Journal de géologie et géophysique
Libre accès
ISSN: 2381-8719
ISSN: 2381-8719
Michael Chukwuma
Deeper plays of mature acreage is part of the new frontiers for petroleum upstream companies in the Nigeria Niger Delta basin, and have helped revive the exploration interest on mature and declining block-X. The mature oil producing block-X which is located in the eastern Niger delta (65 km NW of Port-Harcourt) is currently undergoing facilities upgrade to increase gas production capacity by 50%, end flaring and achieve target level domestic market obligation. The investment on block-X facilities not only leverages on gas caps of depleted oil fields, but will be gearing on undeveloped deep gas reserves and identified prospects in the acreage. Hence, understanding the spatial pressure distribution, pressure generation mechanism and geo-stresses acting in the deeper zone of the basin is paramount for prospecting and unlocking potential economic gas reserves in the block. A pore-pressure study focusing on the southern part of the block (Ubeta/Ihugbogo compartment) was launched by operator with aim of constructing a deep 3D pressure cubes model using 8 existing wells and seismic velocities. Post-mortem analysis performed on the 2 deepest wells in the area (Erema West-2 and Ihugbogo East-1) with depth greater than 3800 m show deviation from the classical Eaton method of pore-pressure prediction in under-compacted shale. The observed departure from the porosity related over-pressure was found to be mainly related to burial and has varying magnitude and spatial distribution (suspected to be fault conduction and proximity degree dependent). Pore-pressure prediction uncertainty due to this observed “unloading” phenomenon in deeper deposits (>3800 mMSL), understanding the structural plumbing network/nature, establishing a workable Normal Compaction Profile (NCP), short hard overpressure transition ramp and narrow drilling mud window are challenging the maturing and drillability of the deeper plays in the block-X.