Speaker
Description
Controlling fluid flow through permeable and fractured media is important in a variety of subsurface contexts including geologic carbon storage (GCS). Low pH and or high salinity conditions create corrosive aqueous environments which would rapidly degrade cement in wellbores or carbonate/clay features in caprocks. Our group has explored the potential to deploy dissolution/precipitation reactions using mineral silicates as a way to plug leakage pathways in GCS contexts. Here, we present a combination of experimental and modeling results using wollastonite and pseudowollastonite, which are high temperature polymorphs of calcium silicate, as seed materials to plug leakage pathways. When calcium silicate is carbonated under reservoir conditions it forms calcium carbonate and amorphous silica. But our high temperature and pressure column experiments indicate that in addition to carbonate a number of secondary mineral phases are also possible. Under certain conditions, we observed the formation of crystalline plate- and flower-like mineral hydrates, which formed on fluid-solid interfaces. The type of hydrate that formed was a function of ionic strength, the partial pressure of CO2, the pH of the system, and the type of mineral surface that was available to initiate nucleation of the mineral phases. In column studies, the formation of these mineral precipitates dropped the permeability by several orders of magnitude. These drops could be understood in terms of the significantly larger molar volumes of the products relative to the reactants. These increases in molar volume were significant when normalized to the availability of cations (calcium in this case). These mineral phases were also strong cements that could either improve the mechanical integrity of the rock or add stress to fractures and pores under confined conditions. A proposed mechanism for the chemistry underlying the carbonation of crystalline calcium silicate will be presented and discussed in the context of a reactive transport model to explore the ways in which particles might be injected and carbonated to produce seals in a GCS context.
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