Experimental study on the permeability evolution of argillaceous sandstone under elevated temperatures

The permeability of the tight sandstone reservoirs will change when the thermal equilibrium in geological for-mations is disturbed. Understanding the permeability evolution under different temperature levels is thus crucial to reservoir evaluation and production prediction. In this study, a series of coupled thermal-hydraulic -mechanical triaxial flow-through tests are conducted to investigate the effect of the elevated temperatures on the permeability evolution and stress sensitivity of a typical argillaceous sandstone from Zhongjiang Gas field in the Sichuan Basin, China. Experimental results show that the initial permeability gradually decreases with the increase of the temperature ranging from 20 degrees C to 100 degrees C, with a decreasing magnitude of up to 1.5 orders. Stress sensitivity also indicates a negative correlation with the temperature levels. Whereas the mechanical parameters are less sensitive to elevated temperatures. According to the Scanning Electron Microscopy (SEM) analysis, the mechanism of the permeability reduction is mainly caused by the thermal expansion of the illite, as well as the pore-filling and throat-clogging effects induced by the newly released particles. Moreover, a modified perme-ability model with the exponential decay form is proposed and validated. This model considers the thermal effect and permeability recovery during the dilation regime and fits well with the experimental data.