The characterization of surfactant candidates for a given reservoir can be improved by the use of linear coreflood residual-oil-saturation profiles measured along the core after chemical flooding. A surfactant formulation's functional relation of oil recovery to slug size can be calculated from a single coreflood with the assumption of a relaxed scaling law. A volumetric linear scaling approach is developed from laboratory coreflood data. Residual-oil-saturation profiles measured in reservoir material with a microwave absorption instrument support this approximate scaling relation. Analysis of 32 linear surfactant-slug corefloods is presented as additional verification. The limits of this scaling law are defined, with emphasis on the role of mixing and dispersion. The procedure for using saturation profiles to calculate oil recovery as a function of slug size is developed and a test case is presented. A recovery relation derived from a single coreflood saturation profile is compared with that determined by multiple conventional corefloods. Introduction Many techniques and instruments are now available for noninvasive measurement of oil/brine saturations along linear cores during secondary and tertiary displacement experiments, these are reviewed briefly in Ref. 1. The most popular recent method is based on the microwave absorption properties of water. Such saturation- profile measurements provide much more information on a given chemical-flood experiment than can be collected merely from effluent material balance. This abundance of data can be used in two ways: to determine relations that would otherwise have to be developed laboriously from many separate conventional corefloods and to develop predictive capability for estimating surfactant- flood performance in new situations. Both applications are possible as an outgrowth of the concept of volumetric linear scaling for chemical flooding proposed by Parsons and Jones. This relaxed scaling technique is supported by the data of Ref. 6 and a wide variety of conventional and scanned corefloods presented in this work. A process can be defined as volumetrically linearly scalable if the fluid compositions and saturations at any point in the matrix at any time are functions only of the PV of fluids injected relative to that point with respect to the injection point. This can be stated simply for a single slug of surfactant: a given-PV slug of surfactant will produce the same compositions and saturation distributions in a core of any physical shape and size. Moreover, a 0. 10-PV slug injected into a 2-m core will produce the same composition and saturation distribution in the first meter of that core as would be produced over the entire length of a 1-m core that had seen a 0.20-PV slug. This is a trivial-but not an obvious-view of the recovery process. Limitations to this relative-sizing concept are discussed in the following paragraph. SPEJ P. 511^
Two microwave absorption spectrometers have been developed for routine monitoring of So distributions during laboratory flooding experiments in field core material. Operating frequencies are 10.525 and 24.125 GHz. Based upon low-power, mass-produced microwave components, these instruments are inexpensive, safe, very compact and rugged and require no special expertise for operation. A core sample cell has been designed which permits So distributions to be determined in narrow rectangular and cylindrical cores. An indirect calibration technique has been developed using the injection of aqueous solutions of 2-propanol to compensate for the porosity variations and irregular Soi and Sorw distributions inherent to segmented field cores. Details of the instrumentation are presented with a theoretical description of instrumental response. The practical utility of this instrumentation for the a priori detection of core defects and quantitative determination of porosity distributions is demonstrated.
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