A Fully Three-Dimensional Thermo-Hydraulic Computation of the Ogachi HDR Reservoir

Abstract

A fully three dimensional simulation code, GEOTH3D is developed to solve thermo-hydraulic features of a Hot Dry Rock (HDR) geothermal reservoir. The objectives of the code development are to help understand experimental data obtained in the CRIEPI's Ogachi HDR site, and optimize design of a planned HDR system by predicting thermal and hydraulic performances. Unique aspect of the GEOTH3D is that the reservoir structure is modeled by porous media of spatially variable permeabilities which are determined with aid of acoustic emission (AE) measurements at an HDR site and local permeability measurement around the wells. Based on the permeability distribution, the GEOTH3D code computes the 3D distribution of Darcy velocity, pressure and temperature, including the interaction between flow and temperature, but not the effects of rock stress and flow apertures.

For validation, the GEOtTG3D code was applied to a thirty day circulation test conducted at the Ogachi site in 1995, using time-dependent pressures at the injection and the production well heads. The temporal changes of the injection and production flow rates are compared with actual rates to quantitatively evaluate the applicability of the code. As a result, the computed flow rates approximately corresponded to the measured rates.