pre trenching for 16" pipeline relocation phe wmo project method statement

PERTAMINA HULU ENERGI WEST MADURA OFFSHORE, MADURA STRAIT – EAST JAVA – INDONESIA

METHOD STATEMENT

PRE-TRENCHING WORK FOR PIPELINE RELOCATION

DOCUMENT NUMBER: PHEWMO-PPP-N-PRC-0004

REV ISSUE PREPARED BY REVIEWED BY APPROVED BY ISSUE DATE

0 For Method Statement

FMA NS 27-08-2014

EAST MARINE PTE. LTD

PERTAMINA HULU ENERGI – WEST MADURA OFFSHORE

METHOD STATEMENT

TITLE DOCUMENT NUMBER REV DATE PAGE


PHEWMO-PPP-N-PRC-0004

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1. Introduction

1.1. Project Title

The Project is called “16 inch Pipeline Relocation PHE WMO Project”, and the Project

Owner is Pertamina PHE WMO (Pertamina Hulu Energi West Madura Offshore).

1.2. Indicative Location of Dredging Works for Access

The working area is located in offshore, west side of Karang Jamuang Island – Bangkalan –

East Java - Indonesia. Indicative location of working area is shown in Figure 1 below.

Figure 1. Indicative location of working area (source : google earth)

SURABAYA , CAPITAL OF EAST JAVA PROVINCE

MADURA ISLAND

PRE TRENCHING FOR PIPELINE RELOCATION ILLUSTRATIVE

LOCATION



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1.3. Document Purpose

The main purpose of this document is to define the method statement to be performed by

East Marine Pte. Ltd. as the sub-contractor, under PT. Rekayasa Industri as main contractor, for pre-trenching work (dredging) at the west side of Karang Jamuang Island – Bangkalan –

Madura - East Java - Indonesia. The objective is to achieve the required work quality within the project specification and the time frame.

2. Quantity, Equipment, and Manpower

2.1. Quantity of Dredging

Pursuant to client request and refer to drawing number PHEWMO-PPP-W-PLD-5003-

REV.B, seabed lengths required to be dredged are 1000m (1km) which start from KP 36.11 to KP 37.09. Seabed contour is various, but trench thickness is determined with the same

thickness with minimum is 4.5m from original seabed level along the pipe route. Actually, refer

to the requirement, the gas pipe need to be buried minimum 4m from original seabed. The pipe itself has 16” OD, so total minimum trench thickness is 4.5m from existing seabed. After

considering the siltation effect, we will dredge extra 0.5m as precaution, so total thickness plan for this pre-trenching work at PHE WO Project is 5m. Design of slope based on drawing no

PHEWMO-PPP-W-PLD-5003-REV.0 is 1:1, so estimate dredging quantity for trench at PHE

WMO project is shown in Table 1 below.

Table 1. Pre-Trenching Estimation Volume KP 36.11 – KP 37.09

Pre-Trenching for Pipeline Installation

KP Material Thickness Top Trench

Width Bottom

Trench Width Length Total Quantity

36.11 – 37. 09 Soft and

Hard Material 5.0 m 14 m 4 m 1,000m 45,000 m3

Total Estimation Volume 45,000 m3

Figure 2 Cross section



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2.2. Vessel

To accomplish above tasks, East Marine will use these vessels as follows:

1. 10 m3 Grab Dredger “Greip” shown on Figure 3

2. 2.000ps Pusher Boat “Tolak-7”, illustration figure shown on Figure 4 3. 10 tons Anchor Boat “Takamaru-2”, illustration figure shown on Figure 5

4. 1.000m3 Split Hopper Barge “MT-18”, illustration figure shown on Figure 6

Figure 3 10.0 m3 Grab Dredger “GREIP”

Figure 4 2000ps Pusher Boat “TOLAK-7”.

Figure 5. 10 tons Anchor Boat “TAKAMARU-2”.



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Figure 6. 1000m3 Split Barge “MT-18”.

Vessel particular, load chart, and general arrangement of vessels are shown in “Appendix-I”.

