Upscaling geochemical reaction rates using pore-scale networkmodeling
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 forheterogeneities 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.
- Research Organization:
- Ernest Orlando Lawrence Berkeley NationalLaboratory, Berkeley, CA (US)
- Sponsoring Organization:
- USDOE Director, Office of Science
- DOE Contract Number:
- AC02-05CH11231
- OSTI ID:
- 902804
- Report Number(s):
- LBNL--61972; BnR: YN0100000
- Journal Information:
- Advances in Water Resources, Journal Name: Advances in Water Resources Journal Issue: 9 Vol. 29
- Country of Publication:
- United States
- Language:
- English
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