EXPERIMENTAL EVALUATION OF GLAUCONITIC SEDIMENTS FOR IN-SITU CARBON SEQUESTRATION

Experiments were conducted with glauconite-bearing Franconian Stage sandstone from the Tunnel City Group to determine the efficacy of iron carbonate precipitation as a trapping mechanism for CO₂. In addition to quartz and glauconite, the rock contained small amounts of dolomite microspar. Mossbauer Spectroscopy analysis indicated that the ratio of ferrous to ferric iron in the rock was 0.367. Intact sandstone cores were jacketed in Teflon, wrapped in foil to reduce CO₂diffusion and inserted into a hydrothermal flow reactor. A computer-controlled fluid delivery system allowed independent control of confining and pore fluid pressure (200 and 150 bar, respectively), as well as fluid flow rate (0.01 ml/min), while temperature was held constant (150°C) by four independently controlled band heaters surrounding the reaction vessel. The source fluid was a 1 molal NaCl brine charged with approximately 0.58 mol CO₂/kg solution. Different brine compositions including bicarbonate and formate were injected into the core on two separate runs to examine the effect of varying alkalinity and redox potential on the formation of carbonate minerals and phase relations involving glauconite. Over the course of the experiments, the pressure differential across the core remained constant, likely due to the samples’ very high initial permeability. The dissolved chemistry of outlet fluid provided evidence of compositional modification of the core. Importantly, we note that approximately 20% of the CO₂ dissolved in the source fluid was removed during interaction with the core, consistent with the dissolution of cation-bearing silicates and the precipitation of secondary carbonate phases. This suggests that glauconitic sandstones may be a favorable host rock for carbon sequestration. Ongoing analyses of X-ray Computed Tomography (XRCT) datasets are being used to identify changes in pore geometries and to quantify secondary mineralization.