X X

2

3

Gonyalax

monilata

y y X X X

2

4

Dinophysis

Ovum

x x X X X

2

5

Shizothrix

calcicola

x y X X X

2

6

Ceratium

schroteri

y y X X X

2

7

Cocconies

littoralis

x y X X X

2

8

Oxpoxum sp. x y X X X

2

9

Gonyaulax

polyedra

y y X X X

3

0

Chaetoceros

diversus

y y X X X

3

1

Nizschia

closterium

x x y y y

3

2

Chaetocerospel

agicus

x x y y y

Note: x- denotes species not found in area, y- denotes species present in area.



64

Table: 3.13 (b) Observed values of Phyto-planktons in S6-S9.

S

No.

Name of the

phytoplankton

S

6

S

7

S

8

S

9

Diversity index Density (No. of

individuals/Litre)

S6 S7 S8 S9 S6 S7 S8 S9

Spermatophyta

3.

1

4.

2

4.

7

3.

5

19

26

41

23

1 Azolla Sp. X X X x

2 Spirodela Sp. Y y y x

3 Wolffia Sp. y X x Y

Chlorophyta

1 Westella x X x y

2 Selenastrum x X x X

3 Zygnema Sp. x X x X

4 Chlorella Sp. X X x X

5 Clostrium Sp x X x X

6 Mougeotia Sp X X x X

7 Oocystis Sp. X X x X

8 Sitchococcos

Sp.

X X x Y

9 Tetrastrum

Sp.

X X x Y

10 Crucigenia

Sp.

X X x Y

11 Pithopora Sp. x X x y

12 Chalamydomo

nas Sp

x y Y X

13 Pediastrum

Sp.

x y Y X

14 Volvox Sp. x y X X

15 Zygnema Sp. y y X X

16 Ulothrix Sp. x y Y X

17 Dictyosphaeri

um Sp

x X Y X

18 Schizomeris

Sp.

x X X X



65

S

No.

Name of the

phytoplankton

S

6

S

7

S

8

S

9


individuals/Litre)

S6 S7 S8 S9 S6 S7 S8 S9

19 Euastrum Sp. y X X X

20 Actinastrum

Sp.

y X X X

21 Nitella Sp. x X Y X

Cyanophyta

1 Gloetrichia

Sp.

x Y X X

2 Phormidium

Sp.

y X Y Y

3 Lingbya Sp. y X Y Y

4 Oscillatoria

Sp.

y Y Y Y

5 Fragelira Sp. x X X X

6 Althrospira

Sp.

x X Y X

7 Cylindrosperm

um Sp

y X X Y

8 Anabena Sp. x Y X X

9 Anacystis Sp. x Y X x

Diatoms

(Bacillareophyceae)

1 Tabellaria Sp. y Y Y Y

2 Synedra Sp. y y Y Y

Chrysophyta

1 Cocconeis Sp. y y Y Y

2 Achnanthes

Sp.

y y Y Y

3 Cyclotella Sp. y y Y Y

4 Rhizosolenia

Sp

y y Y Y

Xanthothytea

1 Botryococcus y y Y Y



66

S

No.

Name of the

phytoplankton

S

6

S

7

S

8

S

9


individuals/Litre)

S6 S7 S8 S9 S6 S7 S8 S9

Sp.

Rhobophyta

1 Gracilaria Sp. y x X x

2 Champia Sp. y x X x


Zooplankton

The secondary production has been estimated to be 18.5 mgC/m2/d for the Bay

of Bengal, with the corresponding annual production rate of 6.0 x 106 t C/y. The

observed zooplankton Diversity Index in the studied area varies from 1.74 to 3.46

whereas; the density varies from 9 to 28 individuals/litre. Details of Diversity

Index and Density for the observed zooplankton in the study area are given the

details given in Table 3.14 (a) and (b).

Table: 3.14 (a) Observed values of Zooplankton in S1-S5.

S.

No

.

Name of

Zoo-

Planktons

S

1

S

2

S

3

S

4

S

5


(Individual/Litre)

S1 S2 S3 S4 S5 S

1

S

2

S

3

S

4

S

5

1 Foraminifera x x x x x

2.6

3

1.9

4

3.4

6

1.9

4

1.9

6

9

1

3

1

6

1

1

1

5

2 Decapoda y y y y y

3 Ciliata y y y y y

4 Hydrozoa y y y y y

5 Rotifera y y y y y

(i)

Brachionus

sp.

y y y y y

(ii)Ashplanc

he brighwelli

x x y y y

(iii) Stentor

sp.

x x y x y

6 Chaetognat x x y y y



67

S.

No

.

Name of

Zoo-

Planktons

S

1

S

2

S

3

S

4

S

5


(Individual/Litre)

S1 S2 S3 S4 S5 S

1

S

2

S

3

S

4

S

5

ha

7 Loxodes sp. x x y y y

8 Copepoda x y y y y

(i)

Macrocyclop

s ater

x y y y y

(ii)Senecella

calanoidea

x y x x x

9 Chaborus

sp.

y y y y x

10 Sarcodina

sp.

y y y y y

11 Mysidaceae x x y x x

12 Rotararia

sp.

x x y y y

13 Calanoida y y y y y

14 Harpacticoid

s

x x x x x

15 Pteropoda y x y y y

16 Cladocera y x x y y

17 Doliolida x x y y y

18 Cyclopoids x x x y y


Table: 3.14 (b): Observed values of Zooplanktons in S6-S9

Sl. No.

Name of the Zooplanktons

S6 S7 S8 S9

Diversity Index/ Density (Individual/Litre)

S6 S7 S8 S9

1 Amoebas 3.1/

28

3.24/

28

2.74/

19

1.74/

21

(i) Naegleria Sp. x y x x

(ii) Actinophrys Sp. x x x x



68

Sl. No.


S6 S7 S8 S9


S6 S7 S8 S9

(iii) Acanthamoeba Sp. x x x y

2 Coelenterates

(i) Hydra Sp. y y x x

(ii) Anthopleura Sp. y y x x

(iii) Obelia Sp. x x y x

3 Rotifers

(i) Philodina Sp. y y y x

(ii) Euchlanis Sp. y y y y

(iii) Proales Sp. y y x x

(iv) Flagellates Sp. y y x x

(a) Ceratium y y x x

(b) Peridinium y y x x

(v) Filinia Sp. x x x x

(vi) Keratella Sp. x x x x

(vii) Epiphanas x x x y

(viii) Monostyla x x y y

(ix) Kellicottia Sp. x x y x

(x) Brachionus Sp. x x x x

4 Cladocera

(i) Daphnia Sp. x y x y

(ii) Alona y x x x

5 Ostracoda

(i) Ostracod Sp. y y y x

6 Mysidacea

(i) Holmesimysia Sp. y y x y

7 Cirripedia

(i) Balanus Sp. y y x y

8 Flagellaes

(i) Haematococcus Sp. x x x x

(ii) Chromulina Sp. x x x x

(iii) Ochromonas Sp. x x x x

(iv) Astasia Sp. x x x x

(v) Lobomonas Sp. x x x x



69

Sl. No.


S6 S7 S8 S9


S6 S7 S8 S9

(vi) Petromonas Sp. x x x x

(vii) Non Pigmented Sp. x x x x

(a) Dinomonas Sp. x x x x

9 Leptostraca

(i) Epinebalia Sp. x x x y

10 Cumacea

(i) Oxyurostylis Sp. x x x y

11 Ciliates

(i) Lionotus Sp. x x y y

(ii) Pleuronenema Sp. x x y y

(iii) Colpoda Sp. x x x y

(iv) Aspidisca Sp. x x x y

12 Cladophora x x y x

13 Copepoda

(i) Diaptomus x x y x

14 Crustacea

(i) Daphnia Sp. x x y x

(ii) Cyclops Sp. x x y x

Note: x -denote species not found in area and y- denote species present in area

Benthos

Benthos, the seafloor biota, contributes substantially to the secondary production

as also to the potential and sustainability of demersal or near bottom living

fishable resources. The sub-tidal benthic standing stock in terms of diversity

index and density varied from 1.28 to 1.42 and 12 to 14 individual /litre

respectively, given in Table 3.15 along with the identify benthos in the study area.



