Analysis of CO2 Pressure Transient Data With Two- and Three-Region Analytical Radial Composite Models

Abstract

SUMMARY The results from this study show that pressure transients influenced by the interaction of fluid flow and phase behavior can behave as a three region composite reservoir. The intermediate region in this study was a high compressibility region that resulted from CO2-oil interaction. Although two-region models have been applied successfully in thermal EOR and geothermal projects, a two-region model is unable to explain pseudo-steady state behavior observed in some miscible gas injection falloff tests. Three-region modeling combined with compositional simulation may be appropriate if pseudo-steady state response is observed, especially when mobility ratio is not large enough to manifest in a pseudo-steady state behavior based on two-region models. A series of injection falloff tests were performed at a West Texas reservoir in an effort to establish injectivities and in situ flow parameters during water and CO2 injection. The results from the field tests in combination with laboratory tests will provide part of the engineering basis for design and operation of future CO2 EOR projects at a West Texas reservoir. Falloff data and interpretation are presented along with experimental and compositional simulation results. In situ parameters such as mobility ratio, swept volume, and average CO2 saturation in the swept region were estimated from the falloff data. The falloff analyses results are in good agreement with laboratory measurements and theoretical predictions. Therefore, this type of injection testing may be desirable in most EOR projects.