Production Decline Curve Analysis of Shallow Marine Sand Reservoirs in OML 60, Offshore Lagos, South West Nigeria

Decline curve analysis is one of the most widely applied empirical tools in petroleum engineering for estimating remaining reserves and forecasting production performance without requiring detailed geological input. This study applies decline curve analysis to production data from shallow marine sand reservoirs in Oil Mining Lease 60, located offshore Lagos State, South West Nigeria. Monthly production records spanning a fifteen-year period from 2008 to 2022 were obtained and subjected to Arps decline curve fitting using hyperbolic, exponential, and harmonic decline models. Best-fit parameters were determined through least-squares regression in Excel-based analytical routines. The hyperbolic decline model provided the most accurate fit for the majority of analysed wells, with b-factor values ranging from 0.35 to 0.72, consistent with solution-gas drive mechanisms in moderate-permeability sandstone reservoirs. Estimated ultimate recovery calculations indicate that the field has produced approximately 61 percent of its technically recoverable resources, suggesting remaining upside potential through infill drilling and artificial lift optimisation. The study also identifies production anomalies in five wells attributable to water encroachment and discusses water handling capacity constraints at the host processing platform. Recommendations are provided for integrating decline curve results with material balance calculations to improve production forecasting accuracy for the remainder of the field life. Keywords: decline curve analysis, OML 60, offshore Lagos, reserve estimation, production forecast.