The mechanical creep property of shale for different loads and temperatures

Abstract

The analysis of the mechanical properties and the failure mechanism of shale with the effect of temperature are of great significance to the shale gas exploitation. In this paper, triaxial creep mechanical tests and AE monitoring method for shale under step loading were carried out at different temperatures and confining pressures. The classic Poynting-Thomson creep model was improved and the modified creep model considering temperature and viscoelastic-plastic deformation were built. The test results showed that the strength of the shale was related to the confining pressures and temperatures. The creep mechanism of shale was analyzed by the acoustic emission parameters. The peak frequency of acoustic emission signals reflected the difference of the rock fracture mode. The Poynting-Thomson model was modified on the theory of nonlinear rheology, which is more suitable for creep deformation of shale. The correlation coefficient of the modified model was higher than that of the classical model. The modified model considering temperature fit the shale creep curve well and could explain the creep characteristics under the influence of temperature and stress. The new model can be widely used in the research of shale creep deformation, such as the deep exploitation of shale gas, wellbore stability and other aspects of engineering problem of shale.