Browsing by Subject "equilibrium"
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Item Adsorption of As(V), As(III) and methyl arsenic by calcite and the impact of some groundwater species(2009-05-15) Jones, Robert GarretThe objective of this research was to investigate the retention of arsenate (iAsV), arsenite (iAsIII), monomethyl arsenate (MMAsV) and dimethyl arsenate (DMAsV) by calcite and assess the impact of dissolved Ca2+, Mg2+, phosphate and sulfate on arsenic solubility, adsorption and precipitation phenomena. Adsorption kinetics of iAsV, evaluated at a low and high concentration, was a relatively rapid process, with a fast initial reaction rate within the first few minutes and a subsequent slower reaction rate as equilibrium was approached. The relative adsorption of arsenicals decreased in the following order: iAsV > iAsIII > DMAV > MMAV. In no case was a clear adsorption maximum observed with increasing dissolved arsenic concentration. Dissolved 0.01 M Ca2+ resulted in an increase in iAsV adsorption; however, in the presence of 0.1 M Ca2+ adsorption of iAsV was decreased. The presence of Mg2+ as 0.01 M Mg(NO3)2 resulted in decreased iAsV adsorption probably the result of a lower iAsV affinity for adsorbed Mg2+ as compared to Ca2+. Phosphate and sulfate were highly competitive with iAsV in adsorption to calcite and both resulted in decreased iAsV adsorption. The total prevention of iAsV adsorption at initial equimolar arsenic/phosphate concentrations > 88 ?M each could be from the consumption of available calcite surface sites by the specific adsorption of phosphate. Equilibrium modeling, using the geochemical and mineral speciation of equilibrium model (MINTEQA2), indicated that at low concentrations of arsenate or phosphate solid-phase precipitation was not likely and adsorption processes likely controlled solubility. At high concentrations of arsenate Ca3(AsO4)2 ? 3 2/3 H2O and Ca3(AsO4)2 ? 4 1/4 H2O solid phases could be controlling arsenate solubility. This study indicates that arsenic adsorption response by calcite was different than that of phosphate suggesting that arsenic may not be specifically adsorbed to calcium at the calcite surface. Reduction and biomethylation of arsenic decreased adsorption, suggesting that processes which could affect the speciation of arsenic in the environment, could increase arsenic mobility in environmental systems where calcite and dissolved aqueous calcium play a predominant role in controlling arsenic solubility. Dissolved aqueous concentrations of magnesium, phosphate and sulfate generally reduced the ability of arsenic to be adsorbed to calcite.Item Guidelines for Optimizing Wireline Formation Testing and Downhole Fluid Analysis to Address Fault Transmissivity in the Context of Reservoir Compartment Connectivity(2011-02-22) Pfeiffer, ThomasReservoir fluids are rarely found in homogeneous structures having homogeneous properties. The various elements and processes of the petroleum system result in complex fluid distributions and compositions. A sound understanding of these complexities can avoid disappointing results and costly mistakes when designing the completion and production of the reservoir. The earlier these complexities are understood in the exploration phase, the better are the chances of a successful decision making process in the design phase of the project. Assessing reservoir compartment connectivity is of paramount importance for a optimal field development. Recent technological advances in wireline formation testing and sampling provide asset teams with a new methodology to evaluate in situ fluid properties and reservoir connectivity. After a review of the technology of downhole fluid analysis (DFA), the currently available methods of modeling equilibrated fluid gradients are presented. Fluid composition equilibrium is a stationary state where all components have reached zero mass flux. A reservoir model is designed to simulate numerically equilibration processes over geologic timescales at isothermal conditions where diffusion and gravity are the active mechanisms. A variety of initial conditions and reservoir fluid types is considered. Non-equilibrium fluid gradients and their transient behavior as they evolve towards fluid composition equilibrium are the main interest of this study. The results are compared in case studies, that are available in published literature. The modeling methods allow modeling of vertical and lateral fluid gradients. After a discussion of the cases, this thesis gives recommendations on 1) what fluid properties should be assessed and 2) how many data points are needed to reduce the chance of misinterpretation of non-equilibrium gradients in the presence of faults. To make best use DFA data, the property that exhibits the largest gradient needs to be investigated, as it yields the greatest potential to assess connectivity. The shape of the distribution of fluid composition within a compartment is found to be an important part in investigating reservoir connectivity. During data acquisition efforts should be made to acquire enough data points to reveal this shape. In combination with the presented techniques to identify non-equilibrium conditions, this will optimize DFA data acquisition and maximize the value of the data.Item Supramolecules with dimolybdenum or chiral dirhodium units(Texas A&M University, 2007-04-25) Yu, RongminThis dissertation concerns the syntheses and characterization of supramolecules with quadruply bonded Mo2 4+ units, Mo2(DAniF)3 + (DAniF = N,N'-di-p-anisylformamidinate) or cis- Mo2(DAniF)2 2+, and chiral organometallic Rh2 4+ units, including racemic cis-Rh2(C6H4PPh2)2 2+ and pure enantiomers of cis-Rh2(C6H4PPh2)2 2+. Molecular pairs of dimolybdenum units in which Mo2(DAniF)3 + units are linked by cyclic diamidate anions or dioxolene anions have been investigated. Linkers impact the electronic communication between the dimetal units in various ways. The symmetry and the energy of the frontier orbitals of the linker are among the factors which influence significantly the properties of the molecular pairs. Nature has provided us a great opportunity to study quantitatively the equilibrium between neutral supramolecules with cis-Mo2(DAniF)2 2+ units. Studies of the concentrationdependent and temperature-dependent equilibria between a molecular triangle and square as well as a molecular loop and triangle using 1H and 19F NMR spectra provide quantitative values for the thermodynamic equilibrium constant K, as well as ??????H????, and ??????S???? for the equilibria. The synthesis and characterization supramolecular compounds containing chiral cis- Rh2(C6H4PPh2)2 2+ units, including three racemic triangles and pure enantiomers of three triangles, a carceplex with T symmetry and two loops are also presented.