Analysis of In-Situ Stress Characteristics in Southern Sichuan Basin Based on Multi-Source Data

In situ stress states are the key to tackle the problem involving geomechanical stability. Based on the analysis of regional tectonic trace, in-situ stress measurement data, focal mechanism data and borehole failure phenomena, this study comprehensively analyzed the in-situ stress characteristics in the southern Sichuan basin. Using a stress inversion method based on focal mechanism solutions, the stress orientations were estimated, while the stress magnitudes were constrained based on the stress polygon method and borehole failure indexes. The results show that the regional stress state in the southern Sichuan Basin is stable, which straddles the boundary between reverse faulting and strike-slip faulting regimes. The orientation of the maximum horizontal principal stress at shallower depth has two preferred directions, NE and NW, while it turns to NWW in deep depth. The zonal characteristics of regional stress fields are not obvious, where the focal mechanism solutions are in consistent and the stress fields are relatively uniform. The estimation of the stress magnitude in the shallow region show that the lateral stress coefficients of different drilling holes are relatively stable, with an average value of k_Hmax=1.72 and k_hmin=0.99, respectively. The stress accumulation index value μ_m ranges from 0.15 to 0.5. When the buried depth is 3207~3716 m, the magnitudes of the maximum and minimum horizontal principal stresses in Weiyuan area are in ranges of 104.5~122.3 MPa and 81.1~96.5 MPa, respectively, while the vertical stresses range from 83.3 MPa to 96.5 MPa. The values of stress accumulation index μ_m are in range of 0.37~0.43, indicating that the regional stress accumulation level is low. This stress estimation and analysis method based on multi-source stress data could lead to a comprehensive understanding of regional stress in southern Sichuan Basin and provide a possible method for stress analysis especially for that lack of in-situ measurement data.