Key words: strength, damage, fluid, oil and gas borehole.
The work is dedicated to research of strength and damage of fluid saturated rocks and has a practical application in petroleum and gas related rock mechanics. In order to understand the influence of fluids on the limit state of rock, triaxial laboratory tests on saturated rocks were conducted. The Mohr Coloumb strength theory is used to describe limit state of fluid saturated rocks. The results of stress distribution around vertical boreholes located in fluid saturated rocks based on the elastoplasticity theory are given. Prediction of limit state zone around vertical borehole shows that if initial stress state is non-hydrostaticthe shape of limit state zone is elliptical. The presents of fluids in the rockswill magnify the size of limit state zone. The assessment of probability of crack formation during hydro fracturing of borehole due to significant fluid and mud pressure is done.
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