- © 2013 Mineralogical Society of America
Interactions between CO2 and H2O fluids and the rocks that host them are of significance for Geological Carbon Storage (GCS) for several reasons. These interactions determine the amount of CO2 that can be trapped in solution and in minerals. The petrophysical properties of reservoir and cap rocks, especially porosity and permeability, are also affected. Carbon storage in fluids and minerals, coupled with potential changes to the petrophysical properties of rocks, have a direct bearing on the long-term effectiveness of GCS.
Many potential reservoir rocks contain a range of minerals that may react at very different rates. In particular, carbonate minerals are widespread minor components of sedimentary rocks and react much more rapidly than silicates, while clay minerals are often much more reactive than minerals such as quartz or alkali feldspars. It follows that the evolution of pore fluid composition in a reservoir into which CO2 is injected may be strongly influenced by kinetic factors. Dissolution of fast-reacting minerals may be limited by the transport of reactants to the mineral surface, while minerals whose surfaces react only slowly may persist out of equilibrium with pore fluid for extended periods. Some reactions, such as congruent dissolution, proceed until the reacting mineral is in equilibrium with the pore fluid, but other, incongruent reactions may involve unstable reactants which never attain equilibrium with the pore fluid, resulting in very extensive mineralogical transformations over time.
This chapter examines interactions between CO2 and H2O fluids and the rocks and minerals that comprise GCS reservoirs, as well as the caprocks that seal these reservoirs, from the perspective of laboratory experiments. Laboratory experiments determine thermodynamic and kinetic parameters and can identify fluid-rock reactions and processes that may have been previously unknown or unappreciated. Experimental studies of equilibrium and kinetic aspects …