Professional Analysis of Optimal Well Spacing and Infill Drilling Targets in the Ijaw Sands of OML 58, Rivers State, Using Reservoir Simulation

Optimal well spacing and infill drilling target identification are fundamental reservoir management decisions that determine the economic efficiency of field development and the ultimate recovery fraction achievable from a reservoir. This study professionally analyses optimal well spacing and ranks infill drilling targets in the Ijaw Sands of OML 58, Rivers State, using numerical reservoir simulation. A full-field three-dimensional three-phase reservoir model of the Ijaw Sands, incorporating 850 active grid cells per layer and 14 reservoir layers, was constructed and history matched against 28 years of production data. Heterogeneous permeability fields were generated using sequential Gaussian simulation constrained to well log data and seismic inversion volumes. The history-matched model was used to evaluate incremental recovery from infill well scenarios at 400-metre, 600-metre, and 800-metre spacing intervals in the identified under-drilled segments of the field. Incremental recovery curves as a function of infill well count were constructed by computing the marginal recovery per additional well at each spacing scenario. Results indicate that infill drilling at 600-metre spacing in the northern plunge of the field yields the highest value per infill well, contributing an average incremental recovery of 2.8 million barrels per well at current production costs and a 65 USD Bonny Light price assumption. Twelve ranked infill drilling targets are identified, with the top-six candidates estimated to recover 24 million barrels of incremental oil. Keywords: well spacing, infill drilling, reservoir simulation, Ijaw Sands, OML 58.