skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Comment on: “Upscaling geochemical reaction rates using pore-scale network modeling” by Li, Peters and Celia

Authors:
;
Publication Date:
Research Org.:
Subsurface Biogeochemical Research (SBR)
Sponsoring Org.:
USDOE Office of Science (SC), Biological and Environmental Research (BER)
OSTI Identifier:
1154174
Resource Type:
Journal Article
Resource Relation:
Journal Name: Advances in Water Resources; Journal Volume: 30; Journal Issue: 3
Country of Publication:
United States
Language:
English

Citation Formats

Peter C.,Lichtner, and Qinjun,Kang. Comment on: “Upscaling geochemical reaction rates using pore-scale network modeling” by Li, Peters and Celia. United States: N. p., 2007. Web. doi:10.1016/j.advwatres.2006.05.005.
Peter C.,Lichtner, & Qinjun,Kang. Comment on: “Upscaling geochemical reaction rates using pore-scale network modeling” by Li, Peters and Celia. United States. doi:10.1016/j.advwatres.2006.05.005.
Peter C.,Lichtner, and Qinjun,Kang. Thu . "Comment on: “Upscaling geochemical reaction rates using pore-scale network modeling” by Li, Peters and Celia". United States. doi:10.1016/j.advwatres.2006.05.005.
@article{osti_1154174,
title = {Comment on: “Upscaling geochemical reaction rates using pore-scale network modeling” by Li, Peters and Celia},
author = {Peter C.,Lichtner and Qinjun,Kang},
abstractNote = {},
doi = {10.1016/j.advwatres.2006.05.005},
journal = {Advances in Water Resources},
number = 3,
volume = 30,
place = {United States},
year = {Thu Mar 01 00:00:00 EST 2007},
month = {Thu Mar 01 00:00:00 EST 2007}
}
  • Geochemical reaction rate laws are often measured usingcrushed minerals in well-mixed laboratory systems that are designed toeliminate mass transport limitations. Such rate laws are often useddirectly in reactive transport models to predict the reaction andtransport of chemical species in consolidated porous media found insubsurface environments. Due to the inherent heterogeneities of porousmedia, such use of lab-measured rate laws may introduce errors, leadingto a need to develop methods for upscaling reaction rates. In this work,we present a methodology for using pore-scale network modeling toinvestigate scaling effects in geochemical reaction rates. The reactivetransport processes are simulated at the pore scale, accounting forheterogeneitiesmore » of both physical and mineral properties. Mass balanceprinciples are then used to calculate reaction rates at the continuumscale. To examine the scaling behavior of reaction kinetics, thesecontinuum-scale rates from the network model are compared to the ratescalculated by directly using laboratory-measured reaction rate laws andignoring pore-scale heterogeneities. In this work, this methodology isdemonstrated by upscaling anorthite and kaolinite reaction rates undersimulation conditions relevant to geological CO2 sequestration.Simulation results show that under conditions with CO2 present at highconcentrations, pore-scale concentrations of reactive species andreaction rates vary spatially by orders of magnitude, and the scalingeffect is significant. With a much smaller CO2 concentration, the scalingeffect is relatively small. These results indicate that the increasedacidity associated with geological sequestration can generate conditionsfor which proper scaling tools are yet to be developed. This workdemonstrates the use of pore-scale network modeling as a valuableresearch tool for examining upscaling of geochemical kinetics. Thepore-scale model allows the effects of pore-scale heterogeneities to beintegrated into system behavior at multiple scales, thereby identifyingimportant factors that contribute to the scaling effect.« less
  • Our paper "Upscaling geochemical reaction rates usingpore-scale network modeling" presents a novel application of pore-scalenetwork modeling to upscale mineral dissolution and precipitationreaction rates from the pore scale to the continuum scale, anddemonstrates the methodology by analyzing the scaling behavior ofanorthite and kaolinite reaction kinetics under conditions related to CO2sequestration. We conclude that under highly acidic conditions relevantto CO2 sequestration, the traditional continuum-based methodology may notcapture the spatial variation in concentrations from pore to pore, andscaling tools may be important in correctly modeling reactive transportprocesses in such systems. This work addresses the important butdifficult question of scaling mineral dissolution and precipitationreactionmore » kinetics, which is often ignored in fields such as geochemistry,water resources, and contaminant hydrology. Although scaling of physicalprocesses has been studied for almost three decades, very few studieshave examined the scaling issues related to chemical processes, despitetheir importance in governing the transport and fate of contaminants insubsurface systems.« less
  • The scale-dependence of geochemical reaction rates hinders their use in continuum scale models intended for the interpretation and prediction of chemical fate and transport in subsurface environments such as those considered for geologic sequestration of CO{sub 2}. Processes that take place at the pore scale, especially those involving mass transport limitations to reactive surfaces, may contribute to the discrepancy commonly observed between laboratory-determined and continuum-scale or field rates. Here, the dependence of mineral dissolution rates on the pore structure of the porous media is investigated by means of pore scale modeling of flow and multicomponent reactive transport. The pore scalemore » model is composed of high-performance simulation tools and algorithms for incompressible flow and conservative transport combined with a general-purpose multicomponent geochemical reaction code. The model performs direct numerical simulation of reactive transport based on an operator-splitting approach to coupling transport and reactions. The approach is validated with a Poiseuille flow single-pore experiment and verified with an equivalent 1-D continuum-scale model of a capillary tube packed with calcite spheres. Using the case of calcite dissolution as an example, the high-resolution model is used to demonstrate that nonuniformity in the flow field at the pore scale has the effect of decreasing the overall reactivity of the system, even when systems with identical reactive surface area are considered. The effect becomes more pronounced as the heterogeneity of the reactive grain packing increases, particularly where the flow slows sufficiently such that the solution approaches equilibrium locally and the average rate becomes transport-limited.« less
  • The scale-dependence of geochemical reaction rates hinders their use in continuum scale models intended for the interpretation and prediction of chemical fate and transport in subsurface environments such as those considered for geologic sequestration of CO 2. Processes that take place at the pore scale, especially those involving mass transport limitations to reactive surfaces, may contribute to the discrepancy commonly observed between laboratory-determined and continuum-scale or field rates. In this study we investigate the dependence of mineral dissolution rates on the pore structure of the porous media by means of pore scale modeling of flow and multicomponent reactive transport. Themore » pore scale model is composed of high-performance simulation tools and algorithms for incompressible flow and conservative transport combined with a general-purpose multicomponent geochemical reaction code. The model performs direct numerical simulation of reactive transport based on an operator-splitting approach to coupling transport and reactions. The approach is validated with a Poiseuille flow single-pore experiment and verified with an equivalent 1-D continuum-scale model of a capillary tube packed with calcite spheres. Using the case of calcite dissolution as an example, the high-resolution model is used to demonstrate that nonuniformity in the flow field at the pore scale has the effect of decreasing the overall reactivity of the system, even when systems with identical reactive surface area are considered. In conclusion, the effect becomes more pronounced as the heterogeneity of the reactive grain packing increases, particularly where the flow slows sufficiently such that the solution approaches equilibrium locally and the average rate becomes transport-limited.« less