Semilog Analysis of Gas Well Drawdown and Buildup Data

The pseudopressure function is well understood and widely used for analyzing gas well drawdown and buildup data. The usefulness of the pseudotime function for analyzing buildup data with drawdown type curves has also been established. Unfortunately, the pseudotime concept is often incorrectly applied when drawdown data are analyzed by semilog methods. This work provides information on appropriate definitions of dimensionless time that yield accurate analysis of data obtained under radial flow conditions. From the practical viewpoint, the most important result is that two Horner time ratios exist - one based on a normalized shut-in time and one based on shut-in pseudotime - that yield an accurate analysis of buildup data, including the correct determination of average pressure using the liquid Matthews-Brons-Hazebroek (MBH) functions.