Effect of Interaction between Carbon Dioxide and Fluid Phase/Rock Interface on Carbon Dioxide Storage

Abstract

The interaction between CO2, formation water, and rock surfaces after CO2 flooding and the mechanism by which it affects CO2 storage were studied in this paper. The results show that variations in the solubility of CO2 in crude oil under pressure are similar to those observed in formation water. The solubility of CO2 increases as pressure increases under a low-pressure conditions. The solubility of CO2 in crude oil increases significantly when crude oil is in a low-viscosity state, and this makes it easier to diffuse CO2 into the oil phase at high temperatures. More resistance is encountered when CO2 diffuses into the liquid-containing space of an irregular core, making the coefficient of diffusion into the oil–water two-phase flow in the porous medium smaller. After the core is corroded by a CO2-saturated aqueous solution, the quartz content in the mineral component increases and the plagioclase and potassium feldspar content significantly decrease. The dissolution of the feldspar leads to the formation of a large amount of secondary kaolinite, thus increasing the kaolinite content. In the early stage of CO2 erosion during dynamic displacement, the combined effect of particle migration and inorganic precipitation leads to a slow growth in core permeability and porosity. As the erosion progresses, the influence of particle migration and inorganic precipitation on permeability gradually decreases, while the porosity of the core gradually increases. The secondary pores play a role, and the erosion of the CO2–water system makes the permeability and porosity of the core gradually increase. During dynamic displacement, CO2 is mainly stored in the reservoir in free and irreducible states. Under the pressure of the reservoir, some of the CO2 participates in erosion reactions and is stored in the rock or the solution in the form of minerals or ions. In addition, a small portion of the CO2 is dissolved in the residual water and residual oil that remain after the dynamic displacement. The results of this paper can provide some theoretical support for the design of a CO2 storage site.