Offshore Geohazard Site Investigation

Seun Familusi

Upstream Oil and Gas Perspective

(Nigerian Oilfield Case Study)

What are Offshore Geohazards?

Introduction Methods Results & Interpretation Conclusion

Why is Offshore Geohazard Site Investigation Required?

Introduction Methods Results & Interpretation Conclusion

Required to obtained detailed seabed and sub-seabed information of any area where

offshore activities are to take place.

Why is Offshore Geohazard Site Investigation Required?

Introduction Methods Results & Interpretation Conclusion

Why is Offshore Geohazard Site Investigation Required?

Introduction Methods Results & Interpretation Conclusion

How is the Investigation Conducted?

Introduction Methods Results & Interpretation Conclusion

Combines the science of HYDROGRAPHY, GEOPHYSICS and GEOTECHNICS

How is the Investigation Conducted?

Introduction Methods Results & Interpretation Conclusion

DGPS Navigation & Positioning . Seabed Imaging & Shallow Geology . Ground truthing

Key Tools and Equipment

Introduction Methods Results & Interpretation Conclusion

Specialized Geohazard Vessel

Investigation Crew

Surveyors

Engineers

Geophysicists

Geologists

Key Tools and Equipment

Introduction Methods Results & Interpretation Conclusion

Differential Global Positioning System (DGPS)

Key Tools and Equipment

Introduction Methods Results & Interpretation Conclusion

Bathymetry (Single Beam & Multi beam Echo sounders)

Key Tools and Equipment

Introduction Methods Results & Interpretation Conclusion

Bathymetry (Multi beam Echo sounder)

Uneven Seafloor Topography

N

Key Tools and Equipment

Introduction Methods Results & Interpretation Conclusion

Seabed Features (Sidescan Sonar)

Key Tools and Equipment

Introduction Methods Results & Interpretation Conclusion

Seabed Features (Sidescan Sonar Record)

Barge Wreck Barge Wreck

So

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r T

ow

lin

e

Key Tools and Equipment

Introduction Methods Results & Interpretation Conclusion

Seabed Features (Sidescan Sonar Movie)

Barge Wreck Barge Wreck

So

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r T

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lin

e

Key Tools and Equipment

Introduction Methods Results & Interpretation Conclusion

Seabed Features (Marine Magnetometer)

Key Tools and Equipment

Introduction Methods Results & Interpretation Conclusion

Shallow Geology (Sub-bottom Profiler)

Key Tools and Equipment

Introduction Methods Results & Interpretation Conclusion

Two-Dimensional 2D Seismic (Streamer & Seismic Gun Source)

Key Tools and Equipment

Introduction Methods Results & Interpretation Conclusion

Two-Dimensional 2D Seismic (Streamer & Seismic Gun Source)

Air Gun Source

Streamer

Key Tools and Equipment

Introduction Methods Results & Interpretation Conclusion

Two-Dimensional 2D Seismic (Streamer & Seismic Gun Source)

Sub Surface Image

Key Tools and Equipment

Introduction Methods Results & Interpretation Conclusion

Geotechnical Investigations (Grab Samplers, Piston Corers)

Grab Sampler

Piston Corer

Equipment Interfacing & Integration

Introduction Methods Results & Interpretation Conclusion

Mobilised Geohazard Vessel

Survey Lines Design

Introduction Methods Results & Interpretation Conclusion

Survey Grid/Lines

Navigation Screen

Introduction Methods Results & Interpretation Conclusion

Online Geohazard Survey

Navigation Screen

Introduction Methods Results & Interpretation Conclusion

Online Geohazard Survey

Geohazard Site Investigation Methods

Introduction Methods Results & Interpretation Conclusion

3km by 3kmSurvey Grid

Gulf of Guinea

Niger-DeltaSedimentary BasinIn Nigeria

Purpose

FloatingProduction StorageandOffloading(FPSO)Tanker

And

Drilling Activities

Bathymetric Overview of Study Area (Single Beam)

Introduction Methods Results & Interpretation Conclusion

31 m

32 m

30 m

Bathymetric Relief of Study Area (Multi Beam)

Introduction Methods Results & Interpretation Conclusion

30 m

31 m

32 m

-25

2627

-28

29

30

-31

32

-33

-34

35

36

-37

38

39

-40

41

42

-43

44

-45

Seabed Features and Magnetic Anomaly (Sidescan Sonar & Magnetometer)

Introduction Methods Results & Interpretation Conclusion

Magnetic Anomaly

Seabed Mosaic (Sidescan Sonar)

Introduction Methods Results & Interpretation Conclusion

N

Shallow Geology (Sub-bottom Profiler)

Introduction Methods Results & Interpretation Conclusion

Unit A

Unit B

Approx. 110 m

Sandy Clayey lens

Clay Sediments

Sea Floor0-10-20-30-40-50-60-70-80-90-100-110-

Seismic Profile of the Study Area

Introduction Methods Results & Interpretation Conclusion

Approx. 100 m

Sandy Clayey lens

Clay Sediments

Shallow Gassy Channel Shallow Gassy

Channel

Gas Chimney?

Amplitude Anomalies within the Study Area

Introduction Methods Results & Interpretation Conclusion

Approx. 100 m

Sandy Clayey lens

Clay Sediments

Stratigraphic Summary from 2D Seismic Survey

Introduction Methods Results & Interpretation Conclusion

Approx. 100 m

Sandy Clayey lens

Clay Sediments

Summary of Geotechnical and Laboratory Test on Core Samples

Introduction Methods Results & Interpretation Conclusion

Approx. 100 m

Sandy Clayey lens

Clay Sediments

Conclusion

Introduction Methods Results & Interpretation Conclusion

Approx. 100 m

Sandy Clayey lens

Clay Sediments

1. Same parts of the study area are considered to be gas charged therefore any drilling activity must be avoided in these areas. The North-West and the Southern parts of the study area.

2. There is no potential risks to placing the Floating Production Storage and Offloading (FPSO) at the study area

3. The study area clear from any form of debris or obstructions.

TAKE HOME MESSAGE

Introduction Methods Results & Interpretation Conclusion

Approx. 100 m

Sandy Clayey lens

Clay Sediments

Geohazard Site Investigation is criticalto all offshore oil and gas activities

and has to be conducted prior to field operations to avoid accidents.