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GRAND CHALLENGE: COMPUTATIONAL THERMODYNAMICS OF COMPLEX FLUIDS AND SOLIDSEssential data collection for Equation of State (EOS) developmentIn applications to real-world problems, EOS formulations must be parameterized fromhighly accurate data sets for fluid mixtures over a range of pressures, temperatures andcompositions (P-T-X) that are as close to the intended application as possible. It issurprising that even for common systems (e.g., CO 2 -H 2 O-CH 4 , Al 3+ -H + -H 2 O-salt),sufficient data do not exist to parameterize a model. In fact for the aluminum system (themost abundant metal in the earth) there is insufficient information to even uniquelydefine the aqueous solute species and their activities for temperatures from ambient tocritical temperatures of water. Yet the aluminum system is one of the most complete datasets. There are fewer data for other charged systems, such as Fe 3+ and UO 2+ 2 , that areencountered in applications such as carbon sequestration and nuclear waste isolation.Solid mineral stability data are also not available for essential systems. For thesematerials the likely future contribution of modeling methods (simulations) will be toidentify the speciation in solution. This is an essential step in the development of an EOSthat succinctly reproduces the behavior of the system and can be parameterized from thelimited data that are likely to be available. A short list of essential data needs includes:• Equation of State and thermodynamic mixing properties of the system CO 2 -H 2 O-CH 4over a wide P and T range• Thermodynamics of gas hydrates, with the possible exception of methane hydratewhose properties are reasonably well known• Properties of two phase mixtures of aqueous brines and high CO 2 gas phases,including densities, over a wide P-T-X range• Solubility of minerals in aqueous electrolytes and nonaqueous mixtures withemphasis on expanding the database for the modeling of aluminum silicate minerals(feldspars, zeolites, etc.) for a range of temperatures up to 300 ° C and for importantspecies encountered in natural and anthropogenically altered waters (SO 2- 4 , F - , etc.)• Descriptions (including theoretical equations) of activities in concentrated multicomponentsalt solutions over a wide P-T-X range• Thermodynamics of major component solid solution mineral phases, including thosesuch as carbonates, in which order-disorder phenomena are important• Thermodynamics of clays and zeolites, including their ion exchange properties• Thermodynamics of incorporation of minor and trace elements (including actinides)into mineral solid solutions• Thermodynamics of mineral phases with ions of variable valence, including iron• Thermodynamics of corrosion products of nuclear fuel, including U(VI) phasesThe fact that most of these are old problems does not make their solution less necessary.There are opportunities here for the interaction of modern experimental andcomputational approaches, and there is a need for complete and easily accessibledatabases.For some systems (e.g., CO 2 , H 2 O, O 2 , N 2 , CH 4 ) it should be possible to developmolecular dynamics models that can calculate phase equilibrium and thermophysicalproperties from first principles. For these systems it would be worthwhile to pursue thedevelopment of very high accuracy interaction models at the molecular level (i.e., forCO 2 -H 2 O, CO 2 -CH 4 interactions). These could then be used to simulate thermodynamicsfor these systems via molecular dynamics and Monte Carlo methods. While this is not adifficult simulation per se, the magnitude of the problem grows quickly when desiredresults are thermodynamic data, especially free energy data. The scaling of present daysimulation algorithms is not good, and it is important to develop highly scalablealgorithms, including those that directly simulate free energy, for implementation onfuture generation computers.74 Basic Research Needs for Geosciences: Facilitating 21 st Century Energy Systems
GRAND CHALLENGE: COMPUTATIONAL THERMODYNAMICS OF COMPLEX FLUIDS AND SOLIDSCourtesy of John Weare, UC San DiegoFigure 26. Pressure-composition predictions of EOS for the CO 2 -H 2 O system. Curves represent EOS predictionsand symbols represent experimental data.EOS for compressible mixtures. For these systems the most convenient variables are usually thetemperature, volume (or density), and the composition. The appropriate thermodynamic functionon which to base an EOS is then the molar Helmholtz free energy. All other properties, e.g., theenthalpy, may be derived from this function by the appropriate derivatives. To provide optimalinterpolation and extrapolation of mixing properties, the functional form of the free energyshould be based on a reasonably accurate molecular-level description of the system. Thethermodynamic perturbation theory originally introduced by Pople (1954) provides a frameworkfrom which such an EOS may be generated (see Gubbins 1985 for a review). To provide the highlevel of accuracy necessary for quantitative description of thermodynamic data, empiricalcorrections must usually be added to the EOS. This level of the theory was successfully appliedto the qualitative analysis of polar fluids and has been used to treat polar systems including thosecontaining associated ions. An example of the accuracy that can be obtained from such anapproach is given in Figure 26 (Weare, unpublished results based on the EOS of Duan et al.1992). Note the poor behavior of the EOS in the critical region. Special scaling methods must bedeveloped to treat this region (Kiselev and Friend 1999). The development of these methods willbe required for application to complex speciation in mixtures.EOS for liquid density complex mixtures of aqueous electrolyte solutions and mixtures with othernonaqueous solutions. For nearly incompressible aqueous mixtures, highly accurate EOS areavailable provided the mixing behavior of the system can be described (Pitzer 1987; Weare1987; Christov and Moller 2004). Examples of the results of these models for complex mixturesare illustrated in Figure 27.Basic Research Needs for Geosciences: Facilitating 21 st Century Energy Systems 75
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TABLE OF CONTENTSBasic Science Chal
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TABLE OF CONTENTSTechnology Impacts
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EXECUTIVE SUMMARYpurpose of linking
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INTRODUCTIONINTRODUCTIONWorldwide e
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INTRODUCTIONway into the rock forma
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PANEL REPORTSMULTIPHASE FLUID TRANS
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PANEL REPORT: MULTIPHASE FLUID TRAN
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Page 122 and 123: PRIORITY RESEARCH DIRECTION:MINERAL
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PRIORITY RESEARCH DIRECTION:DYNAMIC
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PRIORITY RESEARCH DIRECTION: TRANSP
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PRIORITY RESEARCH DIRECTION:FLUID-I
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PRIORITY RESEARCH DIRECTION:BIOGEOC
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CROSSCUTTING ISSUE:THE MICROSOPIC B
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CROSSCUTTING ISSUE:THE MICROSOPIC B
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CROSSCUTTING ISSUE:HIGHLY REACTIVE
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CROSSCUTTING ISSUE:THERMODYNAMICS O
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CROSSCUTTING ISSUE:THERMODYNAMICS O
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REFERENCESBenner, S.G., Hansel, C.M
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REFERENCESChen, J., Hubbard, S., Pe
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REFERENCESEnnis-King, J., Preston,
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REFERENCESHolman, H.-Y., Perry, D.L
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REFERENCESLi, L., and Tchelepi, H.A
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REFERENCESNeal, A.L., Techkarnjanar
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REFERENCESReeves, P.C., and Celia,
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REFERENCESSteefel, C.I., DePaolo, D
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REFERENCESZachara, J.M., Ainsworth,
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AppendicesBasic Research Needs for
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APPENDIX 1: TECHNICAL PERSPECTIVES
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APPENDIX 2: WORKSHOP PROGRAMThursda
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APPENDIX 4: ACRONYMS AND ABBREVIATI
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