Reservoir evaluation and hydrocarbon play assessment in a Niger Delta field

Amidst the blend of trepidation about dwindling petroleum reserves, a latent frenzy towards improving reserves worldwide, and the ironical call for replacement of fossil fuels, the need still persists, to leverage on legacy data and increasing technological advantages to re-characterize existing fields for optimal reserve recovery. Reservoir evaluation and hydrocarbon play assessment of a typical Niger delta field has been carried out in this research work. This involved delineation of reservoir rocks, characterizations of the fluid within the reservoir, and assessment of the structural relations of the seal, source, and trap (Play Type) in the study location. By inspection of the signatures of a suit of petrophysical logs (comprising of resistivity, gamma ray, shale volume, and density), the HD2000 reservoir was delineated. The reservoir is sandwiched between two impermeable shale beds (seals/caps) bordering the top and bottom of the reservoir. Using Lambda-Rho, Mu-Rho, P-Impedance, Vp/Vs Ratio, and porosity, petrophysical cross plot analyses was carried out. Advanced post-stack 3-D acoustic impedance inversion yielded petrophysical attribute slices which helped to validate the observations in the cross plots. Results showed that the wells cut through zones of low values of P- Impedance, Mu-Rho, Lambda-Rho, and Vp/Vs ratio, corresponding to hydrocarbon saturated sands. Event time structure maps at both horizons and a seismicsection showing faults, fractures, and an anticline structural trend, confirmed that the play type is a fault and fracture infested rollover anticline, which combines with the delineated seals/caps at the top and bottom of the reservoir to form a structural trap for hydrocarbon within the reservoir. These observations correspond to the characteristics of plays in the oil rich belt of the Niger delta petroleum field, where rollover anticlines in front of growth faults form the main objectives of oil exploration.