Experimental study on failure criterion of deep tight sandstone under coupling effects of temperature and pressure

Abstract

The mechanical properties and failure mode of rock subjected to high temperature and high pressure are significantly different from those of normal temperature and pressure. Research of rock’s failure criterion under HTHP has important guiding significance for deep drilling and fracturing security. Considering the high temperature and pressure geological environment in deep tight sandstone reservoirs in Qaidam Basin, triaxial tests of rock obtained from deep sandstone reservoir under five groups of different temperatures (20 °C, 80 °C, 120 °C, 140 °C, 160 °C) are performed by RTR-1500 electro-hydraulic and servo-controlled Rock Triaxial Testing System. The results from the tests show that, in the experimental temperature range, the cohesion and internal friction coefficient of the rock decreases with the increase of temperature, the relationship between cohesion and temperature is cubic polynomial, and the internal friction coefficient is also cubic nonlinearly correlated with temperature; along with the increase of temperature, the compressive strength of rock under the same confining pressure gradually decreases, and the compressive strength of rock in different confining pressures tends to be the same. Based on the analysis of data from triaxial tests under different temperatures and the principle of Mohr-Coulomb criterion, the specific expression of the failure criterion for tight sandstone under the coupling effects of temperature and pressure is formulated. This criterion can truly reflect the change rules of sandstone strength with temperature and pressure and can also be used to predict the failure strength under different temperatures and pressures conveniently and easily.