The Ekofisk fractured chalk reservoir located in the North Sea south-west of Norway has been exploited successfully for more than three decades, largely due to injection of sea water. In a study concluded in 2004, air injection was evaluated as a method for additional hydrocarbon recovery beyond the secondary waterflood recovery. Supported by the European Commission through the fifth framework program, the Ekofisk Field owners joined forces with leading European research institutes and a contractor to investigate the potential of air injection as a cost effective IOR method. Through screening studies, extensive laboratory experiments, reservoir simulations, design of processing facilities and project feasibility evaluations, an extensive knowledge base of the air injection process for light oil fractured reservoirs was established.

In the present paper technical results will be presented. Recovery mechanisms related to an air injection process in a fractured light oil reservoir have been studied through laboratory experiments and reservoir modeling. The laboratory experiments verified air injection as a potential IOR method for a light oil fractured chalk field. Laboratory experiments were performed in order to study kinetic properties such as activation energies and ignition temperatures. In addition, diffusion coefficients were estimated through laboratory experiments and verified by numerical simulations. Potential weakening of the chalk due to heat and CO2 was evaluated based on laboratory experiments and geo-mechanical modeling. Combustion tube experiments were conducted in order to study propagation of the combustion front through porous media.

Finally, a field scale air injection feasibility study was performed. The outcome of this study, including an evaluation of potential production benefits and main cost items involved in an air injection project, is presented.

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