Modelling the heat extraction from the rosemanowes hdr reservoir

Abstract

A number of complementary models are developed which successfully analyse the thermal drawdown in the hot dry rock geothermal reservoir created between wells RH12 and RH15 at Rosemanowes Quarry, Cornwall, U.K. Although the reservoir is highly fractured, with an average interfracture distance that is small compared to the diffusive length scale of heat extraction, the highly non-uniform flow through the fractures shows that it is not appropriate to model the reservoir as a porous medium. The most permeable joints must be modelled, and the produced fluid taken to be the weighted average of the individual flow path temperatures. The results are sensitive to the flow distribution, the fracture area and reservoir volume. They are not sensitive to changes that have occurred in the reservoir over its lifetime. It is shown that care must be taken in developing models based on the thermal results alone, since only a few parameters are statistically significant. Introduction of the tracer results effectively constrains the choice of some of these parameters. Good estimates for the remaining free parameters can be found from the well logs and seismic data. Careful use of the model, with appropriate data, would give a good estimate for the thermal performance of an HDR system.