NUMERICAL-SIMULATION OF FLOW AND HEAT-TRANSFER IN FRACTURED CRYSTALLINE ROCKS - APPLICATION TO THE HOT DRY ROCK SITE IN ROSEMANOWES (UK)

This study examines heat transfer during forced water circulation thro ugh fractured crystalline rock using a fully 3-D finite-element model. We propose an alternative to strongly simplified single or multiple p arallel fracture models or porous media equivalents on the one hand, a nd to structurally complex stochastic fracture network models on the o ther hand. The applicability of this ''deterministic fracture network approach'' is demonstrated in an analysis of the 900-day circulation t est for the Hot Dry Rock (HDR) site at Rosemanowes (U.K.). The model d esign with respect to structure, hydraulic and thermal behavior is str ictly conditioned by measured data such as fracture network geometry, hydraulic and thermal boundary and initial conditions, hydraulic reser voir impedance, and thermal drawdown. Another novel feature of this mo del is that flow and heat transport in the fractured medium are simula ted in a truly 3-D system of fully coupled discrete fractures and poro us matrix. While an optimum model fit is not the prime target of this study, this approach permits one to make realistic long-term predictio ns of the thermal performance of HDR systems. (C) 1998 CNR. Published by Elsevier Science Ltd. Ail rights reserved.