70

Table: 3.15 Observed values of Benthos in S1-S5

S.

No

.

Name of

Benthos

S

1

S

2

S

3

S

4

S

5


(Individual/Litre)

S1 S2 S3 S4 S5 S

1

S

2

S

3

S

4

S

5

1 Bivalvos y y Y Y Y

1.4

2

1.3

8

1.4

0

1.3

6

1.2

8

1

4

1

2

1

4

1

4

1

2

2 Decapods y y Y Y Y

3 Polychaetos y y Y Y Y

(i) Nameneris

quadraticeos

y y Y Y Y

(ii) Nereis

lamellose

y y Y Y Y

4 Amphipods y y Y Y Y

5 Gastopods y y Y Y Y

(i) Bellamya

bencalensis

y y y X Y

6 Cermaceans y y Y Y Y

7 Ostrecods y y Y Y Y

8 Microbenthos y y Y Y Y

(i) Nitzschia y y Y Y Y

(ii) Navicula y y Y Y Y

(iii)Pleurosig

ma

y y X Y Y

9 Macrobentho

s

y y Y Y Y

(i) Tonne y y Y Y Y

(ii) Amussium y y Y Y Y

10 Diaoatra

naepolitane

x y y Y Y

Fishes

The well locations are located in Bay of Bengal off the coast of Andhra Pradesh. The

region is endowed with rich Marine inland and Brackish Water Fishery Resources listed



71

in Table 3.16. Apart from this, in these areas prawn seed resources in general and those

of P. monodon and P. indlcus in particular are abundantly available. Post-larve of these

species are commercially exploited in various places such as Ichapuram (Srikakulam

District), Vakapadu (Visakhapatnam District), Kakinada and adjacent mangrove areas of

Godavari estuary (East Godavari District), Perumpalom (West Godavari District),

Kruthivenu and Machilipatnam (Krishna District) and Repalle (Guntur District).

Table: 3.16 Marine Fish Species in KG Basin Coastal Stretch

S. No.

Marine Fish Species

ELASMOBRABCH

ES CLUPEIDS PEACHIS

FLAST FISHES

DRIFT FISHES

MISC. FISHES

1 Shark Wolf Herring

Groupers-Epinephlus Sp.

Halibut India drift fish

Flat heads

2 Skates Oil Sardine

Shappets-Lutjanus sp.

Flounders Other drift fish

Gerrids

3 Rays

Other Sardine

Pigface Breams

Sole (Flat fish)

Barracudas

Lantern fish

4 Eels Hilsa Shad

Silver Grunt (Karkara)

Big jawed jumber

Milk fish

5 Cat Fish Other Shad

Other Perches

Monocle fish

6 Coila Goatfishes Moon fish

7 Anchovies Threadfins Mullets

8 Setipinna Croakers Parrot fish

9

Stolephorus (Anchoveilla)

Silverbellies (Pony fishes)

Sickle fish

10 Thrissina

Sillagas (Whitings)

11

Thrysa(Thrissocies, Engraulis)

Spade Fishes

12

Other Clupeds

Squirrel Fishes

13

Bombay Duck

Surgeon Fishes

14 Lizardfishes Tarpon



72

S. No.

Marine Fish Species

15

Bulls eye (Priacanthids)

Terapon

16

Threadfin bream

Priacanthidas

17

Trigger Fish (Blastids)

18

Unicorn cod (Brgmeeros)

CARANGIDS OTHER

PEALAGIC FISHES

SEERFISHES

OCEANIC TUNAS

NERITIC TUNAS

MACKERALS

1

Trevallies-Caranz Deepsea pomfrtes (Bramidae)

Narrow-Barred Spanish Mackerel

Bullet Tuna

Bullet Tuna

Indian Mackerels

2

Horse Mackerel Dolphin fishes

Indo-pacific Spanish Mackerel

Frigate Tuna

Frigate Tuna

Other Mackerels

3

Scads-Decapterids Flying Fishes

Streadked Spanish Mackerel

Little Tuna (Kawa kawa)

Little Tuna (Kawa kawa)

4 Leather-jackets (Queen Fishes)

Fullbeaks & Half beaks

Wahoo Longtail Tuna

Longtail Tuna

5 Rainbow runner Lancet Fish

Streadked Spanish Mackerel

Other neritiv Tunas

Other neritiv Tunas

6 King fish (Elacate) Sucker Fish Wahoo

7 Seriola Sun Fish

8 Other Carangids

9 Ribbonfishes

POMFRETS DEEP SEA FISHES

LOBSTERS (Littoral)

BIVALVES & GASTROPODS

CEPHALOPODS

OTH. INVERTIBRATES

1 Silver pomfret Green Eye

Panulirus spp.

Bivalves Cuttle Fish Jelly Fish

2 Chinese pomfret

Black ruff (Medusa fish)

Other Lobsters (Littoral)

Gastropods

Octopus Marine turtiles

3 Black pomfret Red baits

Deep Sea Lopsters

Squids



73

S. No.

Marine Fish Species

4 Sack Fish

Squid-Oceanic

5

Deepseashaks

MARINE MAMMALS

SHRIMP (LITTORAL)

OTHER CRUSTACEANS

SHRIMP (DEEP SEA)

1 Dolphin & porpoise

Penaed-Aristaeomorpha spp

Crabs-Charybdis spp

Penaied-Aristeus spp

2 Seacow

Penaeid-Metapenaeus-spp

Crabs-Neptunus spp

Penaeid-Metapenaeus-sp

3

Baleen whale Penaied-Parapernaeopsis-spp

Crabs-Portunus spp

Non-Penaied-Hetrocarpus spp

4

Toothed whale Penaeid-Penaeus spp

Other Crabs

Non-Penaied-Parapandalus spp

5

Penaeid-Solenoceera spp

Stomatopode-Oraposqulilla

Non-Penaied-Plesionikka spp

6

Other Penaeid Shrimp

7

Non-Penaeid shrimps

Source: Statistical Data on Fisheries in East Godavsri District, State Department for Fisheries, 2012



74

CHAPTER-4

Identification, Prediction and Evaluation of Impacts

4.1 Identification and Assessment of Impact

This section presents the likely impacts identified and recommends mitigation measures based

on the proposed project activities and the baseline information provided in Chapter-3, the

activities have potential to impact on the following environmental resources:

Table: 4.1 Identification of Potential Impacts: Activities –Impacts/Risks Interaction

Environmental Sensitivities

Physical Biological Socio-

economic

Impacts/ Risks

Activities

Air

Qu

ality

No

ise

Wa

ter

Qu

ality

Se

dim

en

t Q

uality

Aq

ua

tic

Flo

ra

Aq

ua

tic

Fa

un

a

Lo

cal fi

sh

po

pu

lati

on

Oc

cu

pati

on

al

Ex

po

su

re &

Ge

nera

l S

afe

ty

Ec

on

om

y

Positioning and deployment of

rig

Power generation at site

Drilling Operation

Well completion

Water requirement and

wastewater discharges



75

Environmental Sensitivities

Physical Biological Socio-

economic

Impacts/ Risks

Activities

Air

Qu

ality

No

ise

Wa

ter

Qu

ality

Se

dim

en

t Q

uality

Aq

ua

tic

Flo

ra

Aq

ua

tic

Fa

un

a

Lo

cal fi

sh

po

pu

lati

on

Oc

cu

pati

on

al

Ex

po

su

re &

Ge

nera

l S

afe

ty

Ec

on

om

y

Solid Waste generation

Fuel storage and handling

Transport of personnel and

materials

Note: denotes likely impact, denotes positive impact

Based upon the above interaction matrices following potential impacts have been identified:

A. Physical

Air Quality

Noise

Water Quality

Sediment Quality

B. Biological

Aquatic flora and fauna

Local fish population

C. Socio-economic

Occupational Exposure & General Safety



76

Economy

Drilling and other associated activities would incorporate measures for minimising adverse

environmental impacts. These impacts have been discussed in details in the following sections.

4.2 Impact Prediction

4.2.1 Impact on air environment

There are a number of sources of emissions in the offshore development drilling drilling which

include

Emissions from MODU and support vessels

Emissions from DG sets

Helicopter emissions

Fugitive emissions from diesel storage tanks

The expected pollutants raise from these sources are carbon di-oxide (CO2), oxides of nitrogen

(NOX), Sulphur dioxide (SO2), Carbon Monoxide (CO), Hydrocarbons (HCs), PM10 and PM 2.5.

