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

Bandar D. Al-Anazi
King Saud University, Saudi Arabia
[email protected]

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 the cost of remedial work. For example, a Mohr-Coulomb failure criterion may be used for borehole instability analysis, water-injection de-sign, hydraulic-fracturing design, production-optimization techniques, compaction and sand-production prediction, etc. A Mohr-Coulomb failure criterion is a function of the ap-parent cohesion (ƒäo) and the angle of internal friction (ƒÖ). 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 un-confined (uniaxial) compressive strength was developed. It is based on laboratory data of more than 400 rock samples of different types obtained from the literature. The correlation coefficient of the developed correlation equals to 0.88. Verification of the developed corre-lation using data from other references has shown an average error of estimation less than 10%. Unfortunately, some odd predictions were also noticed and can be attributed to meas-urement errors. 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 unconfined (uniaxial) compressive strength.

AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain