Summary 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.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe objective of this study is to determine parameters that have major impact on the recovery from air injection into low permeable fractured chalk reservoirs that produce light oils, such as the Ekofisk field in the Norwegian North Sea.Earlier works on air injection into light oil reservoirs mainly focused on mathematical modeling of air injection and also on laboratory studies. In this paper, we present results from numerical simulation study.Results show that when recoveries from low permeability and high permeability reservoirs are compared, recovery is accelerated in the former. In addition, for maximum recovery, air should be injected into all layers containing hydrocarbons. The ultimate recovery from air injection was observed to be insensitive to the amount of water injected during the secondary recovery phase. Also, for optimum recovery, there exists a minimum temperature at which air should be injected, this temperature being a function of the injection rate. Lastly, we observed that residual oil saturation to gas does not have any significant effect on the recovery factor from air injection.These results are only valid for single porosity systems and may not all apply to dual porosity systems. Also, no economic analysis was undertaken in this study.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThis paper provides a summary and a guide of the Enhanced