Laboratory Studies on the Stability of Vertical and Deviated Boreholes

Abstract

ABSTRACT Polyaxial or true triaxial tests have been performed on weak and strong sandstones in order to investigate the stability of model boreholes. Both vertical and deviated boreholes in anisotropic stress systems have been studied. The results indicate the decrease in stability of the deviated boreholes with increasing inclination. Boreholes oriented parallel to the maximum horizontal stress direction also produces less stable boreholes compared to those drilled parallel to the minimum horizontal stress. Comparisons of the laboratory test results with simple predictions using linear elasticity, and a Mohr Coulomb failure criterion, show that the boreholes in the strong sandstones are approximately 4 times stronger than predicted; while the weak sandstones are approximately 8 times stronger than predicted.