During the past several decades, significant and considerable research has been carried out on secondary and tertiary recovery of trapped residual oil remaining within the producing formations underground despite the efficient, current primary production strategies and methods. Methods have been sought of increasing oil recovery, while revamping and improving the economic viability and efficiency of operations. One method that has received much attention and intensive study over these past decades is the use of surfactant-based chemical flooding. Initial patents and laboratory tests have shown conclusively that chemical solutions and slugs including surfactants, remove considerable oil from the porous medium normally trapped after initial waterflooding. Oil recovery processes by means of surfactant micellar solutions or microemulsions have included the injection of slugs of varied compositions. Patents on surfactant-based enhanced oil recovery processes (such as dilute surfactant flooding, surfactant/polymer flooding, and alkaline/surfactant/polymer flooding) have been issued, starting from the 1920s and particularly after the 1960s, when the technology was put on a scientific basis. These patents were generally concerned with the chemistry of surfactant-based enhanced oil recovery processes including envisioning the use of chemical solutions (slugs) to decrease the surface tension between oil and the flooding medium, screening of surfactants for oil recovery efficiency, chemical (surfactant) slug designs and formulation to mobilize residual oil, documenting petroleum sulfonates useful in surfactant flooding, and other important factors in the chemistry of surfactant-based chemical flooding processes. Moreover, evaluation and determination of optimum chemical systems (slugs) for the best economics for a specific field application have been disclosed and documented in several large oil companies patents in the surfactant-polymer area. In this article, a full-fledged review of the patents on different aspects of the chemistry of surfactant-based enhanced oil recovery processes is presented.
Surfactant, enhanced oil recovery, chemistry, chemical slug, patent
Chemical&Petroleum Engineering Department, Schulich School of Engineering, University of Calgary, 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada.