The role of advection and dispersion in the rock matrix on the transport of leaking CO2-saturated brine along a fractured zone

Abstract

$CO_{2}$ that is injected into a geological storage reservoir can leak in dissolved form because of brine displacement from the reservoir, which is caused by large-scale groundwater motion. Simulations of the reactive transport of leaking $CO_{2aq}$ along a conducting fracture in a clay-rich caprock are conducted to analyze the effect of various physical and geochemical processes. Whilst several modeling transport studies along rock fractures have considered diffusion as the only transport process in the surrounding rock matrix (diffusive transport), this study analyzes the combined role of advection and dispersion in the rock matrix in addition to diffusion (advection-dominated transport) on the migration of $CO_{2aq}$ along a leakage pathway and its conversion in geochemical reactions. A sensitivity analysis is performed to quantify the effect of fluid velocity and dispersivity. Variations in the porosity and permeability of the medium are found in response to calcite dissolution and precipitation along the leakage pathway. We observe that advection and dispersion in the rock matrix play a significant role in the overall transport process. For the parameters that were used in this study, advection-dominated transport increased the leakage of $CO_{2aq}$ from the reservoir by nearly $305\%$, caused faster transport and increased the mass conversion of $CO_{2aq}$ in geochemical reactions along the transport pathway by approximately $12.20\%$ compared to diffusive transport.

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