A chemical substance is a form of matter having constant chemical composition and characteristic properties. It cannot be separated into components by physical separation methods, i.e. without breaking chemical bonds. Chemical substances can be chemical compounds, or alloys. Chemical elements may not be included in the definition, depending on expert viewpoint. Chemical substances are called'pure' to set them apart from mixtures. A common example of a chemical substance is pure water. Other chemical substances encountered in pure form are diamond, table salt and refined sugar. However, in practice, no substance is pure, chemical purity is specified according to the intended use of the chemical. Chemical substances exist as solids, gases, or plasma, may change between these phases of matter with changes in temperature or pressure. Chemical substances may be converted to others by means of chemical reactions. Forms of energy, such as light and heat, are not matter, are thus not "substances" in this regard.
A chemical substance may well be defined as "any material with a definite chemical composition" in an introductory general chemistry textbook. According to this definition a chemical substance can either be a pure chemical element or a pure chemical compound. But, there are exceptions to this definition; the chemical substance index published by CAS includes several alloys of uncertain composition. Non-stoichiometric compounds are a special case that violates the law of constant composition, for them, it is sometimes difficult to draw the line between a mixture and a compound, as in the case of palladium hydride. Broader definitions of chemicals or chemical substances can be found, for example: "the term'chemical substance' means any organic or inorganic substance of a particular molecular identity, including – any combination of such substances occurring in whole or in part as a result of a chemical reaction or occurring in nature". In geology, substances of uniform composition are called minerals, while physical mixtures of several minerals are defined as rocks.
Many minerals, mutually dissolve into solid solutions, such that a single rock is a uniform substance despite being a mixture in stoichiometric terms. Feldspars are a common example: anorthoclase is an alkali aluminum silicate, where the alkali metal is interchangeably either sodium or potassium. In law, "chemical substances" may include both pure substances and mixtures with a defined composition or manufacturing process. For example, the EU regulation REACH defines "monoconstituent substances", "multiconstituent substances" and "substances of unknown or variable composition"; the latter two consist of multiple chemical substances. For example, charcoal is an complex polymeric mixture that can be defined by its manufacturing process. Therefore, although the exact chemical identity is unknown, identification can be made to a sufficient accuracy; the CAS index includes mixtures. Polymers always appear as mixtures of molecules of multiple molar masses, each of which could be considered a separate chemical substance.
However, the polymer may be defined by a known precursor or reaction and the molar mass distribution. For example, polyethylene is a mixture of long chains of -CH2- repeating units, is sold in several molar mass distributions, LDPE, MDPE, HDPE and UHMWPE; the concept of a "chemical substance" became established in the late eighteenth century after work by the chemist Joseph Proust on the composition of some pure chemical compounds such as basic copper carbonate. He deduced; this is now known as the law of constant composition. With the advancement of methods for chemical synthesis in the realm of organic chemistry. However, there are some controversies regarding this definition because the large number of chemical substances reported in chemistry literature need to be indexed. Isomerism caused much consternation to early researchers, since isomers have the same composition, but differ in configuration of the atoms. For example, there was much speculation for the chemical identity of benzene, until the correct structure was described by Friedrich August Kekulé.
The idea of stereoisomerism – that atoms have rigid three-dimensional structure and can thus form isomers that differ only in their three-dimensional arrangement – was another crucial step in understanding the concept of distinct chemical substances. For example, tartaric acid has three distinct isomers, a pair of diastereomers with one diastereomer forming two enantiomers. An element is a chemical substance made up of a particular kind of atom and hence cannot be broken down or transformed by a chemical reaction into a different element, though it can be transmuted into another element through a nuclear reaction; this is so, beca
An oil is any nonpolar chemical substance, a viscous liquid at ambient temperatures and is both hydrophobic and lipophilic. Oils have a high carbon and hydrogen content and are flammable and surface active; the general definition of oil includes classes of chemical compounds that may be otherwise unrelated in structure and uses. Oils may be animal, vegetable, or petrochemical in origin, may be volatile or non-volatile, they are used for food, medical purposes and the manufacture of many types of paints and other materials. Specially prepared oils are used in some religious rituals as purifying agents. First attested in English 1176, the word oil comes from Old French oile, from Latin oleum, which in turn comes from the Greek ἔλαιον, "olive oil, oil" and that from ἐλαία, "olive tree", "olive fruit"; the earliest attested forms of the word are the Mycenaean Greek, e-ra-wo and, e-rai-wo, written in the Linear B syllabic script. Organic oils are produced in remarkable diversity by plants and other organisms through natural metabolic processes.
