The Eakring Dukeswood oil field: an unconventional technique to describe a field’s geology

Abstract

The Eakring Dukeswood oil field of Nottinghamshire was last produced in 1971. All wells have since been abandoned and the licence ML 1 expired on 22 April 1992. Cumulative production was small by North Sea standards, but during the Battle of the Atlantic the field produced the bulk of the UK's indigenous crude, peaking at 1600 BOPD in 1941. Cumulative recovery was some 6.5 MMSTB from an estimated 25.6 MMSTB in place in the completed horizons. In 1986 a study was undertaken to evaluate the remaining reserve potential.The primary tool for such work would normally be a detailed geological model, but since less than 25% of the 197 grid drilled wells have any wireline logs or cores only structural models existed. There is very little seismic. A further complication is that there were nine productive horizons and the majority of well completions were unsegregated over four of them. Only 20% of cumulative production can be assigned unequivocally to any one reservoir.Reservoir models, and individual reservoir contributions to production, had to be determined using less conventional techniques. Individual well performance under recycled peripheral water flood has proved to be a powerful tool to determine reservoir connectivity. Mapping decline rate reversal and water breakthrough by month indicates the transmissibility fairways and no-flow barriers in the system. It has also proved in some circumstances a useful discriminator of reservoir contribution.The reservoirs are mainly Westphalian A to Namurian B siliciclastics. All were undersaturated at initial conditions. Porosity is often secondary, rarely above 20% and absolute permeability ranges from less than 1 to several hundred mD. Irreducible water saturation (S wi ) from mercury injection data ranges between 30 and 50%o and water flood experiments indicated residual oil saturation (S or ) at 30%>. The oil is waxy, up to 16%) by weight, and has a high viscosity with correspondingly unfavourable mobility. API gravities range from 31.9-37.6°. Most production was obtained from the Loxley Edge Rock, the Sub Alton and Crawshaw sandstones-all by depletion drive, and from the Ashover Grit-in part water driven. Post-war water flooding was directed mainly at the Sub Alton and Crawshaw units.Regional studies and sedimentological examination of two recent adjacent wells established the likely broad reservoir anatomy. This was then refined for the field from the qualitative transmissibility maps constructed from flood front behaviour. Geological models could then be assembled with some confidence and bypassed oil and secondary accumulations were identified. Relative permeability experiments on the modern core indicate an additional field reservoir/accumulation, previously unrecognized.The Eakring Dukeswood oil field of Nottinghamshire ( Fig. 1) was developed during the 1939-1945 war. It provided much of the UK's indigenous crude oil at that time, and was last produced in 1971. Modern reservoir data acquisition was then in its infancy, and less than 25% of the wells have any petroph...

Inversion tectonics of the Variscan foreland of the British Isles

“…The folds are en-echelon in map view and have the geometry of flower structures in cross-section (Corfield 1991). They are of a similar size and trend to those in the Eakring-Dukeswood oilfield in the East Midlands (Storey & Nash 1993), although structural dips appear to be greater in North Staffordshire.…”

Sequence stratigraphy of the Westphalian in the northern part of the Southern North Sea

“…However, the middle and upper parts of the Westphalian B are notably sand free in the offshore and are more similar to the successions in the East Midlands (e.g. Rothwell & Quinn 1987;Fraser & Gawthorpe 1990;Fraser et al 1990;Cope et al 1992;Storey & Nash 1993). Similarly, Besly et al (1993) report that the red bed succession within the Southern North…”

UK oil and gas fields: an overview

“…It is appropriate then that this Memoir contains papers on fields in both the Weald and East Midlands basins. Despite being small in size, owing in part to wartime demand, some of the earliest East Midlands fields (Lees & Tait 1945) were developed via intensive drilling, for example Eakring-Dukeswood (197 wells) produced 6.5 MMbbl of oil (Storey & Nash 1993). Following a change in licensing terms and oil price improvement, a rejuvenation of activity in the 1980s led to many more relatively small pools being discovered by BP and others (Candy 1983).…”