Maarten W. Saaltink

Understanding the effects of mixing-driven precipitation on solute transport behavior is critical for reactive transport predictions, yet its complexity, arising from the interplay of flow dynamics, solute transport, and geochemical reactions, remains a significant challenge. In particular, mineral precipitation modifies the hydraulic properties of porous media. The impact of this process on the solute transport behavior remains largely unexplored and is crucial for accurate reactive transport predictions. This study presents a controlled laboratory investigation of mixing-driven calcite precipitation (MDP) in an intermediate-scale Hele-Shaw cell, simulating a coarse-sand porous medium. The experiment allowed for direct visualization of the spatiotemporal evolution of precipitation while continuously monitoring hydraulic properties. Self-organized heterogeneities in the precipitate structure were observed, with calcite layers forming symmetric patterns aligned with the main flow, contrasting with the asymmetry predicted by a semi-analytical model under idealized conditions. Tracer tests conducted before and after precipitation demonstrated significant impacts on solute transport, including the emergence of strong anomalous transport features, such as earlier solute arrival, a distinct double peak, and pronounced tailing. These findings highlight the critical role of precipitation-induced heterogeneities in shaping transport behavior, emphasizing the need to integrate these dynamics into reactive transport models for improved predictive accuracy.

Understanding the effects of mixing-driven precipitation on solute transport behavior is critical for reactive transport predictions, yet its complexity, arising from the interplay of flow dynamics, solute transport, and geochemical reactions, remains a significant challenge. In particular, mineral precipitation modifies the hydraulic properties of porous media. The impact of this process on the solute transport behavior remains largely unexplored and is crucial for accurate reactive transport predictions. This study presents a controlled laboratory investigation of mixing-driven calcite precipitation (MDP) in an intermediate-scale Hele-Shaw cell, simulating a coarse-sand porous medium. The experiment allowed for direct visualization of the spatiotemporal evolution of precipitation while continuously monitoring hydraulic properties. Self-organized heterogeneities in the precipitate structure were observed, with calcite layers forming symmetric patterns aligned with the main flow, contrasting with the asymmetry predicted by a semi-analytical model under idealized conditions. Tracer tests conducted before and after precipitation demonstrated significant impacts on solute transport, including the emergence of strong anomalous transport features, such as earlier solute arrival, a distinct double peak, and pronounced tailing. These findings highlight the critical role of precipitation-induced heterogeneities in shaping transport behavior, emphasizing the need to integrate these dynamics into reactive transport models for improved predictive accuracy.

Dissolution trapping of CO₂ in brine can mitigate the risk of supercritical CO₂ leakage during long-term geological carbon sequestration (GCS). The dissolution of overlying supercritical CO₂ into brine increases the density of brine in its upper portion, which causes gravity-driven convection (GDC) and thus significantly increases the rate of CO₂ dissolution. To date, most studies on GDC-enhanced dissolution are based on homogeneous media, and only few studies exist on the effect of heterogeneity on GDC-enhanced dissolution. Here, we study the effect of heterogeneity and anisotropy on GDC-enhanced dissolution rate using numerical simulations with randomly obtained permeability fields. Dissolution rates calculated by these simulations are related to properties of the permeability field using least-squares regression. We obtained two empirical formulas for predicting the asymptotic GDC-enhanced dissolution rate. In the first formula the dissolution rate is almost linearly proportional to the dimensionless equivalent vertical permeability. In the second one the dissolution rate is linearly proportional to a dimensionless vertical finger-tip velocity. This indicates that the GDC-enhanced dissolution can be predicted using either the equivalent vertical permeability or the vertical finger-tip velocity. Furthermore, both formulas demonstrate that higher-permeability anisotropy results in lower dissolution rates, suggesting that pronounced horizontal stratification can inhibit the dissolution of CO₂.

Dissolution trapping of CO₂ in brine can mitigate the risk of supercritical CO₂ leakage during long-term Geological Carbon Sequestration (GCS). The dissolution of overlying supercritical CO₂ into brine increases the density of brine in its upper portion, which causes Gravity-Driven Convection (GDC) and thus significantly increases the rate of CO₂ dissolution. To date, most studies on GDC-driven dissolution are based on homogeneous media and only few studies exist on the effect of heterogeneity on GDC-driven dissolution. Here, we study the effect of heterogeneity and anisotropy on GDC-driven dissolution rate by using numerical simulations with randomly obtained permeability fields. Dissolution rates calculated by these simulations are related to properties of the permeability field by using least-squares regression. We obtained two empirical formulas for predicting the asymptotic GDC-driven dissolution rate. In the first formula the dissolution rate is almost linearly proportional to the dimensionless equivalent vertical permeability. In the second one the dissolution rate is linearly proportional to a dimensionless vertical finger-tip velocity. This indicates that the GDC-driven dissolution can be predicted using either the equivalent vertical permeability or the vertical finger-tip velocity. Furthermore, both formulas demonstrate that higher anisotropy results in lower dissolution rates, suggesting that pronounced horizontal stratification can inhibit the dissolution of CO₂.

