A Novel Perspective of Electrofacies and Electro Sequence Analysis: A Case Study of Gracious Field, Niger Delta, Nigeria

Abstract

Electrofacies and electorosequencecharacterization of ‘Gracious’ Field, Niger Delta, were studied, with the aid of tenwireline logs and 3D seismic data volume, to make precise prediction ofthesource rocks and reservoir rocks in the study area ofresearch and also delineate a sequence stratigraphic analysis of the Field. Lithofacies is delineated by analyzing well logs using gamma ray signatures, cross-plotting of neutron density logs and analysis of seismic facies. Using diagnostic characteristics of gamma ray log indicative of a given depositional environment, the detected lithofacies were subjected to electrofacies analysis.The subsurface facies ofGracious field revealedthree (3) sequences that are bounded by four (4) sequence boundaries (SBs) that were mapped and delineated as unconformities due to erosionhavingfour maximum flooding surfaces (MFSs).DelineatedSequences includesthetransgressive-systems-tracts (TST), low-stand-systems-tracts (LST), and high-stand systems tracts (HST). These were revealed during various stages of base level shifts, as depositional systems. Deposits delineatedinside the low-stand systems tracts are fluvialchannel sands, while transgressive systems tracts, overlaid the low-stand systems tracts facies. High-stand systems tracts are composed of upward coarse and superficial deltaic marine (fluvial)sands.The sand units of the distributaries and tidal channels having a thicknessof 60 m and 75 m, and porosity of 21% and 23% respectively were viewed to have good quality for hydrocarbonreservoir.The sequences were deposited in intermediate to superficial marine environments. The reservoirs of the low-stand-systems-tracts and high-stand-systems-tracts and seals from the marine shaleof the transgressive-systems-tracts andhigh-stand-systems-tracts could create stratigraphic traps for hydrocarbon accumulation in the Gracious Field. This study would be a gainful means to guidehydrocarbon exploration and production plans in this field.