Study on the Influence of Brine-Rock Reaction on Rock Physical Property and Seepage Characteristics

In the process of CO2 flooding, the complex brine-rock reaction occurs as the reservoir rock in the acidic circumstance formed by CO2 and brine, resulting in the changes of the physicochemical properties of the rock, thus affecting the seepage of crude oil in the reservoir and oil recovery. Therefore, combined with SEM and XRD analysis, contact angle test, mercury injection and relative permeability experiment, CO2-brine-rock static contact immersion experiment was carried out in this paper to systematically study the influence of brine-rock reaction on rock surface properties, pore throat structure and seepage characteristics of oil and water. The experimental results detected that at the effect of water-rock reaction, a large amount of hydrophilic quartz on the rock surface was exposed, the content of feldspar and calcite reduced, the content of kaolinite increased significantly, and the contact angle of water phase decreased by 15.7°. The solid particles produced by dissolution effect blocked the large pores in a lower permeability core (K ≤ 300 mD), which could reduce the core permeability and damage the core. However, for the core with a higher permeability (K ≥ 700 mD), the dissolution effect could increase the pore size and connectivity, effectively improved the permeability of oil phase and water phase, and reduced residual oil saturation of 10.3%. The results show that the brine-rock reaction can improve the wettability of the reservoir rock surface. The reaction has the effect of expanding pore size and increasing permeability in the higher permeability reservoir, and can improve the mobility of crude oil in the reservoir, and contributes to the oil recovery.