User:Huligan0/Kimmeridge Oil Field

Kimmeridge Oil Field
The "Nodding Donkey"

The Kimmeridge Oil Field is to the northwest of Kimmeridge Bay, on the south coast of the Isle of Purbeck, in Dorset, England.

Location

Kimmeridge is about 6 kilometres (3.7 mi) south of Wareham and about 8 kilometres (5.0 mi) west of Swanage. The Kimmeridge oil field is part of the Wytch Farm oil field and processing facility operated by BP, on the southern shore of Poole Harbour, which is about 3 kilometres (1.9 mi) north of Corfe Castle. Kimmeridge Bay and its cliffs are part of the Jurassic Coast, a World Heritage Site, because of the quality and variety of geological landforms along the coast.

• See also: List of places on the Jurassic Coast

History

In Dorset the search for oil started back in 1935. Between 1958 and 1980 six wells were drilled in Kimmeridge Bay. The first drilling of the Kimmeridge oil field was the B1 to the north of Broad Bench, which revealed neither oil nor gas. The second drilling B2, later renamed K1, was made in 1959 and both oil and gas were discovered. The K2 (drilled 1960) to the east of the car park showed only small amounts oil, but it was retained as an observation well. The drillings K3 (drilled 1959 to 1960) at Broad Bench and K5 (drilled in 1980 near the K1 well) exposed only weak oil contents, while the drilling K4 in 1960, east of Brandy Bay by Long Ebb, revealed no exposures due to a mechanical breakdown.

The Kimmeridge K1 well site, is a small site, with a single beam pump or "nodding donkey" which has been pumping continually since 1961, making it the oldest working oil pump in the UK. The well once produced 350 barrels per day, but currently yields around 65 barrels per day (10.3 m³/d) from the Jurassic strata that lie around 350 metres (1,150 ft) below the cliff. The well has been operating this long because it is tapped into a network of connected reserves, however the yield is decreasing. The oil is transported by tanker to Wytch Farm, from where it is piped to the storage tanks at Hamble-le-Rice on Southampton Water before being shipped to the main refinery. The nodding donkey has a high wire-mesh fence around it. But it can be viewed clearly from all sides, as it bobs up and down, gazing out over the Kimmeridge Ledges and 8 kilometres (5.0 mi) of coast where bedrock extends at least half a kilometre out to sea under the waves.

Formation of Gas and Oil

Drawing of an oil reservoir
in an anticline trap

Millions of years ago the greater part of the planet was covered by oceans or the land was covered by swamps. As the microscopic animals and plants died, their remains were deposited on the sea bed. These remains were combined with materials that were eroded from the higher grounds. Gradually the mixture was compressed to form sedimentary rocks such as sandstone and limestone. Due to the lack of oxygen, the small organisms did not decay. They were transformed by the high pressure from above and the heat from below into gas and oil. As further sediments subsequently formed above, gravity, capillary action and the additional pressure forced the gasses and oils out of their source rock. These gasses and oils were pressed upwards through the porous rocks.

If the rising progress is stopped or prevented by an impermeable sediment tier (Cap rock) and if any sideways movement is prevented by a fold or fault in the earth's structure, then the gasses and oils are trapped in a reservoir and held within the pores between grains. To reach the oil, a hole must to be drilled and the oil has to be sucked out. The oil is not coming from the Kimmeridge Clay, which can be found here at ground level and drops under the surface to about 200 meters below see-level. The source of this oil is almost certainly the deeper laying Early Jurassic (Lias) bituminous shale under the English Channel Basin.