Factors affecting solution gas drive recovery

Abstract

This study investigates the effects of oil producing rate, absolute permeability and well completion interval on oil recovery in a solution gas drive reservoir. The investigation is made using a radial, two-dimensional, three-phase, numerical, reservoir model. Earliest, simplified studies of the effect of oil producing rate on oil recovery concluded that recovery was not affected by producing rate. Recent, more complete studies on linear models have found that oil recovery is a function of oil producing rate, with greatest oil recoveries being achieved at highest production rates. Flow in the vicinity of withdrawal points (wells) is radial, rather than linear. Are the effects of oil producing rate on recovery the same in radial systems as in linear systems? The mathematical model is derived using Darcy's Law and an equation of state for each phase. These equations are combined to form one non-linear, non-homogeneous, second order, partial differential equation with variable coefficients. The dependent variable is oil phase pressure. Finite difference techniques are used to solve the equation. The reservoir is divided into a grid system, and finite difference equations are written at each grid point. The result is a system of linear algebraic equations with variable coefficients. This system of equations is solved in this study using a Gaussian Elimination technique. The reservoir system considered in the study consists of a single well in the center of a circular, bounded, horizontal reservoir. The radius of the reservoir is 372 feet; its thickness is 30 feet. Porosity of the reservoir is 27.1 percent. Three phase drainage and imbibition relative permeabilities are considered in the model. ...