Drilling consumes a considerable amount of electric power and the MODU is equipped with a

power generating capacity of 1430 kVA of each from 4 nos. of DG sets. Anticipated levels of

emissions of these gases are low. The dispersive wind conditions in the area and low emissions

levels expected suggest negligible impacts. Impacts due to CO, HC and SO2 levels at offshore

are not envisaged, considering the height of release (about 30 m above sea surface including

the height of stack of DG set i.e. 5-6 m), wind directions both in North and North East (NNE),

and wind speeds varying from 2-6 m/s, the maximum concentration of NOx at sea surface will

be around 4-5 µg/m3 at a distance of about 1 km in downwind direction. However, the offshore

drilling activity is temporary and limited to 45-90 days (under normal condition), and with a high

wind speed in the open sea area shall lead to greater dilution of pollutants, which shall increase

with increasing distance from the source. Moreover, absence of sensitive receptors shall render

the impacts due to air emission as negligible. Air emissions may result from gas flaring activities

during the well testing only (one or two days). Once the wells are completed sub-sea for

production, no well intervention is envisaged in normal operations. Only life of field services and



77

certain mandatory sub-sea activities are envisaged, which are of short duration in nature. Hence,

no major environmental impacts are envisaged.

Table: 4.2 Emission Characteristics –Model inputs

Sl.No. Particulars DG set (4X 1430 kVA)

1. No.of engines and stacks 4

2. Height above sea level 30 m

3. Diameter 0.5

4. Gas temperature (oC) 300

5. Gas velocity (m/s) 15

6 Emission rate (g/s)

Sulphur dioxide Oxides of Nitrogen

0.0026

0.44

4.2.2 Impact on Noise Quality

High noises are likely to be generated due to DG sets, mud pumps, rig machinery and

compressors and equipment machinery on supply vessels and Helicopter during landing and

take-off. The noise levels generated from various sources during offshore exploratory drilling

operations is as follows:

Helicopter 103 to 105 dB(A)

Diesel Generators 100 to 105 dB(A)

Mud pumps 90 to 100 dB(A)

Miscellaneous 80-85 dB(A)

Rig floor 65-73 dB(A)

Accommodation 50-60 dB(A)



78

However, these impacts shall not cause any physical damage to the marine organisms as the

propagation of sound through water is generally affected by spreading (distance) losses and

attenuation (absorption) losses with sound energy decreasing with increasing distance from the

source. Also, available information on marine fish and other marine mammals indicate that they

are unlikely to intentionally approach operations producing continuous and semi-continuous

noise and thus likely to be avoided by them (Nedwell et al., 2004 and Thomsen et al., 2006).

Therefore, the impacts on the marine fauna due to noise generation during the project activities

have been envisaged to be minimal. The effect of high noise on the people working on the rig

will be reduced by using PPE.

4.2.3 Impact on Water Quality

Number of activities related to various phases of the proposed drilling activity has the potential

to impact marine water quality and consequently marine ecology adjacent to the drilling

locations. Some near shore activities like handling of chemicals and oil may also impact marine

environment. Some of the activities which cause potential impacts to marine environment are:

The base line water quality parameters observed in the sampling areas shown in Table: 3.8 are

well below the minimum prescribed limits. The average D.O is 6.1 mg/l is close to saturation

levels and the heavy metals (Hg, Cr, Pb, Cd, Al, Cu) were below detectable limits. The

concentration of iron was in the range of 0.13 to 1.62 mg/l. Oil content in the range of 2.6 to 3.9

µg/L. As it is confirmed by ICMAM (Integrated Coastal and Marine Area Management) that the

quality of the sea water samples collected from the coast from various distances and locations

were found unpolluted and water beyond 2 km is clean in the east coast Bay of Bengal.

Physical presence of drilling rig

Disposal of drill cuttings and unused mud

Operational discharges like sanitary waste water, washing fluids (deck drainage, rig

floor washings) etc.

Non-routine discharges that may be caused by ballast water, chemical spills etc.

Food waste and residuals.



79

Offshore deployment of floater rig and other sub-sea facilities (BOP) has been envisaged to

cause short term and local increase in turbidity levels due to disturbance of seabed sediments.

Displacement of sea bed sediments may lead to oxidation of anoxic intertidal and offshore mud.

This shall cause local chemical changes in water quality by a subsequent decrease in pH (due

to oxidation of sulphides to sulphate) and increase in BOD levels. However, these impacts have

been envisaged to be local and temporary and water is expected to regain its original

characteristics within short span of time. Water quality can also be affected due to the discharge

of drill cuttings, drilling mud, accidental spillage of chemicals, oil & lubricants during the

deployment of rigs, operation of generators and transportation of vessels. However, impacts

from these sources have been envisaged to be insignificant due to adoption of good work ethics

and suitable mitigation measures throughout the drilling activities.

4.2.4 Impact on Sediment Quality

Deployment of rigs and other sub-sea infrastructure may cause local and temporary disturbance

to the seabed due to sediment suspension and changes in sea bed morphology. However,

these impacts shall not contaminate the sediments as no discharge of pollutants has been

anticipated from operation of drilling equipment or other project activities. Sediment quality is

less likely to be affected due to operational discharges (including liquid and solid discharges) or

accidental spillage of fuel, chemical or lubricant during the project activities. However, these

impacts shall be mitigated by adoption of suitable measures and implementation of waste

management plan.

4.2.5 Impact on Biota

Impact on marine biodiversity may also occur due to accidental spillage of chemicals, oils,

lubricants and operational discharges; release of plastics or other solid wastes. However, these

impacts will be mitigated by adoption of suitable measures and good work ethics.



80

4.3 Impact Evaluation

Operational impacts

Offshore rig deployment shall temporarily affect the local seabed habitats and species but the

area affected being a small percentage of the total area of similar habitats in this offshore

location and consequently the loss of areas of muddy/salty habitat is considered to be of low

magnitude at a community ecology level. The magnitude of these changes will be low. Any

change to habitat conditions is anticipated to be small and expected to only slightly alter the

conditions and dependent community structure. Also, the negative impacts of seabed structures

on benthic communities are assessed as being of minor significance. Stages of drilling and their

impact on environment as given below

4.3.1 Rig Movement and Anchoring.

The use of a DP rig (proposed for deep water exploratory drilling) is likely to cause suspension

and movement of sediments and hence may result in damage of suitable habitats in which

organisms live. The perturbations may however not be significant at these depth recovery time

is expected to be short. Additionally, drilling operations will increase the potential for pollution

from vessels transporting supplies and personnel to and from the rig. The resultant pollution is

however considered relatively small and short termed. The physical presence of the rig could be

an obstacle to passing ships and an attraction to roosting birds and may act as a fish

aggregating device. On the whole drilling operation are not expected to have any deleterious

effects on the environment.

4.3.2 Spudding the Well.

Initial drilling into the sea bed (spudding the well), results in the direct discharge to sediments.

This would lead to suspension, movement and relocation of the sediments which may cause

destruction of suitable habitats for some biological organisms and expose fauna to predators

and hostile environs. The sediment suspension and relocation can also lead to the introduction

of pollutant materials into the water column of the area. The amount of pollutant materials will be

negligible and the impact is temporary as the area affected is expected to be localized within a

few meters of the activity.



81

4.3.3 Discharge of drilling mud and cuttings

The water based drilling mud and cuttings would have low toxicity with LC 50 > 30,000 mg/l. All

the mud additives also have low toxicity levels. Mud system is a closed circulatory system. Mud

coming out from the well bore with cuttings is passed through solid control equipment (shale

shaker, de-sander, de-silter and mud cleaner) and circulated back into the hole after treating for

the rheological parameters. Only small quantity of mud is wasted during drilling approx. 5%

coated with drill cuttings. Un used water based mud after completion of the drilling is discharged

to sea after dilution as per GSR546(E ). Experimental studies conducted in various offshore

regions indicate that even in bulk discharges involving 1000 barrels/h, the resultant turbidity in

water rapidly decreases with distance leaving very low suspended matter beyond 100 m in the

sea surface. Depending on the quantity of cuttings disposed, the bottom dwelling organisms

may be smothered or be forced to migrate to far distances. Water based muds may have a

relatively high level of organic components which can give rise to an organic enrichment that

can modify the benthic fauna in various levels.

