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71-586: Wytch Farm is an oil field and processing facility in the Purbeck district of 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

142-404: 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

213-556: A "major incident". Bournemouth Christchurch and Poole Council leader Philip Broadhead called the leak "unacceptable...some serious questions need to be answered". 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 . The Purbeck Monocline defines the field's southern limit. The field consists of three separate reservoirs known as Bridport, Sherwood and Frome. Bridport,

284-445: A cap rock) is a fundamental part of the trap that prevents hydrocarbons from further upward migration. A capillary seal is formed when the capillary pressure across the pore throats is greater than or equal to the buoyancy pressure of the migrating hydrocarbons. They do not allow fluids to migrate across them until their integrity is disrupted, causing them to leak. There are two types of capillary seal whose classifications are based on

355-406: A consequence, oil and natural gas are often found together. In common usage, deposits rich in oil are known as oil fields, and deposits rich in natural gas are called natural gas fields. In general, organic sediments buried in depths of 1,000 m to 6,000 m (at temperatures of 60 ° C to 150 °C) generate oil, while sediments buried deeper and at higher temperatures generate natural gas. The deeper

426-407: A few, very large offshore drilling rigs, due to the cost and logistical difficulties in working over water. Rising gas prices in the early 21st century encouraged drillers to revisit fields that previously were not considered economically viable. For example, in 2008 McMoran Exploration passed a drilling depth of over 32,000 feet (9754 m) (the deepest test well in the history of gas production) at

497-637: A gravity higher than 45 API. Gas cycling is the process where dry gas is injected and produced along with condensed liquid. Lias (period) The Early Jurassic Epoch (in chronostratigraphy corresponding to the Lower Jurassic Series ) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic–Jurassic extinction event , 201.3 Ma (million years ago), and ends at

568-481: A logistically complex undertaking, as it involves the equipment associated with extraction and transportation, as well as infrastructure such as roads and housing for workers. This infrastructure has to be designed with the lifespan of the oil field in mind, as production can last many years. Several companies, such as Hill International , Bechtel , Esso , Weatherford International , Schlumberger , Baker Hughes and Halliburton , have organizations that specialize in

639-657: A problem that makes correlation between sections in different parts of the world difficult. If this biostratigraphical indicator is used, then technically the Lias Group —a lithostratigraphical division—spans the Jurassic / Triassic boundary. There are extensive Liassic outcrops around the coast of the United Kingdom , in particular in Glamorgan , North Yorkshire and Dorset . The 'Jurassic Coast' of Dorset

710-471: A result of changes in the structure of the subsurface from processes such as folding and faulting , leading to the formation of domes , anticlines , and folds. Examples of this kind of trap are an anticline trap, a fault trap, and a salt dome trap. They are more easily delineated and more prospective than their stratigraphic counterparts, with the majority of the world's petroleum reserves being found in structural traps. Stratigraphic traps are formed as

781-435: A result of lateral and vertical variations in the thickness, texture, porosity, or lithology of the reservoir rock. Examples of this type of trap are an unconformity trap, a lens trap and a reef trap. Hydrodynamic traps are a far less common type of trap. They are caused by the differences in water pressure, that are associated with water flow, creating a tilt of the hydrocarbon-water contact. The seal (also referred to as

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852-502: A significantly higher displacement pressure such that the pressure required for tension fracturing is actually lower than the pressure required for fluid displacement—for example, in evaporites or very tight shales. The rock will fracture when the pore pressure is greater than both its minimum stress and its tensile strength then reseal when the pressure reduces and the fractures close. Unconventional (oil & gas) reservoirs are accumulations where oil and gas phases are tightly bound to

923-430: 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 91 kilometres (57 mi) 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

994-402: Is analogous to saying that the oil which can be extracted forms within the source rock itself, as opposed to accumulating under a cap rock. Oil sands are an example of an unconventional oil reservoir. Unconventional reservoirs and their associated unconventional oil encompass a broad spectrum of petroleum extraction and refinement techniques, as well as many different sources. Since the oil

