Proposing a Coning Correlation for a Low Recovery Factor Mature Reservoir: An Examination of Reservoir Dynamics

The evolution of reservoir engineering and management has led to complex enhanced oil recovery (EOR) techniques. Conventionally, the recovery factor (RF) for a typical reservoir fluctuates between 10% to 60% after forty years of production, averaging at approximately 35%. Unusually, the NGJ field, possessing high porosity (0.25) and permeability (300 to 600 md), maintains an RF of just 6.11% after over four decades, which is uncommon given the favorable reservoir conditions. This study employs traditional as well as advanced methodologies to comprehend the reasons for such low RF in this reservoir. The research included traditional techniques such as production performance analysis, decline curve analysis, and material balance calculation. Subsequently, a dynamic reservoir simulation was formed based on a static petrophysical model. The initial simulation revealed gas coning as a persistent issue in the reservoir. Hence, a concept of a coning correlation function (CCF) was proposed and the procedures for its development were explained. Using the Addington correlation, the critical oil rate was estimated and modified through the proposed time-varying coning correlation. The estimated critical rate through CCF is applied to control the flowing bottom hole pressure (FBHP) in the prediction scenarios. The study proposed an enhanced gas coning correlation, aimed at better-understanding gas production and breakthrough behaviors in the mature oilfield, thereby guiding the optimization of field production rates. The investigation revealed that the critical rate diminishes exponentially as the production time increases for a single well. A greater well perforation interval results in a reduced critical rate, whereas increased horizontal permeability causes a higher critical rate. By applying the correlation to a previously perforated well, the critical oil rate was determined, providing valuable data for optimized FBHP. For an infill well, the optimal critical oil rate helped estimate the distance between the gas-oil contact (GOC) and the top of perforations. Eight prediction schemes were recommended based on these analysis results. The prediction scenario incorporating a mix of workovers and infill drilling could achieve a RF of 8.44% and the highest returns of $50.35 MM in the forthcoming decade. The refined correlation was developed using a multiple-well numerical model, unlike the traditional one-well radial model. The production history was factored in to tweak dimensionless parameters in the correlation. The modified correlation provides a more accurate critical oil rate estimation compared to the traditional Addington correlation.