2.3. Manpower

Structure of East Marine Pte Ltd person in charge for PHE WMO project is mentioned as

follows:

Figure 7 Structure Organization of East Marine Pte Ltd for PHE WMO Project

Naoki Sato

(Project Manager)

Arlin Bin Rianto

(Chief Surveyor / Supervisor)

Fahri Effendi Siregar

(Capt. Greip Grab Dredger / Mother Vessel)

Herianto Siregar

(Capt. Takamaru-2 Anchor Boat)

Ahmad Bin Abdullah

(Capt. Tolak-7 Tug Boat)

Totok Hadi Siswanto

(Surveyor / Assistant Supervisor)

Faris Muhammad Abdurrahim

(Engineer)



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Greip Organization Chart (Mother Vessel)

Figure 8 Structure Organization of Greip 10m3 Grab Dredger

Barge Master Fahri Effendi S.

Chief Engineer Haruyuki

Kawamura

Bosun Rinto

Situmorang

Oiler Jekson Pardede

Oiler Agus Suseno

Bosun Muslich

Bosun Jerry Daichi Soewarno

Operator Restu Noor

Abadi

Operator Angger Dimaz

Galang

Deckhand Irwandi

Deckhand Rendik Iswanto

Operator Adi Saputra

Operator Suntoro

Machinist Sucipto

Purnomo

Welder Arwin Pasaribu

Cook Aripin

Pilot / Pandu Security



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Takamaru-2 Organization Chart

Figure 9 Structure Organization of Takamaru-2 10T Anchor Boat

Tolak - 7 Organization Chart

Figure 10 Structure Organization of Tolak-7 2000PS Tug Boat

Master Herianto Siregar

Chief Engineer Franky Manurung

Chief Officer Bastian Leonardo

Sihite

2nd

Engineer Soman Pangaribuan

Master Ahmad bin Abdullah

Chief Engineer Folmer Pardede

Chief Officer Jevry Hanock

2nd

Engineer Amborsius Napitupulu

Oiler Ginonggom Banjarnahor

Deckhand Andria Kudji

Deckhand Leo Canra Manullung

Deckhand Khoirul Anwar

Deckhand Sebtian Cahya

Setianingati



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2.4. Equipment

To accomplish pre-trenching scope, East Marine Pte Ltd, as Sub-Contractor will use these

marine equipment as follows:

2.4.1. Dredging and Rock Breaking Equipment

Figure 11. Crane MC50 – 170GT

Figure 12. Super Light Duty Clam Shell Bucket 15m3 (20Ton)



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Figure 13. Light Duty Clam Shell Bucket 10m3 (35Ton)

Figure 14. Heavy Duty Clam Shell Bucket 4m3 (40Ton)

Figure 15. 25 Ton Chisel Breaker.



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2.4.2. Survey Equipment

To obtain and to evaluate the dredging result, bathymetric survey required. To carry out the bathymetric survey, East Marine Pte Ltd as subcontractor will use survey equipment as follows:

Figure 16. 1 Set PC or Laptop

Figure 17. LCD Monitor

Figure 18. GPS Trimble SPS 232



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Figure 19. Echo Sounder Knudsen 320 M

Figure 20. Transducer Knudsen 320 M



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Function of each survey equipment described as follow:

Personal Computer : To run the survey software (Hydro-Pro), to record electrical

data of bathymetric survey result, and to display the general information of bathymetric

survey such as: survey line, tide, boat speed, boat position (latitude & longitude), etc.

LCD Monitor : As display for survey boats operator to follow the survey line

GPS Trimbe SPS 232 : As the receiver of information from the satellites using radio

waves to calculate the survey boat exact location.

Echo Sounder Knudsen 320M : Used to determine the depth of water by transmitting

sound pulses into water by Transducer Knudsen 320M. The time interval between

emission and return of a pulse is recorded, which is used to determine the depth of water along with the speed of sound in water at the time. Distance is measured by multiplying

half the time from the signal's outgoing pulse to its return by the speed of sound in the water, which is approximately 1.5 kilometres per second. Illustration how echo sounder

works could be seen in Figure 21 below.