Lipid is the scientific term for the fatty acids and similar chemicals found in the oils produced by living things, while oil refers to an overall mixture of chemicals. Organic oils may contain chemicals other than lipids, including proteins and alkaloids. Lipids can be classified by the way that they are made by an organism, their chemical structure and their limited solubility in water compared to oils, they have a high carbon and hydrogen content and are lacking in oxygen compared to other organic compounds and minerals. Crude oil, or petroleum, its refined components, collectively termed petrochemicals, are crucial resources in the modern economy. Crude oil originates from ancient fossilized organic materials, such as zooplankton and algae, which geochemical processes convert into oil; the name "mineral oil" is a misnomer, in that minerals are not the source of the oil—ancient plants and animals are. Mineral oil is organic. However, it is classified as "mineral oil" instead of as "organic oil" because its organic origin is remote, because it is obtained in the vicinity of rocks, underground traps, sands.
Mineral oil refers to several specific distillates of crude oil. Several edible vegetable and animal oils, fats, are used for various purposes in cooking and food preparation. In particular, many foods are fried in oil much hotter than boiling water. Oils are used for flavoring and for modifying the texture of foods. Cooking oils are derived either from animal fat, as butter and other types, or plant oils from the olive, maize and many other species. Oils are applied to hair to give it a lustrous look, to prevent tangles and roughness and to stabilize the hair to promote growth. See hair conditioner. Oil has been used throughout history as a religious medium, it is considered a spiritually purifying agent and is used for anointing purposes. As a particular example, holy anointing oil has been an important ritual liquid for Judaism and Christianity. Color pigments are suspended in oil, making it suitable as a supporting medium for paints; the oldest known extant oil paintings date from 650 AD. Oils are used for instance in electric transformers.
Heat transfer oils are used both as coolants, for heating and in other applications of heat transfer. Given that they are non-polar, oils do not adhere to other substances; this makes them useful as lubricants for various engineering purposes. Mineral oils are more used as machine lubricants than biological oils are. Whale oil is preferred for lubricating clocks, because it does not evaporate, leaving dust, although its use was banned in the USA in 1980, it is a long-running myth that spermaceti from whales has still been used in NASA projects such as the Hubble Telescope and the Voyager probe because of its low freezing temperature. Spermaceti is not an oil, but a mixture of wax esters, there is no evidence that NASA has used whale oil; some oils burn in liquid or aerosol form, generating light, heat which can be used directly or converted into other forms of energy such as electricity or mechanical work. To obtain many fuel oils, crude oil is pumped from the ground and is shipped via oil tanker or a pipeline to an oil refinery.
There, it is converted from crude oil to diesel fuel, fuel oils, jet fuel, kerosene and liquefied petroleum gas. A 42-US-gallon barrel of crude oil produces 10 US gallons of diesel, 4 US gallons of jet fuel, 19 US gallons of gasoline, 7 US gallons of other products, 3 US gallons split between heavy fuel oil and liquified petroleum gases, 2 US gallons of heating oil; the total production of a barrel of crude into various products results in an increase to 45 US gallons. Not all oils used as fuels are mineral oils, see biodiesel and vegetable oil fuel. In the 18th and 19th cent
Volatile organic compound
Volatile organic compounds are organic chemicals that have a high vapor pressure at ordinary room temperature. Their high vapor pressure results from a low boiling point, which causes large numbers of molecules to evaporate or sublimate from the liquid or solid form of the compound and enter the surrounding air, a trait known as volatility. For example, which evaporates from paint and releases from materials like resin, has a boiling point of only –19 °C. VOCs are numerous and ubiquitous, they include both human-made and occurring chemical compounds. Most scents or odors are of VOCs. VOCs play an important role in communication between plants, messages from plants to animals; some VOCs are dangerous to human cause harm to the environment. Anthropogenic VOCs are regulated by law indoors, where concentrations are the highest. Harmful VOCs are not acutely toxic, but have compounding long-term health effects; because the concentrations are low and the symptoms slow to develop, research into VOCs and their effects is difficult.
