A Model of Limited-Entry Completions Undergoing Spherical Flow

Abstract

SummaryMethods are presented in this study to determine wellbore and reservoir properties from limited-entry tests of very thick formations. This situation is often encountered in the Overthrust Belt and in geothermal operations. Most published limited-entry analysis methods assume the existence of three flow regimes during testing if wellbore storage is small. Theoretically, the regimes are (1) an early cylindrical flow period indicative of the opened interval, (2) a short spherical transition period, and (3) the late-time cylindrical data reflecting the entire productive thickness of the reservoir. The above methods are not applicable to very thick reservoirs because field data are often dominated by wellbore storage and a long spherical flow period.In this study, an analytical solution is presented to analyze the wellbore-dominated and the spherical-flow periods. The model includes cylindrical skin of the open interval and wellbore storage. The solution and resulting type curves allow direct estimates of stimulation potential in situations where wellbore storage and spherical flow dominated pressure-transient behavior. Prior methods to determine damage require late radial-flow data and separate estimates of pseudoskin caused by flow convergence. Field examples from a gas-condensate reservoir and a geothermal well demonstrate the methods. The practical aspects of analyzing other limited-entry data are discussed.