The Andrew and Cyrus Fields, Blocks 16/27a, 16/28, UK North Sea
The Andrew and Cyrus fields lie in UK Blocks 16/27a and 16/28 at the junction of the Witch Ground Graben and the South Viking Graben. The Andrew Fields was discovered in 1974 with well 16/28-1, and Cyrus in 1979 with well 16/28-4. Both fields share a common reservoir the Paleocene Andrew Formation and both are sealed by the overlying Andrew Shale and Sele Formation. Similarly the traps for both fields formed above swells within Zechstein salt. The Andrew and Cyrus Fields differ in their petroleum content. Andrew contains both gas and oil (40API) while Cyrus contains only oil (30API).
Reserves for the Andrew Field are 140MMBBL based upon a 46% recovery factor using natural aquifer drive. The same mechanism will deliver 16.5MMBBL from Cyrus at a 21 % recovery factor. Production began from Andrew in July 1996. Cyrus production began in April 1990 using the SWOPS system until April 1992. The small field was subsequently tied back to Andrew.