Culzean: finding two deep gas reservoirs under a salt diaper in the central North Sea
Discovered in 2008 by Maersk Oil, Culzean is a HPHT gas condensate field in the East Central Graben area of the central North Sea, located 260 km off the coast of Aberdeen. It consists of lean gas accumulations in sandstone of the Jurassic Pentland formation and the Triassic Skaggerak formation.
Because the two deep reservoirs are sitting beneath traditional reservoirs that play in the North Sea, and beneath the Merganser chalk diaper as well, the area had long remained in obscurity. Fully assessing the area had represented quite a challenge.
The already available conventional seismic obtained from conventional Narrow Azimuth streamer (NAZ) data was not sufficient in terms of data quality. However Maersk Oil acquired a High Density Ocean Bottom Cable (HDOBC) acquisition survey in 2010/2011. This Full Azimuth data provided a better delineation of the reservoirs by enhanced illumination around the salt diaper.
With resources now estimated at 250-300 million barrels of oil equivalent, Culzean is the largest UK gas field to be sanctioned for quarter of a century. Its production is expected to start in 2019 and continue for at least 13 years, providing 5% of total UK gas demand.
Total & Maersk Oil
By Michael Borrell
The Culzean story