site surveys_rig safety-link

Rig: Maersk Victory

Date: 16 Nov 1996

Location: Gulf Saint Vincent. Australia

Operator: Apache Energy Ltd. (Australia).

1996 Punch-Through

Findings

The South Australia Department of Mines and Energy Resources (MESA) undertook an investigation in May 1997 and determined that the immediate cause of damage was the failure of the sub-sea sediments beneath the rig. There was no evidence of structural failure of the Ocean Victory contributing to the incident. The report concluded that there was a failure to fully evaluate the risks of a new drilling location, a failure to fully evaluate the geotechnical data of the sub-sea sediments with particular reference to the load bearing capacity of the sub-sea sediments, and a failure in management systems and procedures for locating the rig.

APRIL 2015

Recently some incidents been reported by Rigs and barges from offshore due to the damaged and disturbed seabed and sub-bottom strata, it happened by an extensive jacking up near Well Head Platforms (WHPs). A comprehensive and elaborated Geophysical & Geotechnical Investigation campaign for 61 sites been planned & designed by the Lead surveyor to acquire new data, as the currently available data is aged and requires additional information at the proposed Rig and barge Moves Site locations. additional locations added as demanded from Drilling Department and Sites. For this purpose a new Geophysical and Geotechnical Data Set has been obtained, identifying any seabed and sub–seabed hazards. New Locations out side our fields were also added to the scope.

Identify all possible constraints and hazards such as man-made, natural (punch-through) and geological

features, which may effect the operational or environmental integrity of a proposed drilling operation and to

allow appropriate operational practices to be put in place to mitigate any risks identified.

INITIAL SURVEY PLAN

Geophysical Site Survey: • Conduct Geophysical Site Surveys at each given site for Rig Approach, an area of 400 m x 400 m at

WHPs to determine the seabed and sub-bottom strata at possible Leg Locations to learn the hazards.

Geotechnical Investigations: • Conduct Geotechnical Investigations comprising of 2 X geotechnical boreholes to twenty (20 m)

deep below seabed at given locations followed by jack-up leg penetration analysis reports for expected Rigs/ Barges provided by the company at each site.

Review of the Geophysical survey Data, previously available Geotechnical Data and penetration history to decide Number of Bore holes, Depth of Bore Holes below seabed and any specialised testing requirements for un-seen hazards.

Number of Bore holes, Depth of Bore Holes below seabed, Bore Hole locations been changed during the surveys to get the best results and CPTs were conducted at several locations.

Fields:

Survey Sites are in Very Busy Operational Oil fields

Field is congested with current artificial islands construction related activities and Restricted access due to heavy traffic in field; supply vessels, barges, support vessels/Drill Rigs.

Survey Sites:

Survey sites are measured 400m x 400m at Rig access face of the jackets

Small areas with limited manoeuvrability.

Target locations (BH locations) are very close to jacket faces

The nearest survey line is 10m from jacket face

Currents are the deciding factors for line plan and direction

Weather criteria for survey very stringent and weather forecast is paramount

No towing equipment within the first 40mtrs of jacket face

Accurate mapping of historic rig leg depressions (Size/depth/brittleness depressions/disturbed seabed etc.)

Sub-bottom data is paramount with MBES as the main seabed mapping tool within first 40mtrs

Vessel navigation is important and experienced Masters were onboard to do safe navigation.

Risk assessment approved and TRA prepare for each jacket site based on existing conditions

Seabed not conducive for good sub-bottom penetration

Lack of ideal sub-bottom tool (cost/towing etc. for UHR surveys)

Immediate data processing & review to decide the BH location and Numbers.

Quickest Geophysical Survey’s review by Geophysicists and Geotechnical Engineers to decide on Bore Hole

location, numbers, depth and any extra tests.

Many very urgent sites, as the rigs or barges were already planned.

On-site data review to adjust testing programme if required.

All survey sites are in operational fields & very close to WHPs.

Coordination with Site to manage SIMOPS with many ongoing field activities.

Rig’s aft legs locations in very close proximity to WHPs with vessel at only 10m from WHP.

Shallow waters (<10m LAT) at some sites.

