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Title: Geo-Chemo-Mechanical Studies for Permanent CO{sub 2} Storage in Geologic Reservoirs

This two-pronged study investigated the rates and mechanisms of formation of Ca and Mg carbonate minerals via reaction of aqueous fluids with silicate minerals and rocks, and the geomechanical effects of such reactions. The kinetic studies focused on the separation of variables, following from previous studies demonstrating rapid formation of carbonates via reaction of the mineral olivine with aqueous fluids rich in NaHCO{sub 3} (plus KHCO{sub 3} and RbHCO{sub 3}) and NaCl at a high partial pressure of CO{sub 2}. We wished to separate and quantify the effects of NaHCO{sub 3} and NaCl, and to investigate whether bicarbonate-rich, aqueous fluids would also cause rapid formation of carbonates via reaction with other minerals and rocks. Further, we wished to improve upon previous work by adding precise characterization of grain size distributions and surface area, and their changes as a result of reaction. We confirmed previous reports of very rapid olivine carbonation. We found that at a given temperature and CO{sub 2} partial pressure the previously observed rate enhancement in olivine carbonation is due mainly to NaHCO{sub 3}, and not to dissolved NaCl. Further, though reaction of the mineral plagioclase, and two rock compositions, were all faster in the presence of NaHCO{submore » 3}-rich fluids, compared with saline and de-ionized water, they were all much slower than reaction of olivine. In the experiments showing the fastest reaction rate, average grain size tended to increase during experiments, presumably due to dissolution of small reactant grains plus growth of product phases on reactant surfaces. Porosity/surface area of grains tended to change with reaction progress, due to the formation of dissolution pits and irregular growth of product phases on reactant grain surfaces. Development of a passivating phase (e.g., a layer of silica) due to incongruent dissolution of solid reactants and/or precipitation of solid products was detected, but was relatively minor and did not have a discernable effect on reaction progress. Geomechanical experiments did not identify pressure-temperature-composition conditions under which porous olivine aggregates undergo reaction driven cracking. Little carbonate formed in these experiments. Though we fulfilled the milestones for this project, a variety of reasons for this remain to be investigated in the future. Reaction of porous olivine aggregates with brines rich in NaHCO{sub 3} caused substantial weakening of samples in compression, due to formation of dissolution pits along olivine-olivine grain boundaries, reducing the solid-solid surface area. A preliminary modeling study funded in part by this grant emphasized potential rate enhancements due to reaction-driven cracking. In related research, not funded by this grant, several additional experimental and modeling studies of reaction-driven cracking are underway.« less
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Resource Type:
Technical Report
Research Org:
The Trustees Of Columbia University In The City Of New York Incorporated
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Country of Publication:
United States