The successful geological storage of carbon dioxide (GCS) relies on the sealing properties of shale caprock. This study examines mineralogical changes in shale triggered by the introduction of carbon dioxide (CO2), and the coupled geochemical-geomechanical response of caprock to injection of CO2. Mancos shale was exposed to the CO2-brine mixture for 8 weeks in a stirred heated reactor at a fixed pCO2. We followed the chemical evolution of the system by measuring apparent mineral dissolution-precipitation rates and characterized secondary mineral and amorphous precipitates. Increases in concentrations of calcium, silica, sodium, potassium, and magnesium were observed following the introduction of CO2. The dissolution of calcite and kaolinite and the precipitation of gypsum and amorphous Al (hydr)oxide are indicated by changes in the aqueous chemistry, and further supported by the characterization of the solid samples and geochemical modeling. Nano-mechanical testing of shale altered by CO2-brine mixtures and the implications for the long-term stability of shale caprock will be discussed. This work was supported as part of the Center for Frontiers in Subsurface Energy Security, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0001114. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.

Mancos shale-brine-CO2 interactions and the long-term stability of shale caprock

251st National Meeting (2016)

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