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Berlin Brandenburg

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  • 1
    In: Water Resources Research, February 2011, Vol.47(2), pp.n/a-n/a
    Description: Anhydrous MgSO is considered as a potential sealing material for the isolation of high‐level‐waste repositories in salt rock. When an aqueous solution, usually a brine type, penetrates the sealing, different MgSO hydrates along with other mineral phases form, removing free water from the solution. The uptake of water leads to an overall increase of solid phase volume. If deformation is constrained, the pore volume decreases and permeability is reduced. In order to simulate such processes, especially for conditions without free water, a coupling between OpenGeoSys and thermodynamic equilibrium calculations were implemented on the basis of the commercially available thermodynamic simulator ChemApp and the object‐oriented programming finite‐element method simulator OpenGeoSys. ChemApp uses the Gibbs energy minimization approach for the geochemical reaction simulation. Based on this method, the thermodynamic equilibrium of geochemical reactions can be calculated by giving the amount of each system component and the molar Gibbs energy of formation for all the possible phases and phase constituents. Activity coefficients in high‐saline solutions were calculated using the Pitzer formalism. This model has the potential to handle 1‐D, 2‐D, and 3‐D saturated and nonsaturated thermo‐hydro‐chemical coupled processes even with highly saline solutions under complex conditions. The model was verified by numerical comparison with other simulators and applied for the modeling of SVV experimental data.
    Keywords: Reactive Transport ; Gibbs Energy Minimization ; Saline ; Svv ; Hlw
    ISSN: 0043-1397
    E-ISSN: 1944-7973
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  • 2
    In: Journal of Geophysical Research: Solid Earth, July 2018, Vol.123(7), pp.5609-5627
    Description: This work focuses on the interaction between pressure solution creep and contact area expansion under hydrothermal conditions and proposes an innovative process‐based approach for describing contact area expansion by fracture closure. The formulation is established in the physical context of pressure solution creep and represents the dynamic process of enhanced mineral dissolution over grain contacts, which moves toward equilibrium as a result of decrease of mineral solubility by pressure drop. Then, a theoretical maximum of the contact area ratio is obtained from the formulation whose existence demonstrates that pressure solution is with an energy threshold for activation rather than spontaneously taking place under any circumstances. Based upon the formulation, a 1‐D reactive transport model is developed and applied to investigate dissolution‐induced permeability evolution of a granite fracture under crustal conditions. The applicability of the developed model to a polymineralic system is examined against the experimental measurements reported in Yasuhara et al. (2011, ). This investigation reconfirms the significance of pressure solution creep in fracture permeability evolution under low and moderate temperatures and provides a justified interpretation for the unusual experimental observation that fracture permeability reduction does not necessarily lead to apparent increases of effluent element concentrations. The surface topography of fracture channels markedly affects hydraulic feedback on chemical compaction in terms of both magnitude and rate of change. Temperature elevation contributes to accelerating the progression of pressure solution creep. An innovative process‐based approach is proposed for describing contact area expansion by fracture closure The established formulation represents the dynamic process of mineral dissolution at grain contacts in response to pressure drop Pressure solution has a minimum energy requirement for activation rather than spontaneously taking place under any circumstances
    Keywords: Fracture Permeability Evolution ; Pressure Solution Creep ; Contact Area Expansion ; Water‐Granite Interactions ; Reactive Transport Modeling ; Opengeosys
    ISSN: 2169-9313
    E-ISSN: 2169-9356
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  • 3
    In: Water Resources Research, January 2006, Vol.42(1), pp.n/a-n/a
    Description: The principal idea of this paper is to simulate and evaluate the determination of first‐order degradation rate constants at heterogeneous contaminated sites under realistic conditions. First, a set of heterogeneous and contaminated synthetic aquifers is generated; second, the spreading of a solute plume subject to first‐order degradation is simulated. Third, this plume is investigated using “monitoring wells” placed along the presumed plume center line. Using only piezometric heads, concentrations and hydraulic conductivities obtained at these monitoring wells, first‐order degradation rate constants are calculated by methods typically used in field applications. The estimated rate constants are compared to the “real” value known from the simulations. This comparison is conducted for different degrees of heterogeneity, represented by lognormally distributed random conductivity fields. The results indicate that, with increasing degree of heterogeneity, “measured” degradation rate constants become uncertain with a high variability around the true constant. Measured rate constants tend to overestimate the true constant by up to one order of magnitude. A sensitivity analysis of the influences of source width, transport velocity, and dispersivity shows that (1) with increasing source width, measured rate constants decrease their relative error and increase their accuracy; (2) the choice of dispersivity can produce both over‐ and under‐estimation of the true rate constant; and (3) that large‐scale measurements of hydraulic conductivity yield better estimates of flow velocities as compared to local scale measurements. These results explain in part the high variability of field measured degradation rate constants reported in the literature.
    Keywords: Center Line Method ; Numerical Modeling ; Heterogeneity ; First‐Order Degradation ; Degradation Rate Estimation
    ISSN: 0043-1397
    E-ISSN: 1944-7973
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  • 4
    In: Water Resources Research, June 2002, Vol.38(6), pp.5-1-5-11
    Description: A combined experimental and numerical analysis is used to examine the movement and interaction of saltwater and freshwater in unconfined porous media. Particular emphasis is placed on flow phenomena in the partially saturated region above the water table and along the interface between the saturated and partially saturated regions. While some numerical models are apparently capable of simulating these phenomena, there is still a significant lack of experimental data with which to verify the models. Here a series of laboratory‐scale experiments is considered to evaluate density‐dependent, saltwater‐freshwater flow patterns in both the saturated and partially saturated zones. The laboratory experiments demonstrate clearly that significant lateral flows and coupled density‐driven flow effects may take place in the partially saturated region above the water table and at the interface between the saturated and partially saturated zones. In parallel, a finite element numerical model is developed. The model reproduces effectively the observed flow behaviors; the quality of the results suggests that the numerical model has the capacity to provide realistic predictions.
    Keywords: General ; Water Resources and Supplies;
    ISSN: 0043-1397
    E-ISSN: 1944-7973
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