Displacement of Reservoir Brine by Fresh Water-Four Field Case Histories
Authors: Strange L.K. , Cloud W.B. 
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
Divalent ions and high concentrations of sodium chloride in reservoir connate water have a deleterious effect on the performance of most of the surfactant waterflood processes now being tested in the field. Displacement of this undesirable connate water from the reservoir by fresh water injection before introduction of surfactant has been proposed as a means of alleviating the problem. Results from four separate field test projects, reported here, demonstrated the efficacy of the water brine displacement process under varying conditions of permeability, well spacing, brine concentration, and fluid injection rate. These were conducted in a Gulf Coast Frio sand and in three Mid-Continent sands, two Pennsylvanian, and one Mississippian. Pennsylvanian, and one Mississippian

Introduction
Most presently available formulations of surfactant-based injection materials for improved recovery are intolerant of high salinity. Generally, if the salinity is higher than a few percent, the oil displacement efficacy is unsatisfactory, and further, precipitation of surfactant occurs if divalent cations (calcium and magnesium) are present Since most oil reservoirs contain present Since most oil reservoirs contain saline waters, one approach to recovering tertiary oil from these reservoirs is to reduce the salinity and divalent cation concentrations in the reservoir to an acceptable level before introducing the surfactant. Ideally, the level of calcium and magnesium in the formation water, which is expected to be contacted by the surfactant, should approach zero. Practically, if the total divalent cation concentration can be reduced to about 50 parts per million (ppm) or less, solutions of sodium carbonate and/or sodium tripolyphosphate can then be injected to precipitate these undesirable cations. precipitate these undesirable cations. In the past, there has been some concern that displacement of hostile brine by the injection of fresh water is not feasible. We present herein the results of four separate efforts to distance field brines by the injection of fresh water. In all four cases, the determination whether brine displacement was being effected was based primarily on analyses of aqueous samples taken from observation wells located relatively close to injection wells.