Numerical Modeling of Drilling-Induced Tensile Fractures in Vertical and Sub-vertical Wellbores

Abstract Drilling-induced tensile fractures (DITFs) form because the construction of a wellbore perturbs the in-situ stress such that the effective tangential stress at the borehole wall becomes tensile. In borehole image (BHI) logs, they appear as linear features, typically forming opposed pairs parallel to the borehole axis, and in vertical wells, they indicate the orientation of the maximum horizontal stress at the borehole wall. Frequently, however, DITFs exhibit en échelon traces, i.e., staggered, step-like patterns interpreted to reflect a misalignment between the borehole and a principal stress axis. A recently developed distinct element method (DEM) tool is used in a novel application to forward-model DITFs in vertical and sub-vertical wellbores in a homogenous rock mass. In vertical wellbores, the modeled fracture lengths and aperture profiles show excellent agreement with linear elastic fracture mechanics (LEFM) predictions. In sub-vertical wellbores, the model results are consistent with analytical solutions based on linear elasticity and show how the degree of fracture stepping depends on the deviation of the wellbore from the far-field principal stress plane normal to the least compressive principal stress. The developed DEM workflow, verified against existing analytical solutions, provides a robust foundation for more advanced models that incorporate, for example, pre-existing rock-mass discontinuities, a key factor expected to strongly influence DITF initiation and stepping in natural formations.