Laboratory Core Floods To Support the El Dorado Micellar/Polymer Project

Abstract

Summary Two distinct micellar/polymer processes are being testedin the El Dorado project. In one pilot area, anoil-external micellar system followed by partiallyhydrolyzed polyacrylamide solution is being tested. In the north pattern, an aqueous surfactant system followed byxanthan gum solution is being implemented. Throughoutthe project, laboratory work has been required toevaluate various substitute chemicals when suchsubstitutions were deemed necessary and feasible.Several short core flow tests were conducted using Bereasandstone cores and Admire sandstone (field) cores toinvestigate the effects of various changes on theeffectiveness of the two processes. Among the factorsinvestigated and/or observations were (1) effects of chemical slug size on oil recovery for both oil- andwater-external systems,(2) effects of surfactant andpolymer concentrations on the effectiveness of thehigh-water content system, (3) efficiencies of the systemswhen different commercial polymers were used in thepolymer drives, (4) effects of polymer drive salinity onoil recovery using the aqueous system, and(5) effects ofvarious substitute low-equivalent-weight (LEW) sulfonates on the displacement efficiency of the aqueous surfactantsystem. Introduction The literature contains many performance data formicellar or surfactant systems with quite diversecompositions. Compositions of slugs used in micellar orsurfactant flooding generally include a combination ofsurfactant, water, salt, cosolvent, hydrocarbon, andpolymer. Considerable effort has been spent defining ordetermining the optimal combination of these ingredients for a given set of rock, oil, and brine properties. Inaddition to these compositional variables, other parametersto consider in the surfactant flooding process are mobilitiesof the surfactant slug and the polymer solution, surfactantslug size, type and concentration of polymer for thepolymer drive, composition, size, and pH of a preflush, salinities of all three phases (preflush, surfactant, andpolymer) of the process, and rock properties such aslithology, mineralogy, pore size distribution, andwettability. Considering the number of variables it is notsurprising that there are differing opinions on the optimalsurfactant concentration and surfactant slug size forrecovery of additional oil from waterflooded laboratory cores and field reservoirs. One difficulty in defining theoptimum in such a multidimensional space (manyvariables) is that it is nearly impossible to vary only oneparameter and hold all others constant. For example, changing the surfactant concentration simultaneouslymay cause a change in the slug viscosity, giving rise to acorresponding change in the mobility ratio between theoil/water bank and the surfactant slug. Gogarty compared results for three compositionsdiffering in the active surfactant concentration in thesurfactant slug. Other laboratory work reports the importantor the unimportant nature of the surfactant slug withregard to its external phase and/or surfactantconcentration. Holm found that an oil-external, high-concentration type surfactant slug performs better under the given conditions. For the given surfactant system andtest conditions, Klaus found that lower concentrationslugs (0.5%) yielded a higher oil recovery per gram ofsulfonate injected. Other work on the nature of theexternal phase of micellar systems indicates that therelative amounts of oil and water that a microemulsioncan solubilize are controlled at least partially bycosolvent type and concentration and not by phase externality.Accordingly, an oil-external system was concluded notto be preferred intrinsically over a water-externalsystem. JPT P. 1378^