Figure 21. Basic principle of echo sounding

3. Work Schedule

3.1. Work Schedule

Tentative schedule of pre-trenching works for pipeline relocation at PHE WMO project is

shown in Table 2 below. It is subject to condition of current project schedule and preparation prior to mobilization.

Table 2. Pre-Trenching tentative works schedule by 10m3 GD Greip

Description Quantity Unit 2014

August September October W1 W2 W3 W4 W1 W2 W3 W4 W1 W2 W3 W4

Preparation - -

Mobilization of Dredger and Anchor Boat

1 Trip

Pre Trenching 45,000 m3

Mobilization of Split Barge 1 Trip

Demobilization 1 Trip



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3.2. Work Flow Chart

Illustration about the dredging works sequence shown in Figure 22 below.

Figure 22. Pre-trenching for hard and soft material work sequences.

Shifting to working area

towed by tug boat

Arrive at designated working area then

deploy 4 anchors by anchor boat

4 anchors deployed, shifting

to pre-trench location

Material

Type

Hard Material (UCS>5.0

MPa)

Soft Material

(UCS<5.0MPa)

Direct dredging with light duty

clam shell bucket 10m3

Install 25T chisel

breaker

Chiseling 1st layer (seabed to

-2.5m from seabed)

Complete chiseling 1st layer then change

bucket to heavy duty clam shell bucket 4m3

Dredging 1st layer hard material by 4m

3 clam shell

bucket, load material to split barge or side casting

Complete dredging 1st layer, Install 25T chisel

breaker, shifting for chiseling 2nd

layer

Chiseling 2nd

layer (-2.5 from

seabed to -5.0m from seabed)

Complete chiseling 2nd

layer then change

bucket to heavy duty clam shell bucket 4m3

Dredging 2nd

layer hard material by 4m3 clam shell

bucket, load material to split barge or side casting

Dredging soft material by 10m3 clam shell bucket,

placement material by side casting method

Complete pre-trenching

scope

Material flowing

back to trench

No

Yes

Load the material to split

barge then dredger carry out

anchor positioning to the

designated dumping location

Bathymetric Survey

Yes

Bathymetric survey result indicate that

bottom trench design level achieved

No



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4. Work Methodology

4.1. Preparation Works

4.1.1. Installation of Base Station

Base station for correction of Greip and survey boat GPS will install at Karang Jamuang

Island. Universal Transverse Mercator (UTM) coordinate of our base station at Karang Jamuang Island is mentioned below:

Easting 690919.631

Northing 9233703.524

4.1.2. Pre-Survey for Dredging Works

Bathymetric pre-survey data for this works shall be prepared and conducted before project started. Bathymetric survey shall be performed at all working locations where

associated with this works, include also access route from temporary anchoring location to

designated working location to avoid grounding and provide general view for movement of our pusher boat, anchor boat and for dredger itself.

4.2. Main Works

4.2.1. Positioning System

10m3 grab dredger “Greip” will be utilized for dredging and chiseling works for this pre-trenching scope. Four (4) points mooring system shall be utilized with anchor wire rope.

Anchors will be deployed by anchor boat Takamaru-2.

Pre-trenching work will start from KP 36.5 to KP 36.0, then later will go to KP 37 and

continue pre-trenching works until KP 36.5.

For horizontal control (Positioning), Differential Global Positioning System (DGPS) shall be installed onboard crane barge with full accessories such as Gyro Compass etc., which is

able to achieve 0.3 to 1.0 m accuracy. For vertical control, to determine the dredging level and to avoid over dredge or under dredge, Dredger will use lead sounding method and

also check the marking line which is painted to hoisting wire of clam shell bucket. Base

station for horizontal positioning and tide gauge for vertical control shall be set and installed on land before dredging started.

