Complete stress determination with the HTPF tool in a mountainous region

Abstract

Abstract Stress measurements have been conducted in a 1155 m deep, 60° dipping borehole, in a mountainous environment where none of the principal stress directions are known. Core examination and BHTV log show that no lm long, fracture free, interval exists in the well. But some of these fractures are not seen on the electrical imaging log. This suggests that they are sealed in situ, as confirmed by straddle packer tests. Stress measurements were conducted with the HTPF method, in which hydraulic tests are used to measure the normal stress supported by preexisting fractures. 20 complete tests have been conducted between 850 m and 1150 m. A new inversion algorithm has been developed in which the stress is characterized by a linear function of the distance between test locations. The stress field is characterized by 10 parameters. Results show that one principal stress direction is within 15° from the borehole axis. It corresponds to the mininum principal stress above 950 m. Borehole breakouts have been observed around 900 m with both the BHTV and the electrical imaging tool. Their orientation is about 20° off the intermediate principal stress direction as identified with the HTPF technique.