Comprehensive evaluation of the initial rock stress carried out as part of a 2000m all core borehole investigation

In the field of tectonic stress measurement, it is generally acknowledged that measuring the initial stress with high accuracy is difficult. We think the best approach to evaluate the initial rock stress is to carry out tests using multiple stress measurement techniques, to organize their mutual relationship and after reviewing the results, to performing a comprehensive evaluation, rather than reaching a conclusion based on a single measurement. A hydraulic fracturing test has been carried out in-situ. Using the retrieved core, the DSCA method and a new technique that uses the Diametrical Core Deformation Analysis (DCDA) has been carried out. Furthermore, using BHTV measurements, the breakout of the borehole has been confirmed and its occurrence has been interpreted. In this study, the maximum and minimum principal stress, as well as the direction of the maximum principal stress in the horizontal plane, has been estimated based on a comprehensive evaluation of the above mentioned results. Based on the each tests and the comprehensive evaluation, the direction of the maximum principal stress in the horizontal plane is estimated to be 85 degrees, the magnitude of the maximum principal stress at 1,700m depth to be between approximately 37 and 42MPa, and the magnitude of the minimum principal stress to be between approximately 34 and 38MPa. These results are consistent with the regional stress field derived from focal mechanism analysis.