Speaker
Description
CO2 dissolution is a crucial long-term storage mechanism in subsurface CO2 storage, involving complex multiphase flow coupled with various physicochemical processes. In this study, we propose a novel lattice Boltzmann framework that integrates multiphase flow, solute transport, phase transitions, and chemical reactions to simulate the CO2 dissolution process in saline aquifers under convective conditions. Specifically, the color-gradient lattice Boltzmann model is employed to describe the CO2-brine two-phase flow, while CO2 dissolution is modeled at the phase interface through a reaction model combined with a source/sink term within the multiphase model to represent phase transitions. Additionally, a recolor operator is incorporated into the solute transport model to ensure that dissolved CO2 remains within the brine phase, making the coupling model suitable for convective conditions.
Following extensive validation, the proposed model is applied to study CO2 dissolution mechanisms in a sandstone digital rock obtained from a saline aquifer, with a focus on the effect of convection on dissolution process. First, a CO2-brine drainage-imbibition process is simulated to establish the initial distribution of free CO2. Subsequently, the CO2 dissolution process is simulated under varying convective driving forces. The results indicate that convection significantly enhances CO2 dissolution under low initial free CO2 saturations. Moreover, the dissolution rate increases with stronger convective forces, as convection transports free CO2 to fresh brine, increasing the dissolved CO2 concentration gradient between the phase interface and surrounding brine, thus accelerating dissolution. However, at higher initial free CO2 saturations, convection does not substantially impact the dissolution rate due to the already high dissolved CO2 concentration in the liquid phase.
Finally, the safety of CO2 storage in porous media under gravitational conditions is examined. The results reveal that gravity has an opposing effect on capillary trapping and dissolution trapping. Shrinking free CO2 bubbles can become re-mobilized under gravitational forces due to dissolution, while redistributed CO2 bubbles and the sinking of dense CO2-dissolved brine facilitate dissolution. The initial free CO2 saturation and pore structure play a significant role in this complex coupling process.
These findings provide insight into the influence of convection on CO2 dissolution at the pore scale, offering valuable theoretical perspectives for predicting dissolution processes and solute transport in geological carbon sequestration.
| Country | China |
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