Appraisal geology of the Saltire Field, Witch Ground Graben, North Sea

Saltire is a structurally and stratigraphically complex field that lies within the Witch Ground Graben. It is located 200 km northeast of Aberdeen, Scotland in UK North Sea Block 15/17. Three sandstone reservoirs contain an estimated 224 × 10 6 BBL of oil-in-place within a 2500 acre closure. The field was discovered in 1988. Subsequent appraisal drilling incorporated 3D seismic and detailed stratigraphic studies to produce the coherent geological reservoir models needed for development planning. Field production will begin in 1993. The Upper Jurassic section contains the Piper and Galley sandstone reservoirs which occur within a broad, E-W-orientated fault terrace. Northerly closure results from a down-to-the-south normal fault. Southern and westerly closures result from Piper sandstone erosional truncation and Galley sandstone pinch-out. Both reservoirs have easterly dip closure. The Piper Formation is a fluvial to wave-influenced deltaic marine sequence of latest Oxfordian to mid-Kimmeridgian age. It is up to 280 ft thick. The reservoir is fault separated into Main and Western areas with API oil gravities of 42.5° and 38°, respectively. The Galley sandstone reservoir contains 42.5° API gravity oil and occurs within the northeast area. It is a deep marine turbidite sequence of late Kimmeridgian age and has a maximum reservoir thickness of 205 ft. An Early Cretaceous sandstone reservoir occurs within the upper Valhall Formation. It comprises two marine turbidite sandstones of late Barremian to early Aptian age, with up to 95 ft of composite thickness. The reservoir has three-way dip closure, pinches out by onlap to the north and contains 33° API gravity oil.