The Elgin and Franklin fields: UK Blocks 22/30c, 22/30b and 29/5b

The Elgin and Franklin fields are high pressure/high temperature (HP/HT) (1100 bars, 190°C) gas condensate accumulations lying in the southern Central Graben in UK Blocks 22/30c, 22/30b and 29/5b. The Elgin Field comprises a complex faulted anticlinal structure and the Franklin Field, a tilted fault block. The principal reservoir comprises highly bioturbated, very fine-grained, shallow marine sandstones of the Upper Jurassic Fulmar Formation. A significant amount of secondary porosity (up to half the observed porosity) developed in these deep fields (>5 km subsea) which together with the extreme overpressure (500 bars excess) and stable grain mineralogy resulted in preservation of high quality reservoirs. The hydrocarbons have been sourced from the Upper and Middle Jurassic shales and coals and are sealed by the Upper Jurassic shales and Lower Cretaceous marls. The gas condensates are liquid rich with condensate yields of up to 1345 g Sm −3 in Elgin and 695 g Sm −3 in Franklin. The fields, discovered in 1985 (Franklin) and 1991 (Elgin), are currently being developed with production start-up scheduled for 2000. Recoverable reserves are estimated to be around 25 × 10 9 m 3 (890 × 10 9 SCF) gas and 29 × 10 6 tonnes (245 × 10 6 BBL) condensate for Elgin and 23 × 10 9 m 3 (820 × 10 9 SCF) gas and 15 × 10 6 tonnes (120 × 10 6 BBL) for Franklin.