Since dredging work around Karang jamuang Island will have interface with ship traffic on Alur Pelayaran Barat Surabaya (APBS), Contractor consider to provide 2 personnel pilot

(pandu) from port authority to assist barge movement during pre-trenching work if any interference with other vessel .

4.2.2. Dredging Soft Material

Refer to drawing PHEWMO-PPP-W-PLR-5004, in pre-trenching section, between KP 37 to KP 36, there are 2 soil investigation test had been conducted. From those soil

investigation results, we have got the conclusion that there are 2 general types of soil. Mostly is soft material which contains silty sand, and hard material which contains coral reef. These

data are based on our references in BH (borehole) OSBH-02 for soft material, and BH OSBH-

01 for hard material. Detail data attached in Appendix I. Summary of soil investigation result is presented in the following table:



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Table 3. Soil investigation result at pre-trenching section (OSBH-01 and OSBH-02)

Reference: Document 007-PTC-PTRI-13-R0

For soft material, Greip 10m3 GD will directly use 10m3 clam shell light duty bucket. At

the time when project commence, for shallow area (-5 to -8), contractor will use side-casting method for disposal of dredging material and for deep area (-8 to -12), dredger will load the

material to the split barge then later will be transported to designated dumping location. Detail procedure of material dumping transportation using split barge could be read in the next

chapter (4.2.5 material dumping transportation). For side casting method, dredger should ensure that material will be placed far enough from top slope of trenching area (around 8 to

15m depends on boom angle) to avoid the dredging material from flowing back to the trench.

Illustration of pre-trenching work and side-casting method can be seen in Figure 24, Figure 25, and Figure 28 below.

4.2.3. Dredging Hard Material

If we encounter material which couldn’t grab by clam shell bucket, first of all, we

would like to conduct pre-bathymetric survey to calculate volume and area. For this hard

material (coral reef, UCS>5MPa), we shall need to give additional treatment with chiseling work. Chiseling or breaking the hard material will use 25T chisel breaker. Photo of Greip’s

chisel breaker could be seen in Figure 15 above.

As explained at the work sequences, for chiseling work, we will divide trench into 2

layers. 1st layer is the thickness from original seabed to -2.5m from seabed level. And 2nd layer

is layer between -2.5m from original seabed to bottom of trench (-5.0m from seabed). For hard material, we will follow the original trench design with the slope 1:1. Illustration of hard

material cross section which divided into 2 layers is shown in Figure 23 below.

Figure 23. Hard material cross section



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At first, Greip will dismantle her clam shell bucket and then install the chisel breaker.

She will carry out chiseling work of 1st layer hard material until complete and then dismantle the chisel breaker to install 4m3 heavy duty bucket. After heavy duty bucket installed, she will

dredge all hard material on 1st layer along the hard material route before shift back to

commence point and carry out the chiseling work for the 2nd layer. Next sequence is repeat the chiseling and dredging work for 1st layer hard material.

Illustration of chiseling and dredging work for hard material 1st layer can be seen in Figure 29 and Figure 30. And Illustration of chiseling and dredging work for hard material 2nd

layer can be seen in Figure 31 and Figure 32.

For method of disposal dredging material, Greip will use exactly same method with soft material, which is side casting method for shallow area and load the material to the split barge

for deep area. During side casting, she also should ensure that material will be placed far enough from top slope of trenching area (around 8 to 15m depends on the boom angle) to

avoid the dredging material from flowing back to the trench.

4.2.4. Dredging Production and Monitoring

Productivity of Grab Dredger is always based on the type of dredging material. As we

know before, there are 2 types of material, soft material and hard material. Based on our record, average productivity of Greip for dredging soft material using 10m3 clam shell bucket is

6,000-8,000m3 per day. Whereas average productivity of Greip for dredging hard material using 4m3 clam shell bucket is 3,000-4,000m3 per day. Need to be considered, productivity for

dredging hard material is not include the chiseling work. For chiseling, productivity is almost

same with dredging, which is 3,000m3 per day. So with those value, if combine, dredging and chiseling, Greip’s productivity for hard material (for UCS >5.0 MPa) is 1,500-2,000m3.

