Heat Extraction Tests and Reservoir Modeling for Hot Dry Rock Development

A 15-day flow test (Exp. 8805) was conducted at the hot dry rock reservoir created by hydraulic fracturing at the bottom of injection well, SKG-2 at Hijiori test field in Yamagata Prefecture. The depth of SKG-2 well was about 1, 800m and the bottomhole temperature was about 250°C. Water was circulated at the flow rate of 0.5 t/min for first 10 days and then increased to 1.0 t/min. During the circulation test, fluid pressure, temperature and flow rate were measured at the wellheads of injection well, SKG-2 and production well, HDR-1. Production well temperature increased throughout the test and reached a maximum of 175°C, while the water recovery was about 40%. To evaluate the reservoir performance during Exp. 8805, two models were introduced: one is applied above 1, 500m depth and the other below 1, 500m depth, because we can analyze the performance above 1, 500m as two wells model and must introduce three-dimensional model for the reservoir created in hot dry rock. First, we calculate water temperature in SKG-2 well at the depth of 1, 500m using WBHT (Wellbore Heat Transfer Code). Then, the reservoir performance was simulated by placing two wellbores, SKG-2 and HDR-1 in the finite element mesh of FEHM (Finite Element Heat and Mass Transfer Code) at their relative positions. After the data match to this circulation test, one year simulation was conducted to predict the reservoir performance. Finally, the temperature of production fluid at the wellhead of HDR-1 well was calculated by the WBHT. The results showed that the wellhead temperature of production well reached 180°C and kept almost constant at the flow rate of 0.5 t/min and the recovery of 40%, while it reached 202°C and decreased to 185°C when the flow rate was 1.0 t/min and recovery was 38%.