Steamflooding after Steam Soak - Effect of Water Saturation Build-up on Oil Recovery

Abstract

This paper was prepared for the 48th Annual Fall Meeting of the Society of Petroleum Engineers of AIME, to be held in Las Vegas, Nev., Sept. 30-Oct. 3, 1973. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgement of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers Office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines. Abstract In heavy oil recovery, cyclic steam stimulation is frequently followed with steamflooding, in order to increase the ultimate recovery. It is well known that in the cyclic stimulation phase, a large proportion of the injected condensate is proportion of the injected condensate is retained in the formation. In view of this, two questions arise: First, how does such water saturation build-up affect oil recovery in the subsequent steamflood? And, secondly, how should the steam injection wells be located with respect to high water saturation regions in order to maximize oil recovery? The present study attempts to answer the above two questions principally on the basis of an experimental investigation, which was supplemented by selected simulations. The experimental phase utilized a two-dimensional reservoir model, with simulated adjacent formations. High water saturations were created in four configurations: around the injection well, around the production well, around both wells, and in the center of the pattern. It is shown that, depending on the steamflooding scheme employed, any of these situations may obtain in the field. Forty-five experimental runs were conducted, using several different oils. The theoretical phase employed a steamflood simulator, which permitted changes in the areal fluid saturation distributions. Results of the studies showed that the presence of water saturation build-up near the presence of water saturation build-up near the wellbore may influence the steamflood oil recovery, the magnitude of the effect being dependent on oil viscosity. Thus, the effect is appreciable for low viscosity oils, becoming less pronounced for higher viscosities. It was found that a high water saturation in the vicinity of both the injection and production wells is likely to be unfavorable, and production wells is likely to be unfavorable, and should be avoided in steamflood development. In all cases studied, the water saturation build-up was more injurious to oil recovery in the case of high, rather than low initial oil saturations. In both cases, the oil recovery decreased as the water zone size increased. One phase of the experimental study was designed to determine whether the retained water is dispersed throughout the formation, or it simply creates a high water saturation zone immediately around the wellbore. Results of the experimental study indicate that the latter situation is more probable. However, in actual field tests, this may not be so. Implications of such a situation are discussed.