Reservoir sands characterisation involving capacity prediction in NZ oil and gas field, offshore Niger Delta, Nigeria

Abstract

Hydrocarbon exploration is a high-risk venture; therefore, it calls for pre-determining the reservoirs' capacities, forming the bedrock of actualising oil and gas production events. This study delineates hydrocarbon-bearing sands, determines the reservoir area extent, computes the associated petrophysical parameters and presents the reserve volume estimation based on wireline logs with integrated 3-D seismic surveys. It evaluates and indicates three (3) hydrocarbon-bearing reservoirs sands (N_Z(R1), N_Z(R2) and N_Z(R3)) of varying thicknesses (h) across three (3) wells reservoirs N_Z(R1), N_Z(R2) and N_Z(R3). The reservoir properties, including porosity (Ф), free fluid index (FFI), permeability (K), fluid saturations and reservoir thickness (h), represent potentially viable hydrocarbon reservoir units across the field. It presents the estimation of the recovery factor based on the FFI values. Across the reservoirs, Ф is 0.28 in N_Z(R1), 0.27 in N_Z(R2) and 0.26 in N_Z(R3). FFI is 0.26 in N_Z(R1), 0.25 in N_Z(R2) and 0.26 in N_Z(R3). K is 10388 mD in NZ_(R1), 8304mD in N_Z(R2), and 6580 mD in N_Z(R3). Water saturation (S_w) is up to 0.4, 0.36 and 0.20 with the associated hydrocarbon saturation (S_h) of 0.60, 0.64 and 0.80 corresponding to N_Z(R1), N_Z(R2) and N_Z(R3). Considering the delineated reservoir areas based on the prevailing fault assisted structural style, the total volume of recoverable oil is 11.3×10⁶, while the gas capacity is 1.8 ×10⁹ cuft. These findings will aid the field's oil and gas reservoir developmental activities and serve as reference points to related studies involving similar objectives.