Utilization of Magnetotelluric Data for Evaluation of Geothermal Reservoir Condition Associated with EGS Water Injection at Okuaizu Geothermal Area in Japan

Abstract

Enhanced Geothermal Systems (EGS), with artificial water injection into the geothermal reservoir is one of the effective methods to avoid these problems. A 5-year research project, name of Technology Development for Geothermal Reservoir Evaluation and Management funded by JOGMEC, Japan was started in 2013. An MT survey was conducted at 116 sites and 3D inversion was performed by using the 3D inversion code WSINV3DMT. The optimum model also indicates quite a good matching with resistivity logging data in this zone. It is notable that seeking for the minimum data misfit model is not the best way to choose the optimum model probably due to the observation errors in the MT data. To evaluate the sensitivity of MT responses associated with water injection, we calculated the change of MT responses caused by water injection by using a reservoir simulator, STAR. As a result of simulation, detectable change of apparent resistivity associated with water injection is estimated at the observation sites near the injection well. The result indicates that the continuous-MT observation is effective for monitoring geothermal reservoir associated with water injection.