A comparison of the use of pseudotime and normalized time for gas well buildup analysis in various geometries
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1986, Society of Petroleum Engineers. The real gas flow equation is effectively linearized for drawdown when expressed in terms of pseudopressure and time. Two time functions have been proposed to linearize the flow equation for buildup: pseudotime and normalized time. This paper compares the use of pseudotime and normalized time for a variety of different analysis techniques. The study focuses on buildup following constant rate drawdown for systems in which the reservoir is still infinite acting. For radial flow, analysis methods considered include log-log type curve matching and Horner analysis. Analysis methods for wells with infinite conductivity vertical fractures include linear flow analysis, log-log type curve matching, and Horner analysis. Except for wellbore storage, no major difference in accuracy is found between pseudotime and normalized time. Also compared are two different methods for treating producing time effects when using pseudotime or normalized time. A new method of calculating the equivalent drawdown time function is presented which is independent of initial pressure.
