Jurassic sandstone plays in the Danish central Graben, North Sea - New Results

Recent exploration activities have led to encouraging results in Jurassic - Lower Cretaceous sandstones in the Danish Central Graben. Two Upper Kimmeridgian High-Temperature High-Pressure (HTHP) environment sandstone plays have been investigated. 1) The Hejre wells located in the Gertrud Graben found oil in the Upper Jurassic shallow marine shoreface sandstones at a depth below 5000 m. 2) The Svane-1 well located in the northern part of the Tail End Graben found gas-bearing sandstone successions of deep marine gravity-flow origin below 5300 m. Further, a number of wells drilled within the most recent years adjacent to existing Jurassic discoveries all encounter hydrocarbons in Middle or Upper Jurassic sandstones. The good porosity on the HTHP sandstone plays is linked to dissolution of feldspar grains and to thick pore-lining illite coatings which inhibit quartz precipitation. Upper Jurassic shallow and deep marine sandstones are sourced from the prolific claystones of the Farsund Formation; Middle Jurassic fluvial-deltaic sandstones are sourced from interbedded coals and coaly claystones. The future challenge is to predict the distribution of sandstones that have undergone a favourable diagenetic development. The focus in this review will be on distribution and quality of sandstone reservoirs.