Sedimentology and reservoir heterogeneity of the “G1” reservoir Sandbody, Boga Field, Niger Delta, Nigeria

Abstract

Integration of sedimentologic, ichnologic, and stratigraphic studies of cores from “G1” reservoir, Boga Field, part of the Greater Ughelli depobelt, Niger Delta were undertaken to identify the depositional environment and reservoir heterogeneity. Two wells (Boga 51 and 52) were correlated to establish the lateral continuity of the “G1” reservoir sandbody across the field. Standard core description method was used to identify lithofacies and infer the depositional environment based on grain size and sedimentary structure. The result of the study reveals nine (9) lithofacies, grouped into two facies-assemblages (fluvial and barrier bar), were recognized from the Boga Field. The fluvial facies-assemblage, encompassing a variety of depositional environments includes, fluvial channel sand, tidal channel deposits, and upper-overbank. The shoreface facies assemblage includes upper-shoreface, middle-shoreface, lower-shoreface, and shelfal deposits. The Boga Fields’ depositional system displays a wave-dominated depositional models, with local evidence of tidal action. The fluvial sandstones (facies Cbcms), encountered at the base of “G1” Boga 51, are the highest quality reservoirs. In the barrier bar system, the middle- to upper-shoreface sandstones (facies Mcs and Cbmcs) include reservoirs of high to moderate quality. Lower-shoreface sandstones (facies Bfms and Bmh) will contain relatively poor reservoirs because of their finer grain size and the intense and disruptive bioturbation. The study reveals that sedimentology and depositional environment of facies play a significant control on the reservoir quality. It also revealed a heterogeneous and compartmentalized reservoir, displaying a complex pattern in distribution and connectivity of reservoir sandstones at different heterogeneous scales.