Study of the impact of failure criteria on wellbore stability during drilling

Abstract

The instability of an open wellbore during directional and horizontal drilling is a critical issue that can lead to emergencies and significant economic losses. One of the key methods to prevent wellbore collapse is the careful selection of drilling fluid density based on geomechanical modeling. The objective of this study is a comparative analysis of the influence of the most commonly used failure criteria (Coulomb-Mohr, Drucker-Prager, HoekBrown, Mohr-Coulomb, and Lade) on the calculation of drilling fluid density required to ensure wellbore stability. The work involves one-dimensional geomechanical modeling using the RN-SIGMA 2.0 software package with logging data (density, interval transit times of longitudinal and transverse waves) from five wells obtained from open sources. We calculated profiles of geostatic and pore pressures, dynamic and static elastic properties (Young’s modulus and Poisson’s ratio), strength properties (uniaxial compressive and tensile strength limits, internal friction angle), as well as horizontal stresses according to a poroelastic model. The results showed that the choice of failure criterion significantly affects the required drilling fluid density to prevent wellbore collapse. The lowest density values were obtained using the Lade criterion, while the highest values corresponded to the HoekBrown and Drucker-Prager criteria. The classical linear Coulomb-Mohr criterion yielded intermediate density values. These differences are due to different mathematical formulations of the criteria and their consideration of various rock failure mechanisms. The findings indicate the necessity of carefully selecting a failure criterion appropriate for the lithology and mechanical properties of specific rock intervals.