The Curlew Field, Block 29/7, UK North Sea
In 1964, Block 29/7 was awarded as part of the first licencing round to Shell and Esso (UK). The Curlew area comprises a series of terraces that step down from the Western Platform into the West Central Graben. Exploration drilling started in 1977 but it wasn't until 1990 that well 29/7-4 successfully tested a 100 ft column of undersaturated volatile oil in the Upper Jurassic Fulmar Formation sandstones. Further exploration drillng, aided by 3D seismic data (acquired in 1991), yielded additional discoveries: Curlew C (1993, oil) and Curlew D (1994, condensate-rich gas). In Curlew D new technologies were succesfully applied to described and evaluate the isolated hanging wall compartment. Oil was discovered in what is now called Curlew D South in February 2000.
Hydrocarbon accumulations in the Curlew area occur in dip-closed faulted anticlinal structures. The producing Upper Jurassic Fulmar Formation is a heterogeneous mix of bioturbated shallow marine sandstones. barrier sandstones, and lagoonal/swamp deposits. The range in reservoir quality is reflected in the field porosity (5-27%) and permeability (0.001-800 mD). Reservoir compartments in the field (curlew B, D, and D South) are controlled by complex reservoir architecture, structure and fault geometry. Each reservoir compartment is characterized by a different fluid contact and a distinct fluid type. The reservoir heterogencity provieds potential for bypassed hydrocarbons in undrilled compartments, as was proven by the Curlew D South development.
Curlew B, D, and D South have since been developed. Evacuation of hydrocarbons from the Curlew area is via the Maersk Curlew FPSO, to which the producing wells have been tied back. Gas is fed nto the Fulmar Gas Line and oil is taken onshore by shuttle tankers. The initially-in-place volume in Curlew B at standard conditions is 24 MMSTB of oil and 25 BSCF of solution gas. Curlew B was developed via horizontal well 29/7-10y and came on stream in November 1997 at a rate of about 23 000 STB/D. The initially-in-place volume in Curlew D is 340 BSCF of gas and 100 MMSTB of condensate. Curlew D was developed via two vertical wells, 29/7-8z and 29/7-9, and started production in February 1998 with production rates up to 115 MMSCF/D of gas and 34 000 STB/D. Gas production from the field is constrained. however, by the facilities. Curlew D South is developed by the vertical well 29/7-11 which came on stream in March 2000 after a North Sea record-time tie back of the original appraisal well.