4.3.4 Other Aqueous Discharges.

Aqueous discharges from rigs are usually from segregated caissons situated either above or

below mean sea level. They include sewage, domestic waters, deck drainage and ballast.

Sewage discharges include sanitary waste and grey water, that is, water from showers, sinks,

garbage disposal etc. Generally, it is assumed that one person produces 0.1 m3 per day of

sewage effluent (including flushing). This is in addition to 0.2 m3 per person per day which is

mostly water with traces of edible oils and soaps. The impacts of such discharges depend on

the factors that affect the dispersion and diluting of such effluents. Close to the point of

discharge, the effluent characteristics is dependent on the discharge density, the flow rate and

the ambient water current. At various distances from the point of discharge, the environmental

effects are dependent on recipient environmental conditions in the particular area including

winds, surface and sub-surface currents.



82

4.3.5 Diesel spills.

The likely points of spill for diesel are loading points during ship to rig transfer and leaks from

storage facilities. Diesel is light oil with many aromatic components; as such evaporative losses

after a spill will be very high. Up to 70- 80% of the spilled oil is expected to be lost to evaporation

within the first 24 hours of release. Factors that will affect rate of evaporation include prevailing

environmental conditions.

4.3.6 Blow-outs and other oil spills.

Oil spills include base oil, lube oil or crude oil from a blow-out. During well testing operations, an

oil/condensate spill would occur if incomplete burning at the test flare allowed oil droplets to fall

into the sea. A blow out which results in the sudden uncontrolled gushing of oil out of a well is

perhaps the most potentially ecologically damaging of accidents. In such situations, the sea is

sprayed with an oil jet for a period of time until the blow out is controlled. Crude oil spills from

blowouts can cover a wide area depending on the amount spilled. They are less toxic and easily

evaporated. The direction of the spill movement depends upon the ocean surface winds and

ocean current speeds. The rest may be emulsified with wave action and travel in the direction of

surface currents. This need to be contained, recovered and safely disposed.

The south west monsoon period (June-September) is the worst period from the point of view of

spill management in which the spill may approach the coast of Andhra Pradesh. The spill may

affect the mangroves and prawn culture being carried out along the coast.

4.4 Impact Significance

Evaluation of impacts signifies the potential impacts in terms of its likelihood nature as per the

following criteria:

1. The impacts are further classified based on their spatial distribution, i.e. local, when

impacting an area of approximately 1 km radius from the project area, moderate spread,

when impacting an area of 1 to 2 km radius and regional beyond 2 km;

2. The impacts are classified as short term, moderate term and long term in terms of their

existence in temporal scale. Impacts less than 1 year existence as short term, while

those with 1 to 3 years as moderate term and more than 3 years as long term;



83

3. The negative impacts are termed as adverse impacts while positive impacts as

beneficial;

The significance of environmental impacts of various involved activities has been evaluated

based on the criteria outlined in Table 4.3.

Table: 4.3 Impact Significance Criteria

Impact Significance Criteria

Major Adverse When the impact is of high intensity with high spread and high

duration or of high intensity with medium spread and medium

duration

Moderate Adverse When the impact is of moderate intensity with high spread and

high duration or of high intensity with low/ moderate spread and

low duration

Minor Adverse When the impact is of low intensity but with moderate spread and

moderate duration or of moderate intensity

Insignificant Adverse When the impact is of low intensity, low spread and low duration

Beneficial When the impacts are positive

Based on the above-specified criteria, Tables 4.4 and 4.5 describes potential environmental

impacts due to exploratory drilling and associated activities, without or with mitigation measures

respectively. It is important to note that one activity may have varying impacts on different

receptors i.e. different components of the environment. To avoid repetitions, this section

describes various activities, which may have wide impacts on many receptors. For example,

waste generation and disposal will have impacts on aquatic ecology, sea water surface, odor

nuisance etc, therefore, the impacts of waste generation and disposal have been considered as

one of the key areas of impacts. Similarly, gaseous emissions may be adverse to air quality;

which on exposure may impact upon health of individuals and ecology in the surroundings.



84

Table: 4.4 Potential Environmental Impacts of Proposed Project activity

(Without Mitigation Measures)

Environmental

Sensitivities Nature of Likely Impacts

Impact

Significance

L

ow

In

ten

sit

y

Mo

de

rate

Inte

nsit

y

Hig

h I

nte

ns

ity

Lo

cal

Mo

de

rate

Sp

read

Re

gio

na

l

Sh

ort

Term

M

od

era

te

Term

Lo

ng

Term

Ad

ve

rse

Be

ne

fic

ial

Insig

nif

ican

t

Min

or

Mo

de

rate

Ma

jor

Air Quality

Noise

Water Quality

Sediment Quality

Aquatic Flora

Aquatic Fauna

Local fish

population

Local Economy

Note: For color coding refer Table 4.2

4.5 Impact Mitigation Measures

During the drilling process, the major environmental hazard emanates from the discharge of

drilling wastes and oil spillage from an accidental blowout. Surface spills are considered to be

less harmful than underwater spills. The presence of the rig in the deep sea environment has an

overall positive impact as it can be used as a fish aggregating device. Available environment,

information in this area does not indicate the presence of any protected habitat or endangered

species. Compliance with the existing regulations on the disposal of drilling wastes would

reduce their impacts on the environment.

In initial phase of drilling, ONGC will use water based mud which is more eco-friendly due to its

low toxicity and lesser impact upon its discharge into the sea. Chemicals to be used in water

based mud will have LC50 > 30,000 mg/l. Drilling mud after completion of drilling will be used in



85

drilling operations at other locations. Bulk discharges of drilling fluids are prohibited in offshore

except in emergency situations. Synthetic Oil Based Mud (SOBM) is used to mitigate the

specific hole problems. The SOBM will have low toxicity and meet LC50 > 30,000 mg/l as per

mysid toxicity test or toxicity test conducted on locally available sensitive species. The chemical

additives (mainly organic constituents) used in the preparation of drilling fluid are bio-

degradable. Therefore, impact on biological environment will be minimal.

Drill cuttings generated in the drilling process are naturally occurring earth materials comprising

of chips of sandstone, shale, sand and lumps of clay. Their discharges do not cause significant

impact on marine water column as they settle down to the sea bottom and will not form heaps

due to higher water depths and strong currents. Traces of WBM / SOBM coated on drill cuttings

generally disperse in the water column causing temporary little increase in turbidity in the area

of release.

The domestic waste discharges such as galley wastewater and sewage generated in the drilling

rig increase in turbidity in the water column temporarily. Chlorination is done before discharge.

However, drilling rigs has domestic sewage treatment facilities for waste generated from

accommodation areas and the effluent released to the sea will meet standards prescribed by

MARPOL.

Some quantity of waste oil generated from the machinery of the drilling rig is of concern for its

disposal. Any disposal of waste oil into the sea is prohibited as per Merchant Shipping Act as

well as Environment Protection Act and all oily discharges will be treated to the required

standard. The spent oil will be brought to shore and disposed to authorized recyclers.

Various types of solid wastes are generated on drilling rigs from accommodation area and

process operations. Apart from being aesthetically undesirable, some wastes such as plastic

are not biodegradable and accumulate on the sea floor when released to the sea, causing

nuisance to benthic organisms. These wastes are not allowed to be disposed at sea. The food

wastes from the kitchen, degradable materials like paper etc. however, form food for marine

biota, hence allowed to be discharged in the sea. The impact of drilling operations on fisheries

or fishing activities is considered insignificant as these blocks are 28-250 km away from the

coast.



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4.5.1 Air Environment

Offshore receptors such as fishing vessels and commercial shipping are unlikely to be exposed

to poor quality air other than for very short durations, for example if sailing very close and

downwind of the site during flaring.

Mitigation of air emission impacts is done through:

Good operational controls and high level of monitoring shall be built into the design

operational aspects of the project.

Regular maintenance of engines and generators shall be done to keep the

environment impact minimum.

