Extraction of organic compounds from organic-rich rocks during geologic CO2 sequestration at supercritical conditions

At reservoir conditionscarbon dioxide is a supercritical fluid capable of extraction of naturallyoccurring neutral compounds from formation materials, including carboxylicacids at low pH. We performed a series of experiments designed to quantify theextractable carboxylic acid and neutral aromatic yield from coal of the WilcoxGroup in Louisiana. We determined concentrations of organic species in both the aqueous phase and carbon dioxide phases during batch reactions of rock with the two fluid phases. The concentration patterns observed following preliminary experiments indicate that high concentrations of aromatic acids are observed preferentially in the supercritical phase whereas aliphatic short-chain and dicarboxylic acids are preferentially found in the aqueousphase. We conclude that organic-rich rocks such as coal will be sources of organic acids following geologic CO₂ sequestration. Organic compound liberation from rocks has important implications for the subsurface microbial community and weathering rates of seal and reservoir silicates.