An improved method for numerically modeling the minimum horizontal stress magnitude in extensional stress regimes

摘要

The minimum horizontal stress magnitude, S_(hmin), is a crucial input parameter for a variety of subsurface engineering applications. Several methods, such as the general poro-elastic model, the uni-axial strain model and the concept of frictional equilibrium can be used to simulate S_(hmin) whereby the general poro-elastic model is most commonly used due to its capability to account for tectonic strain in order to match existing stress measurements. If stress measurement data is unavailable this paper introduces a pre-stressing procedure For 3D numerical Mechanical Earth Models that combines the poro-elastic mode! with the frictional equilibrium model to provide lower bounds for S_(hmin) in extensional stress regimes. Assuming common friction coefficients of μ in the range of 0.57 to 1, the necessary horizontal strain can be calculated to limit horizontal stress magnitudes of the whole model domain or of only certain calibration layers by frictional failure. For layers with Poisson's ratios smaller or larger than 0.25, S_(hmin) magnitudes being too low or too high (as predicted by the uni-axial strain model) can thus be prevented. The presented concept is tested for two case studies and the modeling results show that the combination of the poro-elastic model with the frictional equilibrium model can provide a good match to the measured data, even if it is assumed that the calibration data is not available. It is concluded that the combination of the two deformation mechanisms can produce a more physically appealing stress profile and hence may more accurately simulate the sense and relative magnitude of layer-to-layer stress contrasts. In addition, the numerical modeling approach presented can match observations on the near surface variation of the ratio k=S_(hmin)/S_v.