Seawater in Chalk: An EOR and Compaction Fluid

North Sea chalk reservoirs are characterized as pure biogenic,<br>natural fractured, low matrix permeability, and very high<br>porosity, 30-45%. The reservoir temperature is usually high,<br>>90 oC, and the wetting conditions appeared to be moderate<br>water-wet to neutral. Even though the permeability contrast<br>between the matrix and fractures is significant, the injection of<br>seawater has been a great success with the Ekofisk field as an<br>example (estimated oil recovery is now approaching 50%).<br>Seawater appeared to improve the water wetness of chalk,<br>which increases the oil recovery by spontaneous imbibition<br>and viscous displacement.