New analytical solution to pressure transient problems in commingled, layered zones with unequal initial pressures subject to step changes in production rates

Abstract

Evidence of layered zones with unequal initial pressures is often found when analyzing well-test data. However, modeling these in a numerically-tractable manner has been a challenge. This study presents a new analytical solution to the transient flow problems involving a well, which commingles the layered zones with unequal initial pressures. The solution is obtained with the Laplace transformation, and is general in dealing with any combination of infinite, constant pressure or no-flow conditions at the outer boundaries of individual layers. A special technique has been proposed to deal with step changes in production rates, including pre-production and buildup periods. Moreover, skin and wellbore storage effects are included.