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Summary In the past several years, there has been renewed interest in enhanced oil recovery (EOR) by alkaline injection. Alkaline solutions also are being used as preflushes in micellar/polymer projects. Several major field tests of alkaline flooding are planned. are in progress, or recently have been completed. Considerable basic research on alkaline injection has been published recently, and more is in progress. This paper summarizes known Field tests and. where available, the amount of alkali injected and the performance results. Recent laboratory work, much sponsored by the U.S. DOE, and the findings are described. Alkaline flood field test plans for new projects are summarized. Introduction and Past Technology The history of alkaline flooding, dates back- to the early 1920's, with roots in the combination of reservoir engineering and chemistry. Understanding, the interaction of the injected alkaline chemicals with the reservoir oil, water, and rock is a chemical problem, while using the interactions to improve oil recovery is a reservoir engineering problem. Alkaline oil recovery has been attributed to oil/alkali interaction (called "emulsification"), to alkali/rock interaction (called "wettability alteration"), and to chemical precipitation caused by mixing of the injected alkaline solution with the hardness ions in reservoir water. Any or all of these mechanisms can operate in a particular application. Because of the interplay of these mechanisms, alkaline flooding is ail extremely complex oil recovery process and tends to be site-specific in terms of process design and dominant recovery mechanism. Some of the apparent differences in the use of alkali cited in the literature result from the site-specific nature of a process that uses different mechanisms to improve oil recovery in different reservoirs. For this reason, most of the disagreement in the literature can be explained by differences in the recovery processes active in an individual reservoir, Recognition of the individual mechanisms should allow profitable application of alkaline flooding to a wide range of reservoir types. The first attempt to bring together what was known about alkaline flooding was made by Johnson' in 1975. He summarized Field data that had been published and the technology as it then was understood. From 1975 through 1979, when this paper was first written, the number of field tests concluded and described, begun, or planned grew as did research on the processes involved. It became evident that alkaline flooding was not a simplistic technique for enhancing oil recovery but rather a very complex one. From 1979 through mid-1982, the number of field tests planned and initiated increased markedly. This increase is attributed to the favorable economics created by the U.S. DOE's Tertiary Incentive Program. During the program's life from Aug. 1979 through Jan. 1981, 41 alkaline flood projects were certified. JPT P. 209^