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Case Study • Hydrographic, Geophysical, and Geotechnical Survey for a Subsea Pipeline Offshore Cameroon • Lighthouse

Snapshot
Project
Pre-Engineering Subsea Pipeline Survey
Role
Contractor
Client
Confidential
Year
2014
Location
Atlantic Ocean, Cameroon
Environment
Offshore ● Pipeline
Region
Africa
Details

Introduction

Lighthouse performed a pre-engineering marine survey for 280km long gas pipeline route in the Atlantic Ocean offshore Cameroon in 2014. The purpose of the hydrographic, geophysical and geotechnical site investigation was to determine the suitability of the proposed pipeline routes and to identify any geological and bathymetric conditions which could impair pipeline installation and associated burial operations.

Scope of Work

  • The scope of work comprised bathymetric, seabed, and sub-seabed data acquisition, processing and interpretation, performed from Lighthouse's DP1 Odin Finder Geotechnical and Survey Vessel, including:
  • 2D ultra high resolution (UHR) seismic survey
  • Pipeline routes corridor bathymetric and geophysical survey by means of multibeam echosounder (MBES), singlebeam echosounder (SBES), side scan sonar (SSS), sub-bottom profiler (SBP), and magnetometer
  • Pipeline routes geotechnical characterisation by means of shallow vibrocorer sampling and subsequent geotechnical laboratory testing
  • Pipeline routes environmental survey to characterise biologic chemical and physical properties of the seabed and seawater.
  • Data processing, interpretation, final charting, and reporting


Initial 2D UHR Seismic Geophysical Survey

The 2D UHR seismic survey was performed to detect possible hazard in the shallow stratigraphy for the pipelines routes. The main challenge was to provide the Client and engineering consultant with the necessary engineering data within the expected deadlines in order to proceed with the following phases of the survey. All the acquired geophysical data passed through a rigid Quality Control (QC) procedure, and was processed and finally interpreted onboard the survey vessel. A preliminary interpretation was provided before the start of the geophysical survey (24 hours after the end of the last acquired line), and the final interpretation was provided to the Client at the end of the geophysical survey.


Pipeline Routes Corridor Bathymetric and Geophysical Survey

Once the optimal pipeline routes were determined by the Client, the whole corridor was investigated in order to detect any possible hazard for the future pipeline installation and construction. The main challenge was to provide the Client with information and warning of any potential geohazards in advance of any critical milestones which may have impacted route optimisation or design. The results of the bathymetric and subsequent geophysical survey facilitated the scope for the geotechnical and environmental surveys.


Geotechnical and Environmental Sampling Operations
Following the successful completion of the hydrographic and geophysical survey, Lighthouse carried out the geotechnical and environmental sampling phase of the campaign. This is included shallow sub-seabed sampling using a vibrocorer to provide adequate and representative soil samples for further laboratory testing and analysis, such as soil identification and classification, bulk and dry density, particle size distribution (PSD), and photography for input into the Client's engineering design. 


Equipment & Instrumentation

  • Primary Positioning System: DGPS C-Nav 3050
  • Secondary Positioning System: DGPS C-Nav 1010R
  • Gyrocompass/Motion Reference Unit (MRU): GEM Polaris FOG-200
  • Gyrocompass/Motion Reference Unit: Teledyne TSS MAHRS
  • Sound Velocity Probe (SVP): Valeport
  • Navigation Software: QPS QINSy 8.0
  • Bathymetric System: R2 Sonic 2024
  • Bathymetric System: L3 ELAC Nautik Seabeam3030
  • Sub-Bottom Profiler (SBP) System: Teledyne Benthos Chirp III
  • Underwater Positioning System: Applied Acoustics-Easytrak Lite
  • Singlebeam Echosounder (SBES): NAVISOUND 215 (hull mounted)
  • Hydrofone Array: Sercel SEAL Streamer
  • Recording System: Sercel SEAL 408 Recording System
  • Seismic Source: Sercel Ming G Gun
  • QC and Processing System: Promax 2D
  • Water Sampling: NISKIN
  • Multi-parameter probe: Idronaut Probe
  • Vibrocorer: Geo Vibro Corer 6000
  • Seabed Grab Sampling: Van Veen Grab
 
Vessels
IMO:
7031761
MMSI:
247048200
Vessel Operator:
Lighthouse
Flag:
Italy
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Scope of Work

The scope of work comprised bathymetric, seabed, and sub-seabed data acquisition, processing and interpretation, performed from Lighthouse's DP1 Odin Finder Geotechnical and Survey Vessel, including:

Pre-survey route centreline survey

Post-survey route centreline and two wing lines 500m offset each side of centreline survey

Pre-defined corridor survey

Geotechnical characterisation by means of box core sampling, piston coring, and geotechnical laboratory testing and analysis

Data processing, interpretation, and integrated hydrographic/geophysical/geotechnical reporting

Hydrographic & Geophysical Survey

The pre-survey route centreline was investigated by means of multibeam echosounder (MBES) and sub-bottom profiler (SBP) to detect and assess any geohazards or potential issues for the proposed pipeline installation. The survey data was processed onboard simultaneously and provided to the Client in order to facilitate survey optimisation and acquisition of additional data if required. Once the post-survey route was defined, the survey was extended to cover a wider corridor. The geophysical survey was subsequently continued to cover the pre-defined corridor area.

Geotechnical Sampling Operations
Following the successful completion of the hydrographic and geophysical survey, Lighthouse carried out the geotechnical sampling phase of the campaign. This is included shallow sub-seabed sampling using box corers and piston corers to provide adequate and representative soil samples for further laboratory testing and analysis, such as soil identification and classification, bulk and dry density, particle size distribution (PSD), and photography for input into the Client's engineering design.

Equipment & Instrumentation

Primary Positioning system: DGPS C-Nav 3050

Secondary Positioning system: DGPS C-Nav 1010R

Underwater Positioning: Sonardyne Ranger 2 6G

Transponders (Beacon): Sonardyne WSM 8170 6G

Gyrocompass/Motion Reference Unit (MRU): GEM Polaris FOG-200

Gyrocompass/Motion Reference Unit (MRU): Teledyne TSS MAHRS

SVP Probes: Valeport Mini SVP – Mini SVS

Navigation Software: QPS QINSy 8.0

Bathymetric System: L3 ELAC Nautik Seabeam 3030

Sub-Bottom Profiler System: Teledyne Benthos Chirp III

Mini Air Gun: Sercel 20cu.inch

Seabed Sampling Systems: 1,000cm² Box Corer

Nioz Passive Acoustic Monitoring (PAM) System: TLS MK2 PAM
Keywords
Bathymetric SurveyEngineeringGeophysical SurveyGeotechnicalLaboratory TestingMBESOffshoreOffshore Oil & GasSeismic SurveySide Scan SonarSSSSinglebeam EchosounderSBESSite InvestigationSub-Bottom ProfilerSBPVan Veen GrabVibrocore Sampling
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