CO2-BRINE-PORE MINERAL INTERACTIONS IN THE MOUNT SIMON, OHIO

The Mount Simon sandstone of western Ohio has been identified as a potential storage reservoir for CO₂ derived from power plant point sources. Predicting how the Mount Simon will react to CO₂ injection requires the development of kinetic models informed by the mineralogy of rocks accessible to CO₂-bearing fluid. Advancing on previous efforts, we develop models of CO₂-saturated brine in contact with rock that draw upon pore, rather than bulk, mineralogies. 2D mineral and pore scan raster maps of thin sections are obtained using a field emission gun scanning electron microscope (FEG-SEM) equipped with QEMSCAN software that compares backscattered electron (BSE) and characteristic x-ray signals against a database of standard mineral patterns. These methods permit the analysis of how micron-scale mineralogical heterogeneity varies over distances of tens of vertical meters.

The Geochemist’s Workbench is used to model interactions of CO₂-saturated brine and rock at subsurface pressures and temperatures covering the range of natural values (8 – 32 MPa; 25 – 35 degrees C). Kinetic modeling tests the importance of parameters such as heterogeneity in modal mineralogy and pore versus bulk mineralogy on scenarios of CO₂-brine-rock system evolution. When pore and bulk mineralogies are compared, it is found that certain relatively reactive minerals comprising minor proportions of the bulk rock, such as illite and chlorite, are sufficiently abundant adjacent to pores to become determining factors in the modeling of Ph-dependent solution chemistry.

Work is performed by the Subsurface Energy Materials Characterization and Analysis Lab at The Ohio State University, and is sponsored by the Dept. of Energy “Nanoscale Control of Geologic CO₂” Energy Frontier Research Center. Core is provided by the Ohio Department of Natural Resources.