Existing and the proposed DG Sets will comply with the applicable emission norms.

Scrubbers will be provided to minimize the emissions and to maintain the emissions

within the prescribed limits.

Regular monitoring of emissions (from all DG Sets) and ambient air quality will be

carried out as per norms.

Emissions during transportation shall be minimized by ensuring regular maintenance

of the vessels.

Stack height shall be maintained to the optimum levels

4.5.2 Water Environment

Bulk discharge of drilling fluid in offshore is prohibited except in emergency situations.

Water Based Mud WBM will be recycled to the maximum extent. Unusable portion of

WBM will be discharged offshore into sea intermittently, at an average rate of 50 bbl/hr

as per G.S.R. 546 (E), dated 30/08/05, so as to have proper dilution and dispersion

without any adverse impact on marine environment.

Use of only low toxicity chemicals shall be ensured on board.

Sewage will be treated on-board of the rig as per MARPOL regulations. Residual

chlorine of the treated sewage shall not exceed 1mg/L before disposal.

Oily wastewater from deck washing, drainage system, bilges etc will be treated using on

board oil traps and will be disposed to sea as per norms laid by CPCB/APPCB.



87

According to MARPOL regulations the discharge of oil content (without dilution) into sea

shall not exceed 15 ppm.

Adequate well management shall be ensured during well completion activities to

minimize produced water production.

Oil drilling operators shall maintain daily record of discharge of drill cutting & drill fluid to

offshore and also to monitor daily the effluent quality.

In case of oily cuttings, they will be transported on shore for appropriate disposal.

4.5.3 Impact on Biota

All precautionary measures shall be adopted to minimise disturbance to the marine animals due

to deployment and operations of offshore wells. The baseline information on existing marine

species in the area shall be obtained from state/district/regional level authorities and other

sources in an effort to reduce the potential adverse impacts of the project and future activities on

marine species.

4.5.4 Occupational Health Hazards from Noise Pollution

Site workers working near high noise equipment will use personal protective equipment to

minimise their exposure to high noise levels. Good working practices will be implemented to

reduce noise impact on the health and environment.

4.5.5 Noise Impacts due to Drilling Activities

Mobile noise sources such as rig and vessels shall be routed in such a way that

there is minimum disturbance to receptors.

Avoid loud, sudden noises, wherever possible. Integral noise shielding shall be used

where practicable and applicable.

Rubber padding/noise isolators shall be provided at equipment/machinery used

during the project activities.

Regular maintenance of all equipment and transportation vessels shall be ensured.

Idling of vessels or equipment shall be avoided when not in use.



88

4.5.6 Waste Generation and Management

The site would develop and adopt proper system for the management, storage and disposal of

the hazardous and non-hazardous waste, for example measures such as:

Solid waste including domestic waste (from kitchen, gallery, laundries etc),

combustible and recyclable waste shall be collected, segregated and stored in

specified containers and shall be transferred to authorized contractors for their

disposal.

Hazardous waste such as medical waste, waste lube/system oil from machinery,

used oil from generator sets shall be handled as per Hazardous Wastes

(Management, Handling and Trans-boundary Movement) Rules, 2008. The waste will

be carefully stored in drums and transported to MoEF approved recyclers for its final

disposal. All precautions will be taken to avoid spillage from the storage.

Based on foregoing discussion on mitigation measures the impact matrix Fig: 4.4 & 4.5 on

comparision it may be noticed that preventive measures have contributed for the reduction of

impacts and risks due to drilling activities

Table:4.5 Potential Environmental Impacts of Proposed Project activity

(With Mitigation Measures)

Environmental


Impact

Significance

Lo

w In

ten

sit

y

Mo

dera

te

Inte

nsit

y

Hig

h In

ten

sit

y

Lo

cal

Mo

dera

te

Sp

read

Reg

ion

al

Sh

ort

Term

Mo

dera

te T

erm

Lo

ng

Term

Ad

vers

e

Ben

efi

cia

l

Insig

nif

ican

t

Min

or

Mo

dera

te

Majo

r

Air Quality

Noise

Water Quality



89

Environmental


Impact

Significance

Sediment Quality

Aquatic Flora

Aquatic Fauna

Local fish

population

Local Economy

Note: For color coding refer Table 4.2

4.6 Response of Marine Ecosystems to Oil Spills.

The response of marine ecosystems to oil spills is given special consideration since oil spills are

identified as potentially most deleterious to the environment. Crude oil is a very hydrophobic

mixture and therefore does not mix well with water. When both mix, small oil droplets tend to

disperse into the aqueous phase. The large droplets quickly return to the surface oil slick while

the smaller droplets remain in the water. Some water is incorporated into the oil layer in the form

of water-in-oil emulsion. At the same time, its hydrophobic nature causes crude oil to be

adsorbed to particulate matter in seawater and to quickly sediment with it to the bottom.

Petroleum hydrocarbons associated with sediments are also known to be more persistent and to

cause more harm than hydrocarbons in the water column.

4.6.1 Resource Sensitivity Assessment.

The variability in season and geography related to physical-chemical attributes of the marine

environment affect all marine life. As a result, marine organisms may exhibit varying degrees of

ecological adaptation to changing conditions of their existence. With respect to oil spills, the

major concerns in biological resource sensitivity assessment were abundance, initial mortality,



90

population perturbation, fate of survivors and potential for population recovery. The following

biological species within the open sea area are thus considered most sensitive to spilled oil.

Plankton: Some crude components are deleterious to a wide range of planktonic organisms.

However, they have a high recovery potential which reduces any significant impacts to their

populations. Impacts to plankton are usually limited to very transient effects in the vicinity of the

spill release point.

Fish: Adult fish exhibit avoidance behavior initiated by the smell of hydrocarbons. This reduces

the risk to them as a result of exposure to oil. The fish eggs and larvae on the other hand are a

lot more sensitive as single individuals.

Seabird: The most important factors in seabird damage evaluation are; abundance and

diversity, molting and migration patterns. While marine birds can suffer major damage from oil

spills in the near shore areas, diving birds are the most affected as they live on the surface of

the sea and dive for food. As they dive into floating oil they become covered in it. Also during

oiling plumage air is replaced by water causing reduced insulation and buoyancy. Migratory

birds may be less vulnerable due to absence at time of spill but non-migratory birds are hard hit

with the possibility of a colony facing elimination.

Marine Mammals: Contact of these mammals with oil could be injurious particularly during

breeding period.

Deep Sea Benthos: Long term studies at a number of oil spill sites where hydrocarbons have

remained in the sediments have shown amongst others, effects from residue accumulation on

behavior in certain benthic species. The effect on benthic communities covers a small area and

damage is reversible if contamination stops. Several studies of oil spills in different parts of the

world show that different environments have different recovery rates. Generally, open water oil

spills are not known to cause excessive adverse effects on water column organisms. Hence the

open waters are not considered a sensitive habitat. The effect of oil spilled at sea may be

substantial during the spill, but recovery is very rapid and after effects minimal. This is further

confirmed by the results of the oil spill drift and weathering simulations which predict substantial

evaporation of the oil spilled at sea within a relatively short time

.



91

Sensitivity of Coastal Communities: Deep water drilling locations as proposed in this project

are 28-350 km away from the east coast of India. Impact of oil spill on coastal communities will

be minimal if oil spill contingency plan is activated in time prevent its spread.

Fire and Explosion: Where there is appropriate source of heat and fuel, there is a potential for

fire outbreak. Thus, drilling activities have a high potential for fire outbreak.

4.7 Summary of Environmental Impacts

Environmental aspect, impact, management plan and monitoring for deep water drilling

operations has been summarized in the Table:4.6.



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Table: 4.6 Summary of Environmental Impacts due to exploratory drilling and

environment management plan

Sl.No. Aspect Impact Management Plan Monitoring

1 Mobilizatio

n and

demobilizat

ion of

drilling rig

Conflict with

other marine

users of the

study area

Notice to mariners will be issued and

consultations with stake holders i.e.

ports and harbors and local fishing

communities will be undertaken.

Information on the scheduling of rig

movements routed and exclusion

zones will be made available.

Records will be

maintained

2 Presence

of rig

Visual intrusion Although the project drilling

operations are proposed in the

deeper offshore, however,

consultations will be undertaken with

stakeholders if any are likely to be

affected.

