# Study on Permeability Stress-Sensitivity in
###### Abstract  
Accurately predicting the characteristics and influencing factors of permeability stress-sensitivity contributes to improving gas production in gas reservoirs. In this paper, the effects of effective stress on the permeability of fractured deep tight sandstone reservoirs were studied by laboratory tests. With the experimental results, a coupled seepage-geomechanical model for fractured deep tight sandstone gas reservoirs was constructed. The influences of pore pressure and geo-stress on permeability characteristics and gas production were studied by numerical simulation. The results indicate: (1) When the effective stress increases from 0 to 65 MPa, the permeability of the natural sample with fractures decreases by 81.28%, and the permeability of the intact core sample decreases by 54.67%. (2) When the pore pressure decreases from 120 to 85 MPa, the three-dimensional effective stress increases. The largest increase of the effective stress was along the vertical direction, which increased by 11-19 MPa. In addition, the permeability of the fractured zone and the intact rock along the vertical direction decreased by about 40% and 16%, respectively. (3) The mean square error between the historical gas production results and the results by simulation was 2.22 when considering the permeability stress-sensitivity, and 4.01 without considering the permeability stress-sensitivity. The proposed coupled seepage-geomechanical model with permeability stress-sensitivity proved to be more accurate in historical gas production comparison and prediction. This study provides a reliable optimization scheme for the development of fractured deep tight sandstone gas reservoirs. p 2022 2022141 November  
The research on permeability stress-sensitivity by Chinese and foreign scholars is mainly reflected in theoretical and laboratory experiments. [PERSON] et al. [6] found that the permeability stress-sensitivity was more significant in low-permeability rocks compared to high-permeability rocks. [PERSON] et al. [7] found in their experiments that an increase in effective stress caused the decrease in rock porosity and permeability, with a large decrease in the pore-permeability parameters of the fractured cores. [PERSON] et al. [8] conducted stress-sensitive experiments on tight sandstone and found that tight sandstone reservoirs were highly sensitive to stress under high-temperatures and high-pressures. [PERSON] et al. [9], [PERSON] et al. [10], [PERSON] et al. [11] and other scholars have successively used the experimental method of variable pore pressure and constant confining pressure to evaluate the stress-sensitivity, forming a test method for tight sandstone. [PERSON] et al. [12] and [PERSON] et al. [13] fitted the exponential function of permeability vs. effective stress, while [PERSON] et al. [14] fitted functions in power format. [PERSON] et al. [15] improved the exponential function and obtained more accurate fitting results. [PERSON] et al. [16] optimized the calculation method of effective stress coefficients according to the three-dimensional surface fitting method. Numerous experimental studies have shown that the increase in effective stress leads to the decrease in a reservoir permeability and porosity, which is particularly evident in low permeability reservoirs [17; 18; 19]. [PERSON] et al. [20] believed that the stress-sensitivity of the low-permeability rocks should be extremely weak, since it's calculated by the rock compression coefficient and low in the tight reservoirs. However, the mechanism of permeability stress-sensitivity is still unclear in the development of high-temperature and high-pressure tight sandstone gas reservoirs. Using an accurate mathematical model to describe the seepage-geomechanical coupling is the key to complete the numerical simulation of gas reservoirs. Currently, the simulation of rocks with natural fractures is mainly based on the continuous medium model and discrete fracture model [21; 22].