Critical Dynamics of Gravito-Convective Mixing in Geological Carbon Sequestration

Abstract

When CO2 is injected in saline aquifers, dissolution causes a local increase in brine density that can cause Rayleigh-Taylor-type gravitational instabilities. Depending on the Rayleigh number, density-driven flow may mix dissolved CO2 throughout the aquifer at fast advective time-scales through convective mixing. Heterogeneity can impact density-driven flow to different degrees. Zones with low effective vertical permeability may suppress fingering and reduce vertical spreading, while potentially increasing transverse mixing. In more complex heterogeneity, arising from the spatial organization of sedimentary facies, finger propagation is reduced in low permeability facies, but may be enhanced through more permeable facies. The connectivity of facies is critical in determining the large-scale transport of CO2-rich brine. We perform high-resolution finite element simulations of advection-diffusion transport of CO2 with a focus on facies-based bimodal heterogeneity. Permeability fields are generated by a Markov Chain approach, which represent facies architecture by commonly observed characteristics such as volume fractions. CO2 dissolution and phase behavior are modeled with the cubic-plus-association equation-of-state. Our results show that the organization of high-permeability facies and their connectivity control the dynamics of gravitationally unstable flow. We discover new flow regimes in both homogeneous and heterogeneous media and present quantitative scaling relations for their temporal evolution.

Transport of perfluorocarbon tracers in the Cranfield Geological Carbon Sequestration Project

“…This is consistent with our simulation results, which address a two‐phase flow problem and a more complex system in terms of heterogeneity arising from facies architecture. Fluvial depositional systems clearly have a dramatic impact on solute transport in the subsurface in both single and multiphase flow problems because the preferential pathways account for the majority of mass transport . Recently, Kilgallon et al .…”

“…Fluvial depositional systems clearly have a dramatic impact on solute transport in the subsurface in both single and multiphase flow problems because the preferential pathways account for the majority of mass transport. 7,8,34,[49][50][51][52][53][54][55] Recently, Kilgallon et al 56 compared the travel times of noble gases and SF 6 tracer in sandstone core samples, and found that the heterogeneity play a key role at the core-scale as well. They also found that different molecules had different travel times at core-scale level.…”

“…Carbon Capture and Storage (CCS) is a promising technology to mitigate increasing atmospheric carbon dioxide (CO 2 ) concentrations . Identifying and quantifying the processes that affect CO 2 transport in the subsurface are essential to predict CO 2 residence times and to estimate the storage capacity of a reservoir.…”

“…C arbon Capture and Storage (CCS) is a promising technology to mitigate increasing atmospheric carbon dioxide (CO 2 ) concentrations. [1][2][3][4][5][6][7][8][9][10] Identifying and quantifying the processes that affect CO 2 transport in the subsurface are essential to predict CO 2 residence times and to estimate the storage capacity of a reservoir. While reservoir models can be designed to simulate those processes, the accuracy of these simulations depends heavily on the input parameters that represent the in situ conditions, and on careful model validation through field tests.…”

Hydrothermodynamic mixing of fluids across phases in porous media

“…The evolution of and is therefore more similar at both miscibility conditions than those in homogeneous media. In the miscible case, the synergetic effects of both more fingering and channeling result in advection‐dominated flow and ballistic scaling of longitudinal spreading as [e.g., Le Borgne et al , ; Kang et al , ; Soltanian et al , ]. In partially miscible flow, interphase species exchange favors mixing, while a lower degree of fingering results in less spreading with superdiffusive scaling as (Figures g and h).…”