Fulmar Sandstones, Correcting Some Received Wisdoms in the Greater Kittiwake Area (North Sea)

Abstract

The Fulmar Formation Sandstones in the Central North Sea are a prolific oil and gas play with new developments still being added 35 years after the first discovery in 1975. Typically interpreted as shallow marine, shore-face sands, there is a pronounced halokinetic element to the distribution of the hydrocarbon accumulations.The Greater Kittiwake Area, GKA, covers several license blocks in quadrant 21. The Kittiwake oil field was developed standalone with a small platform and tanker export with first production in 1990. A satellite field, Mallard, was added in 1998. The fields and surrounding acreage, including several small Fulmar discoveries, were acquired from the original owners in 2003.Since then Mallard was redeveloped leading to a ten-fold increase in production. Also three Fulmar discoveries were tied-back -Gadwall, Goosander and Grouse. In addition to the production capacity boost, production uptimes were improved and there was sufficient confidence to install an export pipeline. Other satellite discoveries are under consideration as future tie-backs.There have been surprises along this journey that contradicted pre-development assumptions about Fulmar sandstone reservoirs. A key one relates to the unanticipated strength of the aquifer response in the 'new' satellite developments. This flew in the face of received wisdom about Fulmar reservoirs typically not experiencing aquifer drive. It challenges regional expectations about the prerequisite aquifer distribution and size for aquifer drive, also about levels of diagenesis in the water-leg.In GKA, the Fulmar formation often thins off-structure below seismic resolution -coupled with regional depositional models this is difficult to square with field data from which aquifer drive can be inferred unambiguously. Anticipating where aquifer influx will likely be experienced is important for future developments, as pressure maintenance by waterflood is otherwise required for such tie-backs bringing higher costs and complexity. * Previously Venture Production plc