Enhanced Oil Recovery - An Overview

Nearly 2.0 × 1012 barrels (0.3 × 1012 m3) of conventional oil and 5.0 × 1012 barrels (0.8 × 1012 m3) of heavy oil will remain in reservoirs worldwide after conventional recovery methods have been exhausted. Much of this oil would be recovered by Enhanced Oil Recovery (EOR) methods, which are part of the general scheme of Improved Oil Recovery (IOR). The choice of the method and the expected recovery depends on many considerations, economic as well as technological. This paper examines the EOR methods that have been tested in the field. Some of these have been commercially successful, while others are largely of academic interest. The reasons for the same are discussed. The paper examines thermal and non-thermal oil recovery methods. These are presented in a balanced fashion, with regard to commercial success in the field. Only a few recovery methods have been commercially successful, such as steam injection based processes in heavy oils and tar sands (if the reservoir offers favourable conditions for such applications) and miscible carbon dioxide for light oil reservoirs. Other recovery methods have been tested, and even produced incremental oil, but they have inherent limitations. The current EOR technologies are presented in a proper perspective, pointing out the technical reasons for the lack of success. Methods for improving oil recovery, in particular those concerned with lowering the interstitial oil saturation, have received a great deal of attention both in the laboratory and in the field. From the vast amount of literature on the subject, one gets the impression that it is relatively simple to increase oil recovery beyond secondary (assuming that the reservoir lends itself to primary and secondary recovery). It is shown that this is not the case. Many reservoirs suitable for steam injection and carbon dioxide have already been exploited and are approaching maturity. Other EOR methods suffer from limitations that have little to do with economics. Recovering incremental oil is complex and costly, and has been successful only for a few processes under exacting conditions. Nevertheless, EOR will continue to have an important place in oil production, in view of the escalating energy demand and the tight supply. It is suggested that much research is needed to develop technologies for recovering over two-thirds of the oil that will remain unrecovered in reservoirs. Key references are indicated.