Fluid-Mineral-CO2 Interactions During Geological Storage of Carbon Dioxide

In order utilise geological carbon dioxide storage (GCS) at an industrial scale predictions of reservoir scale behaviour, both chemical and physical must be made. In order to ground-truth the geochemical data underlying such predictions, laboratory experiments at temperatures and CO2 pressures relevant to GCS are essential.
Mineral dissolution rate, CO2 solubility and pH data has been collected from batch experiments carried out on quartz, K-feldspar, albite, calcite, dolomite and Sherwood Sandstone materials. These experiments were designed to assess the influence of a variety of factors on dissolution rates: changes in grain size from 125μm - 180μm to 500μm - 600μm; changes in fluid composition from deionised water to 1.36M NaCl solution; changes in CO2 pressure from 4 bar to 31 bar; changes in temperature from 22°C to 70°C. Experiments carried out on the Sherwood Sandstone material also included work on consolidated rock, rather than the powder used in other experiments.
Calculated dissolution rates for silicates were found to agree well with values calculated from literature-sourced dissolution equations and the USGS-produced general rate equation (USGS 2004) was found to be suitable for predicting these rates. Calculated dissolution rates for the carbonate minerals was found to be strongly retarded due to transport effects, with literature-sourced equations significantly over-predicting dissolution rates.
Dissolution of the sandstone material was found to be dominated by K-feldspar and dolomite dissolution, rates of which compare favourably with those obtained from the single mineral experiments. A significant increase in porosity was observed in the core flow-through experiment, associated with dolomite dissolution.
Several experiments were carried out using a Hele-Shaw cell in order to visualise the formation and migration of density plumes which form as CO2 dissolved into unsaturated fluids. Introduction of NaCl and decreases in permeability were found to significantly retard migration of CO2 saturated fluid, while minor heterogeneities in the cells served to focus and accelerate plume movement. Modelling work suggests that predictive models currently underestimate the rapidity of formation and migration of these plumes.