1065-403: Is being pursued at a higher rate because of the scarcity of conventional reservoirs around the world. After the discovery of a reservoir, a petroleum engineer will seek to build a better picture of the accumulation. In a simple textbook example of a uniform reservoir, the first stage is to conduct a seismic survey to determine the possible size of the trap. Appraisal wells can be used to determine

1136-452: Is best to manage the gas cap effectively, that is, placing the oil wells such that the gas cap will not reach them until the maximum amount of oil is produced. Also a high production rate may cause the gas to migrate downward into the production interval. In this case, over time the reservoir pressure depletion is not as steep as in the case of solution-based gas drive. In this case, the oil rate will not decline as steeply but will depend also on

1207-426: Is called the stock tank oil initially in place . As a result of studying factors such as the permeability of the rock (how easily fluids can flow through the rock) and possible drive mechanisms, it is possible to estimate the recovery factor, or what proportion of oil in place can be reasonably expected to be produced. The recovery factor is commonly 30–35%, giving a value for the recoverable resources. The difficulty

1278-490: Is contained within the source rock, unconventional reservoirs require that the extracting entity function as a mining operation rather than drilling and pumping like a conventional reservoir. This has tradeoffs, with higher post-production costs associated with complete and clean extraction of oil being a factor of consideration for a company interested in pursuing a reservoir. Tailings are also left behind, increasing cleanup costs. Despite these tradeoffs, unconventional oil

1349-438: 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 4 ) from ethane (C 2 H 6 ). There is a depropaniser to remove propane (C 3 H 8 ) and a debutaniser to remove butane (C 4 H 10 ). Some of the gases – the methane and ethane – are used as fuel gas on

1420-481: Is exported by road tanker. 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. 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

1491-524: Is often associated with the pioneering work of Mary Anning of Lyme Regis . The facies of the Lower Jurassic in this area are predominantly of clays , thin limestones and siltstones , deposited under fully marine conditions. Lias Group strata form imposing cliffs on the Vale of Glamorgan coast, in southern Wales . Stretching for around 14 miles (23 km) between Cardiff and Porthcawl ,

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1562-542: Is probably paraphyletic ). All these plesiosaurs had medium-sized necks and large heads. In the Toarcian , at the end of the Early Jurassic, the thalattosuchians (marine " crocodiles ") appeared, as did new genera of ichthyosaurs ( Stenopterygius , Eurhinosaurus , and the persistently primitive Suevoleviathan ) and plesiosaurs (the elasmosaurs (long-necked) Microcleidus and Occitanosaurus , and

1633-649: Is shared between Iran and Qatar . The second largest natural gas field is the Urengoy gas field , and the third largest is the Yamburg gas field , both in Russia . Like oil, natural gas is often found underwater in offshore gas fields such as the North Sea , Corrib Gas Field off Ireland , and near Sable Island . The technology to extract and transport offshore natural gas is different from land-based fields. It uses

1704-413: Is that reservoirs are not uniform. They have variable porosities and permeabilities and may be compartmentalized, with fractures and faults breaking them up and complicating fluid flow. For this reason, computer modeling of economically viable reservoirs is often carried out. Geologists, geophysicists, and reservoir engineers work together to build a model that allows simulation of the flow of fluids in

1775-940: Is usually necessary to drill into the Earth's crust, although surface oil seeps exist in some parts of the world, such as the La Brea Tar Pits in California and numerous seeps in Trinidad . Factors that affect the quantity of recoverable hydrocarbons in a reservoir include the fluid distribution in the reservoir, initial volumes of fluids in place, reservoir pressure, fluid and rock properties, reservoir geometry, well type, well count, well placement, development concept, and operating philosophy. Modern production includes thermal , gas injection , and chemical methods of extraction to enhance oil recovery. A virgin reservoir may be under sufficient pressure to push hydrocarbons to