None required

3 Emission

from power

generation

and flaring

Emission of

combustion

products

Routine maintenance and efficient

operations will be undertaken to

minimize emissions. Prior to flaring

the rig management will ensure that

measures are in place to prevent

flameout are understood and critical

equipment tested.

The operation of the flare

during well testing will be

monitored and

communications

maintained with

personnel in charge of

the well test.

As the wind speeds in

the block areas is very

high (6.0 m/s), the air

pollutants generated will

disperse very fast.

4 Disposal of

drilling

waste

Primary impact

on water /

sediment quality,

secondary

impact on

benthic fauna

Because of high

sea surface

currents the

discharges (drill

cuttings and

Only low toxicity water based

additives will be used in drilling fluid

formulation including contingency

arrangement for foreseeable

emergency situations. Cuttings will

be washed before discharge to

reduce the amount of mud

discharged along with cuttings.

Samples of drilling fluid

formulations and cuttings

will be retained for

analysis.



93

mud) will

disperse and not

reach the bottom

to affect benthic

fauna.

5 Disposal of

solid waste

Secondary

impact on air

water and land

Solid waste will be segregated.

Appropriate storage will be used for

each type of waste. Skips will be

covered to prevent waste escaping

during transport and disposed of to

an appropriate facility onshore. Oil

and oily contaminated waste will be

stored in sealable containers and

transported to shore for appropriate

disposal. Training and information

will be provided for operational staff

responsible for waste disposal.

Facilities on board of the

rig will be examined for

suitability prior to

mobilization. An

inventory of waste

detailing volume and

type will be kept and on

shore disposal facilities

and contractors for

suitability

6 Discharge

of Aqueous

effluents

Primary impact

on water quality

Appropriate deck draining and

treatment systems are in place as

per MARPOL. Where practicable

the handling of oil will be undertaken

in areas, which drain into the

oil/water separation tank.

Deck drainage and water

treatment systems will be

inspected prior to

mobilization. The

performance of the oil

water separator will be

checked to ensure that

the concentration of oil in

water discharged is

complying with

MARPOL.

7 Oil spills Primary impacts

on water quality

and secondary

impacts on

habitat species

and socio-

economic

sources

Operation procedures will be

implemented to reduce the risk of oil

spillage. The probability of the oil

spill will be reduced by implementing

of oil spill prevention procedures

during loading and un-loading of

diesel oil and bulk drilling fluid

additives from supply vessels.

The vessel fuel transfer hoses will be

equipped with break away cut off

valves and floatation collars. The

capacity of receiving tanks will be

checked before receipt. Critical

Oil spill preparedness will

be assessed prior to

mobilization. The

awareness of the oil spill

contingency plan will be

assessed corrective

actions identified. A

record will be kept of all

oil spill incidents.



94

equipment i.e hoses and gauges will

be maintained.

Provisions of appropriate equipment,

implementation of oil spill response

measures and training of personnel

will be ensured.

Equipment maintenance is important

in the prevention of blowouts and

specific. Oil spill response

arrangements are detailed in Oil spill

Response Plan.

8 Blow out Primary impact

on air and water

quality and

secondary

impact on marine

species.

Blow out contingency plan

Oil spill contingency plan

Regular BOP function

check and maintenance

of hydraulic activator.

Regular mud parameters

check for density

changes.



95

CHAPTER-5

Environment Management Plan

Offshore drilling operations may interact with marine environment and result in physical,

chemical and biological changes. Impacts of these changes are to be mitigated by adopting

industry specific standards, guidelines and prevailing regulatory requirements.

Environmental monitoring helps in detecting changes in the environment resulting from

discharges from oil & gas drilling operations, Environment Management Plan provides a

delivery mechanism to address the adverse environmental impact of a project during its

execution. It aims at mitigating potential impacts associated with exploratory drilling activity

based on baseline data. To develop EMP, the effects of the following due to offshore

exploratory drilling and contingency plans to mitigate / avoid these impacts are described in

this chapter.

1. Physical presence of drilling rig and movement of associated vessels

(MSV/OSV)

2. Emissions and discharges from actual drilling operations

3. Blowout and Oil spill combatment

4. Occupational Hazards

5. H2S emission

5.1 Physical Presence of drilling rig and Movement of Vessels

The drilling rig and associated MSV/OSV’s may cause disruption to marine traffic and fishing

during mobilization and de-mobilization. To prevent this, ONGC issues notice to concerned

authorities / marine users. Consultations are held with the Ports and Harbor authorities and

local fishing communities about ONGC’s operations. Information on the scheduling of the rig

movements, routes, exclusion zones and durations are furnished. Any change in the

program is informed well in advance to the concerned authorities. Proper records of

consultations are maintained.



96

5.2 Emissions and Discharges from Drilling Operations

5.2.1 Atmospheric Emissions:

Burning of HSD for generating power for the drilling operation results in atmospheric

emission of SO2, NOx, CO, particulates and possibly hydrocarbons. Emissions from diesel

gensets (SO2, NOx, CO, Particulates and possibly hydrocarbons) are likely to occur.

However, with the prevailing wind speeds in open sea the dispersion of air pollutants will be

very high and will not accumulate in the vicinity of the working area of the rig. Measures to

ensure minimal impacts include:

Adequate stack height of the DG sets and its placement at safe distance from

working area

Appropriate management of power generation

Use of low Sulphur diesel oil (185 ppm Sulphur content)

Fugitive emissions of VOC’s from diesel fuel to be reduced by appropriate

Storage and handling

5.2.2 Noise levels and Noise abatement

Noise levels will generally remain in permissible limits within short distance from the source.

However, the following mitigation measures are followed;

Acoustic enclosures for all generators

Exhausts are provided with silencers

Operators / personnel working near the high noise source at the rig shall be

Provide with earmuffs and earplugs etc.

Deployment of drilling crew in high noise area for short duration.

5.2.3 Marine Discharges

The offshore drilling rig generates two major and four minor waste streams. These include

Major discharge

Unused Drilling fluid

Drill cuttings

Minor discharge



97

Sanitary waste,

Domestic waste and

Well fluid and deck drainage

Drilling Fluids

Drilling fluids are mostly water based and in the event of specific hole problem synthetic oil

based mud (SOBM) are used in exploratory drilling to maintain hydrostatic pressure control

in the well and to lubricate the drill bit. Drilling fluid system is circulatory system and mud

coming out from the well is passed through solid control equipment and treated and re-

circulated into the well. Only small portion of the mud is wasted during drilling along with

cuttings and solid control equipment. Non-usable portion will be discharged intermittently (50

bbl/hr) in sea with proper dilution as per GSR 546 (E). SOBM will be not be discharged into

sea, completely recycled and reused after completion of the well it will be transported to the

new location.

Drill Cuttings

The drill cuttings removed from the well are rock debris and mineral particles generated by

drilling into the underground formation, are separated at shale shaker and washed

thoroughly before discharging to sea. Cuttings generated while drilling 36” & 17-1/2” hole

size will be discharged to sea bed whereas cuttings from 12-1/4” & 8-1/2” hole size will be

discharged to sea surface in a phased manner. Impact of cuttings along with associated

water based mud will be reduced significantly due to dilution effect and wave currents.

Proposed control measures for reducing the wastage of drilling mud and disposal of drill

cuttings include:

Efficient maintenance of solid control equipment to minimize mud waste.

Proper maintenance of valves / flanges of mud tanks and mud circulation

Systems to reduce risks of leaks.

Strict adherence to standard operational procedures of the rig.

Thoroughly washed drill cuttings separated from WBM / SOBM will be discharged into sea

intermittently at an average rate of 50 bbl/hr as per GSR 546 ( E) from the rig so as to have

proper dilution and dispersion without any adverse impact on marine environment. The water

depths in these block varies from 600 m to 2500 m therefore, the impact of disposal of drill

cuttings on sea bed will be minimal. If cuttings are found toxic, these will be brought to shore



98

for safe disposal. Approximate quantities of cuttings that would be generated during drilling

of typical offshore well is given in Table- 6.1

Domestic waste

Kitchen waste is separated into bio-degradable and non-biodegradable components. Non-

biodegradable waste (plastic, glass and metal etc) is packed, labelled and sent to Base for

further safe disposal. The biodegradable garbage separated from other domestic wastes,

will be ground in a crushing machine and dumped overboard in biodegradable jute bags.

