Decline curve analysis using rate normalized pseudo-cumulative function in a boundary dominated gas reservoir

Abstract

This paper presents a new and mathematically rigorous method to analyze declining gas production and pressure data using type curve. This method incorporates the pseudo parameters such as pseudo-cumulative production, real gas pseudopressure and a new pseudotime function for the first time to analyze rate-time curve.The pseudotime function provides a convenient approach to handle variations in viscosity-compressibility values more rigorously with pressure since viscosity-compressibility ratio is a function of cumulative production.The proposed method is based on the use of the new material balance pseudotime (Ta), called the rate normalized pseudo-cumulative function. A new algorithm is presented to compute the gas-in-place, and reservoir properties such as permeability, reservoir drainage area, and the pseudosteady sate constant.This method is also capable to analyze the behavior of production data more rigorously for constant bottomhole pressure, variable rate/variable pressure drop, and strong depleted reservoir condition. The proposed method is a direct application of pseudosteady state relation that avoids iterations and extrapolation of data during analysis.Finally, detail analysis and interpretation strategies are presented for both simulated and field data. The results obtained are in good agreement with previously reported results. The proposed method is strictly valid for boundary-dominated flow regime in gas reservoirs.