Improving the State of the Art of Western Canadian Heavy Oil Waterflood Technology

Abstract Heavy oil waterfloods have been operated in Saskatchewan and Alberta for up to 50 years, yet remarkably little discussion of the theory or operation of heavy oil waterflooding has been published. Conventional waterflood theory is based on assumptions that are not encountered in heavy oil reservoirs, and those theoretical and operational experiences should not be substituted. This editorial draws upon information from the relatively small number of significant theoretical and field discussions of Western Canadian heavy oil waterflooding available in the public domain to establish that the "state of the art," including proposed production mechanisms, prediction of performance, and improvement of performance, is extremely limited. Introduction An immediate challenge is deciding which waterflooded pools to include under the "heavy oil" umbrella, as imprecise definitions of heavy oil are used by both government agencies and waterflood operators. Definitions have at times been based on API gravity (a value of = 20 ° API is sometimes used), but often the driving criterion is geography. If a waterflood is located in an area near heavy oil cold production, it is sometimes simply classified as heavy oil, and given to a heavy oil group to operate. Emphasis on an oil-gravity-based definition of heavy oil is convenient, but unfortunate, as it de-emphasizes oil viscosity even though viscosity has repeatedly been shown to be a controlling parameter. Aversion to a viscosity-based definition for heavy oil may be due to occasional problems obtaining consistent heavy oil viscosity measurements(1, 2), and confusion about whether available viscosity values were collected using dead oil, live oil, or something in between. In stark contrast to this general neglect of viscosity data in heavy oil waterflood papers and articles, the most common informal statement about heavy oil waterfloods is, "you can't have a successful heavy oil waterflood if the dead oil viscosity is greater than" a particular value. Values in the 1,000 to 2,000 cp dead oil viscosity range (at reservoir temperature) are often cited as "the limit," but no study establishing a limit appears to exist. Searching the literature for information can be misleading. "Heavy oil" is often used in the title of waterflood articles because conventional oil waterflood technical staff consider oil with viscosity in the range of 3 to 10 cp (much lower than the hundreds to thousands of cp oil more typically waterflooded in Western Canada) to be heavy oil. The technology of Canadian heavy oil waterflooding likely started as conventional oil waterflood theory. It has evolved in a generally empirical manner, and in some ways is still more "art" than "science". The mobility ratio is so adverse that the "flood" process is likely over very quickly. The subsequent process is circulating water which brings enough oil with it for the process to be economic. This much longer "post-flood" period of Western Canadian heavy oil waterfloods is optimized using empirical methods that are often done differently by each oil company, engineer, pumper, etc. The result is a very limited written state of the art.

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