Flooding cation concentration

It is apparent from the table that the phase behavior of the system under discussion is much more sensitive to the multivalent cation concentration at low surfactant concentrations than at high surfactant concentrations. This means that the exact ionic composition of the brine in the surfactant bank is more critical near the end of a chemical flood than it is in the beginning. It means also that the effect of ion exchange on the phase behavior and, hence, on the oil displacing activity of the surfactant-brine-oil system becomes more pronounced as the chemical flood proceeds. 

Figure 3.7 Changes in the concentrations of cations in solution following flooding of four rice soils (Kirk et al, 2003). The corresponding changes in E, pH, HCOs, CEC and soil Fe are shown in Figures 2.6 and 2.7. Reproduced by permission of Blackwell Publishing...

There may also be effects via the concentrations of competing cations at the root surface. In studies of short-term uptake of Zn by rice from nutrient solutions containing realistic Zn " " concentrations, Giordano and Mortvedt (1974) found uptake was inhibited by various metabolic inhibitors and by Fe +, Mn +, Ca and Mg + as Cl salts at typical concentrations in flooded soil solutions. Translo-... 

One of the most important requirements that must be met is the membrane s ability to prevent excessive transfer of water from one half cell to the other. The preferential transfer of water can be a problem in the vanadium battery as one half-cell (the negative half cell in the case of cation exchange membranes) is flooded and becomes diluted, while the other becomes more concentrated, adversely affecting the overall operation of the cell. Most of the membranes show good initial water transfer properties, but their performance deteriorates with exposure to the vanadium solutions. Sukkar et al. ° evaluated various polyelectrolytes to determine whether they could improve the selectivity and stability of the membranes in the vanadium redox cell solutions. Both the cationic and anionic polyelectrolytes evaluated improved the water transfer properties of the membranes, although upon extended exposure to the vanadium electrolyte the modified membranes did not maintain their improved water transfer properties. The solvent based Nuosperse 657 modified membrane displayed exceptional properties initially but also failed to maintain its performance with extended exposure to the vanadium solutions. 

The primary reaction of alkali with reservoir water is to reduce the activity of multivalent cations such as calcium and magnesium in oilfield brines. Upon contact of the alkali with these ions, precipitates of calcium and magnesium hydroxide, carbonate, or silicate may form, depending on pH, ion concentrations, temperature, and so on. If properly located, these precipitates can cause diversion of flow within the reservoir, leading to better contact of the injected fluid with the less-permeable and/or less-flooded flow channels. This then may contribute to improved recovery. Also, this reduction of reservoir brine cation activity will lead to more surfactant activity, resulting in lower IFT values (Mayer et al., 1983). 

EQBATCH is based on the framework established by Bhuyan (1989), which has been presented elsewhere (e.g., Bhuyan et al., 1990). In EQBATCH, local thermodynamic equilibrium is assumed. It is also assumed that precipita-tion/dissolution, and cation exchange have a negligible effect on porosity and permeability. Ideal solutions are assumed so that the activity coefficients of the species are equal to unity. As a result, it is possible for activities to be replaced by their respective molar concentrations. For pure solids, activities are considered equal to unity. There are many species and reactions in alkaline flooding. 

The geochemical balance of a 103 acre watershed underlain by silicate bedrock was investigated. Base flow composition of the stream water was essentially constanty but flood flows showed a decrease in concentration of silica, bicarbonate, and sodium and an increase in sulfate, magnesium, calcium, and potassium. Laboratory experiments indicate that fresh rock or soil reacts rapidly with distilled water and achieves a composition similar to the stream water, suggesting control of water composition by reaction with the silicate minerals. The aluminosilicate minerals react with CO charged water to form kaolinite, releasing cations and silica to solution. The products of weathering are removed as particulate matter (0,28 metric tons per year) and dissolved material (1,5 metric tons per year). 

For most surfactant systems used in chemical flooding, optimal salinity for oil displacement in the presence of multivalent cations decreases as surfactant concentration decreases. One reason for conducting a chemical flood in a salinity gradient is to keep the surfactants at optimal salinity as their concentration is reduced by adsorption and dispersion during the flood. 

Multivalent cations affect phase behavior, hence, optimal salinity, more than the effect of an equal molar quantity of monovalent cations and the multivalent to monovalent cation effectiveness ratio increases with decreasing surfactant concentration. Consequently, ion exchange during a chemical flood can influence... 

It was determined from dynamic displacement experiments that alkaline flooding of acidic oils with hydroxides of certain divalent cations increased the production and recovery efficiencies above that obtained by alkaline floods with hydroxides of univalent ions with or without high electrolyte concentration. The increased efficiencies resulted from an Emulsification and Coalescence mechanism. 

Recently, Wellington and Richardson [J5] presented an interesting paper discussing the mechanism of low surfactant concentration enhanced water flood. The surfactant system consisted of alkyl-PO-EO glyceryl sulfonate with small amounts of an ethoxylated cationic surfactant to control phase behavior, interfacial activity, and surfactant loss. The surfactant systems had the ability to reduce their cloud point and interfacial tension when diluted, which was regarded as very useful for an effective flood performance. A surfactant concentration of about 0.4% removed essentially all the residual oil from sand packs in just over f PV with a surfactant loss of less than O.f PV. Mobility control by polymer was strongly required for good displacement and sweep efficiency and to reduce surfactant loss. 

Polymer Viscosity/Concentration Relationships. A polysaccharide broth [PS(B)J, a polysaccharide powder [PS(P)J, a polyacrylamide liquid [PAA(L>], and a polyacrylamide powder [PAA(P>] were evaluated for the proposed polymer flood. Polysaccharide polymers gave substantially higher solution viscosities than polyacrylamide polymers (Fig. 2). The magnitude of the difference in viscosity between the two basic polymer types was at first surprising, in view of the relatively low-salinity brines used in the study. On the other hand, each of the brines had a relatively high ratio of divalent cations to total dissolved solids (TDS). Results from the laboratory have consistently shown that such brines act as if they were high-salinity brines. 

The data on solubility of CaO and ZnO in the chloride melts permit to follow the effect of the acidic properties of the melt constituent cation on the metal oxide solubilities. The ratio of solubilities in K, Na and Lf-based melts is as follows 1 1.5 15. The total solubilities are discussed and the obtained data are distorted by contribntion of appreciable concentrations of non-dissociated oxide, which is not sensitive to the melt acidity changes. It should be emphasized that, since we do not know the ratios of the ionized fraction to the non-dissociated fraction in the melts studied, we cannot quantitatively estimate the oxoac-idic properties of these melts. The metal oxide dissociation was neglected because studies were conducted in 1923, whereas the Lux-Flood definition was formulated only in 1939. 

Cation exchange membranes. The most commonly used cation exchange membrane (CEM) is Nafion 117 (Dupont Corp., available from Ion Power, Inc.) (Fig. 5.4). The code 117 is used to distinguish the thickness of the membrane (0.019 cm) from other Nafion membrane thicknesses. This membrane was developed for use in an HFC and thus was optimized to create a stable and conductive environment for high proton concentrations (low pH) under conditions where the water content is carefully controlled. However, this material becomes completely saturated (flooded) with water in an MFC, producing a pH reflective of the solution properties (likely neutral pH). Thus, it does not function according to its intended purpose in an MFC as it cannot operate under its designed conditions. 

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