Stress Distribution of Wellbore under Non-Uniform <i>In Situ</i> Stress

Abstract

The distribution of the non-uniform in situ stress around wellbore will impair the stability of the rock of wellbore wall. Drilling the underbalanced wells and depleted formations, the instability of the wellbore can result in the drilling failure. Mechanics model of the wellbore wall rock is developed. According to the relationship between the stress function and components of stresses, the superposition principle is adopted to develop the formulas of the radial, hoop, and shear stresses of the wellbore wall under the non-uniform in situ stress. The formula of the mud density which do not crash the rock of wellbore wall is derived. The error of the mud density between fitting formula developed in the paper and theoretical method is less than 2.5%. The mud density that ensure the stability of wellbore is determined.