The other solid wastes will be collected, compacted and stored in containers or placed in

special metal baskets or plastic bags for transport to onshore.

Sanitary Waste

Sanitary waste is treated in the sewage treatment plants on board of the drilling rig and

disposed to sea after maintaining the required disposal parameters. Waste water generated

is expected to be approximately 20 M3 (0.22 m³/day/person grey water and 0.11 m³/Day /

person for Black water for 50-60 persons)

The following criteria are strictly followed before disposing to sea:

BOD5 : 50 mg/l or less

COD : 250 mg/l or less

Suspended solid : 30-40 mg/l or less

Coliform count : 200 /100 ml

Residual Chlorine : 1 PPM.

Well fluid and deck drainage

Produced water during well testing operation, deck floor washings and spent oil etc., are the

hazardous waste generated during the offshore drilling. Produced water which is generated

during production testing is treated in the produced water handling system where oil is

separated and water is disposed to sea after meeting the standards (oil content < 40 ppm).

Spent oil is collected, labeled and sent back to base for further safe disposal through

authorized recyclers. Deck drainage is collected and treated separately for oil removal by

gravity separation before discharge.



99

5.3 Oil Spill Contingency Plan

During exploration and production of hydrocarbon oil and oil-based products are accidentally

spilled into sea. This poses risks to human health and environmental quality. Every effort

must be made to prevent oil spills and to clean them up quickly.

The entire offshore facilities are designed, installed and operated in such a way, so as to

minimize possibility of any oil spills. Facilities and resources supplied by outsourced

agencies also meet international pollution prevention design and operation standards. Oil

spill risks are identified and measures to prevent and contain oil spill have been outlined in

contingency plan given below;

To establish response procedures for oil spills

To combat, contain, recover, clean up and dispose off the spilled oil

To provide training and drill schedule for keeping the system in place, and

To meet statutory requirements.

Activation of plan starts with notification of “Oil spill” and spill assessment. Immediate action

is taken to disconnect the source. Further action is taken based on Short Term and Long

Term strategies for spill combatment.

Strategy during First six Hours:

Depending upon nature of emergency at sea and weather conditions booms will be laid

around source of spill for containment. Recovered oil will be stored for further disposal as

per laid down procedures.

If some quantity of oil has spread prior to deployment of booms or some oil has slipped away

during containment and recovery process, following factors will be taken into consideration

prior to taking decision on application of dispersant:

a) Spilled oil shall not be more than 4 hours old.

b) Oil is moving towards shoreline.

c) Spilled crude characteristics are amenable to use of dispersants.



100

d) Prevailing weather conditions are conducive to dispersant applications.

Prior approval from Coast Guard for use of dispersant will be obtained.

Spraying of Dispersants:

During rough weather, monsoon, low visibility or in case of delayed deployment of

equipment, the spraying of dispersants is considered one of the options, because this

strategy needs very less reaction time (resource mobilization time) and can be initiated by

the boat /vessels crew operating in that area. Spray of dispersants can be done through

Helicopters also. Response equipment such as Containment Booms will be deployed for

protection of Godavari river estuary, mangroves, shrimp farms and other sensitive areas

such as river mouths to deflect spills towards other areas of the shoreline where it shall

cause less harm to the environment.

Shore Cleanup

Despite best efforts to contain and recover spilled oil, there is always a likelihood of spilled

oil reaching shorelines. Shoreline cleanup technique will be practiced for the left over oil as

per topography of the coastline.

Monsoon Conditions (South West and North East)

Day Time Operations: In SW monsoon, especially in the month of May & June, the sea

conditions are pretty rough, winds are strong, heavy rainfall reduces the visibility, and

operations of smaller vessels becomes difficult. Observation / tracking of oil slick become

much more difficult and hence, deployment of Oil Spill Response Equipment will become

difficult and unsafe for men to work from small boats. Cyclonic weather would further hamper

the operations.

Night Time: During night time the visibility further goes down and the problem is

compounded when it starts raining or weather becomes cyclonic. In this situation keeping

the track of oil spill and conduct of safe operations becomes very difficult.

Strategy for Offshore Zones

Strategy for Offshore Zones

The strategies for responding to Offshore Oil Spills are as follows;



101

a) Monitor and Evaluate: If the oil spill is not approaching coast speedily, it is to be

monitored continuously by boats/vessels operating in that area, or by helicopter, as the

situation demands. The Emergency Control Room (ECR) shall start plotting the position and

monitoring the oil slick every 15–30 minutes or as directed. The ECR would study the inputs

received from various sources, evaluate the size of oil spill and declare it as minor or major

oil spill or as Tier 1, Tier 2 or Tier 3 level type. PRP/Dispersant Spraying shall also predict

the fate of spilled oil and action to be initiated.

b) Containment and Recovery: If weather is favorable and response action can begin in

time, the spilled oil will be collected with the help of booms and skimmers and are sent to

CPCB accredited waste oil recyclers.

c) Dispersant Spraying: If the spill is moving away from the coast, dispersant spraying may

be commenced by the vessels operating in that area. If the oil spill is of higher magnitude the

ECR may decide for containment and recovery operation. Use of dispersants spraying may

also be under taken if the oil slick is moving towards the shore with very slow speed and

some reaction time is available for OSR Team for preparation of containment and recovery

operations ashore. Coast Guard guidelines will be adhered to, during decision making on

dispersant application.

As a strategy using dispersants means using chemicals to enhance the process of natural

dispersion, but due care shall be taken by getting the water samples analyzed at frequent

intervals so as to determine the limit of use of dispersant in those waters. NOSDCP of Coast

Guard also provides guide lines about the use of dispersants.

5.4 Occupational Health

Occupational hazards associated with offshore drilling include illness from exposure to

geographical and climatic elements. Work in offshore can involve exposure to hazardous

substances, noise, vibrations, hot or cold conditions, heavy manual handling activity on the

derrick floor etc. Drilling rigs especially in deep water drilling are isolated, workforce travels

to work by helicopter and perform shift duties. Extended long distance travelling,

psychological stress resulting from physical isolation due to remoteness of site and shift duty

pattern, sea sickness and exposure to extreme weather conditions are other hazards.

Harsh climate, parasitic diseases and infections may result in respiratory tract diseases.



102

On board qualified doctor is available 24 hrs. on the drilling rig for the immediate treatment

and first aid. For serious injuries and diseases patient is evacuated by the emergency

Helicopter exclusively meant for emergencies to the nearest base.

Occupational Health Hazards

Occupational health hazards identified during drilling operation are given below:

Chemical Hazards

Noise Hazards

Radiation Hazards

Illumination Hazards

Vibration Hazards

Temperature Extremes

Biological Hazards

Ergonomic Hazards

Stress related Hazards

Health Hazard Control is done by adopting following measures

Prioritize the health hazards based on their risk potential.

Identify specific work groups affected by each hazard.

Determine the controls required to manage these identified hazards. The cost of

each identified control versus benefits of its implementation may be evaluated.

Develop an action plan identifying work to be done

The health and hygiene of the personnel working at the Drilling Rig will be monitored through

periodic health checks of the persons. All employees undergo a periodic medical

examination (PME). The record of the health checkup will be maintained centrally off site in

confidential file by the medical section. The medical officer at base recommends appropriate

treatment for the persons found to be having any health problems requiring attention.



103

During the proposed drilling operations, inspections of cleanliness are carried out. First aid

boxes are provided at different strategic locations on the drilling rig. The medical officer on

board shall regularly inspect the first aid boxes and ensures that their contents are in order.

Majority of the employees on the drilling rig are trained in first aid. Regular mock drills and

lectures on first aid are carried out at the rig. Occupational Health Surveillance Programme

is summarized in Table 6.2.

Table: 5.1 Occupational Health hazards and mitigating measures

Cause of health hazard Risk Mitigation Measures

Noise (Generators, Cranes,

Fire, Water pump, Hot oil

pumps, Crude dispatch pumps)

Hearing loss Use of PPEs in high noise

area and written

operational procedures to

be followed.

