Accelerating CO₂ Dissolution in Saline Aquifers for Geological Storage — Mechanistic and Sensitivity Studies

Abstract

One of the important challenges in geological storage of CO 2 is predicting, monitoring, and managing the risk of leakage from natural and artificial pathways such as fractures, faults, and abandoned wells. The risk of leakage arises from the buoyancy of free-phase mobile CO 2 (gas or supercritical fluid). When CO 2 dissolves into formation brine, or is trapped as residual phase, buoyancy forces are negligible and the CO 2 may be retained with minimal risk of leakage. Solubility trapping may therefore enable more secure storage in aquifer systems than is possible in dry systems (e.g., depleted gas fields) with comparable geological seals. A crucial question for an aquifer system is, what is the rate of dissolution? In this paper, we address that question by presenting a method for accelerating CO 2 dissolution in saline aquifers by injecting brine on top of the injected CO 2 . We investigate the effects of different aquifer properties and determine the rate of solubility trapping in an idealized aquifer geometry. The acceleration of dissolution by brine injection increases the rate of solubility trapping in saline aquifers and therefore increases the security of storage. We show that, without brine injection, only a small fraction (less than 8%) of the injected CO 2 would be trapped by dissolving in formation brine within 200 years. For the particular cases studied, however, more than 50% of the injected CO 2 dissolves in the aquifer as induced by brine injection. Since the energy cost for brine injection can be small (<20%) compared to the energy required for CO 2 compression for a 5-fold increase in dissolution, such reservoir engineering techniques might be viable and practical for accelerating dissolution of CO 2 . The environmental benefit would be to decrease the risk of CO 2 leakage at reasonably low cost.

Modeling mass transfer of CO2 in brine at high pressures by chemical potential gradient

“…CO 2 geological storage is a promising means to mitigate CO 2 emission [1][2][3][4][5] and storage in deep saline aquifers appears to hold the largest potential capacity [4,[6][7][8]. The sequestration capacity, long-term CO 2 behavior in receptor formations, and the quantification of possible CO 2 leaks are the main concerns [2,4,9,10], and there remains a need to study the potential mobility of CO 2 dissolved in brines over a wide range of spatial and temporal scales [4,9,11], the CO 2 concentration distribution in saline aquifers, as well as the density distribution in geological media [8].…”

Active Role of a Color Indicator in Buoyancy-Driven Instabilities of Chemical Fronts

“…Conversely, one can address the question: how can chemical reactions influence natural convection or even be at the very source of hydrodynamic motion? These issues are at the heart of numerous applications in combustion, 1,2 polymer processing, 3,4 extraction techniques, 5,6 microfluidic devices, 7À9 bioconvection, 10 traveling fronts, 11À13 and CO 2 sequestration, 14,15 to name a few.…”

“…Conversely, one can address the question: how can chemical reactions influence natural convection or even be at the very source of hydrodynamic motion? These issues are at the heart of numerous applications in combustion, 1,2 polymer processing, 3,4 extraction techniques, 5,6 microfluidic devices, 7À9 bioconvection, 10 traveling fronts, 11À13 and CO 2 sequestration, 14,15 to name a few.To answer such questions, experimental studies have for instance investigated chemically driven convective mixing and enhanced extraction from one phase to another, induced by reactions between reactants initially contained separately in immiscible solvents. 5,16À18 In that case, it has been shown that the flow around the interface and within the bulk solutions result from (i) the coupling between transfer of chemical species at the interface, (ii) changes by the reaction of the density of the solutions which can trigger buoyancy-driven convective motions, and (iii) reaction-induced Marangoni effects, that is, fluid motion generated by surface tension changes at the immiscible interface.…”

Numerical Simulation and Optimization of Sleipner Carbon Sequestration Project

“…GA-TOUGH2 is employed to determine the optimal WAG operation for maximum CO 2 sequestration efficiency while minimizing the water usage. Inspired by the practice in oil industry, the potential of WAG operation for GCS has been surmised by several investigators that intermittent injection of CO 2 and water could lead to better CO 2 storage efficiency by reducing the migration of CO 2 plume [13], [14], enhancing the residual trapping [15], [16], and accelerating the CO 2 dissolution [17], [18]. Improved (reduced) CO 2 -brine mobility ratio and accelerated CO 2 dissolution are the two important characteristics that motivate the adoption of WAG operation to SAGCS.…”