Experiences after 10 years of waterflooding the Ekofisk Field, Norway

This paper describes the experiences and results after more than 10 years of waterflooding the fractured Ekofisk chalk formations from a reservoir engineering and reservoir management perspective. Water injection was initiated at Ekofisk in 1987 following two successful pilot projects. The waterflood was implemented in a series of stages, and currently 800,000 BWPD is being injected into the entire vertical column of the reservoir using 38 injectors in a staggered line drive pattern. A total of 2 billion barrels of water has been injected in the first 10 years of waterflood operations. Field average water production is currently below 80,000 BWPD. Oil rate responses, GOR declines and low water production rates indicate a very efficient oil displacement process is occurring. Examples of waterflood performance in terms of areal and vertical sweep efficiency, production responses and displacement efficiency will be reviewed together with overall reservoir management aspects including seabed subsidence and reservoir compaction.