Numerical investigation of convective dissolution of fluid CO2 in water during its storage in an underground porous formation

The study addresses an important environmental problem related to harmful effects of greenhouse gases on Earth's temperature and climate and the need to reduce anthropogenic carbon dioxide emissions into the atmosphere. One-sided density-driven convection developed inside a porous formation during dissolution of supercritical CO2 fluid in water is investigated in reference to the technologies of carbon dioxide storage in underground water-saturated formations. The hydrodynamic model includes equations of continuity, motion (based on the Darcy's law), convection-diffusion and a non-linear equation of state that relates the density of fluid medium with the concentration of CO2. A fluid is described as a single-phase two-component medium with variable viscosity. Based on the data available in the literature, the physical properties of the CO2 + H2O system were determined in the ranges of temperature T=307.7 - 342.8 К and pressure P=8.07 - 31.42 MPa. Numerical simulation of hydrodynamic processes in this system was carried with the aid of the developed finite-difference numerical code. In particular, the code was employed to study how the characteristics of convective dissolution depend on the temperature and the pressure. It has been found that with increase of these parameters the convective dissolution of CO2 fluid in water is more intensive. For example, the time during which half of CO2 dissolves in water and is transported down by a convective flow is reduced almost twice. Thus, an increase in temperature and pressure ensures more reliable storage of carbon dioxide in underground water-saturated formations.