Nonisothemal Injectivity Index can Infer Well Productivity and Reservoir Transmissivity

Abstract

In geothermal wells injection tests are commonly used to obtain well and reservoir data. These tests are typically conducted in a'series of step rates followed or preceded by a complete shutin. Usually the temperature of the injected fluid is different from that of the reservoir fluid. Because of the strong temperature dependence of fluid viscosity and to a lesser extent, fluid density, nonisothermally related pressure responses must be considered. The nonisothermal injectivity index obtained from these tests depends on the mobility ratio of the cold region to the hot reservoir and the extent of the cold spot. This paper proposes a method of estimation of the apparent viscosity which accounts for these effects and relates the nonisothermal injectivity index to the isothermal injectivity index.