Convective Dissolution of Carbon Dioxide in Deep Saline Aquifers: Insights from Engineering a High-Pressure Porous Visual Cell

Abstract

We present the first experiments of dissolution-driven convection of carbon dioxide (CO2) in a confined brine-saturated porous medium at high pressures. We designed a novel Hele-Shaw cell that allows for both visual and quantitative analyses, and address the effects of free-phase CO2 and brine composition on convective dissolution. The visual examination of the gas volume combined with the measurement of pressure, which both evolve with dissolution, enable us to yield insights into the dynamics of convection in conditions that more closely reflect the geologic conditions. We find and analyze different dissolution events, including diffusive, early and late convection, and shutdown regimes. Our experiments reveal that in intermediate regime, a so-called "quasi-steady" state actually never happens. Dissolution flux continuously decreases in this regime, which is due to a negative feedback loop: the rapid reduction of pressure following convective dissolution, in turn, decreases the solubility of CO2 at the gas-brine interface and thus the instability strength. We introduce a new scaling factor that not only compensates the flux reduction but also the nonlinearities that arise from different salt types. We present robust scaling relations for the compensated flux and for the transition times between consecutive regimes in systems with NaCl (Ra ∼ 3271-4841) and NaCl+CaCl2 mixtures (Ra ∼ 2919-4283). We also find that NaCl+CaCl2 mixtures enjoy a longer intermediate period before the shut-down of dissolution, but with a lower dissolution flux, as compared to NaCl brines. The results provide a new perspective into how the presence of two separate phases in a closed system as well as different salt types may affect the predictive powers of our experiments and models for both the short-and long-term dynamics of convective dissolution in porous media. * brostami@ut.ac.ir

Thermal Effects on Flow and Salinity Distributions in Coastal Confined Aquifers

“…Density‐driven convective flow is ubiquitous in natural systems, such as water infiltration into soil (Assouline, 2013), atmospheric movement (Hodges & Thorncroft, 1997) and oceanic currents (Ruddick & Gargett, 2003). Density‐driven convection has an wide application for flow in porous media, including geothermal energy production (Cheng & Minkowycz, 1977), oil separation from sand (Taylor, 2018), and carbon dioxide sequestration (Amooie et al, 2018; Mahmoodpour et al, 2019). It is well identified that when dense fluid sits above less dense fluid due to solute concentration and/or temperature, the system is easy to lose its equilibrium.…”

New Spectrophotometric Method for Quantitative Characterization of Density-Driven Convective Instability

“…CO 2 dissolution in brine causes density-driven convection, which is a key mechanism for the efficient trapping of CO 2 . CO 2 convective dissolution accelerates the CO 2 mass transfer rate and reduces the risk of leakage, which is favorable for long-term sequestration [ 7 ]. Although there are some CCS pilot projects distributed in different parts of the world, there is still a lack of relevant knowledge concerning convective dissolution in CCS projects.…”

“…As the spatial and temporal scales involved make it difficult to analyze these dynamics in situ, the experimental research on convective dissolution at the laboratory scale is receiving more and more attention [ 18 , 19 , 20 ]. Three main types of experimental methods have been used to analyze CO 2 convective dissolution in aqueous solutions: PVT (pressure-volume-temperature) reactor experiments [ 21 , 22 , 23 ], Hele–Shaw cell experiments [ 7 , 16 , 24 , 25 ], and bead pack experiments [ 18 , 19 , 26 , 27 ]. PVT reactor experimental results can be used to easily quantify the total dissolved CO 2 mass and mass transfer rate at high pressures and elevated temperatures; however, they have limited ability to visualize the convective dissolution process.…”

Direct experimental observations of the impact of viscosity contrast on convective mixing in a three-dimensional porous medium

“…The small density difference of the CO 2 -brine system that drives the convective mixing process is replicated in these fluids 5,9,10 . More recently, a few studies have attempted to examine convective mixing at conditions that more closely reflect that in the field, particularly by performing experiments using actual CO 2 -brine 11 at high-pressure conditions within a porous medium [12][13][14] .…”