Effects of Permeability Variations on CO2 Convection in Anisotropic and Heterogeneous Saline Formations

Abstract

This study simulated the natural convection of dissolved carbon dioxide (CO 2 ) in a small-scale heterogeneous saline formation using the state module ECO2N equation in the TOUGHREACT model. A one-way downscaling approach that involves using a series of sub-models in simulation procedures was proposed to efficiently simulate problems with high-scale discrepancies. This study evaluated the effects of different degrees of small-scale permeability variations on the vertical migration of dissolved CO 2 . The sequential Gaussian simulation model was used to generate unconditional random permeability fields for different natural logarithm of permeability (lnk) variations (i.e., lnk variances and correlations in x and z directions). The results showed an identical transition zone of dissolved CO 2 near the top boundary, where a constant CO 2 gas saturation was specified. The local permeability variations can trigger fingerings and enhance the vertical convection of the dissolved CO 2 . The number of fingerings depends on the variations in permeability near the front interface of the dissolved CO 2 (i.e., the bottom edge of the transition zone for the dissolved CO 2 ). However, the fingering patterns and developments are constrained by the permeability variations along the fingering paths. At the same mean lnk permeability the convection fluxes increase with an increase in lnk variances. However, an increase in lateral correlations (i.e., increase in the correlation lengths in the x direction) can slightly reduce the convection fluxes at the same lnk variance. The highly variable flux rates of the dissolved CO 2 occur early and the variations in the flux rate decrease with time.

Visual investigation of CO2 dissolution and convection in heterogeneous porous media at reservoir temperature and pressure conditions

“…54 In heterogeneous permeability experiments, a horizontal low-permeable layer in between high-permeable layers attenuated the density-driven convection, while density-driven convection occurred in a vertical high-permeable layer rather than in the low-permeable layers surrounding it. The results also coincide with the results of simulations performed by Lin et al 38 and Chen et al 46 in which relatively high local permeability values just below the CO 2 -water interface was found to trigger instabilities in the diffusive layer and influence the number of fingers developing initially. Also, their findings that the finger development was substantially controlled by the permeability below the fingers and along their paths match our experimental results.…”

“…They have found out that the mass flux into the system is inversely proportional to the barrier length and proportional to the horizontal and vertical space of the barriers. Lin et al 38 have conducted a simulation study of natural convection of dissolved CO 2 in small-scale heterogeneous saline formation. In their study, they have focused on the effects of small-scale permeability variations to the dissolved CO 2 in water.…”