oa Prediction of Apparent Cohesion, Angle of Internal Friction and Poisson's Ratio of Various Types of Rocks Using Laboratory Measured Unconfined (Uniaxial) Compressive Strength

The evaluation of Mohr-Coulomb failure criterion as well as other mechanical properties for reservoir<br>rocks is essential for well planning, development and characterization of oil and gas reservoirs. This is<br>because the understanding of the rock-stress relationship can solve many reservoir problems and avoid<br>cost of remedial work. For example, a Mohr-Coulomb failure criterion may be used for borehole<br>instability analysis, water injection design, hydraulic fracturing design, production optimization<br>techniques, compaction and sand production prediction, etc.<br>A Mohr-Coulomb failure criterion is a function of the apparent cohesion and the angle of internal<br>friction The evaluation of these two parameters requires testing of many rock samples using an<br>expensive and time-consuming triaxial testing set-up.<br>In this study, a correlation between the apparent cohesion and the unconfined (uniaxial) compressive<br>strength was developed. It is based on laboratory data of more than 282 rock samples of different<br>types obtained from the literature.<br>The correlation coefficient of the developed correlation equals to 0.88. Verification of the developed<br>correlation using data from other references has shown an average error of estimation less than 10%.<br>Unfortunately, some odd predictions were also notices and can be attributed to measurement errors.<br>Therefore, the Mohr-Coulomb failure criterion’s parameters as well as Poisson’s ratio can be estimated<br>using the developed correlation based on fast and cheap measurements of the unconfined (uniaxial)<br>compressive strength.