Estimation of Effective Geostress Parameters Driven by Anisotropic Stress and Rock Physics Models with Orthorhombic Symmetry

The estimation of effective geostress parameters is fundamental for the trajectory design and hydraulic fracturing in the shale formation. In the paper, a shale anisotropic rock-physics effective model with orthorhombic symmetry is first to be built based on the comprehensive analysis of minerals, pores, cracks or fractures, and fluids of shale formation, and it helps to calculate the anisotropic parameters and the geomechanical parameters such as Young’s modulus and Poisson’s ratio under the orthorhombic assumption. Then, an orthogonally anisotropic stress models with orthorhombic symmetry are introduced compared with the isotropic stress models and the transversely isotropic stress models. Combining the effective estimation of the pore pressure and the vertical stress parameters, the effective geostress parameters including the minimum and maximum horizontal stress parameters can be estimated ultimately using the established rock-physics model and the orthogonally anisotropic stress models, and it can provide some useful guide for the trajectory design and hydraulic fracturing. Of course, the optimal choice of hydraulic-fracturing area should consider varieties of factors such as the rock brittleness, the cracks or fractures, and hydrocarbon distribution except for the estimated effective geostress parameters.