Thermal Well Test Analysis Using an Analytical Multi-Region Composite Reservoir Model

Abstract

Abstract For thermal recovery processes, the use of well test analysis to determine the swept volume is an important concern. Well tests conducted on wells undergoing a thermal recovery process have been typically idealized using a two- or three- region composite reservoir model. However, simulated thermal falloff tests have shown that mobility and storativity may be continuously changing in the swept region. For these reservoirs, a two- or three- region composite model may not be appropriate, while a multi-region composite model is suitable. A multi-region, composite reservoir analytical model has been developed to study the effects of various trends of mobility and storativity variations, within the swept region, on well tests for reservoirs undergoing a thermal recovery process. Pressure transient responses from this multi-region composite reservoir model show that on a log-log graph, the intermediate-time semi-log pressure derivative data falling on a straight line, whose slope is less than unity, is due to continuously changing mobility or storativity. The preceding behavior has been observed on several simulated thermal well tests. However, no theoretical explanation for this phenomenon has been advanced prior to this study.