Determination of Average Reservoir Pressure from Constant-Rate Drawdown Tests

Abstract This paper presents a method that can be used to analyze constant-rate drawdown tests to determine average reservoir pressure as a function of flowing time. The proposed method couples the pseudosteady state equation with its integral function to yield a unique plotting function that results in a zero slope (i.e., a constant value on the ordinate), which, based on the definition of stabilized flow equation, is equivalent to the difference between the average reservoir pressure and the bottom-hole flowing pressure. The average reservoir pressure history is, thus, obtained since the bottom-hole flowing pressure profile is known. As opposed to derivatives, the proposed approach yields smooth data; and is very diagnostic on the cartesian plot. Extension to gas wells is also considered. The significant contribution of this paper is that average reservoir pressure profile can directly be estimated using constant-rate drawdown test. Also, our proposed approach is based on a sound theoretical background. We demonstrate the validity of the proposed method with simulated and field data that are already published in the literature.