Experimental study on the effect of CO2 dynamic sequestration on sandstone pore structure and physical properties

Tight sandstone reservoirs have huge potential for geological sequestration of CO 2 . In the process of CO 2 injection, the stability and safety of the reservoir pore structure and physical properties are the basis for CO 2 sequestration. However, due to the interaction between CO 2 -water-rocks, the mineral composition and physical properties of the reservoir can be affected, leading to changes in the pore structure of the rocks and destabilizing the reservoir under high-pressure environments. The changes in pore distribution, rock surface microstructure, and rock mechanical properties of cores with different mineral compositions treated with carbonated water under different confining pressures were investigated through nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), and rock mechanics experiments. The effects of the dynamic CO 2 sequestration process on the pore structure of the tight reservoir and the physical properties of the rocks were analyzed. The results demonstrate that following CO 2 injection, the pore volume of the rock decreased due to the generation of debris by chemical dissolution and the plastic deformation of the pore structure was more significant under high pressure, resulting in pore closure and a reduction in pore space. Concurrently, the dissolution of gap-fillers, such as chlorite and kaolinite, between mineral grains in the pore space occurred, and the formation of microfractures. The formation of microfractures decreased the overall stability of the rock. Additionally, feldspar is easily dissolved chemically under CO 2 -water conditions, and this process is more pronounced in rocks with a higher feldspar content. The compressive strength and elastic modulus of these rocks are significantly reduced. Consequently, in the context of CO 2 geological sequestration, it is recommended that rocks with a high quartz content, a low feldspar content, a moderate porosity, and stable physicochemical properties be selected as injection targets. Furthermore, a phased injection strategy should be employed to accommodate the structural changes in the rocks due to pressure and to enhance the injection efficiency, thereby optimizing the long-term geological sequestration of CO 2 and its safety.