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.