Dissolution trapping of CO₂ in brine can mitigate the risk of supercritical CO₂ leakage during long-term Geological Carbon Sequestration (GCS). The dissolution of overlying supercritical CO₂ into brine increases the density of brine in its upper portion, which causes Gravity-Driven Convection (GDC) and thus significantly increases the rate of CO₂ dissolution. To date, most studies on GDC-driven dissolution are based on homogeneous media and only few studies exist on the effect of heterogeneity on GDC-driven dissolution. Here, we study the effect of heterogeneity and anisotropy on GDC-driven dissolution rate by using numerical simulations with randomly obtained permeability fields. Dissolution rates calculated by these simulations are related to properties of the permeability field by using least-squares regression. We obtained two empirical formulas for predicting the asymptotic GDC-driven dissolution rate. In the first formula the dissolution rate is almost linearly proportional to the dimensionless equivalent vertical permeability. In the second one the dissolution rate is linearly proportional to a dimensionless vertical finger-tip velocity. This indicates that the GDC-driven dissolution can be predicted using either the equivalent vertical permeability or the vertical finger-tip velocity. Furthermore, both formulas demonstrate that higher anisotropy results in lower dissolution rates, suggesting that pronounced horizontal stratification can inhibit the dissolution of CO₂.

Dissolution trapping of CO₂ in brine can mitigate the risk of supercritical CO₂ leakage during long-term Geological Carbon Sequestration (GCS). The dissolution of overlying supercritical CO₂ into brine increases the density of brine in its upper portion, which causes Gravity-Driven Convection (GDC) and thus significantly increases the rate of CO₂ dissolution. To date, most studies on GDC-driven dissolution are based on homogeneous media and only few studies exist on the effect of heterogeneity on GDC-driven dissolution. Here, we study the effect of heterogeneity and anisotropy on GDC-driven dissolution rate by using numerical simulations with randomly obtained permeability fields. Dissolution rates calculated by these simulations are related to properties of the permeability field by using least-squares regression. We obtained two empirical formulas for predicting the asymptotic GDC-driven dissolution rate. In the first formula the dissolution rate is almost linearly proportional to the dimensionless equivalent vertical permeability. In the second one the dissolution rate is linearly proportional to a dimensionless vertical finger-tip velocity. This indicates that the GDC-driven dissolution can be predicted using either the equivalent vertical permeability or the vertical finger-tip velocity. Furthermore, both formulas demonstrate that higher anisotropy results in lower dissolution rates, suggesting that pronounced horizontal stratification can inhibit the dissolution of CO₂.

Dissolution trapping of CO₂ in brine can mitigate the risk of supercritical CO₂ leakage during long-term Geological Carbon Sequestration (GCS). The dissolution of overlying supercritical CO₂ into brine increases the density of brine in its upper portion, which causes Gravity-Driven Convection (GDC) and thus significantly increases the rate of CO₂ dissolution. To date, most studies on GDC-driven dissolution are based on homogeneous media and only few studies exist on the effect of heterogeneity on GDC-driven dissolution. Here, we study the effect of heterogeneity and anisotropy on GDC-driven dissolution rate by using numerical simulations with randomly obtained permeability fields. Dissolution rates calculated by these simulations are related to properties of the permeability field by using least-squares regression. We obtained two empirical formulas for predicting the asymptotic GDC-driven dissolution rate. In the first formula the dissolution rate is almost linearly proportional to the dimensionless equivalent vertical permeability. In the second one the dissolution rate is linearly proportional to a dimensionless vertical finger-tip velocity. This indicates that the GDC-driven dissolution can be predicted using either the equivalent vertical permeability or the vertical finger-tip velocity. Furthermore, both formulas demonstrate that higher anisotropy results in lower dissolution rates, suggesting that pronounced horizontal stratification can inhibit the dissolution of CO₂.

Dissolution trapping of CO₂ in brine can mitigate the risk of supercritical CO₂ leakage during long-term Geological Carbon Sequestration (GCS). The dissolution of overlying supercritical CO₂ into brine increases the density of brine in its upper portion, which causes Gravity-Driven Convection (GDC) and thus significantly increases the rate of CO₂ dissolution. To date, most studies on GDC-driven dissolution are based on homogeneous media and only few studies exist on the effect of heterogeneity on GDC-driven dissolution. Here, we study the effect of heterogeneity and anisotropy on GDC-driven dissolution rate by using numerical simulations with randomly obtained permeability fields. Dissolution rates calculated by these simulations are related to properties of the permeability field by using least-squares regression. We obtained two empirical formulas for predicting the asymptotic GDC-driven dissolution rate. In the first formula the dissolution rate is almost linearly proportional to the dimensionless equivalent vertical permeability. In the second one the dissolution rate is linearly proportional to a dimensionless vertical finger-tip velocity. This indicates that the GDC-driven dissolution can be predicted using either the equivalent vertical permeability or the vertical finger-tip velocity. Furthermore, both formulas demonstrate that higher anisotropy results in lower dissolution rates, suggesting that pronounced horizontal stratification can inhibit the dissolution of CO₂.

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