1846-668: The West Country ); the Cornish would pronounce the layers of limestone as ' laiyers ' or ' lias '; leac is Gaelic for "flat stone". There has been some debate over the actual base of the Hettangian Stage, and so of the Jurassic System itself. Biostratigraphically , the first appearance of psiloceratid ammonites has been used; but this depends on relatively complete ammonite faunas being present,

1917-560: The aquatic ecosystem , which is usually a sea but might also be a river, lake, coral reef, or algal mat , the formation of an oil or gas reservoir also requires a sedimentary basin that passes through four steps: Timing is also an important consideration; it is suggested that the Ohio River Valley could have had as much oil as the Middle East at one time, but that it escaped due to a lack of traps. The North Sea , on

1988-407: The buoyancy forces driving the upward migration of hydrocarbons through a permeable rock cannot overcome the capillary forces of a sealing medium. The timing of trap formation relative to that of petroleum generation and migration is crucial to ensuring a reservoir can form. Petroleum geologists broadly classify traps into three categories that are based on their geological characteristics:

2059-518: The pliosaur Hauffiosaurus ). On land, a number of new types of dinosaurs—the heterodontosaurids , scelidosaurs , stegosaurs , and tetanurans —appeared, and joined those groups like the coelophysoids , prosauropods and the sauropods that had continued over from the Triassic. Accompanying them as small carnivores were the sphenosuchian and protosuchid crocodilians. In the air, new types of pterosaurs replaced those that had died out at

2130-580: The 1950s. 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. The field was discovered by the British government owned British Gas Corporation in December 1973 and began producing oil in 1979. Wytch Farm was sold to BP which took over as operator in 1984. In May 2011, BP announced that it had agreed to sell its majority interest in Wytch Farm to Perenco , which became

2201-671: The Blackbeard site in the Gulf of Mexico. ExxonMobil 's drill rig there had reached 30,000 feet by 2006, without finding gas, before it abandoned the site. Crude oil is found in all oil reservoirs formed in the Earth's crust from the remains of once-living things. Evidence indicates that millions of years of heat and pressure changed the remains of microscopic plants and animals into oil and natural gas. Roy Nurmi, an interpretation adviser for Schlumberger oil field services company, described

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2272-410: The actual capacity. Laboratory testing can determine the characteristics of the reservoir fluids, particularly the expansion factor of the oil, or how much the oil expands when brought from the high pressure and high temperature of the reservoir to a "stock tank" at the surface. With such information, it is possible to estimate how many "stock tank" barrels of oil are located in the reservoir. Such oil

2343-784: The first discovery, is in the Jurassic Bridport Sands 900 metres (3,000 ft) 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 1,600 metres (5,200 ft) and extends under Poole Bay . The Frome reservoir is in a shelly limestone within the Frome Clay at 750 metres (2,460 ft). The field extends eastwards from Sandbanks and Studland for around 10 kilometres (6.2 mi) under

2414-416: The following properties: Oil field Reservoirs are broadly classified as conventional and unconventional reservoirs. In conventional reservoirs, the naturally occurring hydrocarbons, such as crude oil ( petroleum ) or natural gas , are trapped by overlying rock formations with lower permeability , while in unconventional reservoirs the rocks have high porosity and low permeability, which keeps

2485-402: The gas bubbles drive the oil to the surface. The bubbles then reach critical saturation and flow together as a single gas phase. Beyond this point and below this pressure, the gas phase flows out more rapidly than the oil because of its lowered viscosity. More free gas is produced, and eventually the energy source is depleted. In some cases depending on the geology the gas may migrate to the top of

2556-684: The globe, on land and offshore. The largest are the Ghawar Field in Saudi Arabia and the Burgan Field in Kuwait , with more than 66 to 104 billion barrels (9.5×10 m ) estimated in each. In the modern age, the location of oil fields with proven oil reserves is a key underlying factor in many geopolitical conflicts. Natural gas originates by the same geological thermal cracking process that converts kerogen to petroleum. As

