From Bureau of Economic Geology, The
University of Texas at Austin (www.beg.utexas.edu).
For more information, please contact the author.
Bureau Seminar, May 21, 2010
Geochemical Reactive Transport Modeling of Evaporative
Concentration of Aqueous Solutions in Geological Formations
Link to streaming video TBA: available 05.21.2010 at 8:25am
Dr. Guoxiang Zhang
Royal Dutch Shell
Evaporation, a common phenomenon that occurs at liquid surfaces/interfaces, removes pure water from an aqueous solution, leading to concentration of solutes in the residual solution. Evaporation can be enhanced in extreme environments such as deserts, an underground nuclear waste repository, some petroleum reservoirs, and CO2 sequestration reservoirs. Enhanced evaporative concentration not only leads to changes in chemical composition of aqueous solutions, but also can cause minerals/salts to precipitate (i.e. formation of evaporites) and release acid gases. Injection of dry CO2 into a deep saline aquifer, for instance, can induce strong evaporation of water from the brine (due to the mutual solubility of CO2 and brine), leading to further concentration of the brine, changes in brine chemistry and precipitation of salts/minerals that could impair porosity and permeability of host rocks. Geologists and petroleum engineers need to understand and predict these processes. Modeling studies of enhanced evaporative concentration processes to help understand and predict them are presented. These models were performed using a multiphase flow and geochemical reactive transport simulator (TOUGHREACT) based on thorough understanding of the processes; a proper geochemical conceptual model (i.e. Pitzer ion-interaction ionic activity model for concentrated aqueous solutions); effective numerical technology; and validation using experimental results. These modeled cases include evaporation-driven thermo-hydrochemical processes that occur at a nuclear waste repository, and CO2-brine-rock interactions near injector wells for a CO2 sequestration project.
All the results presented can be found in:
Xu, T., Sonnenthal, E. Spycher, N., and Pruess, K., 2006. TOUGHREACT — A simulation program for non-isothermal multiphase reactive geochemical transport in variably saturated geologic Media: applications for geothermal injectivity and CO2 geologic sequestration. Computers and Geosciences, 32, 145.
Zhang, G., Spycher, N., Xu, T., Sonnenthal, E., and Steefel, C. 2006, Reactive geochemical transport modelling of concentrated aqueous solutions with TOUGHREACT - supplement to TOUGHREACT users' guide for Pitzer ion-interaction model, Lawrence Berkley National Laboratory, LBNL-57873, Berkeley, California
Zhang, G., Spycher, N., Sonnenthal, E., and Steefel, C., 2008, Modeling reactive multiphase flow and transport of concentrated solutions, Journal of Nuclear Technology. 164 (2), 180-195. LBNL-60016