Wytch Farm is an oil field and processing facility in Dorset, England. It is the largest onshore oil field in Western Europe. The facility, taken over by Perenco in 2011, was previously operated by BP. It is located in a coniferous forest on Wytch Heath on the southern shore of Poole Harbour, two miles (3.2 km) north of Corfe Castle. Oil and natural gas (methane) are both exported by pipeline; liquefied petroleum gas is exported by road tanker.

History

Name

The oil field takes its name from the neighbouring Wytch Farm which had existed on the site for many centuries on the fringes of Wytch Heath.

Pre-1973

The earliest industry in the Wytch Farm area dated to the early medieval period and featured multiple salt production workshops. The workshops, adjacent to the modern oilfield, were part of a medieval salt industry owned by Milton Abbey. The site was excavated by Bournemouth University under the directorship of Dr Derek Pitman.

The Isle of Purbeck's oil shale, or "Kimmeridge Coal" which has been won from the cliffs to the east of Kimmeridge since the early 17th century, is no longer used commercially. Similar deposits were found at Wytch Farm in the 1890s,

The Isle of Purbeck's oil industry began in 1936 with the first unsuccessful and then experimental wells drilled at Broad Bench near Kimmeridge by D'Arcy Exploration. It was not until 1959 that a borehole at Kimmeridge showed that oil was seeping out, and 1960 that BP's Kimmeridge Oil Field was discovered. In May 2011, BP announced that it had agreed to sell its majority interest in Wytch Farm to Perenco, which became the new operator. Premier Oil has a 30.1% stake in the field. On 17 May 2011, BP announced the sale of its interests in the Wytch Farm, Wareham, Beacon and Kimmeridge fields to Perenco and the sale of the Dimlington gas terminal to Perenco in February 2011. In September 2012, Perenco UK applied to Dorset County Council (DCC) for permission to extend the life of 39 planning permissions at three of the oilfields. DCC's Planning Committee recommended approval of the applications on 6 September 2013, thereby extending to 2037 the operational life of the oilfields, beyond their original end-date of 2016.

2023 oil spill

On 26 March 2023, the Poole Harbour Commissioners reported that around 200 barrels of "reservoir fluid" had leaked into Poole Harbour from one of the oil field's pipelines. The Environment Agency described it as a "major incident". Bournemouth Christchurch and Poole Council leader Philip Broadhead called the leak "unacceptable...some serious questions need to be answered".

Geology

The field is located in a faulted block of Jurassic and older rocks beneath the Hampshire Basin, close to the steeply sloping monocline in the overlying chalk. It forms part of the Wessex Basin.

The Purbeck Monocline defines the field's southern limit. The field consists of three separate reservoirs known as Bridport, Sherwood and Frome. Bridport, the first discovery, is in the Jurassic Bridport Sands below Poole Harbour, with an oil source in the Lower Lias. The much larger Sherwood (discovered 1978) is below this in the Triassic Sherwood Sandstone at and extends under Poole Bay. The Frome reservoir is in a shelly limestone within the Frome Clay at . The field extends eastwards from Sandbanks and Studland for around under the sea to the south of Bournemouth.

Environment

thumb|Wytch Farm oil wells

Most of the field is protected by various conservation laws, including the Jurassic Coast World Heritage Site, Purbeck Heritage Coast and a number of sites of special scientific interest, areas of outstanding natural beauty and nature reserves (including Studland and Brownsea Island), so the gathering centre and most of the well sites are small and well screened by trees. Directional drilling has also contributed to reducing the impact on the local environment, with extended reach drilling from the Goathorn Peninsula attaining distances in excess of 10 km.

Production and reserves

thumb|right|Well site M, Goathorn Peninsula

Production grew from in 1984 and eventually peaked at in 1997; by 2002 this had declined to . that will last until 2020 and 2025 respectively.

Oil is also transported to Wytch Farm for processing from two smaller Dorset oilfields, Wareham (discovered in 1964) by pipeline and Kimmeridge Oil Field (discovered in 1959) by road.

Oil is piped about from Wytch Farm via Fawley to a terminal on the far side of Southampton Water at Hamble, for export by tanker. Natural Gas (methane) is piped to Sopley, north of Christchurch, for use in the national domestic gas supply network. Smaller quantities of liquefied petroleum gas are transported by road. Oil is routed to the first stage separator where initial separation of the well fluids into its component parts takes place. Produced water settles to the bottom of the horizontal separator vessel, oil floats on the water layer and gas (vapour) occupies the top of the vessel. These three fluids are withdrawn continuously from the vessel to downstream plant.

Oil flows to further separators operating at lower pressures, where further vapour and produced water are separated and removed. The oil then passes to a desalter to reduce the salt content. Fresh water is added to the oil and the oil-water mixture which is allowed to settle. The salt dissolves preferentially in the water phase reducing the salt content of the oil. Treated oil is cooled and stored in tanks before finally being pumped through the 16-inch (0.4 m) pipeline to the storage and loading facility at Hamble.

The vapour from the separators is cooled, compressed and dehydrated by counter-current contact with glycol. It is chilled by refrigeration and routed to a series of fractionation towers. These include a de-ethaniser which separates the methane (CH<sub>4</sub>) from ethane (C<sub>2</sub>H<sub>6</sub>). There is a depropaniser to remove propane (C<sub>3</sub>H<sub>8</sub>) and a debutaniser to remove butane (C<sub>4</sub>H<sub>10</sub>).

The oil product sent to Hamble has the following properties:

{| class="wikitable"

!Parameter

!Value

|-

|API Gravity

|40.2°API

|-

|Density at 15&nbsp;°C

|0.8237&nbsp;kg/l

|-

|Sulphur by weight

|0.12 %

|-

|Nitrogen

|590 ppm

|-

|Reid Vapour Pressure

|65.5 kPa

|-

|Pour Point

|0&nbsp;°C

|-

|Total Acid Number

|0.1 mgKOH/g

|-

|Viscosity at 40&nbsp;°C

|4.4 cSt

|-

|Viscosity at 50&nbsp;°C

|3.6 cSt

|-

|Vanadium

|0.2 ppm

|-

|Nickel

|1 ppm

|}

See also

  • Energy policy of the United Kingdom
  • Energy use and conservation in the United Kingdom

References

  • Radio 4 In Living Memory July 2009 with Chris Ledgard