Stress field determination from local stress measurements by numerical modelling

A back analysis using a three-dimensional (3D) boundary element method (BEM) is used to calculate the far-field stress state from local stresses measured in situ. The far-field stresses are decomposed into tectonic and gravitational components and account for the influence of localized faulting and topography. Therefore, the far-field stresses are taken to consist of a constant term, a term that varies linearly with depth, and a hyperbolic term, with one of the principal stresses being vertical. A BEM for inhomogeneous bodies is introduced to calculate elastic gravitational stresses, which is necessary for determination of the far-field stresses.An application to the stress field determination for the Mizunami underground research laboratory (MIU) is carried out. Based upon the local stresses generally measured by conventional hydraulic fracturing (HF), the unknown stress state at MIU is estimated and compared with the measurements carried out recently by the improved HF method with flow rate measurements at the position of straddle packer. After calculating the far-field stress state by BEM back analysis, 3D-finite difference methods (FDM) forward analysis was carried to calculate the in situ stresses at certain locations. The 3D FDM results roughly coincide with the measured results.