New Model for Estimation of Wellbore Gas Injection Pressure for Vertical Wells in Depleted Hydrocarbon Reservoirs

Abstract Gas injection is one of the most dynamic field development strategies to maximize hydrocarbon recovery, through pressure maintenance and improved oil displacement (either miscible or immiscible mechanisms). It also provides a means for underground storage purposes. Gas injection rates and pressures are strong considerations during the design stage and operational periods of the injection schemes. Numerical modelling and leak-off tests are approaches mostly used in the industry for such estimations, and so a great deal of time and money is expended. This work therefore presents new model for estimation of gas injection rate and pressure, especially for oil rim reservoirs, formulated from the results of numerous gas injection well performance simulations carried out for vertical wells under various reservoir, fluid and pipe properties and surface operating conditions. From the simulated results, the minimum and maximum injection pressure gradients have values of approximately 0.2 psig/ft and 0.47 psig/ft, respectively. Multiple linear regression approach was used for the development of the injection pressure models, using the simulated results dataset. The percentage error bandwidth of the predicted injection pressure falls in the range of −29 % and +25-63 %, with an absolute average error of 6.89 %. The developed models can be a quick tool for predicting gas injection rate and pressure, when constrained to factors such as; minimum miscibility pressure (MMP), fracture pressure gradient, surface facilities’ conditions, gas availability and supply, and among others.