Results from a Discrete Fracture Network Model of a Hot Dry Rock System

Abstract

The dream of clean, economic power derived from the huge volumes of naturally hot rock that lie beneath us (Parsons, 1904) is as yet unfulfilled. The technical difficulties in engineering hcat-exchangers of sufficient area and volume at depth have not yet been solved (Garnish et al, 1992). In the mid 1970s and early 1980s models of HDR systems assumed "penny-shaped" hydraulic fractures (for example MAGES 1979), which were assumed to have been created by hydraulic fracturing of a homogeneous, isotropic, impermeable, elastic crystalline host-rock. Even at this time some authors were drawing attention to the importance of natural fracture systems (Batchelor, 1976, 1977). Subsequent experience during all large scale field tests has shown that the interaction between the in-situ stress field and the natural fracture system is of supreme importance and new models such as FRIP (Pine and Cundall, 1985) were developed. These models were vital for the understanding 01 field experiments such as those performed at Rosemanowes (Parker, 1989). However, these models only considered a gross idealisation of the natural fracture system. The work described in the Summary of the Work section represents a move towards better representations of the natural fracture system. The discrete fracture network model used during the study was the NAPSAC code (Grindrod et al, 1992). NAPSAC has been developed as part of the OECDiNEA Stripa Project.