Procedures to be followed

as per MSDS of all

hazardous chemicals for

safe handling.

Eye wash showers near

chemical dosing areas.

Handling of heavy equipment

and material (Manual handling

of material)

Back problem

Handling of chemicals

(Chemical stores, Chemical

dosing areas, Chemical labs)

Eye problems and

chemical ingestion,

Dermal effect of

chemicals

Periodic Medical Examination Policy

Periodic Medical Examination (PME) is applicable to all regular employees. PME is carried

out at regular intervals depending on the nature and extent of the risk involved, after the

initial pre-employment health examination as follows

Table: 5.2 Periodicity of PME

Type of PME Employees to be covered Periodicity

General Employees up to 45 years age 5 years

Employees in age group of 46 to 55 years. 3 years

Employees in age group of 56 years and

above.

2 years



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Specific Employees having hazard based profiles As per

requirement

Random On need basis- Up to 10 % of employees

examined.

Every year

PME is conducted at accredited laboratories.

5.5 H2S Protection in Drilling Operations

H2S is not expected in this field. However being the exploratory nature of the drilling the

following control measures will be taken if presence of H2S is detected any time of drilling.

H2S Detection System Presence

A four channel H2S gas detection system will be provided. Sensors will be positioned at

optimum points for detection, actual locations being decided onsite but likely to be: Well

Nipple, Rig flour, Shaker Header tank and Substructure cellar pit:

The detection system will be connected to an audio visual (siren and lights) alarm system.

The two levels of alarm are as follows:

10 ppm H2S low level alarm triggers a light signal but does not indicate danger for all.

Persons are required to stand by to check the installation after announcement on

public address system (PA) by the tool pusher, otherwise, to proceed to the upwind

side.

20 ppm H2S high level triggers a sound alarm and also red light on the control panel.

Emergency alarm is sounded by two short rings of bell intermittently. This requires

breathing equipment to be used immediately and the hazard area to be vacated

unless announcement on Public Address System (PA) by the tool pusher provides

other instructions.

The mud logging will have a completely independent detection system which is connected to

an alarm in the cabin. This system will be adjusted to sound an alarm at a concentration

level of 10 ppm as suggested in the Drilling and Production Safety code for onshore

operations issued by the Institute of Petroleum.

A stock of H2S scavenger will be kept at drilling site for emergency use.



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Visual Warning Signs

In case of high level H2S alarm, the following warning signs will be displayed to alert

helicopter and vessels in the vicinity of the drilling rig.

Red flag 90cm X 60 cms on each side of the rig.

Danger boards painted yellow with black lettering 30 cms high indicating "DANGER

H2S".

Muster stations and escape routes

Since H2S is heavier than air, it is likely to settle down at lower levels particularly in

still air or in light winds and cut off the natural escape route to the boat landing; this

situation gives rise to the following requirements:

Sufficient stair cases on the upwind side of prevailing winds for escape route up the

stairs or down to the lifeboat.

Muster stations for operating personnel in the event of gas alarm, areas in the open

on the upper deck which can be kept free of H2S by the wind.

Ventilation

Forced air ventilation to disperse any accumulation of H2S will be provided by fans (bug

blower) at the following points:

Shale shaker

Mud tanks

Derrick floor

If higher levels of H2S >10 ppm are found following steps will be taken.

Driller will shut down rotary and pumps pickup so that drill pipe in BOP and chain

down the break.

One pre-assigned rough neck will go to doghouse and put on breathing apparatus.

All other rig personnel will evacuate the rig and move in up-wind direction to

designated muster point.

Driller and rough neck will return to the rig floor and commence circulating H2S

scavenger slowly and reciprocating pipe.



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The level of H2S will be checked in all work areas. H2S scavenger will be added to

the mud and circulated. If H2S levels drop, drilling will be continued with scavenger-I

the mud. Approximately 30% of hydrogen peroxide (H2O2) solution will neutralize

H2S gas in the mud at 20 gallons of H2O2 per 100 barrels of mud.

The workers will be provided with personal H2S detectors along with self-containing

breathing apparatus.

Control measures

H2S will cause a sudden drop of mud pH. The mud man will therefore organize and

supervise continuous pH checks while drilling. Checks should be as frequent as possible

and always made following a formation change.

Following control measures will be taken in case of small levels of H2S detection.

H2S scavenger will be added to mud

H2S levels will be checked at regular intervals for possible increase

All personnel of the rig will be informed about the presence of H2S and current wind

direction

Operation will be commenced in pairs

Sub base and cellar out of bounds will be rendered without further checking levels in

this area

The workers will be provided with personal H2S detectors along with SCBA.

H2S Kick control

The control of H2S kick may be achieved either by bulldozing gas back into formation or

circulating it out. The actual method to be adopted will depend upon the condition of the

well. When a gas kick occurs, estimate the quantity of H2S present taking adequate

precautionary measures of wearing self-contained breathing apparatus (SCBA). The

following procedure will be adopted:

Close BOP, monitor SIDPP, SICP & pit gain.

If the concentration is high and cannot be circulated out due to H2S hazard in

atmosphere, bulldoze the gas into formation by pumping through kill line.

Raise mud wt. and pH as required.



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Load H2S scavenger like zinc carbonate and ironite sponge as may be

necessary in the active mud pit.

Circulate the gas through choke and degasser and burn off the gas.

The following factors will also be kept in view:

All persons on the drilling floor, shale shaker area, mud pump and tank should put on

self-contained breathing apparatus when the kick is to be circulated out.

Persons who are not required for the control operation will be withdrawn to a safe

area, where adequate ventilation is arranged.

Frequent checks with portable H2S gas detector will be made.

Supply vessels (in case of Offshore) should stay upwind on power and maintain

continuous radio and visual watch.

5.6 Summary of Environmental Management Plan

Marine Environment

Low toxicity WBM, having 96 h LC50 > 30000 mg/l will be used

The water based drilling muds will be re-cycled and reused to maximum extent.

Drill cuttings, thoroughly washed and separated from WBM, will be discharged to the sea

intermittently as per GSR546 ( E ).

In order to mitigate the specific hole problem, Synthetic oil based mud(SOBM) with low

toxicity of 96 h LC50 > 30,000 mg/l as per mysid toxicity test or toxicity test conducted on

locally available sensitive species will be used.

Waste water generated on drilling rigs is treated as per MARPOL and CPCB guidelines,

before disposal to the sea. Modular treatment plants are available for on board to treat

domestic wastewater.

As discharge of waste oil into the sea is prohibited, oily wastes is collected and sent to

base for disposal.

Emissions from DG sets are controlled through efficient maintenance and stack heights.

Barite in drilling fluids contains < 1 mg/kg Mercury and < 3 mg/kg Cadmium.

The biodegradable garbage separated from other domestic wastes, is grounded in a

crushing machine, filled into Jute bags and discharged in sea. The non-biodegradable

solid wastes is collected, compacted and stored in containers, or placed in special metal

baskets or plastic bags for transport to onshore facilities.



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Sewage is treated at the facilities available at the rig and chlorination of treated sewage

is done to achieve 1 mg/l residual chlorine before discharging into sea.

The left over drilling fluids after drilling is completed will be transported next site for

reuse. SOBM mud is always recycled and not discharged in to sea whereas only non-

usable WBM is occasionally discharged into sea with proper dilution as per guidelines.

Based on risk assessment studies it is suggested that during drilling activity, fishing

should be restricted to 500 m zone from the drilling locations.

Oil spill contingency plan exists to combat any accidental spills or blowout

Air Environment

All equipments would be operated within specified design parameters during drilling

operations.

The DG set emissions meet standards stipulated by CPCB.

Any dry, dusty materials (chemicals), mud etc. are stored in bags or sealed containers.

Quantity of flared gas during well testing is kept minimum and restricted to the short

duration.

H2S detection system will be installed at optimum points for detection like: Well Nipple,

Rig flour, Shaker Header tank and Substructure cellar pit.

Noise Environment

Noise barriers / shields are provided around the high noise units wherever possible.

Use of ear muffs / plugs and other protective devices are provided to the workforce.

Acoustic enclosures around high noise sources are provided depending on the size

of the unit.

eia for the proposed additional exploratory drilling in

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