Heterogeneity‐enhanced gas phase formation in shallow aquifers during leakage of CO₂‐saturated water from geologic sequestration sites

Abstract

A primary concern for geologic carbon storage is the potential for leakage of stored carbon dioxide (CO 2 ) into the shallow subsurface where it could degrade the quality of groundwater and surface water. In order to predict and mitigate the potentially negative impacts of CO 2 leakage, it is important to understand the physical processes that CO 2 will undergo as it moves through naturally heterogeneous porous media formations. Previous studies have shown that heterogeneity can enhance the evolution of gas phase CO 2 in some cases, but the conditions under which this occurs have not yet been quantitatively defined, nor tested through laboratory experiments. This study quantitatively investigates the effects of geologic heterogeneity on the process of gas phase CO 2 evolution in shallow aquifers through an extensive set of experiments conducted in a column that was packed with layers of various test sands. Soil moisture sensors were utilized to observe the formation of gas phase near the porous media interfaces. Results indicate that the conditions under which heterogeneity controls gas phase evolution can be successfully predicted through analysis of simple parameters, including the dissolved CO 2 concentration in the flowing water, the distance between the heterogeneity and the leakage location, and some fundamental properties of the porous media. Results also show that interfaces where a less permeable material overlies a more permeable material affect gas phase evolution more significantly than interfaces with the opposite layering.

Relative Permeability Measurements during the Exsolution and Dissolution of Hydrogen Gas Produced by the Hydrolysis of Sodium Borohydride

“…It also agrees with previous findings that although the aqueous relative permeability may differ between internal and external drainage at lower water saturations (higher gas saturations), there was little difference at higher water saturations (Egermann and Vizika, 2001; Zuo et al, 2012). This may be particularly relevant for applications of gas exsolution or gas injection and migration in homogeneous porous media, where gas saturations have been shown to be low (e.g., Plampin et al, 2014b; Van De Ven and Mumford, 2019).…”

Intermediate‐Scale Experimental Study to Improve Fundamental Understanding of Attenuation Capacity for Leaking CO2 in Heterogeneous Shallow Aquifers

“…Therefore, to extend the findings from previous studies on multiphase CO 2 evolution in shallow aquifers (Plampin et al, 2014a(Plampin et al, , 2014bPorter et al, 2015) into larger, more complex, multidimensional groundwater systems, experiments were performed in a large 2-D laboratory test system for this study. The experiments were designed to test the validity of the hypothesized conceptual model described above.…”

“…The injected water was infused with aqueous CO 2 under a gauge pressure (''saturation pressure,'' P sat , as defined by Plampin et al, 2014a) between 13 and 20.7 kPa. These limits were controlled by the physical dimensions of the Mariotte bottle setup; if the system functioned as designed, P sat would remain at 13 kPa throughout the experiment, but if the container was not completely rigid or perfectly sealed and the pressure of an entirely filled drum was applied to the membranes, P sat could have approached 20.7 kPa.…”

“…While several larger-scale laboratory experiments (e.g., Plampin et al, 2014aPlampin et al, , 2014bSakaki et al, 2013) and accompanying modeling efforts Plampin et al, 2014b;Porter et al, 2014Porter et al, , 2015 have isolated particular system parameters and elucidated their effects on CO 2 transport through shallow aquifers, it is still not possible at this time to predict the combined effects of multiphase CO 2 evolution and concurrent water flow on the overall fate of CO 2 in realistic groundwater systems. For instance, compared to widely studied small-scale, 1-D, and/or homogeneous systems, large-scale, multidimensional, heterogeneous systems allow for the natural mixing of high concentration aqueous CO 2 solutions with cleaner flowing water, a process that has not been rigorously tested from a fundamental physical perspective through large-scale laboratory experiments.…”

Interactions Between Stratigraphy and Interfacial Properties on Flow and Trapping in Geologic Carbon Storage

“…The trapping and migration of CO 2 as a distinct phase (e.g., not dissolved) is driven by three forces: (1) advective forces created by overpressurization; (2) the capillary force created by the surface tension between the fluids and the pore walls; and (3) buoyant forces that result from the lower density of CO 2 relative to the connate brine (Bryant et al, ; Mouche et al, ; Plampin et al, ). Influencing these driving forces are three physicochemical characteristics of the system: (1) pore size and permeability contrast between the two layers in the column, which determines capillary pressure contrast; (2) temperature and pressure conditions and the subsequent fluid density and surface tension; and (3) interfacial properties between solid and fluid phase, such as surface wettability.…”