Effects of supercritical CO₂/water imbibition under dynamic pressures on shale mechanics and acoustic emission characteristics
Effects of supercritical CO₂/water imbibition under dynamic pressures on shale mechanics and acoustic emission characteristics
复制标题
DOI：
10.1016/j.fuel.2022.124087
复制
发表时间：
2022
期刊：
影响因子：
7.4
通讯作者：
Q. Lyu;Kaixi Wang;Chenger Hu;Jindong Shi;Jingqiang Tan;G. Zhang;Shefa Chen;P. Ranjith
中科院分区：
文献类型：
--
作者：
Q. Lyu;Kaixi Wang;Chenger Hu;Jindong Shi;Jingqiang Tan;G. Zhang;Shefa Chen;P. Ranjith
During exploitation of shale gas and geological sequestration of CO2in shale gas reservoirs, the temperature and pressure of shale are increased with depth, whereas the reservoir pressure is gradually decreased with depth as exploitation proceeds. Therefore, it is important to investigate the effects of CO2and water on the mechanical properties of shale under dynamic pressure conditions. In this study, we have investigated the effects of supercritical CO2and water immersion on the mechanical properties of shale under different dynamic pressures (pressure 1: 20–8 MPa; pressure 2: 40–28 MPa), respectively. The test results indicate that after soaking in supercritical CO2and water, the uniaxial compressive strength (UCS) of shale is decreased by 51.05% and 58.36% (pressure 1), and by 35.98% and 36.84% (pressure 2), respectively. The strength and Young's modulus of shale are decreased more significantly after water immersion compared to supercritical CO2immersion. Due to the matrix compression effects, the mechanical properties of shale are changed more significant under lower imbibition pressures. Supercritical CO2immersion leads to increase in the Poisson's ratio along with more complex fracture patterns, whereas water immersion results in slight decrease in the Poisson's ratio along with shear fractures only. The acoustic emission (AE) signals have obvious stage characteristics during the compressional deformation of samples, and the AE energy is mainly generated in the unstable crack propagation stage. Supercritical CO2immersion plays an important role in crack generation, whereas water immersion is dominated by the alteration of pore structure. Compared with the constant pressure imbibition, the dynamic pressure imbibition changes the microstructure of shale and weakens its mechanical properties more significantly. The results of this study may help to better evaluate the effects of CO2and water on the mechanical properties of shale during exploitation of shale gas.
