Carbonate mineral reactions during geological carbon sequestration, and implications for induced seismicity
September 13, 2022 at Noon Central
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Geologic carbon sequestration in deep saline aquifers results in a low pH brine plume that pushes into subsurface storage reservoirs and can access pre-existing or induced (micro)fractures and possibly induce shear slip.  To investigate this phenomenon, an artificial fracture was created in a Bandera Gray sandstone sample, and it was held under shear stress in a custom flow cell housed within an industrial CT scanner. Acidic (pH 4) or reservoir-simulated (pH 8.3) brine was pumped through the artificial fracture for seven days. CT imaging shows that acidic brine resulted in greater shear slip than reservoir-simulated brine, and fracture surfaces exposed to acidic brine had rougher surfaces and lower fracture toughness. SEM images of fracture surfaces indicate a loss by area of carbonate cementing crystals after exposure to the acidic brine, as well as a corresponding porosity increase. These results motivated more fundamental studies on carbonate mineral dissolution using freshly cleaved calcite.  The effects of solution pH, carbonic acid, and the presence of an anionic surfactant on calcite dissolution kinetics and etch pit morphology were probed in a high pressure and temperature reactor, and complemented with density functional theory calculations.  Results indicate that carbonic acid promotes much faster dissolution than protons or water, and that the anionic surfactant inhibits dissolution by competing with carbonic acid for calcium edge sites on the calcite surface.  Hence, addition of anionic surfactants to injected CO2 may inhibit calcite dissolution and slip along existing fractures. 


Dr. Charles J. Werth is a Professor & Bettie Margaret Smith Chair of Environmental Health Engineering in the Department of Civil, Architecture, and Environmental Engineering at the University of Texas at Austin. He joined the UT faculty in August of 2014, after spending 17 years on the faculty at the University of Illinois at Urbana-Champaign. Werth’s research and teaching focus on the fate and transport of pollutants in the environment, the development of innovative catalytic technologies for drinking water treatment, and the mitigation of environmental impacts associated with energy production and generation. He is presently the Principal Investigator of an NSF NRT on “Reducing Energy Barriers for Novel Water Supply Use in Sustainable Agriculture”, an NSF LEAP-HI on “Smart Sensing and Forecasting of Water Quality in the Water Distribution Network for Protection of Public Health”, two DOD SERDP projects related to the fate of chlorinated solvents and PFAS compounds in groundwater, and an NSF CBET project on “Electrocatalytic Reduction of Nitrate in Drinking Water”.  Werth’s past recognition includes appointment to the USEPA’s Science Advisory Board (SAB), as a Wiley Research Fellow at the Department of Energy’s Environmental Molecular Science Laboratory, and as a Mercator Fellow of the German Research Society. He’s twice received the Editor’s Choice Best Paper Award from Environmental Science and Technology, and was recognized for having a most cited paper in Journal of Contaminant Hydrology. Werth also received a Humbolt Research Fellow Award, a National Science Foundation CAREER Award, and a BP Award for Innovation in Undergraduate Instruction. Werth received a B.S. in Mechanical Engineering from Texas A&M University, an M.S. and Ph.D. in Environmental Engineering from Stanford University, and a Ph.D. minor in Chemistry from Stanford University.