Key Physicochemical Processes Affecting Seals during Geologic CO2 Sequestration

Geologic CO2 sequestration (GCS) is a promising means of mitigating anthropogenic CO2 emissions. To realize this promise, we must achieve a holistic understanding of the potential physicochemical processes of seals (i.e., caprocks and wellbores) under GCS conditions that can impact operational safety and sustainability. This presentation will focus on the mechanisms and kinetics of key reactions at supercritical CO2–brine–caprock mineral (or cement) interfaces and how these chemical processes can be linked to mechanical property changes in seals. We studied mica and cement because mica is abundant in both formation rock and caprock at potential CO2 sequestration sites, and because the integrity of wellbore cement is important in maintaining the safety and efficiency of GCS. To characterize nanoscale morphological changes resulting from the dissolution of pre-existing minerals and the precipitation of new mineral phases, fluid chemistry results are incorporated with high resolution X-ray diffraction, atomic force microscopy, and scanning electron microscopy combined with energy dispersive X-ray spectroscopy. In mica systems, the dissolution of mica and formation of nanoscale amorphous silica and illite at mica surfaces were observed after reaction times as brief as a few hours. Furthermore, the CO2 wettability of the mica decreased. Formation and relocation of these nano- and micro-particles can result in pore clogging and consequently affect the permeability of the formation rock. In cement systems, CO2 attack caused a layer structure development of the cement. By incorporating heterogeneous reactivity in pore structure and new mineral precipitations in fractures and pores, we improved a reactive transport model code of CrunchTope and predicted the wellbore cement reaction extent more accurately. This study provides important fundamental information for enabling a better reactive transport prediction of GCS systems and designing safer GCS operations.

Dr. Young-Shin Jun is the Harold D. Jolley Career Development Associate Professor of Energy, Environmental & Chemical Engineering (EECE) and the EECE Director of Graduate Studies at Washington University, where she leads the Environmental NanoChemistry Laboratory. She is also Washington University’s McDonnell International Scholars Academy Ambassador to Seoul National University, South Korea. Dr. Jun received a 2011 U.S. National Science Foundation CAREER award and a 2008 Ralph E. Powe Junior Faculty Enhancement Award. She serves on the Advisory Board of Environmental Science: Processes & Impacts, the Editorial Board (Associate Editor) of Geochemical Transactions, and is the Division Chair of the American Chemical Society’s Geochemistry Division. Prof. Jun has been named a 2015 Kavli Fellow by the U.S. National Academy of Sciences and a 2016 Frontier of Engineering Fellow by the U.S. National Academy of Engineering. Her research group aims at providing more environmentally sustainable CO2 sequestration strategies, improving our understanding of the fate and transport of contaminants and nanoparticles, and developing water purification methods for securing potable water. Prior to her position at Washington University, she conducted postdoctoral research in Nanogeoscience at the University of California at Berkeley/Lawrence Berkeley National Laboratory (2005-2007). She holds a Ph.D. in Environmental Chemistry from Harvard University (2005).