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A new class of surfactants has been developed and tested for chemical enhanced oil recovery that shows excellent performance under harsh reservoir conditions. These novel Guerbet alkoxy carboxylate surfactants fulfill this need by providing large, branched hydrophobes, flexibility in the number of alkoxylate groups, and stability in both alkaline and nonalkaline environments at temperatures up to at least 120 °C. The new carboxylate surfactants perform better than previously available commercial surfactants, they can be used under harsh reservoir conditions, and they can be manufactured at a lower cost from widely available feedstocks. A formulation containing the combination of a carboxylate surfactant and a sulfonate co-surfactant resulted in a synergistic interaction that has the potential to further reduce the total chemical cost. Both ultralow interfacial tension with the oils and a clear aqueous solution even under harsh conditions such as high salinity, high hardness and high temperature with or without alkali can be obtained using these new large-hydrophobe alkoxy carboxylate surfactants. Both sandstone and carbonate corefloods were conducted with excellent results. Formulations have been developed for both active oils (contains naturally occurring carboxylic acids) and inactive oils (oils that do not produce soap/carboxylic acid) with excellent results. The new class of surfactants is a major breakthrough that greatly increases the commercial potential of chemical enhanced oil recovery. SPE 154261Experimental Materials and Procedure Surfactants and Materials.Anionic Surfactants. Guerbet alkoxy carboxylates were synthesized from Guerbet alkoxylates in the laboratory at University of Texas. The Guerbet alkoxylates, internal olefin sulfonates (IOS), alcohol propoxy sulfates (APS) and alkyl benzene sulfonates (ABS) were obtained from Harcros Chemicals, Stepan Company, Huntsman Chemicals and Shell Chemical Company.Cosolvents. Isobutyl alchohol (IBA), diethylene glycol mono butyl ether (DGBE), and triethylene glycol mono butyl ether (TEGBE) were received from Aldrich Chemicals.Polymers. The polymers Flopaam 3630S and 3330s were received from SNF Floerger (Cedex, France). Electrolytes and Brines. Sodium chloride, sodium carbonate, calcium chloride, magnesium chloride hexahydrate, and sodium sulfate were obtained from Fisher Chemical. Specific synthetic brines were made and used based on each specific reservoir application.Crude Oils. Several dead crude oils, as well as surrogate oils (a mixture of dead crude and a low-EACN hydrocarbon to match the live oil EACN) were used in this study (Table 1). It is well established that reservoir pressure and solution gas can significantly change the microemulsion phase behavior, and thus should not be ignored. The understanding of equivalent alkane carbon number (EACN) concept is very useful in modeling the live oil (Cayias et al., 1976;Salager et al., 1979;Glinsmann, 1979;Puerto and Reed, 1983;Roshanfekr et al., 2009, Roshanfekr, 2010. It is more difficult and expensive t...

With recent advances in Alkaline-Surfactant-Polymer (ASP) flooding, the demand for high performance EOR surfactants is rapidly increasing. This is accompanied by the need for a diverse raw material base. We have successfully developed and tested a novel class of hydrophobes for anionic surfactants that satisfy this need at low cost. The hydrophobe for these novel surfactants is Tristyrylphenol (TSP), which is based on the petrochemical feed stocks, phenol and styrene. TSP based surfactants have unique structural features that can be exploited to fit many EOR surfactant needs. We illustrate the performance of this class of TSP surfactants for a waxy crude oil with a high acid number. Selecting a formulation proved difficult due to the high molecular weight of the crude. The TSP surfactant has four benzene rings that enhanced the solubility of the heavy components of the crude oil, including asphaltenes, making it an attractive choice. The dead crude oil was diluted with either decalin or cyclohexane to match the equivalent alkane carbon number (EACN) of the live crude oil. The TSP alkoxy sulfate molecules with varying lengths of propoxy (PO) and ethoxy (EO) chains were tested in microemulsion phase behavior experiments in order to obtain ultra-low IFT at optimum salinity with low microemulsion viscosities. The ASP formulation was successfully tested in reservoir core floods using both surrogate oil and live oil.

Several classes of new surfactants have recently been tested for enhanced oil recovery. These new surfactants were needed for oil field applications under reservoir conditions that made it difficult or impossible to find conventional surfactants with the desired behavior such as ultra-low interfacial tension, aqueous stability, thermal stability at high temperature, low retention, tolerance to high salinity and so forth. We illustrate results for several of these new surfactants and discuss under what conditions they are suitable, how we developed formulations using them and some of the general principles that can be applied to future applications. A common theme of this development is the need for surfactants with large hydrophobes (carbon numbers above 18) even for some light oils. A second common theme is the advantages and flexibility of propylene oxide and ethylene oxide linkages between these large hydrophobes and the sulfate or carboxylate end group. A third common theme is the advantages of highly branched hydrophobes regardless of the other characteristics of the surfactant structure help prevent undesirable viscous phases. Finally, a fourth common theme is the advantages of using surfactant mixtures with diverse structures and sizes. These common elements enable us find surfactant formulations that are highly effective and that can be made from available feedstocks at reasonable cost.

Co-solvents are used with surfactants in modern chemical enhanced oil recovery (CEOR) formulations to avoid formation of viscous microemulsion phases (and reduce costs) in porous media. Modeling the effect of co-solvents on phase behavior is critical to CEOR reservoir simulations. The state-of-the-art is to use HLD (Hydrophilic Lipophilic Difference) with a modified form of NAC (Net Average Curvature) as an Equation of State (EoS) to model microemulsion phase behavior. In this paper, we use an alternative EoS flash algorithm and couple it with an alcohol partitioning model to predict physical phase behavior. In this paper, we show that the net curvature equation in NAC is not valid for overall compositions away from typical experimental conditions, specifically in Type I and II systems. Alternatively, we use experimental evidence to correlate the harmonic average of oil and brine solubilization ratios to HLD. We use the average solubilization ratio equation with boundary conditions that allow for microemulsion phase type regions to be well defined, thus making the flash calculations robust. To model the co-solvent effect, we couple the newly developed average solubilization theory (AST) based EoS with the Prouvost-Pope-Rouse model to capture co-solvent partitioning across oil, brine and microemulsion phases. The resulting AST theory allows for a HLD based EoS to predict physical two-phase regions with no discontinuity in phase behavior thereby making it a more robust alternative to HLD-NAC. We used 80 phase behavior experiments over a wide range of hydrocarbons and temperatures to validate our approach. The coefficient of determination between the actual experimental data and the predicted model output was found to be above 0.9.