, ' SPE SPE 10371 Society of Petrolet.m EngineeI"S of A 1M E Physicochemical Mechanics of the Propagation of the Stabilized Oil Bank Formed During Di!ute Surfactant Flooding by Gregory R. King, * Turgay Ertekin, * C. Drew Stahl, * J. H. Jones, R. Nagarajan, and A.J. Yarzumbeck, The Pennsylvania State University *Member SPE-AIME Copyright 1981 American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. This paper was presented at the 1981 Eastern Meeting of the Society of Petroleum Engineers of AIME, held in Columbus, Ohio, November 4-6, 1981. The material is subject to correction by the author. Permission to copy is restricted to an abstract of not more than 300 words. Write to 6200 N. Central Expwy., Dallas, Texas 75206. ABSTRACT Recent displacement tests have indicated that under certain conditions the stabilized oil bank formed during dilute surfactant flooding may be composed of as many as three distinct oil banks. These secondary oil banks are characterized by the arrival of high oil cuts, high sulfonate concentra- tions, and low interfacial tensions in the effluent stream. The mechanisms governing the formation of these three banks, although different for each bank, are related to the interactions between the oil, rock, surfactant solution, and mobility buffer. To determine the mechanisms governing the for- mation of these banks, a series of core floods was designed to isolate and study each bank separately. The experimental results, including the production histories and effluent analysis of these tests are presented and discussed. The results of these tests indicate that two of the banks are formed by the chromatographic sep- aration of high and law equivalent weight su1fon- ates, while the third is farmed by the desorption of sulfonate during the injection of low saline fluids (mobility buffers). Also discussed are the means to alter the production profiles of displace- ment tests by manipulation of these mechanisms. INTRODUCTION Previous investigators 1 ,2,3 have attempted to describe the mechanisms governing the development and propagation of the stabilized oil bank formed during surfactant/polymer flooding. Davis and Jones l presented experimental results which indi- cated a region of high oil cut at oil breakthrough. The ail cuts decreased and eventually stabilized later in the flood. This behavior was attributed to the mobile water bank advancing on and beyond the stabilized ail bank. The oil cut was observed to decrease as the water bank invaded the oil bank. Gladfelter and Gupta 2 reported a similar trend References and i 1 ltll"tr .. i, at end ,f paper. 97 in their experimental work. Using a microwave scan- ning apparatus, they observed a "hump" region in the oil saturation profile of linear sandstone cores at the leading edge of the stabilized oil bank. This region of high oil saturation was fallowed by a steady state region of lower oil saturation. They determined that the "hump" was formed through the hysteresis in the relative permeability curves and the related hysteresis in the fractional flow curve. The growth of the "hump" was found to be solely dependent on the extent of hysteresis and the fraction of ail flowing in the lower steady state region. Wasson et al. 3 described the development and production of two oil banks farmed during low con- centration surfactant flooding. The formation of these two oil banks was found to be related to the mobilities or the injected fluids. The first bank was formed by the fingering of the law viscosity slug through the more permeable channels of the care. The surfactant solution in these channels came into contact with enough ail to form an oil bank. The second bank was formed during the injec- tion of the mobility buffer. It was believed that the plug flaw associated with high viscosity fluids was responsible for the formation of this bank. Production histories of early displacement tests in this study indicated that three distinct oil banks were being produced. Examples of these banks are shown in Figures 1-3. The arrivals of the first twa banks were observed after 50% PV and 100%· PV of fluid production. The third bank. sim- ilar to that observed by Wasson, was produced at the end of the buffer injection. The purpose of this paper, therefore, is to give a detailed de- scription of the stabilized oil bank formed by the law concentration slugs studied and attempt to de- scribe the mechanisms governing the formation of these secondary oil banks. MA'T'RRT AT.e; CRUDE OIL The crude oil chosen for this study was the