For monitoring work, every 100m progress, east marine will perform the progress survey using survey boat. This progress survey will be conducted with 10m interval and 1 long

line for long section. Purpose of bathymetric progress survey is to obtain the actual level of the

trench. With that information, we could do the evaluation to improve quality of dredging result.

4.2.5. Material Dumping Transportation

To anticipate material flowing back to trench, contractor will provide 1 split barge named MT-18 which has 1000m3 cargo hold capacity. Dredger will load dredging material to

split barge and then after fully loaded, dredger will carry out by anchor positioning to the

designated dumping location. Dredger captain shall ensure that anchors deployed far enough to accommodate this movement. Illustration of material dumping transportation using this

method could be seen in Figure 26 and Figure 27.

Detail arrangement for disposal of dredging material explained at “Appendix-3

Disposal material sequence with or without split barge”. Illustration of disposal material result could be seen at “Appendix-3 Dumping simulation at KP 36 - KP 36.5 and dumping simulation

at KP 37 - KP 36.5”.

For arrangement of dumping location at this PHE WMO project, the material shall not be dumped to waterways or channel, also could not be dumped along the pipeline route.

Materials shall be dumped with the distance minimum 50m from the pipeline. East Marine has to ensure the material placed in accordance with the proper arrangement to avoid any hazard

in future. For this PHE WMO project, because west side of the trench is outer channel of

shipping line, so proposed dumping location is 50m from trench to east direction or to Karang Jamuang Island direction.

In case dumping area at the east side of the trench is shallow area, especially at KP 37.0 until KP 36.90, Greip will choose new designated dumping area at the north or north-west

side of trench. This arrangement based on pre-survey data that in the north or north-west side of Karang Jamuang Island is deep area which has elevation more than -10m.



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Prior to carry out this special dumping job, contractor will always make coordination

with pilotage who stay onboard Greip and certainly has to get approval from them as well. This arrangement also valid for side casting method.

4.3. Closing Works

4.3.1. Post-Survey

Bathymetric post-survey for this work shall be conducted after pre-trenching work

complete. Bathymetric post-survey shall be performed to all area along the pre-trenching section, which is start from KP 36 to KP 37. Bathymetric data at the boundary or intersection

between pre-trenching area and post trenching area shall be obtained as well. Furthermore,

post trenching survey shall be conducted to all area of dumping location, to provide general view of bathymetric information for pipe laying installation (PLB) or other purpose in future.

Purpose of bathymetric survey is to obtain the actual level of the trench. Bathymetric post-survey will be performed per 20m grid for cross section and 1 long line at the center of

trench for long section. The design level of bottom trench shall be fulfilled by East Marine as

sub-contractor, which minimum level after dredged is -4.5m from the original seabed or -4.0m from top of pipe. This requirement is refer to drawing no PHEWMO-PPP-W-PLD-5003-

REV.0. If there are still have several high spot, dredger should shift back to those high spot area and carry out the dredging work one more time until the design level achieved.



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Figure 24. Illustration of pre-trenching work by Greip 10m3 Grab Dredger (soft material)

50T HOOKAUX; HOST

B.L

UPP. DK.C.LUPP. DK.C.L

2 4 6 8 10 12 14 16 18 20 22 24 26 28AP 1 3

STBD VIEW

GREIP

Existing Seabed (Soft Material)

Final Pre-Trenching Target Elevation

-5.0 m from Original Seabed



Seabed Level

Various -6 to -11

10 M LIGHT DUTY BUCKET3



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Figure 25. Illustration of dredging using side casting method using Greip 10m3 GD for PHE WMO Project

Slope (1:3) for soft material




Bottom Trench (4m Width)

15 m

4 m

Placing Material by Side Casting Method

Bottom Trench (4m Width)

GREIP

15 m

15 m

4 m

15 m



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Figure 26. Illustration of dumping dredging material by anchor positioning

Slope 1:3

Slope 1:3Slope 1:3

Slope 1:3

Minimum 50m



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Figure 27. Illustration of dumping dredging material by anchor positioning (cross section)



