Publications

The oil industry has conducted extensive research on many different oil recovery methods in its effort to recover more oil from petroleum reservoirs than is economically possible using conventional primary and secondary methods. Although these improved oil recovery methods are frequently referred to as "tertiary oil recovery" processes, this name has gradually been replaced by "enhanced oil recovery" or "EOR, methods since in some applications it is desirable to initiate the process before the reservoir has been depleted by conventional primary or secondary methods. The amount of oil that can be recovered using conventional recovery methods and therefore the amount remaining as a target for EOR techniques varies considerably from reservoir to reservoir. The East Texas Reservoir in the United States is an example of a reservoir in which over 80% of the OOIP can be recovered using conventional production technology. However, in many other reservoirs, the application of conventional recovery methods alone would frequently leave as much as 40 to 80% of the original-oil-in-place unrecovered at abandonment. It is these latter reservoirs which provide the incentive and challenge for the development of the sometimes simple, sometimes exotic recovery processes referred to above as enhanced oil recovery, or EOR methods. The three basic types of enhanced recovery processes are chemical methods, such as surfactant, polymer and alkaline-water flooding, miscible displacement processes, such as enriched gas or CO2 miscible methods, and thermal processes including steam stimulation, steam drive and insitu combustion. This paper is concerned primarily with the status of surfactant flooding and miscible processes, but also includes comments on immiscible secondary and tertiary gas injec- tion techniques for increasing oil recovery.