Preinjection of Polymers to increase Reservoir Flooding Efficiency
Authors: Dabbous Mahmoud K. , Elkins Lloyd E. 
Published: December 2007

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.
This paper was prepared for the Improved Oil Recovery Symposium of the Society of Petroleum Engineers of AIME, to be held in Tulsa, Okla., March 22–24, 1976. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL 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. 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
Preinjection of high-molecular-weight Preinjection of high-molecular-weight polyacrylamide polymers in advance of a polyacrylamide polymers in advance of a miscible slug is proposed as a means of improving reservoir sweep efficiency by reducing the degree of "permeability" contrast between wells in a moderately heterogeneous system. The use of polymers in a preinjected mode is radically different from their "conventional" use to provide a favorable mobility condition between in-place and injected fluids and so maximize areal sweep even in a flood of a "homogeneous" sand.
Theory and model flow tests were employed in an investigation of polymer preinjection in advance of a miscible flood. Flood test s in physical models of heterogeneous porous media physical models of heterogeneous porous media showed that preinjection of polymers could result in better flooding efficiency because of increased volumetric sweep. This was concluded from tracer performance data and oil recovery response. Studies of the interactions between the preinjected polymer and a subsequent micellar flood indicated that prior polymer flow had no adverse effects on oil polymer flow had no adverse effects on oil displacement efficiency by a micellar fluid and appeared to decrease surfactant loss to the rock. Additional mobility control requirement in micellar floods as a result of decreased mobility of fluids was moderate.
Because laboratory models cannot be scaled to reproduce the complex heterogeneities encountered in reservoirs, extensive field testing of polymer preinjection in a real environment and under carefully controlled test conditions is suggested. This is highly desirable since the timing of development is an important factor if the full value of having available sweep improvement methods is to be realized.

Introduction
While considerable attention has been given to the chemistry of miscible flooding, little published work is available which discusses effects of variations in formation rock texture on reservoir flooding efficiency by these improved recovery methods. Reservoir rock heterogeneity can result in an injected fluid bypassing significant portions of a reservoir under flood. Circulation of large volumes of water to achieve higher ultimate sweep in a waterflood is tolerable because of the low cost of injected water.