Static and dynamic alteration effect of SC-CO2 on rock pore evolution under different temperature and pressure: A comparative study

The efficient exploitation of geological resources using supercritical carbon dioxide (SC–CO₂) is seriously hindered by the inaccurate mastery of pore evolution laws of reservoir rocks. It is thus aimed to elucidate the temperature and pressure effects of SC-CO₂ on the rock pore evolution in this study. Static and dynamic alteration tests were performed under 9 conditions of different temperature and pressure. The porosity evolution shows consistently positive correlation with the pressure of SC-CO₂, while inconsistent correlation with temperature. The inconsistent temperature effect is caused by the weakened alteration process of calcite with temperature increasing, which is opposite to the enhanced alteration process of other minerals. The fundamental reason is that the alteration rate of mineral with low activation energy E_a is significantly reduced by temperature increase. With the increase of E_a, however, the reducing effect of temperature increase on alteration rate gradually becomes weaker and hardly turns into an enhancing effect until E_a = 26,000 J/mol. With the help of resistance kinetics equation, two kinds of calculation methods of porosity evolution were proposed based on rock alteration volume and soluble mineral alteration extent, respectively. In addition, considering dynamic alteration effect, the rock pore evolution process is weakened because of the weakened alteration process of soluble minerals, and the differential porosity evolution of sandstone, granite and marble can respectively reach 0.95%, 0.11% and 0.15% at most.