Influence of CO₂-brine-rock Interactions on the Physical Properties of Tight Sandstone Cores via Nuclear Magnetic Resonance

For sandstone reservoirs with extra-low permeability, CO₂ injection is regarded as a valid method to enhance oil recovery. When CO₂ injection is implemented in such reservoirs, the physical properties of the formation could be altered owing to the interactions between CO₂, water, and rock. In this study, the influence of CO₂–brine–rock interactions on the physical properties of tight sandstone cores was analyzed by comparing the obtained T₂ spectrum before and after CO₂ injection. The results revealed that the T₂ spectrum after CO₂ injection was significantly different from the original T₂ spectrum. CO₂ injection changed the pore size distribution of the core samples. When the injection pressure was low, the pore volume decreased from micropores to macropores leading to a decrease in both permeability and porosity. As the injection pressure increasing, the dissolution of CO₂ in the micropores was enhanced thus improving the pore-throat connectivity; which ultimately improved the reservoir physical properties.