INVESTIGATION RELATED TO CO2 STORAGE IN DEEP SALINE AQUIFERS
We have investigated the interaction between the reservoir and seal rocks of the Hontomin site and the formation groundwater. Currently, in Hontomín (Spain), a technology demonstration plant for CO2 storage in a deep saline aquifer where the main reservoir rock is primarily limestone is being developed. CO2 will be injected at a depth of approximately 1500 m. where it will reach supercritical conditions (pressure P > 74 bar and temperature T > 31 °C) and will react with the resident solution, which is sulfate-rich (at equilibrium with gypsum) and has an ionic strength of 0.6 M. Dissolution of CO2 into the resident saline solution may induce the dissolution of carbonates and because the solution contains sulfate, secondary mineral precipitation (gypsum or anhydrite) may occur. These reactions imply changes in porosity, permeability and pore structure of the repository rocks.
A set of column (crushed rock) and percolation (fractured cores) experiments which consist of injecting a CO2-rich solution through the samples under high pressure conditions (P = 10-150 bar) and variable temperature (25-60 °C). Experiments were performed under different flow rates (from 0.2 to 60 mL/h) to assess changes in the initial sample properties (e.g., porosity, permeability and fracture dimensions and morphology) and investigate the role of secondary minerals by varying the sulfate content of the injected solution (sulfate-free and sulfate-rich).
Furthermore, we investigated the effect of H2SO4 (corresponding to a worst case of 0.4% SO2 in the flue gas, anticipating total conversion of SO2 into H2SO4) on the reactivity of the reservoir (limestone and sandstone) and cap (marl) rocks at P = pCO2 = 10 bar and 60 °C using flow-through column experiments.
Garcia-Rios et al. (2014) Interaction between CO2-rich sulfate solutions and carbonate reservoir rocks from atmospheric to supercritical CO2 conditions: experiments and modeling. Chemical Geology 383, 107–122.
Garcia-Rios et al. (2015) Influence of the flow rate on dissolution and precipitation features during percolation of CO2-rich sulfate solutions through fractured limestone samples. Chemical Geology 414, 95–108.
Davila et al. (2016) Interaction between a fractured marl caprock and CO2-rich sulfate solution under supercritical CO2 conditions. International Journal Greenhouse Gas Control 48, 105-119
Dávila G., Luquot L., Cama J., and Soler J.M. (2016) 2D reactive transport modeling of the interaction between a marl and a CO2-rich sulfate solution under supercritical CO2 conditions. International Journal of Greenhouse Gas Control 54, 145-149.
Dávila G., Cama J., Luquot L., Soler J.M., and Ayora C. (2017) Experimental and modeling study of the interaction between a crushed marl caprock and CO2-rich solutions under different pressures and temperatures. Chemical Geology 448, 26-42.
Thaysen E.M., Soler J.M., Boone M., Cnudde V., and Cama J. (2017) Effect of dissolved H2SO4 on the interaction between CO2-rich brine solutions and limestone, sandstone and marl. Chemical Geology 450, 31-43.
Given the time scale associated with geological CO2 sequestration, the use of alternative cements that are not subject to the harmful effects of carbonation would be advisable. For instance, reactive magnesium oxide (MgO) can be successfully blended together with Portland cement and result in improvements in sustainability, strength and many other properties of concretes (Harrison, 2001; WIP Organisation (Ed.), Reactive Magnesium Oxide Cements. Australia). The advantages of MgO over Portland cement include precipitation of higher resistance secondary phases, less sensitivity to impurities, and that it can be obtained as a by-product from other industrial processes (Unluer and Al-Tabbaa, 2013; Cem. Concr. Res. 54, 87–97). We have studied caustic magnesia (MgO) as an alternative to Portland cement, not only to be used in the space between the well casing and the rock but also to seal rock fractures (grouting). At this stage, the reactivity of MgO, excluding MgO-Portland cement blends, is studied in a range of pCO2 and T relevant for CO2 injection cases.
- The goal of our investigation was to study the overall process of MgO carbonation in aqueous solutions equilibrated with respect to calcite under subcritical (pCO2 of 10 and 50 bars and T of 25, 70 and 90 °C) and supercritical (pCO2 of 74 bar and T of 70 and 90 °C) CO2 conditions. Stirred batch experiments were conducted in an autoclave and the experimental results were numerically reproduced using the CrunchFlow reactive transport code (Steefel et al., 2015; Comput. Geosci. 19, 445–478). A possible application case (CO2- rich water interacting with MgO in a borehole), using the laboratory results, was simulated.
Davila et al. (2016): Efficiency of magnesium hydroxide as engineering seal in the geological sequestration of CO2. International Journal Greenhouse Gas Control 48, 171-185.