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2002 Conference Proceedings

Numerical Investigations of Multifluid Hydrodynamics During Injection of Supercritical CO2 into Porous Media

M. D. White1 and B. P. McGrail2

1Hydrology Group, Pacific Northwest National Laboratory, Richland, WA
2Applied Geology and Geochemistry Group, Pacific Northwest National Laboratory, Richland, WA

Proceedings of GHGT-6, Sixth International Conference on Greenhouse Gas Control Technologies, Kyoto, Japan.

Abstract

Design and risk assessment of field-scale systems for injecting supercritical CO2 into deep saline aquifers demands numerical simulation of the multifluid injection process to capture the displacement of the brine with CO2, dissolution of CO2 into the brine, Rayleigh convection of the brine with CO2 dissolution, and nonisothermal effects. Critical factors for assessing the technical viability of particular injection design and sequestration reservoir include CO2 dissolution rates into the brine, spreading rates for the supercritical- CO2 bubble, chemical reactions between CO2-brine and the aquifer minerals, cap rock integrity and seismicity potential with changes in the effective stress. Applying numerical simulation techniques to the understanding of field-scale applications much simpler than those proposed for deep formation sequestration of CO2, is often complicated by uncertainties in hydrologic parameters and geologic features. Although geologic sequestration in deep aquifers offers promise for reducing emissions of anthropogenic CO2, the analytical tools used to evaluate these coupled engineered and hydrogeologic systems must provide a realistic representation of the physical and chemical processes. Assessing a numerical simulator's ability to model the complex and coupled processes of injecting supercritical CO2 into saline aquifers benefits from having controlled hydrogeologic conditions. Numerical simulations are presented of supercritical CO2 injection experiments into idealized porous media (e.g., glass beads and quartz sands) and compared against laboratory measurements for a similar system. Capabilities for solving the nonlinear conservation equations for three mass constituents (i.e., water, NaCl salt, and CO2) and thermal energy have been incorporated into multifluid subsurface flow and transport simulator. Chemical reactions with the aquifer minerals and mechanical stress effects on the porous media are ignored. The emphases of this validation exercise are the hydrodynamics of multifluid flow in porous media, buoyancy driven convection of the brine, the representation of thermophysical properties of sub- and supercritical CO2 and dissolved CO2 in aqueous saline solutions, and numerical algorithms for handling phase appearances and disappearances.

Estimating hydraulic parameters of heterogeneous soil at the Hanford site using a parameter-scaling concept

Z.F. Zhang, A.L. Ward, G.W. Gee
Pacific Northwest National Laboratory, Richland, WA

Proceedings of the 2002 SSSA Annual Meeting, Denver, CO

Abstract

Determination of the soil hydraulic parameters of heterogeneous soils remains a challenge since inverting for too many parameters can lead to the non-uniqueness of parameter values. In this research, the parameter-scaling method of Zhang et al. (2002) was used to reduce the number of parameters to be estimated at field scale. The heterogeneous soil is classified into different texture units. The scaling factor is defined as the ratio of a parameter of a texture unit to the corresponding parameter of the reference texture. It is assumed that the scaling factor associated with each parameter is invariant over observation scales. Parameter-scaling factors are determined using local-scale parameter values. By assigning scaling factors to the corresponding soil textures in the field, the reference hydraulic parameter values at the field scale can be estimated through inverse modeling of field experiments. The parameter-scaling method was tested by inverting field injection experiments in three-dimensional heterogeneous soil at the Hanford site. The results show that simulation errors were significantly reduced after applying parameter scaling and inverse modeling.

A parameter scaling concept for estimating field-scale hydraulic functions of layered soils

Z.F. Zhang, A.L. Ward, G.W. Gee
Pacific Northwest National Laboratory, Richland, WA

Proceedings of the International Groundwater Symposium, Berkely, CA (2002).

Abstract

Predicting flow and transport in unsaturated porous media is often hampered by insufficient and uncertain constitutive property information. Some studies have used inverse flow modeling for parameter estimation to overcome these limitations. However, determination of the soil hydraulic parameters of layered soils remains a challenge since inverting for too many parameters can lead to the non-uniqueness of parameter values. Here we propose a parameter scaling method that reduces the number of parameters to be estimated. Parameter scaling factors are determined using local-scale parameter values. By assigning scaling factors to the corresponding soil textures in the field, the reference hydraulic parameter values at the field scale can be estimated through inverse modeling of well-designed field experiments. Parameters for individual textures are then obtained through inverse scaling of the reference values using a priori relationships between reference parameter values and the specific values for each texture. The proposed method was tested using two infiltration-drainage experiments in layered soils. The numerical simulator, STOMP, was combined with the inverse modeling program, UCODE, to estimate the hydraulic parameters. The results show that the simulation errors were significantly reduced after applying parameter scaling and inverse modeling. When compared to the use of local-scale parameters, parameter scaling reduced the sum of squared weighted residue by 93-96%.

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