Diverse definitions of the term VOC are in use. The definitions of VOCs used for control of precursors of photochemical smog used by the U. S. Environmental Protection Agency and state agencies in the US with independent outdoor air pollution regulations include exemptions for VOCs that are determined to be non-reactive, or of low-reactivity in the smog formation process. In the US, regulatory requirements for VOCs vary among the states. Most prominent is the VOC regulation issued by the South Coast Air Quality Management District in California and by the California Air Resources Board. However, this specific use of the term VOCs can be misleading when applied to indoor air quality because many chemicals that are not regulated as outdoor air pollution can still be important for indoor air pollution. California's ARB uses the term "reactive organic gases" to measure organic gases after public hearing in September 1995; the ARB revised the definition of "Volatile Organic Compounds" used in the consumer products regulations, based on their committee's findings.
Health Canada classifies VOCs as organic compounds that have boiling points in the range of 50 to 250 °C. The emphasis is placed on encountered VOCs that would have an effect on air quality; the European Union defines a VOC as "any organic compound having an initial boiling point less than or equal to 250 °C measured at a standard atmospheric pressure of 101.3 kPa." The VOC Solvents Emissions Directive is the main policy instrument for the reduction of industrial emissions of volatile organic compounds in the European Union. It covers a wide range of solvent using activities, e.g. printing, surface cleaning, vehicle coating, dry cleaning and manufacture of footwear and pharmaceutical products. The VOC Solvents Emissions Directive requires installations in which such activities are applied to comply either with the emission limit values set out in the Directive or with the requirements of the so-called reduction scheme. Article 13 of The Paints Directive, approved in 2004, amended the original VOC Solvents Emissions Directive and limits the use of organic solvents in decorative paints and varnishes and in vehicle finishing products.
The Paints Directive sets out maximum VOC content limit values for paints and varnishes in certain applications. The People's Republic of China defines a VOC as those compounds that have "originated from automobiles, industrial production and civilian use, burning of all types of fuels and transportation of oils, fitment finish, coating for furniture and machines, cooking oil fume and fine particles," and similar sources; the Three-Year Action Plan for Winning the Blue Sky Defence War released by the State Council in July 2018 creates an action plan to reduce 2015 VOC emissions 10% by 2020. The Central Pollution Control Board of India released the Air Act in 1981, amended in 1987, to address concerns about air pollution in India. While the document does not differentiate between VOCs and other air pollutants, the CPCB monitors "oxides of nitrogen, sulphur dioxide, fine particulate matter and suspended particulate matter." VOCs are defined in the various laws and codes under which they are regulated.
Other definitions may be found from government agencies advising about VOCs. EPA regulates VOCs in the air and land; the federal regulations issued under the Safe Drinking Water Act set maximum contaminant level standards for several organic compounds in public water systems. EPA publishes wastewater testing methods for chemical compounds, including a range of VOCs, pursuant to the Clean Water Act. In addition to drinking water, VOCs are regulated in pollutant discharges to surface waters, as hazardous waste, but not in non-industrial indoor air; the Occupational Safety and Health Administration regulates VOC exposure in the workplace. Volatile organic compounds that are classified as hazardous materials are regulated by the Pipeline and Hazardous Materials Safety Administration while being transported. Not counting methane, biological sources emit an estimated 1150 teragrams of carbon per year in the form of VOCs; the majority of VOCs are produced by the main compound being isoprene. The remainder are produced by microbes.
Microbial volatile organic compounds can be beneficial, when used to control plant pathogens, for instance. The strong odor emitted by many plants consists of a subset of VOCs. Emissions are affected by a variety of factors, such as temperature, whi
Petrochemicals are chemical products derived from petroleum. Some chemical compounds made from petroleum are obtained from other fossil fuels, such as coal or natural gas, or renewable sources such as corn, palm fruit or sugar cane; the two most common petrochemical classes are aromatics. Oil refineries produce aromatics by fluid catalytic cracking of petroleum fractions. Chemical plants produce olefins by steam cracking of natural gas liquids like propane. Aromatics are produced by catalytic reforming of naphtha. Olefins and aromatics are the building-blocks for a wide range of materials such as solvents and adhesives. Olefins are the basis for polymers and oligomers used in plastics, fibers, elastomers and gels. Global ethylene and propylene production are about 115 million tonnes and 70 million tonnes per annum, respectively. Aromatics production is 70 million tonnes; the largest petrochemical industries are located in the Western Europe. There is substantial inter-regional petrochemical trade.
