Occurrence of Gas Charged Sediments and Pock Marks in “Semob” Fields Offshore Western Niger Delta: Implications for Offshore Operations

The safe delivery of operations in offshore province is dependent on the availability of high fidelity information of the geological state of the sea floor. Sediments and sedimentary processes determine the sea bed composition and bathymetry. The study was done in the inner shelf environment of Gulf of Guinea, in Niger Delta. The acoustic equipment used is side scan sonar and sub-bottom profiler and they work with geophysical principles of sea floor sediments acoustic reflectivity and refraction. The acquisition, processing and interpretation of data reveal the existence of gas charged sediments between the sea bed and the lithified layer(strong seismo stratigraphic layer) and the existence of genetically related depressions with surrounding rings of sand called pock marks which vary between 3 m-10 m in diameter on the sea floor. The gas charged sediments thickness ranges from 20 m-25 m. The areas of the ‘Semob’ fields that have gas charged sediments and pock marks are liable to endanger the installation and safety of subsea facilities, offshore operations and sea going vessels. Therefore, are geohazards areas and should be avoided.