Coupled Two-Phase Flow and Density-Driven Convective Dissolution in a Deep Saline Aquifer during CO2 Sequestration

Abstract

The rise in greenhouse gas emissions has led to an increase in the Earth’s temperature. Carbon dioxide sequestration is chosen as a critical technology for reducing CO2 emissions into the atmosphere. Significant progress has already been made in CO2 sequestration, with numerous pilot projects and field-scale operations underway. The trapping mechanisms involved in deep saline aquifers help in long-term storage. However, the studies on the coupled effects of flow and various trapping mechanisms are limited. Therefore, in the current work, the coupled two-phase flow and density-driven convective dissolution were studied using numerical simulations in COMSOL Multiphysics. The model is assumed to be isothermal and homogeneous. The primary results showed that pressure and saturation changes during injection and after shutdown have a significant impact on convective dissolution, which differs from single-phase models. In the mathematical framework, a solubility model is implemented to understand the effect of equilibrium concentration on convective dissolution quantitatively, followed by a sensitivity analysis conducted by varying the composition of brine, permeability, and Rayleigh number. From the brine composition sensitivity study, brine density, viscosity, and equilibrium concentration variation with brine composition were identified as crucial for convective dissolution as well as CO2 plume migration. Later, permeability variation showed that convective dissolution accelerated with an increase in permeability. Then, the combination of fluid and rock properties used in the Rayleigh number investigation showed a significant impact on saturation and pressure changes in the aquifer. Hence, the integration of two-phase flow dynamics is found to be pivotal for characterizing the convective dissolution trapping in a deep saline aquifer.