Interactions of Supercritical Carbon Dioxide with Porous Silica and Montmorillonite Clay
Abstract
The high and increasing level of carbon dioxide (CO2) in the atmosphere resulting from burning of fossil fuels is likely to cause global warming. Large-scale carbon capture and sequestration (CCS) of CO2 produced in power plants may play an important role in controlling the level of this greenhouse gas in the atmosphere. In this process, CO2 is stripped from the emissions, compressed, and stored in subsurface reservoirs in very large quantities. The specific CO2-rock interactions control the storage capacity of the reservoir and the fluid mobility. The dominant interactions of supercritical CO2 with reservoir rocks over the first couple of years after injection are sorption and capillary trapping. By combining sorption measurements and neutron scattering data in the Adsorbed Phase Model we obtain a full microstructural characterization of the pore fluid. We studied mesoporous CPG-10 silica materials with pore sizes of 75 Å and 350 Å at pressures from 0-200 bars and temperatures of 35°C and 50°C, covering a range typical for carbon storage sites. Porous silica glass serves as a proxy for quartz-rich rocks, including sandstones that may serve as reservoir rocks. The CO2 excess sorption isotherms were measured using a high-pressure sorption balance. Strong adsorption of CO2 to the silica was found at low fluid pressure and density, followed by formation of a maximum in the excess sorption isotherm. The excess sorption exhibited small or even negative values at high pressure. An inverse temperature dependence of the sorption strength was found in the adsorption region at low and intermediate pressure, while the excess sorption showed little temperature dependence at high pressure. A shift of the excess sorption maximum to higher fluid density was observed with increasing pore width. From small-angle neutron scattering data the density and volume of the sorption phase of CO2 is calculated. Caprocks overlying the porous reservoir rock serve to retain buoyant plumes of CO2. Caprocks can be comprised of thick layers of clay or mudstones, thought to be impenetrable to CO2. To quantify the interactions of caprock with CO2, we measured the excess sorption of supercritical CO2 at Na-montmorillonite clay, a proxy for cap rock materials. Very limited amounts of CO2 adsorbed to this clay mineral at low fluid densities. Using neutron diffraction, the change of the clay interlayer spacing was measured as a function of the CO2 density. A jump-like increase of the interlayer spacing upon CO2 addition was found at low pressures, and remained constant with further additions of CO2. These results indicate suitability of montmorillonite clay for carbon storage caprock applications.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.V14A..05R
- Keywords:
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- 1043 GEOCHEMISTRY / Fluid and melt inclusion geochemistry