Dynamic Faults in the Ekofisk Field?

Nina E. Hagen
Conocophillips, Tananger, Norway

The Ekofisk field is the largest in the North Sea Chalk play. After more than 30 years of production, more than two billion barrels of oil has been produced, but still approximately one billion barrels of oil to be produced. After injecting more than three billion barrels of water during 19 years, large part of the reservoir is water-flooded. In order to place new wells in an optimum position in order to reduce the risk of early water breakthrough, accurate modeling of the water movement has turned out to represent a significant challenge.

Recently, a core was cut in a well drilled 70 m from an injector that had been injecting for 19 years. Data from the well showed a very effective sweep through all flow units leaving no oil zones behind. Wells drilled outside the most mature water-flooded areas, often shows oil and water zones controlled by a combination of faults and fractures, layer-dependant properties, and/or capillary forces. Layer dependent properties will not be covered by the talk.

Seismic 4D effects between 4 different seismic vintages have proven to be a valuable dataset in evaluating areas of compactions. Further analysis of amplitude differences between the surveys gives a good correlation with the water-flooded zones.

The 4D effects are constrained by faults in some, but not all cases. Water breakthrough zones are related to, and often constrained by faults. In additions we see that in areas were the water-flood is mature a very effective sweep is achieved.

Examples like this may be indicative to that fault in the Chalk change, or at least alter behavior, as the field is being produced and/ or re-pressurized by injection.

AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery