This paper provides a summary and a guide of the enhanced-oil-recovery (EOR) technologies initiated in the North Sea in the period from 1975 until beginning of 2005. The five EOR technologies that have been initiated in this region are hydrocarbon (HC) miscible gas injection, water-alternating-gas (WAG) injection injection, simultaneous water-and-gas (SWAG) injection, foam-assisted WAG (FAWAG) injection, and microbial EOR (MEOR). Each EOR technology that has been initiated in the North Sea was identified with its respective maturity level and/or maturation time frame, technology use restrictions, and process efficiency on the basis of incremental oil.
Apart from WAG at Ekofisk and FAWAG at Snorre central fault block (CFB), all technologies have been applied successfully (i.e., positive in economic terms) to the associated fields. HC miscible gas injection and WAG injection can be considered mature technologies in the North Sea. The most commonly used EOR technology in the North Sea has been WAG, and it is recognized as the most successful EOR technology.
The main problems experienced were injectivity (WAG, SWAG, and FAWAG projects), injection system monitoring, and reservoir heterogeneities (HC miscible gas injection, WAG, SWAG, and FAWAG projects). Approximately 63% of all the reported EOR field applications have been initiated on the Norwegian continental shelf (NCS), 32% on the UK continental shelf, and the remainder on the Danish continental shelf. Statoil has been the leader in conducting EOR field applications in the North Sea. The majority of future research will concentrate on microbial processes, CO2 injection, and WAG (including SWAG) injection schemes.
In this review, laboratory techniques, global statistics, simulation tools, and economical evaluation were not considered and are considered outside of the scope of this paper.
In the North Sea, current average recovery factors (Hughes 2004; Xia 2004; Hansen and Westvik 2000; Blaker et al. 2006) are above 40%. As of 2003, the estimated oil reserves (OG21 2006) on the NCS are approximately 3850 million sm3, translating to an average recovery factor of 45% as shown in Fig. 1. The Ministry of Petroleum and Energy of Norway established the OG21 Task Force in 2001 to address the challenge of targeting a 50% average oil recovery factor set by the Norwegian Petroleum Directorate (NPD). This will yield 600 million sm3 additional oil. Among other technologies, EOR is one of the solutions to meet this goal.
Since 1982, several major Norwegian increased-oil-recovery (IOR) programs (Hinderaker et al. 1996), as listed in Table 1, have been initiated for additional oil recovery. Approximately 50 million USD has been invested in these Norwegian research programs (1982-1995). In 2003, the Oil and Gas in the 21st Century (OG21 Task Force) identified nine technology target areas to obtain the average recovery factors of 50% for oil and 75% for gas on the NCS (Blaker et al. 2006). On the basis of 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; and (c) MIOR.
Priority 2: (a) waterflooding; (b) massive depressurization; and (c) air injection.
Priority 3: (a) gas condensate; (b) water additives; and (c) N2 and flue-gas injection.
Apart from these research programs, it is important to review the EOR technologies that have been initiated in the North Sea. The application of EOR technologies in the North Sea environment is more complex than, 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 main objectives of this survey are to categorize the different EOR technologies initiated in the North Sea with respect to their respective maturity level to recognize important EOR related data such as reservoir fluid, formation properties, injection parameters, and enhanced production. In addition, we attempt to identify the EOR frontrunner in the North Sea by method, technology, location and company, lessons learned/key issues regarding EOR processes in the North Sea, and the EOR trend in the North Sea.
We would also like to emphasize that this review is based purely upon open literature and, therefore, may lack some important data that are not accessible through this source. This review should be considered as a guide for the EOR technologies initiated in the North Sea.