Primary petrochemicals are divided into three groups depending on their chemical structure: Olefins includes Ethene, Propene and butadiene. Ethylene and propylene are important sources of industrial plastics products. Butadiene is used in making synthetic rubber. Aromatics includes Benzene and xylenes, as a whole referred to as BTX and obtained from petroleum refineries by extraction from the reformate produced in catalytic reformers using Naphtha obtained from petroleum refineries. Benzene is a raw material for dyes and synthetic detergents, benzene and toluene for isocyanates MDI and TDI used in making polyurethanes. Manufacturers use xylenes to produce synthetic fibers. Synthesis gas is a mixture of carbon hydrogen used to make ammonia and methanol. Ammonia is used to make the fertilizer urea and methanol is used as a solvent and chemical intermediate. Steam crackers are not to be confused with steam reforming plants used to produce hydrogen and ammonia. Methane, ethane and butanes obtained from natural gas processing plants.
Methanol and formaldehyde. In 2007, the amounts of ethylene and propylene produced in steam crackers were about 115 Mt and 70 Mt, respectively; the output ethylene capacity of large steam crackers ranged up to as much as 1.0 – 1.5 Mt per year. The adjacent diagram schematically depicts the major hydrocarbon sources and processes used in producing petrochemicals. Like commodity chemicals, petrochemicals are made on a large scale. Petrochemical manufacturing units differ from commodity chemical plants in that they produce a number of related products. Compare this with specialty chemical and fine chemical manufacture where products are made in discrete batch processes. Petrochemicals are predominantly made in a few manufacturing locations around the world, for example in Jubail & Yanbu Industrial Cities in Saudi Arabia, Texas & Louisiana in the US, in Teesside in the Northeast of England in the United Kingdom, in Rotterdam in the Netherlands, in Jamnagar & Dahej in Gujarat, India. Not all of the petrochemical or commodity chemical materials produced by the chemical industry are made in one single location but groups of related materials are made in adjacent manufacturing plants to induce industrial symbiosis as well as material and utility efficiency and other economies of scale.
This is known in chemical engineering terminology as integrated manufacturing. Speciality and fine chemical companies are sometimes found in similar manufacturing locations as petrochemicals but, in most cases, they do not need the same level of large scale infrastructure and therefore can be found in multi-sector business parks; the large scale petrochemical manufacturing locations have clusters of manufacturing units that share utilities and large scale infrastructure such as power stations, storage tanks, port facilities and rail terminals. In the United Kingdom for example, there are 4 main locations for such manufacturing: near the River Mersey in Northwest England, on the Humber on the East coast of Yorkshire, in Grangemouth near the Firth of Forth in Scotland and in Teesside as part of the Northeast of England Process Industry Cluster. To demonstrate the clustering and integration, some 50% of the United Kingdom's petrochemical and commodity chemicals are produced by the NEPIC industry cluster companies in Teesside.
In 1835, Henri Victor Regnault, a French chemist left vinyl chloride in the sun and found white solid at the bottom of the flask, polyvinyl chloride. In 1839 Eduard Simon, discovered polystyrene by accident by distilling storax. In 1856, William Henry Perkin discovered Mauveine. In 1888, Friedrich Reinitzer, an Austrian plant scientist observed cholesteryl benzoate had two different melting points. In 1909, Leo Hendrik Baekeland invented bakelite made from formaldehyde. In 1928 synthetic fuels invented using Fischer-Tropsch process. In 1929, Walter Bock invented synthetic rubber Buna-S, made up of styrene and butadiene and used to make car tires. In 1933, Otto Röhm polymerized the first acrylic glass methyl methacrylate. In 1935, Michael Perrin invented polyethylene. After World War II, polypropylene was discovered in the early 1950s. In 1937, Wallace Hume Carothers invented nylon. In 1946, he invented Polyester. Polyethylene terephthalate bottles are made from paraxylene. In 1938, Otto Bayer invented polyurethane.
