In Situ Stress Distribution and Variation Monitored by Microseismic Tracking on a Fractured Horizontal Well: A Case Study from the Qinshui Basin

In situ stress is an important parameter regulating the production of coalbed methane (CBM), and the monitoring of rock deformation can provide a description of the state of stress. Microseismic monitoring in a multistage fractured horizontal CBM well was conducted as a case study with a completion depth of 1445.36 m. The results show that there is a good correlation among the seismicity parameters, b-value, stress drop, fracture length, fracture density, and orientation. In the stress concentration region, the fracture is longer with a smaller density, where the b-value is lower. On the contrary, in the stress relaxation zone, the fracture is shorter with a complex shape, where the b-value is higher. Stress drop is relatively higher where fractures are concentrated, which indicate the areas with successful reservoir stimulation. The reliability of the above results was verified by the normal fault occurring between stages 7 and 8. In the area affected by the hanging wall of the normal fault (stage 6 and 7), the b-value is 0.38-0.39, while in the area affected by the footwall (stage 8 and 9), the b-value is 0.64-0.66. This phenomenon reflects an obvious stress concentration in the hanging wall of normal fault, which is consistent with the conventional understanding. The microseismic source parameters have great potential in evaluating reservoir stress. With further exploration of source parameters, microseismic will provide more support for CBM development.