Victor N. Balashov

Electrical conductances of aqueous Na2SO4, H2SO4, and their mixtures : Limiting equivalent ion conductances, dissociation constants, and speciation to 673 K and 28 MPa

The electrical conductivities of aqueous solutions of Na(2)SO(4), H(2)SO(4), and their mixtures have been measured at 373-673 K at 12-28 MPa in dilute solutions for molalities up to 10(-2) mol kg(-1). These conductivities have been fit to the conductance equation of Turq et al.(1) with a consensus mixing rule and mean spherical approximation activity coefficients. Provided the concentration is not too high, all of the data can be fitted by a solution model that includes ion association to form NaSO(4)(-), Na(2)SO(4)(0), HSO(4)(-), H(2)SO(4)(0), and NaHSO(4)(0). The adjustable parameters of this model are the dissociation constants of the SO(4)(-) species and the H(+), SO(4)(-2), and HSO(4)(-) conductances (ion mobilities) at infinite dilution. For the 673 K and 230 kg m(-3) state point with the lowest dielectric constant, epsilon = 3.5, where the Coulomb interactions are the strongest, this model does not fit the experimental data above a solution molality of 0.016. Including the species H(9)(SO(4))(5)(-) gave satisfactory fits to the conductance data at the higher concentrations.

A model describing flowback chemistry changes with time after Marcellus Shale hydraulic fracturing

Between 2005 and 2014 in Pennsylvania, about 4000 Marcellus wells were drilled horizontally and hydraulically fractured for natural gas. During the flowback period after hydrofracturing, 2 to (7 to ) of brine returned to the surface from each horizontal well. This Na-Ca-Cl brine also contains minor radioactive elements, organic compounds, and metals such as Ba and Sr, and cannot by law be discharged untreated into surface waters. The salts increase in concentration to () in later flowback. To develop economic methods of brine disposal, the provenance of brine salts must be understood. Flowback volume generally corresponds to ∼10% to 20% of the injected water. Apparently, the remaining water imbibes into the shale. A mass balance calculation can explain all the salt in the flowback if 2% by volume of the shale initially contains water as capillary-bound or free Appalachian brine. In that case, only 0.1%–0.2% of the brine salt in the shale accessed by one well need be mobilized. Changing salt concentration in flowback can be explained using a model that describes diffusion of salt from brine into millimeter-wide hydrofractures spaced 1 per m (0.3 per ft) that are initially filled by dilute injection water. Although the production lifetimes of Marcellus wells remain unknown, the model predicts that brines will be produced and reach 80% of concentration of initial brines after ∼1 yr. Better understanding of this diffusion could (1) provide better long-term planning for brine disposal; and (2) constrain how the hydrofractures interact with the low-permeability shale matrix.

Fe-Modified, Pt-Based Cathodic Electrocatalysts for Oxygen Reduction Reaction with Enhanced Methanol Tolerance

Iron-modified carbon-supported platinum electrocatalysts were synthesized by the Bonnemann colloidal method. Physical characterization by the methods of Brunauer-Emmett-Teller, transmission electron microscopy, and X-ray diffraction measurements were conducted to explore the catalyst surface area and particle size, particle distribution, degree of metal alloy, and phase structure. Electrochemical measurements were carried out to characterize the catalyst oxygen reduction reaction (ORR) activity under the condition of with and without methanol present. The catalyst performance was evaluated by rotating disk electrode sweep voltammetry and cyclic voltammetry techniques. The PtFe catalysts showed enhanced methanol tolerance and catalytic activity compared to Pt catalyst. The PtFe catalysts with atomic compositions of Pt/Fe = 9:1 and Pt/Fe =1:1 showed more enhanced methanol tolerance and catalytic activity than the Pt/Fe =3:1.

Metasomatic zoning: Appearance of ghost zones in the limit of pure advective mass transport

Abstract The properties of mineral reaction zones which propagate without changing shape are investigated for a hypothetical two-component system involving advective and diffusive transport in a porous medium. Given sufficient time the width of such zones, referred to as ghost zones, is constant and proportional to the characteristic diffusion or dispersion length of the system. The proportionality factor depends only on the equilibrium constants of the reacting minerals and on the composition of the inlet fluid. As the fluid velocity increases the width of the ghost zone decreases in the case of diffusive transport, and remains constant for dispersive transport for a dispersion coefficient proportional to the fluid velocity. This behavior is contrary to that of normal reaction zones which increase in width in proportion to the fluid velocity. For pure advective transport under conditions of local chemical equilibrium, a ghost zone has zero width. Nevertheless, minerals contained in the ghost zone buffer the downstream fluid composition in spite of their material absence, whence the term ghost . By taking into account transport by diffusion or dispersion, the width of a ghost zone has a finite, non-zero value with a well-defined modal composition. In a surface controlled representation of mineral reaction rates for pure advective transport, the width of the ghost zone is finite, but tends towards zero as the kinetic rate constant approaches infinity.

Metamorphism of Marbles: Role of Feedbacks between Reaction, Fluid Flow, Pore Pressure and Creep

In many applications of chemical transport modelling to geological problems, it is very important to take into account the changes to the transport properties of the porous medium that will result from chemical reactions driven by the component fluxes which are being modelled. This is particularly true where the reactions involve breakdowr of carbonate minerals, because they produce very large changes in solid volume, but there are many other fluid-rock reactions, involving both precipitation and dissolution, that are capable of perturbing the pattern of flow that originally triggered the reaction. This paper is concerned with the growth of calc-silicate minerals replacing marbles in metamorphism, which we model through the simplest possible metamorphic reaction:

Modeling metamorphic fluid flow with reaction-compaction-permeability feedbacks

Cal + Qtz \rightleftharpoons Wo + C{O_2}

Predictive modeling of CO2 sequestration in deep saline sandstone reservoirs: Impacts of geochemical kinetics

(17.1) However, our approach is equally appliable a wide range of skarn-forming reactions.