In 1941, Roy Plu
The North Sea is a marginal sea of the Atlantic Ocean located between the United Kingdom, Norway, Germany, the Netherlands and France. An epeiric sea on the European continental shelf, it connects to the ocean through the English Channel in the south and the Norwegian Sea in the north, it is more than 970 kilometres long and 580 kilometres wide, with an area of 570,000 square kilometres. The North Sea has long been the site of important European shipping lanes as well as a major fishery; the sea is a popular destination for recreation and tourism in bordering countries and more has developed into a rich source of energy resources including fossil fuels and early efforts in wave power. The North Sea has featured prominently in geopolitical and military affairs in Northern Europe, it was important globally through the power northern Europeans projected worldwide during much of the Middle Ages and into the modern era. The North Sea was the centre of the Vikings' rise. Subsequently, the Hanseatic League, the Netherlands, the British each sought to dominate the North Sea and thus access to the world's markets and resources.
As Germany's only outlet to the ocean, the North Sea continued to be strategically important through both World Wars. The coast of the North Sea presents a diversity of geographical features. In the north, deep fjords and sheer cliffs mark the Norwegian and Scottish coastlines, whereas in the south, the coast consists of sandy beaches and wide mudflats. Due to the dense population, heavy industrialization, intense use of the sea and area surrounding it, there have been various environmental issues affecting the sea's ecosystems. Adverse environmental issues – including overfishing and agricultural runoff and dumping, among others – have led to a number of efforts to prevent degradation of the sea while still making use of its economic potential; the North Sea is bounded by the Orkney Islands and east coast of Great Britain to the west and the northern and central European mainland to the east and south, including Norway, Germany, the Netherlands and France. In the southwest, beyond the Straits of Dover, the North Sea becomes the English Channel connecting to the Atlantic Ocean.
In the east, it connects to the Baltic Sea via the Skagerrak and Kattegat, narrow straits that separate Denmark from Norway and Sweden respectively. In the north it is bordered by the Shetland Islands, connects with the Norwegian Sea, which lies in the north-eastern part of the Atlantic; the North Sea is more than 970 kilometres long and 580 kilometres wide, with an area of 570,000 square kilometres and a volume of 54,000 cubic kilometres. Around the edges of the North Sea are sizeable islands and archipelagos, including Shetland and the Frisian Islands; the North Sea receives freshwater from a number of European continental watersheds, as well as the British Isles. A large part of the European drainage basin empties into the North Sea, including water from the Baltic Sea; the largest and most important rivers flowing into the North Sea are the Elbe and the Rhine – Meuse watershed. Around 185 million people live in the catchment area of the rivers discharging into the North Sea encompassing some industrialized areas.
For the most part, the sea lies on the European continental shelf with a mean depth of 90 metres. The only exception is the Norwegian trench, which extends parallel to the Norwegian shoreline from Oslo to an area north of Bergen, it has a maximum depth of 725 metres. The Dogger Bank, a vast moraine, or accumulation of unconsolidated glacial debris, rises to a mere 15 to 30 m below the surface; this feature has produced the finest fishing location of the North Sea. The Long Forties and the Broad Fourteens are large areas with uniform depth in fathoms; these great banks and others make the North Sea hazardous to navigate, alleviated by the implementation of satellite navigation systems. The Devil's Hole lies 200 miles east of Scotland; the feature is a series of asymmetrical trenches between 20 and 30 kilometres long and two kilometres wide and up to 230 metres deep. Other areas which are less deep are Fisher Bank and Noordhinder Bank; the International Hydrographic Organization defines the limits of the North Sea as follows: On the Southwest.
A line joining the Walde Lighthouse and Leathercoat Point. On the Northwest. From Dunnet Head in Scotland to Tor Ness in the Island of Hoy, thence through this island to the Kame of Hoy on to Breck Ness on Mainland through this island to Costa Head and to Inga Ness in Westray through Westray, to Bow Head, across to Mull Head and on to Seal Skerry and thence to Horse Island. On the North. From the North point of the Mainland of the Shetland Islands, across to Graveland Ness in the Island of Yell, through Yell to Gloup Ness and across to Spoo Ness in Unst island, through Unst to Herma Ness, on to the SW point of the Rumblings and to Muckle Flugga all these being included in the North Sea area.
An oil platform, offshore platform, or offshore drilling rig is a large structure with facilities for well drilling to explore, extract and process petroleum and natural gas which lies in rock formations beneath the seabed. In many cases, the platform contains facilities to house the workforce as well. Most oil platforms engage in activities on the continental shelf, though they can be used in lakes, inshore waters and inland seas. Depending on the circumstances, the platform may be fixed to the ocean floor, may consist of an artificial island, or may float. Remote subsea wells may be connected to a platform by flow lines and by umbilical connections; these sub-sea solutions may consist of one or more subsea wells, or of one or more manifold centres for multiple wells. Offshore drilling presents environmental challenges, both from the produced hydrocarbons and the materials used during the drilling operation. Controversies include the ongoing U. S. offshore drilling debate. There are many different types of facilities from which offshore drilling operations take place.
