Usually, well tests from enhanced oil recovery projects, such as steam injection, in-situ combustion, and CO2 flooding projects, are analyzed using a radial, two-region composite reservoir model. However, a three-region model may be more appropriate in many cases. An analytical solution for the transient pressure response of a well in a radial, three-region reservoir is available. But a detailed study of the transient pressure and/or pressure derivative response of a well in a three-region reservoir has not been presented in the literature.

Using an analytical solution, this study establishes the ratio of the intermediate region radius to the inner region radius as a correlating parameter for the transient pressure derivative responses for a three-region reservoir. Additional four parameters are related to the mobilities and the storativities of different regions. This study shows that the deviation time method would result in an estimate for the inner region radius, if the effects of the mobilities and the storativities of the inner and the intermediate regions are not balanced in a way to produce an incorrect deviation time.

Analytical expressions for the effective porosity-compressibility product and mobility are developed for the analysis of pressure transient data by the pseudosteady state (PSS) method. The PSS method would result in an estimate of the combined volume of the inner and the intermediate regions, if an effective porosity-compressibility value is used to analyze the pseudosteady data. However, at times, the development of an apparent pseudosteady state may yield an overestimated volume. An idea about the development of an apparent pseudosteady state may be obtained by calculating the effective dimensionless time corresponding to the time to start of an approximately constant Cartesian slope for the pressure transient data in question.

You can access this article if you purchase or spend a download.