Night drilling

A total of 66 sites surveyed in Zakum, Satah, UAD and OC-1 Fields

149 boreholes drilled at 62 sites in in Zakum, Satah, UAD and OC-1 Fields

192,000 man-hours w/o LTI

Quality data collected from Geophysical Survey and Geotechnical Investigation

Successfully drilled borehole at shallow water-depth locations (WD < 10 m) with DP II vessel with drilling rig mounted on cantilever frame

Successfully salvaged two (2) no. lost drill pipes at OC-01 site

GEOTECHNICAL INVESTIGATION


130 Hazard Observation reported to improve QHSE

150 Tool-box talks

Over 20 safety drills

2 Incidents (2 x Loss of Equipment), Out side operational Fields.

GEOPHYSICAL SURVEY


2 Hazard Observation reported to improve QHSE

71 Tool-box talks

7 safety drills

ZERO Incidents

Details Vessel Calendar

Geophysical Campaign Seacor Mariner February – May 2014

Geotechnical Campaign Sea Conquest May-July 2014

Geotechnical Campaign Fugro Adventurer April, July-Oct 2014 & Mar 2015

• Multibeam Echo sounder - Reson 7101 MBES, 240 kHz Frequency

• Single Beam Echo Sounder - Knudsen 320 Ms, 33/210 kHz

• Side Scan Sonar c/w USBL- GeoAcoustics 159D, 100/500 kHz, 50/75 m Range

• Pinger Sub-bottom Profiler (all time Vessel Mounted)- GeoPulse 5430A, 3.5 kHz, 40ms Records

• Boomer Sub-bottom Profiler - AAE Boomer Catamaran, 40 ms Records

• UHR Seismic – Geometrics GEODE, 24-C MicroEEL Streamer, 3.125m GI, 0.25s Record, 0.125ms Sample rate

Survey Area (400 m x 400 m)

21 lines parallel to platform face

• Twelve (12) lines at 5 m and 10 m line intervals

• Five (5) lines at 20 m line interval

• Four (4) lines at 50 m line interval

2 cross lines, 20 m apart from platform centre, at a possible stern legs of the rigs and to get the pipelines approaches

2 lines crossing stbd. and port rig leg positions and intersecting at the rig bow-leg position

1 line opposite side of conductor side to delineate the WHP legs

The survey lines were designed to result-in the acquisition of a comprehensive geophysical data at each of the proposed leg positions of the Rigs and while achieving a maximized coverage over the planned 400 m x 400 m Rig move sites.

The survey line plan and usage of towed sensors was made keeping in view the safe operating distances from the WHPs to the survey vessel and the towed sensors

Available historical data within Company and with contractor were referenced in the evaluation of each site for its potential hazards for the proposed Rig Move

Jack-up Zoning Plan for various Rigs

Previous Rig Move History to the Platform Sites

Previous Geotechnical Data

Pinger Sub-bottom Profiler Images

MBES and Side Scan Sonar Images

3-D view of Sonar Contact (Debris) from MBES and Side Scan Sonar data within

the PW 131 platform site

Side Scan Sonar and MBES Image showing Debris (PW-146 DB01) –PW 146

platform site

• Side Scan Sonar Image showing seabed features close to PU3 / WHP3 Platform Site

• Side Scan Sonar Image showing seabed features - PN 152 Platform Site

Side Scan Sonar Image showing seabed features and pipelines – PW 53 Platform Site

Side Scan Sonar Image showing Seabed features and pipelines - PW30 Platform Site

Side Scan Sonar Images

Borehole Drilling Plan

Based on the geophysical assessment and review by the Geotechnical Engineering Department, geotechnical boreholes were according to three (3) scenarios:

One borehole – at the Centre Position of the proposed Rig

Three boreholes

– one each at the proposed leg position

Two boreholes

– one at the bow-leg position – one at the centre position of Port and Stbd. Legs

Recommendations based on the Assessment

Geotechnical Investigation & Engineering

- Equipment : DP2 Vessel with rotary geotechnical drill rig - Field Operations : Geotechnical Drilling - Logging, In-situ Testing, O/b Laboratory Testing - Geotechnical Data Interpretation & Field Reporting

- Onshore Laboratory Testing - Final Borehole Log, Factual Reporting - Engineering Report : Parameter Selection, LPA Curve


Equipment : Geotechnical Investigation

FMR 200 : mounted on the central moon-pool

FMR 202 : mounted on the cantilever (over-the-side)

- Seabed Frame (SBF) : Act as both a re-entry for the drill string and reaction mass.