2627-475: The hydrocarbons trapped in place, therefore not requiring a cap rock . Reservoirs are found using hydrocarbon exploration methods. An oil field is an area of accumulated liquid petroleum underground in multiple (potentially linked) reservoirs, trapped as it rises to impermeable rock formations. In industrial terms, an oil field implies that there is an economic benefit worthy of commercial attention. Oil fields may extend up to several hundred kilometers across

2698-737: The impact on the local environment, with extended reach drilling from the Goathorn Peninsula attaining distances in excess of 10 km. Production grew from 4,000 to 6,000 barrels per day (640 to 950 m/d) in 1984 and eventually peaked at 110,000 barrels per day (17,000 m/d) in 1997; by 2002 this had declined to 50,000 barrels per day (7,900 m/d). In 2002 it was estimated that the field contained reserves of 65.40 million tonnes of oil (479.6 million barrels), 4.73 million tonnes of natural gas liquids and 1.42 billion cubic metres (50 × 10 ^  cu ft) of natural gas that will last until 2020 and 2025 respectively. Oil

2769-575: The large-scale construction of the infrastructure to support oil field exploitation. The term "oilfield" can be used as a shorthand to refer to the entire petroleum industry . However, it is more accurate to divide the oil industry into three sectors: upstream ( crude oil production from wells and separation of water from oil ), midstream (pipeline and tanker transport of crude oil) and downstream ( refining of crude oil to products, marketing of refined products, and transportation to oil stations). More than 65,000 oil fields are scattered around

2840-434: The liquid sections applying extra pressure. This is present in the reservoir if there is more gas than can be dissolved in the reservoir. The gas will often migrate to the crest of the structure. It is compressed on top of the oil reserve, as the oil is produced the cap helps to push the oil out. Over time the gas cap moves down and infiltrates the oil, and the well will produce more and more gas until it produces only gas. It

2911-415: The local cliffs. There was a local jetty to export the oil shale, and smaller operations occurred at nearby Bencliff Grit east of Osmington Mills . 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. The area had long been mined for oil shale and tar, but was only prospected for crude oil in

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2982-438: The location of oil-water contact and with it the height of the oil bearing sands. Often coupled with seismic data, it is possible to estimate the volume of an oil-bearing reservoir. The next step is to use information from appraisal wells to estimate the porosity of the rock. The porosity of an oil field, or the percentage of the total volume that contains fluids rather than solid rock, is 20–35% or less. It can give information on

3053-482: The national domestic gas supply network. Smaller quantities of liquefied petroleum gas are transported by road. A rail terminal at Furzebrook connecting to the Swanage Railway between Corfe Castle and Wareham is now closed and mothballed. The well fluids from the field and the remote well sites are combined at the gathering station. Oil is routed to the first stage separator where initial separation of

3124-516: 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

3195-438: The oil and form a secondary gas cap. Some energy may be supplied by water, gas in water, or compressed rock. These are usually minor contributions with respect to hydrocarbon expansion. By properly managing the production rates, greater benefits can be had from solution-gas drives. Secondary recovery involves the injection of gas or water to maintain reservoir pressure. The gas/oil ratio and the oil production rate are stable until

3266-508: 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. 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

3337-724: The other hand, endured millions of years of sea level changes that successfully resulted in the formation of more than 150 oil fields. Although the process is generally the same, various environmental factors lead to the creation of a wide variety of reservoirs. Reservoirs exist anywhere from the land surface to 30,000 ft (9,000 m) below the surface and are a variety of shapes, sizes, and ages. In recent years, igneous reservoirs have become an important new field of oil exploration, especially in trachyte and basalt formations. These two types of reservoirs differ in oil content and physical properties like fracture connectivity, pore connectivity, and rock porosity . A trap forms when

3408-406: The placement of the well with respect to the gas cap. As with other drive mechanisms, water or gas injection can be used to maintain reservoir pressure. When a gas cap is coupled with water influx, the recovery mechanism can be highly efficient. Water (usually salty) may be present below the hydrocarbons. Water, as with all liquids, is compressible to a small degree. As the hydrocarbons are depleted,

