POTENTIAL GEOCHEMICAL REACTIONS FROM CARBON SEQUESTRATION IN THE LAMOTTE AND BONNETERRE FORMATIONS IN SOUTHWEST MISSOURI

City Utilities of Springfield, MO is investigating the potential for injecting CO₂ into the Lamotte or Bonneterre Formations as part of a shallow carbon sequestration pilot demonstration (Missouri Carbon Sequestration Project). Shallow sequestration depths (<800m) must be used due to underlying Precambrian granite which prevents injection to greater depths in this region. To obtain a better understanding of the carbon dioxide-fluid-rock interaction process, rocks and minerals similar to those expected to occur at the injection site have been obtained and were exposed in a laboratory setting to carbon dioxide and water in either open vessels with bubbling CO₂ or sealed reaction vessels. Reaction progress was monitored and fluid samples were taken throughout the reaction and analyzed by Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) for major element composition to obtain the dissolution rate of the sample material. Preliminary results indicate rapid reaction rates ( > 100mM m^-2 day^-1 ) during the first day of exposure for various carbonate minerals and glauconite ((K,Na)(Mg,Fe)_0.33(FeAl)_1.67((Si,Al)₄O₁₀)(OH)₂), with release rates of Ca and Mg that fall off exponentially with time. A release rate between 10 and 375mM m^-2 day^-1was observed after seven days of exposure. Optical microscopy and scanning electron microscopy (SEM) were also used to examine dissolution processes and find evidence of mineral precipitation. Evidence of carbonate dissolution was observed on some samples at thin grain edges under SEM. Although secondary minerals have yet to be observed, longer exposures in open reaction vessels, and reactions in sealed vessels are expected to yield magnesite-siderite (MgCO₃-FeCO₃) following reactions with glauconite-rich samples that occur in the upper-Lamotte and to the Bonneterre Formations. Reactions with feldspars used to represent the arkosic sandstones in the lower-Lamotte Formation may produce the carbonate mineral dawsonite (NaAlCO₃(OH)₂), trapping the CO₂. Combined results can then be used to predict the rate and type of reaction of CO₂with the minerals located at the Springfield, MO pilot site.