HR: 11:05h
AN: B32B-04    [Abstracts]
TI: Scaling of geochemical reaction kinetics in heterogeneous porous media using pore-scale network modeling AU: * Li, L
EM: lili@lbl.gov
AF: Lawrence Berkeley national lab, 1 cyclotron road, Berkeley, CA 94720 United States
AU: * Li, L
EM: lili@lbl.gov
AF: Princeton University, Dept. Civil and Eniron. Engin., Princeton University, Princeton, NJ 08540 United States
AU: Peters, C
EM: cap@princeton.edu
AF: Princeton University, Dept. Civil and Eniron. Engin., Princeton University, Princeton, NJ 08540 United States
AU: Celia, M
EM: celia@princeton.edu
AF: Princeton University, Dept. Civil and Eniron. Engin., Princeton University, Princeton, NJ 08540 United States
AB: Geochemical reaction rate laws are often measured using crushed minerals in well-mixed laboratory systems that are designed to eliminate mass transport limitations. Such rate laws are often used directly in reactive transport models to predict the fate of chemical species in natural porous media. Due to the inherent heterogeneities of natural porous media, such use of lab-measured rate laws may introduce errors. In this work, we use network models to examine the effects of pore-scale heterogeneities on continuum-scale rates of anorthite and kaolinite reactions, and identify conditions under which the effects of pore-scale heterogeneities are significant in reaction rate up-scaling. The network is constructed to represent consolidated sandstone, with various percentage of reactive minerals (anorthite and kaolinite) distributed in reactive pore clusters according to prescribed configurations. The reaction rates computed from the network model account for heterogeneities of both physical and mineral properties. These rates are compared with those from a continuum model, which calculate reaction rates by directly using spatially-averaged concentrations in lab-measured reaction rate laws. Simulation results show that aqueous concentrations at the pore scale vary by orders of magnitude. These concentration heterogeneities lead to significant spatial variations in pore-scale reaction rates. As a result, the continuum-scale rates from the network model are significantly different from those from the continuum model. The scaling effects are influenced by spatial distributions of reactive minerals, as well as their relative abundance. With relatively small percentages of reactive minerals, the effect of their spatial distribution is significant. Spatial distributions of reactive clusters that enhance pore-to-pore mass transport, such as small clusters, lead to smaller variations in pore-scale concentrations and reaction rates, and are better represented by lab-measured reaction rate laws. The scaling effect decreases with increasing percentage of reactive minerals. The scaling effects are also affected by hydrodynamic conditions. These results provide guidelines for the conditions under which scaling effects are significant in determining mineral reaction rates in heterogeneous porous media.
DE: 1099 General or miscellaneous
SC: Biogeosciences [B]
MN: Fall Meeting 2005