Time Effect Law of Physical and Chemical Properties of Siltstone under Supercritical CO₂

To investigate the evolutionary behavior of the physical and chemical properties of reservoirs following the injection of supercritical CO₂, a custom-built constant temperature and pressure supercritical CO₂-water-rock heat flow curing coupling experimental system was used to conduct supercritical CO₂ soaking experiments on siltstone. The changes in cation concentration within the reaction solution were analyzed, and the evolution of the porosity, permeability, and water/gas saturation of the reservoir core samples was examined before and after the reaction; the experimental results were compared with numerical simulations. The reaction rate constant and activation energy were adjusted, and a method for eliminating the error associated with the time effect on the reservoir's physical and chemical properties during CO₂ geological sequestration was proposed. Additionally, the long-term changes in the physical and chemical properties of the reservoir during prolonged supercritical CO₂ sealing were examined. The results indicate that with prolonged exposure to supercritical CO₂, the pH of the reaction solution decreases from 7.19 to 5.68. Calcite had the fastest dissolution rate, followed by potassium feldspar and, finally, Illite. During CO₂ injection, both the porosity and permeability of the reservoir increased rapidly, but the increase was smaller after CO₂ injection ceased, eventually stabilizing. The time-dependent behavior of the physical and chemical properties of siltstone under supercritical CO₂ conditions was determined, providing valuable insights into the pore permeability characteristics of reservoirs under long-term mineralization.