3479-431: The preferential mechanism of leaking: the hydraulic seal and the membrane seal. A membrane seal will leak whenever the pressure differential across the seal exceeds the threshold displacement pressure, allowing fluids to migrate through the pore spaces in the seal. It will leak just enough to bring the pressure differential below that of the displacement pressure and will reseal. A hydraulic seal occurs in rocks that have

3550-429: The pressure. As the reservoir depletes, the pressure falls below the bubble point , and the gas comes out of solution to form a gas cap at the top. This gas cap pushes down on the liquid helping to maintain pressure. This occurs when the natural gas is in a cap below the oil. When the well is drilled the lowered pressure above means that the oil expands. As the pressure is reduced it reaches bubble point, and subsequently

3621-485: The process as follows: Plankton and algae, proteins and the life that's floating in the sea, as it dies, falls to the bottom, and these organisms are going to be the source of our oil and gas. When they're buried with the accumulating sediment and reach an adequate temperature, something above 50 to 70 °C they start to cook. This transformation, this change, changes them into the liquid hydrocarbons that move and migrate, will become our oil and gas reservoir. In addition to

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3692-491: The reduction in pressure in the reservoir allows the water to expand slightly. Although this unit expansion is minute, if the aquifer is large enough this will translate into a large increase in volume, which will push up on the hydrocarbons, maintaining pressure. With a water-drive reservoir, the decline in reservoir pressure is very slight; in some cases, the reservoir pressure may remain unchanged. The gas/oil ratio also remains stable. The oil rate will remain fairly stable until

3763-729: The remarkable layers of these cliffs, situated on the Bristol Channel are a rhythmic decimetre scale repetition of limestone and mudstone formed as a late Triassic desert was inundated by the sea. During this period, ammonoids , which had almost died out at the end-of-Triassic extinction, radiated out into a huge diversity of new forms with complex suture patterns (the ammonites proper). Ammonites evolved so rapidly, and their shells are so often preserved, that they serve as important zone fossils . There were several distinct waves of ammonite evolution in Europe alone. The Early Jurassic

3834-408: The reservoir pressure drops below the bubble point when critical gas saturation is reached. When the gas is exhausted, the gas/oil ratio and the oil rate drops, the reservoir pressure has been reduced, and the reservoir energy is exhausted. In reservoirs already having a gas cap (the virgin pressure is already below bubble point), the gas cap expands with the depletion of the reservoir, pushing down on

3905-409: The reservoir, leading to an improved estimate of the recoverable resources. Reserves are only the part of those recoverable resources that will be developed through identified and approved development projects. Because the evaluation of reserves has a direct impact on the company or the asset value, it usually follows a strict set of rules or guidelines. To obtain the contents of the oil reservoir, it

3976-410: The rock fabric by strong capillary forces, requiring specialised measures for evaluation and extraction. Unconventional reservoirs form in completely different ways to conventional reservoirs, the main difference being that they do not have "traps". This type of reservoir can be driven in a unique way as well, as buoyancy might not be the driving force for oil and gas accumulation in such reservoirs. This

4047-577: The sea to the south of Bournemouth . 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

4118-461: The site by road tanker. Produced water from the separators is combined with treated site surface water and seawater and is injected into the reservoir via five wells. This provides a disposal route for oily water and maintains pressure in the reservoir. There are several facilities that support oil and gas production, these include: The produced oil has a gravity of 37/38°API, and a sulphur content of 0.1 to 0.2%. The oil product sent to Hamble has

4189-480: The site, the rest is compressed, odorised (with tertiary butyl mercaptan ) and is routed via a 8-inch (0.2 m) pipeline to Sopley near Christchurch where it enters the National Gas Grid. Propane and butane (known collectively as LPG or liquefied petroleum gas ) are maintained as liquids, they are odorised (with ethyl mercaptan ) and stored in horizontal vessels on the site. LPG is sold and transported from

