Future Work

1. H51C-0911 Reactive Transport Modeling of Induced Calcite Precipitation Fronts in Porous Media Using a Parallel, Fully Coupled, Fully Implicit Approach LuanjingGuo*, Hai Huang, Derek Gaston, Don Fox, George Redden and Yoshiko Fujita Idaho National Laboratory; * luanjing.guo@inl.gov, P.O. Box 1625, Idaho Falls, ID 83415-2107 Summary Background Continuum Scale Modeling • Simulations are carried out at continuum scale for future integrated studies with field-scale applications as well as laboratory flow cell experiments. • A fully coupled fully implicit simulator, RAT, is applied with massively parallel computing and state-of-art linear and nonlinear solvers. • A parallel, fully coupled fully implicit reactive transport simulator (RAT) was developed at INL for tightly coupled reactive transport systems. • RAT was applied to simulate, at a continuum-scale, a system of induced calcium carbonate mineral precipitation where reactants are injected sequentially into a 2-D heterogeneous porous medium. • The model simulated the formation of the solid phase as the two reactants mixed and exceeded mineral saturation, and dissolution behind the mixing front when the mixture was undersaturated with respect to the mineral. • Inducing mineral precipitation is a potential strategy for immobilizing metal or radioactive contaminants in the subsurface [1]. Multiple fundamental processes are involved in this strategy, including fluid flow, transport of reactants, biogeochemical reactions and changes in media properties. Numerical modeling is used to investigate the complex nonlinear coupling effects among these processes. Conventionally, a de-coupled solution approach has been used that solves the transport and reaction equations sequentially; however, such an approach has limited applicability to engineered biogeochemical systems where induced chemical conditions are far from equilibrium and processes such as reaction and media property changes are strongly coupled. A parallel, fully coupled, fully implicit simulator (named RAT for ReActive Transport) was developed based on the massively parallel computing framework Multiphysics Object-Oriented Simulation Environment (MOOSE) [2] at Idaho National Lab (INL), and applied to simulating calcium carbonate precipitation induced by sequential injection of calcium and carbonate into a heterogeneous porous medium (Figure 1). Governing Equations in RAT Model Implementation Table 1 Reaction network considered for the calcite precipitation system (equilibrium constants are 10-based logarithm values [3] ) Figure 2. Simulation results for transport of tracer in the heterogeneous medium. Future Work Figure 3. Natural logarithm of K distribution and its histogram that satisfies a normal distribution of N(-11.3, 1.0) generated by Geostatistical Software Library. • Modifying the current model and applying it to the ongoing experimental work at INL in a fracture cell with heterogeneous aperture sizes. • Enhancing the model by implementing different relationships between precipitation and media property changes in different flow and reaction regimes. Aqueous equilibrium and kinetic species and solid phase kinetic species are substituted into the transport equations for primary species, thus solving this set of governing equations in RAT is modeling reactive transport with a fully coupled approach. Reference Fujita, Y., et al. (2004), Strontium incorporation into calcite generated by bacterial ureolysis.Geochimica Et CosmochimicaActa, 68(15): p. 3261-3270. D. Gaston, et al. (2009) , MOOSE: A parallel computational framework for coupled systems of nonlinear equations, Nucl. Engrg. Design, 239: 1768–1778. T. Wolery (1992), EQ3/6, a software package for geochemical modeling of aqueous systems: Package overview and installation guide (version 7.0), Tech. Rep. UCRL-MA-110662 PT I, Lawrence Livermore National Laboratory. Simulation Results Figure 4. Simulation results for transport of tracer in the heterogeneous medium. T=4.0 s T=30.0 s T=4.0 s T=40.0 s Figure 5. Simulation results of spatial and temporal distribution for calcium carbonate mineral precipitation and dissolution. T=80.0 s T=120.0 s T=90.0 s T=120.0 s Acknowledgments This research is supported by the Subsurface Biogeochemical Research Program, U.S. Department of Energy,under contract DE-AC07-05ID14517. CO32- Ca2+ Figure 1 Calcium and carbonate containing solutions are mixing and reacting via sequential injection in a 2-D heterogeneous medium (or simulated fracture) composed of textured glass plates stacked to create a variable aperture field. • In this synthetic study, hydraulic conductivity values range over 3 orders of magnitude, corresponding to materials of silt/fine sand and medium sand. • Preliminary simulations of tracer transport exhibit fingering concentration edges in an advection-dominated transport regime, and the fingering phenomenon becomes more prominent as the front moves forward. • In precipitation simulations, the formation of precipitation takes place within a mixing zone between the two reactant solutions. As the reaction front moves forward, dissolution occurs as the saturation index falls below 0. For the conditions tested, no porosity/permeability changes are observed due to the small amount of solid formed.