‘Ductile v. Brittle’ – Alternative structural interpretations for the Niger Delta

Abstract

Abstract A wealth of subsurface information gathered from over 60 years of hydrocarbon exploration offshore Nigeria provides a reference study area on the interaction between sedimentation, structure and overpressure in a large delta system. The current geological paradigm is that structuration and synkinematic sedimentation is governed by shale mobility from the deeper parts of the delta. This concept is largely the result of interpretations derived from vintage seismic data and insufficient calibration of the deeper parts of the delta. Long-cable seismic data are providing new insights into this interpretation conundrum. A first-order problem, which is of particular interest here, relates to the linkage between the extensional structures updip with the compressional structures downdip. The translational zone between extension and compression is key to unravelling the nature of this link and any associated structural material balance discrepancies. The primary focus of the current paper is to interrogate seismic data and to provide alternative interpretations to the accepted paradigm. Two end-member interpretations of the Niger Delta regional seismic dip lines – referred to here as the ‘ductile model’ and the ‘brittle model’ – are presented. Aside from their internal geometrical dissimilarities, these interpretations suggest fundamentally different kinematic and geomechanical models. The latter may offer a wider scope for deep – largely neglected – hydrocarbon exploration targets. Ultimately, these ideas could provide the conceptual framework that, in conjunction with improved seismic efforts, could lead to rejuvenated exploration portfolios.