Geophysical 3D Seismic Appraisal of Okpella Field within Offshore Niger Delta Basin of Nigeria

Abstract

Okpella Field is currently experiencing a decline in production which was revealed by the analysis of the production data. The Field had an annual production of 430175 MBO (Million Barrel of Oil) in 2008, but declined significantly to 7839 MBO (Million Barrel of Oil) per annum. Therefore, to sustain the Field hydrocarbon productivity, an appraisal study was carried out to identify viable bypassed hydrocarbon reservoirs for development. This involves integrating 3D seismic interpretation, petrophysical analysis, and production data to characterize and estimate the productivity of the Bypassed hydrocarbon reservoir zones. Six hydrocarbon reservoirs were identified by the producing company: Major reservoirs Sand A, B, C, D, E, and F. Three additional hydrocarbon reservoirs were identified within the study: Bypassed Sand A, Bypassed Sand B, and Bypassed C. From the fluid distribution and analysis within the Bypass Reservoirs, Bypass A is gas, Bypass B is oil and gas while Bypass C is oil. The petrophysical analysis estimated the reservoir’s petrophysical parameters such as volume of shale, porosity, net to gross, and water saturation for the Bypassed reservoisr. The Seismic interpretation delineates the structural style and hydrocarbon traps, generates time maps, attribute maps (Root Mean Square attribute), depth maps, and estimates the bulk volumes of the bypassed reservoirs. The stock-tank oil initially in place, gas initially in place, and hydrocarbon productivity were estimated by integrating the results from the petrophysical analysis, seismic interpretation, and production data. From this analysis, the most prolific bypassed reservoir is Bypass B. The productivity of all the Bypassed reservoirs were estimated to sustain the field for an additional three years.