Sulfonate Retention and Residual Oil Saturation

This paper describes an empirical relationship between sulfonate retention and final residual oil saturation achieved by a micellar/polymer oil-recovery process. Using this relationship and certain assumptions, one can derive expressions for predicting oil recovery performance in coreflood experiments. The equations contain two experimental constants:sulfonate retention anda factor related to the oil-recovery efficiency of the sulfonate slug in cores, specific to both the slug and core material. This same relationship applies to both linear and radial cores. The equations derived predict nonlinear scaling effects. These effects have been demonstrated in laboratory corefloods. Introduction Sulfonate retention, as defined in the literature, represents the loss of a critical component and consequently affects the efficiency of micellar/polymer oil-recovery processes. In this case, sulfonate retention is discussed in connection with laboratory corefloods. An operational definition of the retained sulfonate is that quantity of sulfonate remaining in the core, by whatever mechanism, after a core has been flushed with drive fluid to final oil saturation. The remainder of the originally injected sulfonate has presumably been propagated through the core. For the systems studied. a relationship has been found between residual oil saturation after a micellar/polymer flood and the net amount of sulfonate propagated through a given element of core. This relationship was established by determining residual oil saturation and sulfonate retention in successive sections of flooded cores taken along the direction of increasing travel of micellar slug. The measurements were obtained by a postflood extraction of these core sections and subsequent analysis of the extract. These data were analyzed by viewing a coreflood as a series of smaller sequential floods of the core elements where each successive element was treated with less sulfonate. Effect of Sulfonate Retention on Residual Oil Saturation Linear Cores Coreflood data were collected using Slug A and Henry crude oil in fired Berea sandstone cores that previously had been waterflooded to residual oil saturation. Slug composition is given in Appendix A. Each coreflood experiment was performed using four cylindrical cores connected in series to form one composite core. The individual core segments were each 2 in. × 1 ft long (5.2 cm × 30.5 cm), so that the composite core was 4 ft (1.2 m) long. Experimental details of the flooding method are discussed in Appendix B. After a micellar/polymer flood was completed, the composite core was separated and the individual core elements were analyzed for oil saturation and sulfonate retention. The analytical procedure is described in Appendix B and is patterned after the method described by Smith et al. By performing the experiments in this way, we obtain the average residual oil saturation over the individual segments of a flooded core. We have called these values "point oil saturation," (Sor)m, to distinguish them from the average oil saturation over the composite core, which we have called average oil saturation," S orj. Fig. 1 shows two interpretations of these tandem corefloods. Fig. 1a shows the quantities that are measured experimentally. The amount of sulfonate initially injected (m 1) is known, as is the weight of each core segment (mCi). SPEJ P. 349^