Geochemical Reactions for Sequestration of CO2 in Ohio's Deep Saline Aquifers

摘要

Deep saline aquifers are potential long-term repositories for CO_2 from power plant emissions. The extent, form, and duration of CO_2storage depends on chemical reactions between the injected CO_2, aquifer brines, and formation minerals. The Rose Run sandstone of eastern Ohio is one of Ohio's deep formations that has potential for CO_2 injection and storage. The dominant minerals in t he sandstone are quartz, K- and Na- feldspars, and glauconite. Car bonat e layer s int er bedded with t he sandst one cont ain dolomite, calcite, and sider ite. Dissoluti on experiment s and geochemical simulations are ongoing to evaluate likely CO_2-brine-rock reactions following injection of CO_2 into the mixed car bonate-siliciclastic formation.I nexpensive high-temper at ure and high-pressure, rocking t ube reactors allow for multiple reaction experiments to run simultaneously. Dissolut ion rate experiments ar e conduct ed f or silicate and carbonate minerals, inCO_2-pressurized KCl brine solutions, at a range of pressures and t emperat ures represent at ive of deep aquifer conditions. Results from t ube-react or experiments are compared with results from experiments run under identical operating conditions in a commercial Parr sti rred reactor, and with results from t he published literature.Equilibrium, path of reaction, and kinetic geochemical modeling is conducted using Geochemists Workbench to simulate t he experimental reactions and likely geochemical reactions in the Rdse Run aquifer. Geochemical modeling of simple and complex mineral-brine-CO_2 mixt ures makes it possible to evaluate the impact of temper at ure, pressure, mineralogy, brine composition, CO_2-fluid-rock ratio, and CO_2 fugacity on mineral dissolution and precipitation, amount of CO_2 sequestered, and the form of sequestration.For example, for a representative Rdse Run carbonate, addition of 1 mole of CO_2(g) causes a dissolut ion of calcite and si derite. Increasi rgt he CO_2-to-brine ratio lowers the pHand increases carbonate dissoluti on. However, remaining CO_2 ist rapped as bicarbonate and as dissolved CO_2(aq). Tine proportion of CO_2 that remains free increases as the CO_2 to brine ratioincreases. For the silicate case, geochemical reactions convert some of theCO_2 to car bonate minerals such as siderite, calcite, and dolomite, absorbing more of theCO_2 than for the compar able carbonate case. For higher CO_2-to-brine ratios, all the reactive minerals are consumed by reactions with t he CO_2 such t hat t he f ree CO_2 remaining in t he syst em at equilibrium is very small as compared to t he car bonat e case. Generalizing t hese results t o a front of injected CO_2 displacing water, at the nose of the displacement profile, where the satiration of CO_2 is small, all the CO_2 can be consumed by dissolving into water or reacting with the rock. Close to the injection site, there will be free CO_2.