Stability Analysis of Vertical Boreholes Using a Three-DimensionalHoek-Brown Strength Criterion

摘要

Borehole stability analysis plays an important role in the design of oil and gaswell drilling. A main aspect of borehole stability analysis is the selection of anappropriate rock strength criterion. The two most commonly used rock strengthcriteria in borehole stability analysis are the Mohr-Coulomb criterion and theDrucker-Prager criterion. However, the Mohr-Coulomb criterion ignores the effect ofthe intermediate principal stress and is too conservative in estimating the criticaloverbalance pressure required to maintain borehole stability; while the Drucker-Prager criterion overestimate the effect of the intermediate principal stress and mayresult in non-sensible stability predictions. In this paper, a simple model based on athree-dimensional (3D) Hoek-Brown strength criterion is developed for stabilityanalysis of vertical boreholes. Examples are presented to show the application of the3D Hoek-Brown strength criterion for analyzing the stability of vertical boreholes andthe results are compared with those using the Mohr-Coulomb and Drucker-Pragercriteria. It shows that the 3D Hoek-Brown strength criterion predicts criticaloverbalance pressure values that are less conservative than those predicted by theMohr-Coulomb criterion yet are not as unconservative as those predicted by theDrucker-Prager criterion.