Accounting for dynamic alteration effect of SC-CO2 to assess role of pore structure on rock strength: A comparative study

Supercritical carbon dioxide (SC–CO2) is an ideal working fluid to develop geological resources, while the efficient development and utilization are seriously hindered by the unclear dynamic alteration effect on reservoir properties. To overcome this obstacle, the static and dynamic alteration tests are performed. By comparatively analysing the change laws of mineral and microstructure, the dynamic alteration mechanism of SC-CO2 is revealed to inhibit the dissolution of soluble minerals and promote the exfoliation of insoluble minerals. Based on the porosity effect on strength of intact rocks, the altered strength also exponentially decreases with porosity increasing. Under dynamic alteration, the effects of pore structure evolution are differently expressed on the mechanical damage according to different types of rocks, exhibiting as the enhanced effect for the rocks controlled by insoluble minerals and the insignificantly differential effect for the rocks controlled by soluble minerals. More remarkable effect of pore size distribution is found on the altered strength than that of porosity, and more severe damage is caused by the alteration of pores with larger size. In addition, the proposed mineral content ratio index ISR shows universal and credible influence trend on the strength-pore structure relationship of different types of rocks under SC-CO2 alteration. •Dynamic alteration inhibits soluble mineral dissolution, weakening pore evolution.•Despite weakened reaction, scouring effect promotes insoluble mineral spallation.•Pore effect on strength is enhanced for rocks with frameworks of insoluble minerals.•Effect of pore size distribution is stronger on strength than that of porosity.•Altered pores with larger size shows stronger impact on mechanical damage.