- 53 kW HP Power Swivel with 175 N.m max. torque and 20T SWL.

- Drill-string and SBF motion compensator of 3 m stroke each.

- 2 Diesel driven hydraulic power packs to power the drill units.

Open-hole rotatory drilling in Soil and coring in Rock

Drill Pipe : API-type, 3.5 inch ID / CHD, 5.1 inch ID

Rock Coring : PQ core barrel (83.5 mm – core dia) & Fugro-Marine core barrel (FMCB) (61.1 mm – core dia).

Push Sampling : 72mm dia, with constant rate of penetration into undisturbed strata.

Hammer Sampling : 2” split spoon, 80kg hammer with 1.5m max. stroke.

Cone Penetration Testing (CPT) : 90kN thrust capacity and 1.5m stroke, F5 type cone, refusal at 60 MPa.


Field Operations : Geotechnical Drilling


Drilling Operations


Logging, In-situ Testing, On-board Laboratory Testing

Rock cores /samples were logged according to Clark and Walker (1977) for Middle Eastern sedimentary rocks.

Field visual analysis : rock type, colour, grain size, inclusions and anomalies – fractures, infill, cavities.

O/b Testing : Water content, Unit Weight, Carbonate Content Indication ,Visual Inspection, Uniaxial Compressive Strength (UCS), Point Load Test (PLT), Torvane (TV), Pocket Penetrometer (PP), Unconfined Un-drained (UU) Compression Test in cohesive soil.

In-situ CPT Testing : Direct measurement of Cone Tip Resistance, Sleeve Friction, Pore Pressure which can be used for classification and derivation of un-drained shear strength, relative densities and soil behaviour.


Soil Samples - Clay

Soil Samples - Gypsum


Onshore Laboratory Testing, Final Borehole Log, Geotechnical Engineering Reporting

On-site storage in core boxes, cores wrapped in plastic, soil in plastic bags, outside sunlight and in a controlled environment. Additional Lab testing are performed on selected samples in Fugro’s onshore laboratories.

Tests include, but not limited to: Water content, Particle Density, Particle Size Distribution, Atterberg Limits, Chemical Analysis, Confined Undrained Compressive Strength Test (CU), UU, PLT and UCS.

Results from both onshore and offshore laboratory testing are used to QC the Preliminary Geotechnical borehole logs to generate Final Borehole Log.

The results from onshore testing (such as particle density, unit weight) are used as in input for finalizing the CPT plots.

The factual information after QC are presented in second Issue of the Field Report as Factual Report (which will not include the Engineering, LPA).


Engineering : Leg Penetration Analysis (LPA)

Assessment of data supplied by the Client;

Selection of procedures and models for analysis; selection of parameters;

Application of models and evaluation of results;

Providing recommendations for jack-up installation.

Parameters for LPA

Soil parameters are selected based on laboratory testing and observations during site investigation.

Angle of Internal Friction : The friction angles are estimated using the rock type and the carbonate content. The friction angles were adjusted for size effects according to SNAME (2008).

Static Un-drained Shear Strength : The un-drained shear strength is estimated using the UCS values. Competent rock layers, with high RQD, were modelled as cohesive material with un-drained shear strength values estimated as half of the UCS value.


LPA are executed following the recommendations of the Joint Industry Recommended Practice SNAME (2008) and Fugro’s experience.

Using design soil parameters with spudcan geometry from available drawings and the pre-load details as provided by the Client, LPA are carried out with Fugro’s ‘in-house’ software Gerrit using conventional bearing capacity theory according to SNAME 2008.

The results from LPA and recommendations are presented in the Engineering Report.

Engineering : Leg Penetration Analysis (LPA)


Parameter Values for Soil Strata


Leg Penetration Analysis


Penetration Behavior Risk Identification

Foundation

Penetration Curves

Safe Approach

Thank You

site surveys_rig safety-link

Documents

site locations

new locations

geophysical survey data

survey sites

additional locations

available geotechnical

new data

hole locations