Supercritical CO2 can reduce formation fracture pressure, form more complex fractures in the near-well zone, and replace methane to complete carbon sequestration, which is an important direction for the efficient development of deep shale gas with carbon sequestration. In this paper, based on the scCO2 fracturing field test parameters and the characteristics of common shale calcite filled natural fractures, we simulated the porosity change in shale with three kinds of fractures (no fracture, named NF; axial natural fracture, named AF; and transversal natural fracture, named TF) under scCO2 seepage, and carried out the experimental verification of shale under supercritical CO2 seepage. It was found that: (1) At the same pressure, when the temperature is greater than the critical temperature, the shale porosity of three kinds of fractures gradually increases with the injection of CO2, and the higher the temperature, the more obvious the increase in porosity. (2) At the same temperature and different pressures, the effect of pressure change on the porosity of shale specimens was more obvious than that of temperature. (3) Multi-field coupling experiments of shale under supercritical CO2 seepage revealed that the porosity of all three shale specimens at the same temperature and pressure increased after CO2 injection, and the relative increase in shale porosity measured experimentally was basically consistent with the numerical simulation results. This paper reveals the mechanism of the effect of different temperatures and pressures of scCO2 and different natural fractures on the change in shale porosity, which can be used to optimize the CO2 injection in supercritical CO2 fracturing and carbon sequestration.
This paper investigated the analytical solution of the bond strength between ribbed steel bar and engineered cementitious composites (ECC). In this method, ECC cover was regarded as a thick-walled cylinder subjected to the uniform internal pressure which consisted of an elastic uncracked outer ring and a partially cracked inner ring. For the uncracked outer ring, it can be solved by the elastic mechanics theory. To solve the partially cracked inner ring, two key problems that had to be investigated were the crack width and the tensile stress-crack width relationship of ECC. According to the steady-state cracking mode, the hoop deformation of ECC was expressed by the equal distribution and then the crack width can be determined.
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