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Figure 28. Illustration of dumping dredging material by side casting (cross section)



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Figure 29. Illustration of chiseling using chisel breaker for 1st layer of hard material

Existing Seabed (Hard Material)

50T HOOKAUX; HOST

B.L


2 4 6 8 10 12 14 16 18 20 22 24 26 28AP 1 3

STBD VIEW

25 TON CHISEL BREAKER

1st Layer

Hard Material





Seabed Level

Various -6 to -111st Layer

Hard Material

GREIP

-2.5 m from Existing Seabed -2.5 m from Existing Seabed2nd Layer -2.5 m Thickness



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Figure 30. Illustration of dredging hard material 1st layer using 4m3 heavy duty bucket

Existing Seabed

(Hard Material)



Seabed Level

Various -6 to -11



50T HOOKAUX; HOST

4 M HEAVY DUTY BUCKET3

B.L


2 4 6 8 10 12 14 16 18 20 22 24 26 28AP 1 3

STBD VIEW

Existing Seabed

(Hard Material)

1st Layer

Hard Material

1st Layer

Hard Material

GREIP

-2.5 m from Existing Seabed -2.5 m from Existing Seabed2nd Layer -2.5 m Thickness



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Figure 31. Illustration of chiseling using chisel breaker for 2nd layer of hard material

Existing Seabed (Hard Material)

50T HOOKAUX; HOST

B.L


2 4 6 8 10 12 14 16 18 20 22 24 26 28AP 1 3

STBD VIEW

25 TON CHISEL HAMMER

2nd Layer

Hard Material



1st Layer Completely Dredged2nd Layer

Hard Material

GREIP





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Figure 32. Illustration of dredging hard material 2nd layer using 4m3 heavy duty bucket

(Hard Material)

50T HOOKAUX; HOST

B.L


2 4 6 8 10 12 14 16 18 20 22 24 26 28AP 1 3

STBD VIEW

(Hard Material)

2nd Layer

Hard Material 2nd Layer

Hard Material





4 M HEAVY DUTY BUCKET3

GREIP

1st Layer Completely Dredged



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4.4. Contingency Plan

4.4.1. Non-Working Condition

For this pre-trenching work PHE WMO project, there is non-working condition which require all pre-trenching activity to be stopped, the table could be seen in Table 4 below.

Table 4. Non-working condition

Kind Standard

Wind Velocity More than 10 m/s (in average 10 minutes)

Precipitation More than 10 mm/h

Lightning When see the lightning

Wave height More than 1.5 m

Visibility Less than 1 km

Beside non-working condition, there is also an extreme condition which needs to carry out the

evacuation, explained in Table 5 below:

Table 5. Evacuation condition

Kind Extreme

Wind Velocity More than 20 m/s (in average 5 minutes)

Wave height More than 2.5 m

Current Velocity More than 5 knots (in average 5 minutes)

4.4.2. Shelter Area

Shelter area of Greip group when the extreme weather occurred is Karang Jamuang Island. Fortunately, Karang Jamuang Island is located very near with the pre-trenching area

which is between KP 37 to KP 36. During extreme weather condition, Greip group will go to

calm water nearby the island. Greip and Toak-7 will deploy their emergency anchor and 2 (two) spuds as well after arrive at the shelter point. Illustration of shelter point for East Marine

spread when inclement weather occurred could be seen in the Figure 33 below.

Figure 33. Illustration of shelter area for dredging equipment during extreme weather condition

Wind, wave and current direction

Wind, wave and current direction

Shelter Point



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APPENDIX I (GA, VESSEL PARTICULAR, LOAD CHART)



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APPENDIX II (PERSONNEL TRANSFER)



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APPENDIX III (DISPOSAL MATERIAL PLAN)

pre trenching for 16" pipeline relocation phe wmo project method statement

Engineering

number phewmoppp

illustration figure

project titlethe project

phe wo project

project owner

project specification

total minimum trench

required work quality