Fluid‐Rock Interactions in Clay‐Rich Seals: Impact on Transport and Mechanical Properties

Abstract

Fluid‐rock interaction in low‐permeable clay‐rich seal units is an important topic for the evaluation of the long‐term seal integrity during geological storage of CO2. In low‐permeable sealing units, the diffusion of CO2 into the matrix is a slow process, and studies of CO2‐initiated fluid‐rock interaction in seals are challenging. In this paper, we present an overview of CO2 transport mechanism and fluid‐rock interaction processes that might alter mechanical and transport properties of seals. The review includes theoretical considerations and simulations, experimentally demonstrated processes, and field examples of flow and fluid‐rock interaction in intact clay‐rich seals as well as for fractures. For clay‐rich seals dominated by minerals like quartz, illite, and smectite, the reactivity due to drop in pH is found to be low, and most reaction observed is found to involve calcite. Only minor porosity changes are observed, and implications for flow and CO2 transport are uncertain due to limited data available. Swelling and shrinking property of smectites due to CO2 sorption and CO2 alterations within fractures in clay‐rich seal is hardly addressed in the literature.

Fluid‐Rock Interactions in Clay‐Rich Seals: Impact on Transport and Mechanical Properties