Field Experience With Chemical Oil Recovery Methods

Abstract Typically, when an oil reservoir becomes uneconomic to produce -- after primary and secondary methods have been exhausted -- over two-thirds of the original oil is still in the reservoir. Many chemically based oil recovery methods have been proposed and tested in the laboratory and field. Indeed, chemical oil recovery methods offer a real challenge in view of their success in the laboratory and lack of success in the field. This paper examines this question, looking at the field test results for selected chemical oil recovery methods, and comparing them with laboratory response. The answer lies in the inadequacy of laboratory experiments on one hand, and the very limited knowledge of the reservoir characteristics on the other. Field test performances of polymer, alkaline, and micellar flooding methods are examined for nearly 50 field tests, results for which are tabulated. The oil recovery performance of micellar floods is the highest, followed by polymer floods. Alkaline floods have been largely unsuccessful. The reasons underlying success or failure are examined, and research needs for the future are outlined. Introduction Over two-thirds of the original oil is left unrecovered in a typical oil reservoir when it reaches economic limit (i.e. after primary and secondary -- waterflood -- recovery). Many methods - often called "tertiary recovery" -- have been proposed for recovering this "unrecoverable" oil. The class of "chemical methods" is of particular interest, because it largely permits the use existing oilfield equipment and facilities. The interest in tertiary oil recovery, and particularly the field activity, rises and falls with the prospect of increasing or decreasing oil prices, and also with the perceived foreign oil supply situation and government incentives. Thus economics dominate much of the oil recovery activity reflected by the extensive field project surveys published by the Oil & Gas Journal every two years (Moritis 1). The large number of field projects for a given method does not necessarily mean that the method is technically successful. Similarly, very few field tests of a particular process do not imply that the process is technically ineffective. Figure 1 shows a plot of the number of chemical flooding field projects by year, while Fig. 2 shows the total daily oil production for the projects. The peaks in 1986–88 correspond to special tax concessions introduced by the government for those years only. Eor - enhanced oil recovery Oil recovery methods can be broadly classified as non-thermal and thermal methods, depending on whether heat is employed in some form. Figure 3 shows a classification of EOR methods; the more promising methods from the commercial point of view are highlighted. Non-thermal EOR methods broadly consist of chemical and miscible processes. Chemical methods include polymer, surfactant, caustic and micellar/emulsion floods, and combinations thereof. The general features of these methods and field experience form the subject of this paper. Even though chemical floods have had limited success in the field, they hold promise for the future. Miscible methods include high pressure miscible drives, using a hydrocarbon gas nitrogen or carbon dioxide, as well as displacement by liquid hydrocarbons. Many variations are possible in the application of these processes, an important one being alternate injection of the miscible agent and water.