Ekofisk Formation Pilot Waterflood

Abstract

ABSTRACT This paper describes the design, operation and evaluation of a pilot waterflood project initiated in the Lower Ekofisk Formation of the Ekofisk Field located in the Norwegian sector of the North Sea. Previously, a pilot waterflood project in the Tor Formation led to approval in 1983 of full scale water injection in the Tor Formation. The Ekofisk and Tor Formations are both low matrix permeability chalks characterized by intense natural fracturing. This natural fracturing has enhanced overall permeability and made commercial production possible from these volumetric solution gas drive reservoirs. The Ekofisk Formation was initially given lower waterflood priority based on spontaneous imbibition laboratory experiments. However, the large values of initial oil in place, in combination with the recognition that mechanisms other than imbibition may play a role in waterflood performance necessitated a pilot be performed. Additionally, the pilot was designed to evaluate rock stability and injectivity in this fractured chalk reservoir. The pilot project consisted of one injector and three producers in an unconfined four spot pattern. As of May 1988, a total of 10 million barrels of water had been injected over a 22 month period. Results have been favorable and have been utilized to justify expansion of the waterflood to the Lower Ekofisk Formation. Factors which were taken into consideration during the analysis include lack of both vertical and horizontal confinement, significant initial gas saturation, influence of gas injection, regional permeability variations, anisotropy and layering effects. Three dimensional simulation results are included which tie all the parameters together and form the basis for extrapolating results to full field.