These include bottom founded drilling rigs, combined drilling and production facilities either bottom founded or floating platforms, deepwater mobile offshore drilling units including semi-submersibles and drillships. These are capable of operating in water depths up to 3,000 metres. In shallower waters the mobile units are anchored to the seabed, however in deeper water the semisubmersibles or drillships are maintained at the required drilling location using dynamic positioning. Around 1891, the first submerged oil wells were drilled from platforms built on piles in the fresh waters of the Grand Lake St. Marys in Ohio; the wide but shallow reservoir was built from 1837 to 1845 to provide water to the Miami and Erie Canal. Around 1896, the first submerged oil wells in salt water were drilled in the portion of the Summerland field extending under the Santa Barbara Channel in California; the wells were drilled from piers extending from land out into the channel. Other notable early submerged drilling activities occurred on the Canadian side of Lake Erie since 1913 and Caddo Lake in Louisiana in the 1910s.
Shortly thereafter, wells were drilled in tidal zones along the Gulf Coast of Texas and Louisiana. The Goose Creek field near Baytown, Texas is one such example. In the 1920s, drilling was done from concrete platforms in Lake Maracaibo, Venezuela; the oldest offshore well recorded in Infield's offshore database is the Bibi Eibat well which came on stream in 1923 in Azerbaijan. Landfill was used to raise shallow portions of the Caspian Sea. In the early 1930s, the Texas Company developed the first mobile steel barges for drilling in the brackish coastal areas of the gulf. In 1937, Pure Oil Company and its partner Superior Oil Company used a fixed platform to develop a field in 14 feet of water, one mile offshore of Calcasieu Parish, Louisiana. In 1938, Humble Oil built a mile-long wooden trestle with railway tracks into the sea at McFadden Beach on the Gulf of Mexico, placing a derrick at its end - this was destroyed by a hurricane. In 1945, concern for American control of its offshore oil reserves caused President Harry Truman to issue an Executive Order unilaterally extending American territory to the edge of its continental shelf, an act that ended the 3-mile limit "freedom of the seas" regime.
In 1946, Magnolia Petroleum drilled at a site 18 miles off the coast, erecting a platform in 18 feet of water off St. Mary Parish, Louisiana. In early 1947, Superior Oil erected a drilling/production platform in 20 ft of water some 18 miles off Vermilion Parish, Louisiana, but it was Kerr-McGee Oil Industries, as operator for partners Phillips Petroleum and Stanolind Oil & Gas, that completed its historic Ship Shoal Block 32 well in October 1947, months before Superior drilled a discovery from their Vermilion platform farther offshore. In any case, that made Kerr-McGee's well the first oil discovery drilled out of sight of land; the British Maunsell Forts constructed during World War II are considered the direct predecessors of modern offshore platforms. Having been pre-constructed in a short time, they were floated to their location and placed on the shallow bottom of the Thames and the Mersey estuary. In 1954, the first jackup oil rig was ordered by Zapata Oil, it was designed by R. G. LeTourneau and featured three electro-mechanically-operated lattice type legs.
Built on the shores of the Mississippi river by the LeTourneau Company, it was launched in December 1955, christened'Scorpion'. The Scorpion was put into operation in May 1956 off Port Aransas, Texas, it was lost in 1969. When offshore drilling moved into deeper waters of up to 30 metres, fixed platform rigs were built, until demands for drilling equipment was needed in the 100 feet to 120 metres depth of the Gulf of Mexico, the first jack-up rigs began appearing from specialized offshore drilling contractors such as forerunners of ENSCO International; the first semi-submersible resulted from an unexpected observation in 1961. Blue Water Drilling Company owned and operated the four-column submersible Blue Water Rig No.1 in the Gulf of Mexico for Shell Oil Company. As the pontoons were not sufficiently buoyant to support the weight of the rig and its consumables, it was towed between locations at a draught midway between the top of the pontoons and the underside of the deck, it was noticed that the motions at this draught were small, Blue Water Drilling and Shell jointly deci