In-situ stress measurements and regional stress field assessment in the Xinjiang candidate area for China's HLW disposal

Altogether 180 hydraulic fracturing (HF) in-situ stress measurements were conducted in a pre-selected area in the Xinjiang Uygur Autonomous Region, China, which is being considered as one of the candidate areas for China's high-level radioactive waste (HLW) repository. In-situ stress magnitudes and orientations in three sub-areas (i.e., Yamansu, Tianhu and Aqishan sub-areas) were obtained from 163 valid measurement points in eight sub-vertical boreholes at depths ranging from 17 to 647 m, and the variation of the in-situ stress components with depth was analyzed. The measurement results show that the maximum horizontal stress is larger than the vertical stress within most of the measurement depth ranges, indicating that the regional stress field is dominated by tectonic horizontal stress rather than by the overburden stress (σv). Within the range of the tested depths, the stress field is characterized by σH > σv > σh, where σH and σh are the maximum and minimum horizontal stresses, respectively. Fracture impression results reveal that the maximum horizontal stress is dominantly oriented in the NEE-SWW direction, which is in general in agreement with the orientation of regional tectonic stress field generated from movement of the Earth's tectonic plates and is consistent with those interpreted by GPS measurements and focal mechanism solutions. In addition, an abnormal phenomenon in performing stress measurements in one borehole was noticed and the result was discussed using borehole injection test data.