Estimation of In-situ Stress State of Hijiori Hot Dry Rock Site using DSCA

Though in-situ stress state is one of the key factors for development of hot dry rock (HDR), a reliable method to estimate the stress state has not been established. The depth and the high temperature prevent us to apply a conventional method of in-situ stress measurement, such as a strain relief method or a hydraulic fracturing method. We have tried to estimate the stress state of an actual HDR reservoir, located in Yamagata prefecture, using DSCA (Differential Strain Curve Analysis). DSCA is one of new methods of stress measurement, based on a laboratory work for an oriented core. We compared the results of DSCA to phenomena reflecting in-situ stress state of the reservoir and results obtained by other stress measuring methods applied in that field. Through the comparison, we found that the DSCA results of principal stress directions generally matched with a stress state that controlled the direction of the actual HDR reservoir.