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The effect of co-solvent on phase behavior was evaluated and an optimal surfactant/co-solvent formulation was selected based upon a combination of simulations and laboratory experiments. The co-solvent altered phase behavior, thereby necessitating a different approach for inducing effective salinity gradients. We present an approach where the hydrophilic nature of the co-solvent is used to maintain effective salinity gradients to optimize surfactant behavior but more importantly mitigate viscous microemulsions and reduce surfactant retention. By using a combination of laboratory experiments and simulations to match co-solvent behavior in UTCHEM, Using an understanding into co-solvent partitioning was developed such that the optimal conditions of ultra-low interfacial tensions are maintained for a longer duration during chemical flooding. We demonstrated that by adding the appropriate co-solvent and the correct amount of electrolyte in the chase solutions, we could maintain Winsor type III conditions for extended durations even with a small surfactant slug. The optimal co-solvent/electrolyte gradient recovered more than 90% of the residual oil in laboratory corefloods. The result illustrate the importance of characterizing the effect of co-solvent on surfactant phase behavior and the need for numerical modeling to optimize chemical flood design when co-solvent is used. Introduction The success of surfactant flooding rests on the ability of surfactant-oil mixtures to rapidly coalesce to form fluid and stable microemulsions with ultra-low tensions. Recent developments in the area of surfactant synthesis and screening have allowed the selection of high performance surfactant formulations for enhanced oil recovery.1, 2 These high-performance surfactant formulations require co-solvents toimprove phase behavior;reduce microemulsion viscosity; andensure surfactant-polymer compatibility. 1, 2 Such surfactant/co-solvent formulations show high oil recovery and low surfactant retention in corefloods. Numerical simulations are an important component to scale-up chemical flooding from lab to field-scale. Numerical simulations require matches of surfactant phase behavior and corefloods to obtain parameters for field-scale simulation. In typical simulation studies, the effect of co-solvent is usually neglected 3, 4, 5 and gross surfactant parameters are often used to capture chemical phase behavior. While this approach may be appropriate for formulations that use no co-solvent a design that includes the effect of co-solvent on surfactant phase behavior is preferred for accurate field-scale predictions. Co-solvents used for oil recovery are amphiphiles 6, 7 and have the ability to partition into aqueous, oleic and microemulsion phases. The ability to partition between the three phases allows co-solvents to significantly alter phase behavior. When a hydrophilic co-solvent is mixed with an anionic surfactant, an increase in optimal salinity is observed. Conversely, a lipophilic co-solvent will induce a reduction in optimal salinity. From these observations, Hedges8 used co-solvent scans to identify the appropriate co-solvent for a fixed optimal salinity. While co-solvents have been used widely in surfactant trials, their effect on phase behavior is often neglected due to the complexity of experimental measurements and incorporation into numerical simulation. An adverse consequence of ignoring co-solvent behavior could be chromatographic separation from the surfactant due to preferential partitioning. Such separation would induce changes in overall surfactant/co-solvent compositions along a dilution path and undesirable phase behavior.

Straw of the halophyte Salicornia bigelovii was chemically analyzed for lignocellulosic components, extractives, and ash in relation to varying cultivation conditions (namely, irrigating water salinity and fertilizer grade). Irrigation water contained 10−50 ppt salt, and fertilizer application varied between 1 and 2 gN/m 2 . Composition of the biomass was comparable to traditional lignocellulosic biomasses, containing glucan (up to 27 g/100 g total solids (TS)), xylan (up to 23 g/100 g TS), and lignin (24 g/100 g TS), but also high amounts of ash (up to 53 g/100 g TS) and water−ethanol soluble extractives (up to 25 g/100 g TS). As most of the ash is extractable (up to 90%), a simple water wash is sufficient to bring the ash content down to a typical value found in the lignocellulosic materials. It was found that increasing water salinity used for the plant irrigation decreases lignocellulosic components content, increases ash content, and does not affect extractives content. The fertilizer application rate was not found to influence any of the responses, except for ash composition (lowering mineral content) and its amount in the flowering spike fraction. Stem and spike fractions were found to be significantly different in composition, with stems being closer to a typical lignocellulosic material.