A STUDY ON THE STRESS FIELD AROUND A BOREHOLE IN ANISOTROPIC FORMATION

Because of the complexity of the problem, most of the studies on borehole stability simplify the geologic medium as isotropic. Based on the theory of anisotropic elasticity, this paper established a model to calculate the stress distribution around an inclined borehole in anisotropic formation by means of complex function method. The analytical expressions for the stress field are formulated which can reflect the influences of the formation anisotropy, the bedding plane inclination and orientation, the borehole deviation and azimuth angles, the pressure of the drilling slurry, the direction and the ratio of the in-situ stresses. The stress contour maps obtained can be used to estimate the position, the extent, the depth and even the shape of fractured or collapsed borehole. The formulation might provide a more realistic basis of theory for analyzing the stability of the wellbore and optimizing the well trajectory in anisotropic formation.