Low Surfactant Concentration Enhanced Waterflooding
- Scott L. Wellington | Edwin A. Richardson
- Document ID
- Society of Petroleum Engineers
- SPE Journal
- Publication Date
- December 1997
- Document Type
- Journal Paper
- 389 - 405
- 1997. Society of Petroleum Engineers
- 1.8.5 Phase Trapping, 4.1.5 Processing Equipment, 5.3.4 Reduction of Residual Oil Saturation, 1.6.9 Coring, Fishing, 5.2.1 Phase Behavior and PVT Measurements, 5.4.7 Chemical Flooding Methods (e.g., Polymer, Solvent, Nitrogen, Immiscible CO2, Surfactant, Vapex), 5.6.5 Tracers, 5.3.2 Multiphase Flow, 2.5.2 Fracturing Materials (Fluids, Proppant), 4.3.4 Scale, 6.5.2 Water use, produced water discharge and disposal, 1.2.3 Rock properties, 2.4.3 Sand/Solids Control, 5.4.1 Waterflooding, 4.1.2 Separation and Treating, 5.1 Reservoir Characterisation
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A new gradient scaled flooding test procedure indicated that oil is mobilized by the leading edge of the surfactant dispersion curve where the concentration is low, 1 to 10 ppm. Under optimum, highly interfacially active blends of anionic and cationic surfactants were formulated to take advantage of the displacement mechanism. Essentially all the initial or residual crude oil was removed from shaly sand packs using approximately 0.4 percent surfactant with less than 0.1 pore volume loss.
Previously, microemulsions composed of anionic surfactants, alcohols, brine, and crude oil were sought for their ability to produce ultralow interfacial tension between the excess brine and oil phases at an optimal condition for a particular oil reservoir.1,2 Although various microemulsion flooding field pilots were successful, full-scale applications have not followed for numerous technical, economic, political, and psychological reasons.
A proposal for successful mobilization and recovery of residual oil in reservoirs is described. To be effective, the surfactant, at approximately 0.5 weight percent or less concentration, should lower the interfacial tension between hard brines and crude oil to millidyne/cm values, transport without significant loss under reservoir conditions, and be chemically stable. To avoid high surfactant loss from phase trapping, an underoptimum system, where only oil and water phases are present at all times during the flood, is required. To accomplish this goal, surfactants capable of producing low interfacial tension between brine and oil without forming emulsions and microemulsions were designed and synthesized. To minimize project life time and reduce costs, surfactant injection should begin with or as soon as possible after water injection begins. The methods outlined in this paper may also be used for soil remediation.
Surfactant Structure, Activity Screening and Flooding Methodology
A brief outline of the surfactant structures and activity screening tests follows. If publication space becomes available in the future, a more complete discussion of molecular structure requirements and the statistical analysis of 6,000 screening measurement results on 40 anionic, 25 cationic, and 120 surfactant combinations can be presented.
To achieve ultralow interfacial tension between brine and oil using a monolayer, the surfactant must (1) completely cover the interface, (2) separate the brine and oil to a sufficient distance so that their potential fields do not overlap, and (3) grade from being completely lyophilic to hydrophilic in a gradual manner. These essential requirement are not usually met since common surfactants bunch up into domains at the interface and allow microscopic portions of the bulk oil and water phases to interact.
Graded lyophilic to hydrophilic anionic surfactants with the following general structure were synthesized under the direction of J.K. Borchardt and T.D. Hoewing at Shell's Westhollow Technology Center in Houston, Texas. The molecules contained a straight or branched alkyl chain, a branched propylene chain, and an ethylene chain terminated with a glyceryl sulfonate. The alkyl chain normally originates from a NEODOLä alcohol. Thus the surfactants are named NEODOL Propoxy Ethoxy Glyceryl Sulfonates (NPEGS). The molecular weight and structure of the alkyl chain and the number of moles of propylene and ethylene oxides can be tailored to obtain optimal performance for a specific application. The method of preparation assures that these are not pure monodisperse chemicals but are mixtures to enhance their surfactant properties. All other surfactants were used as received from the manufacturers.
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