Abstract: High Resolution Tectono-Sedimentary Modelling of Niger Delta Reservoirs

H. Williams, G. Ugueto

It has long been recognized that Niger Delta reservoirs comprise wave-dominated and tidally-influenced sandbodies whose thickness may be influenced by growth faulting, and this model was used with great success during early phases of exploration and field development. However, the increased difficulties of exploring in a mature hydrocarbon province, and optimizing production from the more problematic reservoirs have created a need for a more refined model which can accurately predict sand development. Using neutron-density and resistivity logs a technique has been developed to systematically recognize the position of marine flooding surfaces. In addition resistivity and neutron log trends between flooding surfaces reveal stacking patterns which allow the recognition of maximum floodin and sequence boundary surfaces. This chronostratigraphic framework allows high resolution correlation of deltaic sandbodies and reveals that shoreface sandbody geometries vary systematically, those in the highstand systems tract possess more lobate geometries while those of the transgressive systems tract are thinner but more laterally continuous along strike. Analysis of the growth index across contemporaneously active faults has revealed a link between systems tracts and growth trends. The growth index increases upward to the sequence boundary, then gradually decreases upward to the next maximum flooding surface, indicating that growth fault movement was controlled by base level fluctuations. This revised tectono-sedimentary model of Tertiary Niger delta deposition can more accurately predict the position, geometry and architecture of sandbodies in the vicinity of growth faults, and increases the certainty of correlations made within and between fields.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994