This paper provides a summary and a guide of the Enhanced Oil Recovery (EOR) technologies initiated in the North Sea in their period from 1975 until today. The five EOR technologies which have been initiated in the North Sea were hydrocarbon miscible gas injection, WAG injection, SWAG injection, FAWAG injection and MEOR. Each EOR technology which has been initiated in the North Sea was identified with its respective maturity level and / or maturing time frame, technology use restrictions and process efficiency on the basis of incremental oil.
Apart from WAG at Ekofisk and FAWAG at Snorre CFB, all technologies have been applied successfully on the corresponding fields. Hydrocarbon miscible gas injection and WAG injection can be considered as mature technologies in the North Sea. The most commonly used EOR technology in the North Sea was WAG and recognized as the most successful EOR technology.
The main problems experienced were injectivity (WAG, SWAG and FAWAG projects), injection system monitoring and reservoir heterogeneities (hydrocarbon miscible gas injection, WAG, SWAG and FAWAG projects). About 63% of all the reported EOR field applications have been initiated on the Norwegian Continental Shelf, 32% on the U.K. Continental Shelf and the remainder on the Danish Continental Shelf. Statoil was the leader in conducting EOR field applications in the North Sea. In the future, the majority of research will be conducted on microbial processes, CO2 injection and WAG (including SWAG) injection schemes.
In this review laboratory techniques, world statistics, simulation tools and economical evaluation was not considered and is outside the scope of this paper.
In the North Sea, current average recovery factors[1,2,3,55] are above 40%. As of 2003, the estimated oil reserves55 on Norwegian Continental Shelf (NCS) are about 3850 Msm3, translating to an average recovery factor of 45% as shown in Figure 1. However, 50% average oil recovery factor has been set as a target by Norwegian Petroleum Directorate (NPD) and Oil and Gas in the 21st Century (OG21), which will give 600 Msm3 additional oil. Among other technologies, Enhanced Oil Recovery (EOR) is one of the solutions to meet this goal.
Since 1982, several major Norwegian IOR programs, as listed in Table 1, have been initiated for additional oil recovery. About 50 million USD have been invested in these Norwegian research programs (1982 - 1995). In 2003, Oil and Gas in the 21st Century (OG21) identified nine technology target areas to obtain the average recovery factors of 50% for oil and 75% for gas on the NCS. Based on the IOR-potential for each method and an evaluation of the importance and complexity of the technology gap, they proposed the following ranking of the different recovery methods:
Priority 1: (a) HC gas injection, WAG / SWAG and FAWAG (b) CO2-flooding (c) MIOR
Priority 2: (a) Waterflooding (b) Massive Depressurization (c) Air Injection
Priority 3: (a) Gas Condensate (b) Water additives (c) N2 and flue gas injection
Apart from these research programs, it is important to review the EOR technologies which have been initiated in the North Sea. The application of EOR technologies in the North Sea environment is more complex and quite different from onshore applications. Thus, it is necessary to identify the applied EOR technologies in the North Sea with their respective maturity level, technology use restrictions and process efficiency on the basis of incremental oil.
The intention of this review is to sort out the different Enhanced Oil Recovery (EOR) technologies which have been initiated in the North Sea. This review work doesn't introduce any new technology for Enhanced Oil Recovery (EOR) in the North Sea, rather it should be considered as a guide for the Enhanced Oil Recovery (EOR) technologies initiated in the North Sea.