An optimized inversion method for in-situ stresses based on Rhino accurate modeling and large-scale transverse isotropic theory

Abstract

In-situ stresses are significantly important for underground mining geotechnical design and coal seam gas management in underground coal mines. The past research always assumed an isotropic elastomer in the rock mass so that they could propose multivariate linear regression to predict the in-situ stresses. However, such a method normally led to a huge error if some extreme ground conditions presented such as massive bedding structures and frequent variations in the dip angles of discontinuities. The Guodishan fault area has complex geological conditions. In order to study the distribution characteristics of regional geostress field, this paper established an accurate 3D geological model of the area near the Guodishan fault by Rhino. Combined with the idea of large-scale transverse isotropy, we successfully extrapolated the original in-situ stress near the fault by using finite difference software, and determined the relationship between the gas hazard of coal seam in the fault and the in-situ stress. It was found that the 3D model development in Rhino could increase the accuracy of the geological conditions so that the accuracy of the in-situ stress inversion can be improved consequently. Based on the transverse isotropic modelling methods for numerical calculations, a more accurate in-situ stresses field could be obtained. The coal seam F16-17 at the foot wall of the fault has a K ratio greater than one indicating a significant influence of the fault structures on the in-situ stresses distribution. Between levels − 300m and − 900m, the seam at the hanging wall area of the fault is deeper than seam at the foot wall area leading the original in-situ stress at hanging wall as much as 1.69 times that at the footwall. This would pose a greater gas risk in the hanging wall area than the foot wall area. The area close to the fault has a higher stress gradient which might lead to a higher risk of hazards.