Simple Correlation to Evaluate Mohr-Coulomb Failure Criterion Using Uniaxial Compressive Strength

The evaluation of Mohr-Coulomb failure criterion as well as other mechanical properties for reservoir rocks is essential for well planning, development and characterization of oil and gas reservoirs. This is because the understanding of the rock-stress relationship can solve many reservoir problems and avoid cost of remedial work. For example, a Mohr-Coulomb failure criterion may be used for borehole instability analysis, water injection design, production optimization techniques, compaction and sand production prediction, etc. A Mohr-Coulomb failure criterion is a function of the apparent cohesion (τ0) and the angle of internal friction (φ). The evaluation of these two parameters requires testing of many rock samples using an expensive and time-consuming triaxial testing set-up. In this study, a correlation between the apparent cohesion and the uniaxial compressive strength was developed. It is based on laboratory data of more than 200 rock samples of different types obtained from the literature. The correlation coefficient of the developed correlation equals to 0.82. Verification of the developed correlation using data from other references has shown an average error of estimation equal to 10%. Therefore, the Mohr-Coulomb failure criterion’s parameters as well as Poisson’s ratio can be estimated using the developed correlation based on fast and cheap measurements of the uniaxial compressive strength.