Basic Research Needs for Geosciences - Energetics Meetings and ...

CROSSCUTTING ISSUE:HIGHLY REACTIVE SUBSURFACE MATERIALS AND ENVIRONMENTSas well as phase separation and critical phenomena. In addition, isotope effects in the C-O-H-N-Ssystem will be a useful probe for investigating intermolecular forces, as well as the motion ofmolecules in condensed phases. Accordingly, experimental, theoretical, and simulation studieson the isotope effects (liquid/solid-vapor fractionation, pressure effects) are needed to understandthe fundamental behavior of fluid species in the C-O-H-N-S system and to better use isotopes astracers of subsurface fluid processes.Studies are required that measure and assess rates of dissolution-precipitation in time-serieswhere the controlling parameters (T, P and fluid composition) are varied in such a way as topromote reaction—i.e., at conditions both close to and far from equilibrium. In particular, novelapproaches such as H + relaxation can be used to quantify near-equilibrium rates for key pHdependent dissolution-precipitation reactions (Bénézeth et al. 2007). Novel chemical imaging(e.g., Secondary Ion Mass Spectrometry, SIMS) and characterization tools (e.g., ICP-MS) areavailable to assess not only the chemical and isotopic signals resulting from mineraltransformations, but also chemical and isotopic communication (e.g., 18 O, D, 13 C, 41 K, 26 Mg)between fluid species and mineral surfaces from the nano to pore scales. Neutron and X-rayscattering methods are particularly well suited for interrogating the structural features of startingminerals, reaction products, the reaction zone, and the reaction interface as complements to thechemical interrogation of mineral-fluid systems. These analytical techniques will providecrucially important information on the structural and dynamic properties of the fluids confinedwithin micropores. In particular, the penetrating capability of neutrons, and their high sensitivityto hydrogen isotopes, will be useful in tracking the mobility of water and other H-bearing speciesduring reactions. Quantifying structural and chemical patterns at the reactive interface can alsoutilize advanced microscopy techniques such as Atomic Force Microscopy (AFM) and HighResolution Transmission Electron Microscopy (HRTEM). Most importantly, studies of specificmineral suites from natural systems (e.g., sedimentary basins and geothermal resource areas) thatexhibit micro- to macroscale reaction features analogous to those produced at the bench scalewill complement and verify results from laboratory-based investigations.SCIENTIFIC IMPACTSA comprehensive and technically rigorous understanding of the volumetric properties andenergetics of C-O-H-N-S fluids is needed to correctly interpret fluid-solid interactions relevant tokey sequestration scenarios. Previous PVT and activity-composition studies of mixed-volatilefluids containing H 2 O-CO 2 -CH 4 -N 2 -H 2 coupled (Anovitz et al. 1998; Blencoe et al. 1996, 1999,2001, Seitz and Blencoe, 1999; Seitz et al. 1996) with Equations of State (EOS) modeling(Blencoe 2004) has demonstrated that departure from ideal mixing can be profound, particularlyat near-critical conditions. While theoretically robust EOS have been developed to representexperimental results, a molecular-level understanding of complex fluid behavior is lacking,which in turn severely limits the predictive capability needed to model fluid behavior insubsurface geochemical environments. Additionally, it is becoming increasingly clear thatorganic molecules in aqueous and mixed-volatile fluids—ranging from simple hydrocarbons andcarboxylic acids to branched and cyclic compounds, to proteins and humic substances—may alsoplay a major role in controlling deviations for ideality.Despite the utility of the equilibrium approach in quantifying the elemental and isotopic behaviorin mineral-fluid systems, there is mounting evidence that chemical (and isotopic) heterogeneity162 Basic Research Needs for Geosciences: Facilitating 21 st Century Energy Systems