Injection capability at the Raft River Geothermal Site

Abstract

The Raft River Geothermal Resource Area in southern Idaho is the first location for an electric power plant utilizing a medium temperature (approx. = 145/sup 0/C) geothermal resource. For the projected 5 MWe pilot geothermal plant, a supply of 2500 gpm of the geothermal fluid is needed. The State of Idaho prefers that the spent brine be reinjected into zones deeper than the known agricultural aquifers. Wells RRGI-6 and 7 are to be used for injection. The objective of this study is to evaluate the injection capability of the formation. An analysis is presented of several injectivity tests performed by EG and G on RRGI-7 to characterize the injection capability of the formation. The available geological information about the area and preliminary results of a spinner survey have been included in the injectivity test analysis. A wellhead pressure limit of 500 psi has been imposed to prevent injection formation fracturing. The approach to analysis is to use a two dimensional radial numerical simulator with parameters determined by the test results and from geological data.