4260-410: The source, the "drier" the gas (that is, the smaller the proportion of condensates in the gas). Because both oil and natural gas are lighter than water, they tend to rise from their sources until they either seep to the surface or are trapped by a non-permeable stratigraphic trap. They can be extracted from the trap by drilling. The largest natural gas field is South Pars/Asalouyeh gas field, which

4331-490: The start of the Middle Jurassic 174.7 ±0.8 Ma. Certain rocks of marine origin of this age in Europe are called " Lias " and that name was used for the period, as well, in 19th-century geology. In southern Germany rocks of this age are called Black Jurassic . There are two possible origins for the name Lias: the first reason is it was taken by a geologist from an English quarryman 's dialect pronunciation of

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4402-454: The structural trap, the stratigraphic trap, and the far less common hydrodynamic trap . The trapping mechanisms for many petroleum reservoirs have characteristics from several categories and can be known as a combination trap. Traps are described as structural traps (in deformed strata such as folds and faults) or stratigraphic traps (in areas where rock types change, such as unconformities, pinch-outs and reefs). Structural traps are formed as

4473-478: The surface, meaning that extraction efforts can be large and spread out across the area. In addition to extraction equipment, there may be exploratory wells probing the edges to find more reservoir area, pipelines to transport the oil elsewhere, and support facilities. Oil fields can occur anywhere that the geology of the underlying rock allows, meaning that certain fields can be far away from civilization, including at sea. Creating an operation at an oil field can be

4544-452: The surface. As the fluids are produced, the pressure will often decline, and production will falter. The reservoir may respond to the withdrawal of fluid in a way that tends to maintain the pressure. Artificial drive methods may be necessary. This mechanism (also known as depletion drive) depends on the associated gas of the oil. The virgin reservoir may be entirely semi-liquid but will be expected to have gaseous hydrocarbons in solution due to

4615-407: The water begins to be produced along with the oil, the recovery rate may become uneconomical owing to the higher lifting and water disposal costs. If the natural drives are insufficient, as they very often are, then the pressure can be artificially maintained by injecting water into the aquifer or gas into the gas cap. The force of gravity will cause the oil to move downward of the gas and upward of

4686-431: The water reaches the well. In time, the water cut will increase, and the well will be watered out. The water may be present in an aquifer (but rarely one replenished with surface water ). This water gradually replaces the volume of oil and gas that is produced out of the well, given that the production rate is equivalent to the aquifer activity. That is, the aquifer is being replenished from some natural water influx. If

4757-442: The water. If vertical permeability exists then recovery rates may be even better. These occur if the reservoir conditions allow the hydrocarbons to exist as a gas. Retrieval is a matter of gas expansion. Recovery from a closed reservoir (i.e., no water drive) is very good, especially if bottom hole pressure is reduced to a minimum (usually done with compressors at the wellhead). Any produced liquids are light-colored to colorless, with

4828-444: 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

4899-414: The word "layers"; secondly, sloops from north Cornish ports such as Bude would sail across the Bristol Channel to the Vale of Glamorgan to load up with rock from coastal limestone quarries (lias and Carboniferous limestone from South Wales was used throughout North Devon/North Cornwall as it contains calcium carbonate to 'sweeten' (i.e.neutralise) the acidic Devonian and Carboniferous soils of

4970-476: Was an important time in the evolution of the marine reptiles. The Hettangian saw the already existing Rhaetian ichthyosaurs and plesiosaurs continuing to flourish, while at the same time a number of new types of these marine reptiles appeared, such as Ichthyosaurus and Temnodontosaurus among the ichthyosaurs, and Eurycleidus , Macroplata , and Rhomaleosaurus among the plesiosaurs (all Rhomaleosauridae , although as currently defined this group

5041-549: 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, but were commercially exploited until only circa 1900, and only at a low level. The Kimmeridge Oil and Carbon Company reported that in 1890 it had dug 5,000 feet (1,500 m) of tunnels at Kimmeridge on four levels into

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