At high salinities

Cross-linked xanthan gums have also been used to reduce the permeabiUty of thief 2ones. Trivalent chromium is the preferred cross-linker (54). Cross-linker effectiveness is less at high salinity. However, Cr(III) has been used ia the field at salinities as great as 166,000 ppm total dissolved soHds (55). 

Atchafalaya and Mississippi Rivers. Florida Bay waters, which overlie U-rich sediments, contain much higher ( Ra/ " Ra) activity ratios than other estuaries. The increased ( Ra/ " Ra) values observed at high salinities in the Mississippi/Atchafalaya systems indicate preferential decay of the shorter-lived ""Ra over Ra during estuarine mixing. 

Mannhardt, K. Novosad, J.J. Adsorption of Foam-Forming Surfactants for Hydrocarbon-Miscible Flooding at High Salinities in Foams, Fundamentals and Applications in the Petroleum Industry, Schramm, L.L. (Ed.), American Chemical Society Washington, 1994, pp. 259-316. 

Yale, J. Bohnert, H. J. (2001). Transcript expression in Saccharomyces cerevisiae at high salinity. Journal of Biological Chemistry, 276, 15 996-6007. 

Of the surfactants tested, AEGS surfactants produced the most persistent foams at high salinity and elevated temperatures in the presence of synthetic and crude oils (in one atmosphere experiments). ... 

Many surfactants have been suggested as candidates for CO2 foam. However, at high salinity and temperature in the presence of oil, most surfactants foam poorly due to partitioning and emulsion formation and fail to control mobility during CO2 injection. This behavior is analogous to that observed in chemical (microemulsion) oil recovery (5-1). As the salinity, hardness and temperature increase, surfactants form water/oil emulsions, precipitate surfactant-rich coacervate phases, and partition into the oleic phase. CO2 decreases further the solubility of surfactant in the aqueous phase. 

Addition of salting-out type electrolytes to oil-water-surfactant (s) systems has also a strong influence on their phase equilibria and interfacial properties. This addition produces a dehydration of the surfactant and its progressive transfer to the oil phase (2). At low salinity, a water-continuous microemulsion is observed in equilibrium with an organic phase. At high salinity an oil-continuous microemulsion is in equilibrium with an aqueous phase. At intermediate salinity, a middle phase microemulsion with a bicontinuous structure coexists with pure aqueous and organic phases. These equilibria were referred by Vinsor as Types I,II and III (33). 

Rysgaard et al. (1999) tested the effect of salinity on nitrification in a Danish estuary to determine whether the increased desorption of NH4+ from sediments was responsible for the decreasing nitrification rates at high salinity. They concluded that salinity influenced nitrification rates independently of NH4+ concentrations and suggested that some physiological factor must be involved. 

High-Salinity Diffusion Phenomena. Just as at intermediate salinities, the TRS system exhibited extensive convection at high salinities. The rate of phase equilibration was extremely rapid. Typically, the interfaces in this system moved further in a few hours than those in the PDM system moved in two weeks. 

Calculated diffusion paths also successfully predicted the occurrence of spontaneous emulsification in the systems. Near optimum salinity where this phenomenon first appeared, brine drops spontaneously emulsified in the oil but were isolated from the bulk brine phase by a microemulsion. At high salinities, a more common type of spontaneous emulsification was seen with brine emulsifying in the oil directly above a brine layer. 

Figure 23. Calculated diffusion path at high salinity.

El-Alfy, A. and D. Schlenk. Potential mechanisms of the enhancement of aldicarb toxicity to Japanese medaka, Oryzias latipes, at high salinity. Toxicol. Appl. Pharmacol. 152 175—183, 1998. 

Equation 7.147 shows that when Com is small, which corresponds to a type I microemulsion, co is close to 1 and k is close to k when C m is small, which corresponds to a type II microemulsion, co is close to 0 and km, is close to kjo. The prediction from Eq. 7.147 is consistent with the assumption of Hirasaki et al. (1983) that the microemulsion relative permeability approaches the water relative permeability at low salinities and oil relative permeability at high salinities. 

Adsorption of Foam-Forming Surfactants for Hydrocarbon-Miscible Flooding at High Salinities... 

The experimental data in Figure 6 indicate that many surfactant systems allow for sufficient surfactant propagation even at high-salinity conditions, but clearly, the proper choice of surfactant is essential for a successful foam-flood. The following sections outline some surfactant systems suitable for foam-flooding at high salinity, and give a detailed review of the adsorption properties of these surfactants. 

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