Visualizing Wellbore Instability and Fracture Direction by Application of Principal Stress Trajectory Analysis
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This study furthers our understanding of the causes of wellbore failure by thoroughly analyzing key properties (e.g., in-situ stress regime, formation and pore pressures, and rock properties) associated with wellbore instability. Regardless of whether a wellbore is planned to be drilled underbalanced or overbalanced, local formation pressures, and even operational practices (e.g., shutting off the pumps while drilling) can quickly render a wellbore locally unstable. Near-borehole stress mechanics associated with stress cages (overbalanced holes) and with fracture cages (underbalanced holes) are further studied, including an analysis showing the impact tangential and radial stress magnitudes have on principal stress trajectory patterns. With a deeper understanding of stress cages and fracture cages, wellbore failure can, consequently, be quantified and visually evaluated to a greater extent. Stress trajectory analytical solutions can be rapidly applied for a wide range of in-situ stress and pressure conditions, which enable us to better predict, and therefore mitigate, wellbore instabilities associate with tensional and shear failure, and also estimate more assuredly unknown parameters that drive wellbore instability. The wellbore stress model in this study accounts for different in-situ stress regimes, borehole net fluid pressures, and poroelastic effects. Drilling software equipped with these tools may help reduce the occurrence of failure, saving drillers from countless hours of non-productive time and other associated costs.
Thomas, Ned C (2017). Visualizing Wellbore Instability and Fracture Direction by Application of Principal Stress Trajectory Analysis. Master's thesis, Texas A & M University. Available electronically from