The field tests for extracting the energy from Hot Dry Rock had been conducted at Hijiori test field in Yamagata Prefecture since 1984. In 1989, a 1-month flow test (Exp. 8902) was conducted using a injection well (SKG-2) and production wells (HDR-1 and HDR-2). In Exp. 8902, 40°C water was injected at the flow rate of 17 kg/s and 170°C hot water was recovered from production wells. The production rate from HDR-1 was 1.5 to 1.6 kg/s and that from HDR-2 was 4.2 to 4.9 kg/s. Although these production rates was not so high but the thermal output during the experiment reached to as high as 6 MW. This experiment was modeled by WBHT (Wellbore Heat Tranfer Code) and FEHM (Finite Element Heat and Mass Transfer Code), The simulation results showed that the permeability between SKG-1 and HDR-1 had 2 orders of magnitude more than the surrounding rocks. The calculated pressure distribution around the injection well showed that there was a high degree of pressure drop at the vicinity of injection well. The Gringarten's model was also used to estimate the area of heat transfer using the temperature draw down during the experiment.
This paper proposes a new numerical model on tracer response analysis of a fractured geothermal reservoir. The multiple paths model has been generally used for analysis of tracer response. However, such a model is so complex that it has a lot of parameters to be determined. The model proposed in the paper has only one main path, composed of fracture and semi-fracture layers, and has fewer number of parameters to be specified than the multiple paths model does.The conclusions are as follows:(1) Good agreements are found between calculations by this model and observation data of tracer response in a geothermal reservoir.(2) It is possible to say that flow path in the reservoir is not always made up of multiple paths but of one main path composed of fracture and semi-fracture layers.
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