A Downhole Pump Test on a 2km Deep Hot Dry Rock Geothermal System

Abstract

During the continuing long-term circulation programme of the 2 km deep Hot Dry Rock (HDR) geothermal system at Camborne, a downhole pump was installed in the production well and used to investigate the effects of sub-hydrostatic pressure on reservoir performance. This condition is expected to occur naturally in a 6 km deep HDR reservoir. Tracer test results showed a change in the flow distribution but no overall change in the effective circulating volume of the reservoir and this was confirmed by the unchanged thermal behaviour of the reservoir. Although the production flow rate did increase during the test the impedance was also increased and indicated that the increased effective stress acting on the joints close to the production well was causing them to close up.