• Hydrates are compounds formed by the union of water with some other substance, generally forming a neutral body, as certain crystallized salts.
• A clathrate or clathrate compound is a chemical substance consisting of a lattice of one type of molecule trapping and containing a second type of molecule.
• Clathrate hydrates are a class of solids in which gas molecules occupy "cages" made up of hydrogen-bonded water molecules.
• Gas hydrates are clathrate hydrates: water ice with gas molecules trapped within.
• Methane clathrate hydrate is a form of water ice that contains a large amount of methane within its crystal structure. This is probably the most common type of gas hydrate deposit on Earth, although small amounts of other ethanes have also been found in gas hydrate samples.

There is a lot more to say on the theory of hydrates and hydrates on the sea bed. But these are not my area of interest. Feel free to add this material here. Hydrates are compounds formed by the union of water with some other substance, generally forming a neutral body, as certain crystallized salts. ... A clathrate or clathrate compound is a chemical substance consisting of a Greek klethra, meaning bars (in the sense of a lattice). ... Clathrate hydrates are a class of solids in which gas molecules occupy cages made up of hydrogen-bonded water molecules. ... Burning ice. Methane released by heating burns, water drips. ... Ethane is a chemical compound with chemical formula C2H6. ...

Gas hydrates in pipelines is the topic of this article.

Gas hydrates in pipelines

Hydrates consist of a water lattice in which light hydrocarbon molecules are embedded resembling dirty ice. Hydrates normally form when a gas stream is cooled below its hydrate formation temperature in the presence of free water i.e. the gas is colder than its water dew point temperature. Hydrates are compounds formed by the union of water with some other substance, generally forming a neutral body, as certain crystallized salts. ... In chemistry, a hydrocarbon is any chemical compound that consists only of carbon (C) and hydrogen (H). ... A molecule is the smallest particle of a pure chemical substance that still retains its chemical composition and properties. ... The dew point or dewpoint of a given parcel of air is the temperature to which the parcel must be cooled, at constant barometric pressure, for the water vapor component to condense into water, called dew. ...

The two major conditions that promotes hydrate formation are thus:

• High gas pressure and low gas temperature
• The gas at or below its water dew point with "free water" present

Secondary conditions such as high gas velocity, agitation and the formation of a nucleation site may also help form hydrates. Pressure is the application of force to a surface, and the concentration of that force in a given area. ... Bubbles in a soft drink each nucleate independently, responing to a decrease in pressure. ...

Hydrate formation is undesirable because the crystals might cause plugging of flow lines, valves and instrumentation. This could reduce line capacity and could cause physical damage to pipe line and equipment.

Hydrate formation prevention and mitigation philosophy

The formation of hydrate should be avoided because of the fact that the hydrate does not dissociate at the same conditions at which they are created. Significantly higher temperature and/or lower pressure are required. Even at these conditions the hydrates to dissociation is a slow process. Furthermore hydrates have a strong tendency to agglomerate and to stick to the pipe wall and thereby plug-ging up the pipeline. Agglomerate - Wikipedia /**/ @import /skins-1. ...

A hydrate prevention philosophy could typically be based on three levels of security listed in prioritised order:

1. Avoid operational conditions that might cause formation of hydrates
2. Temporarily change operating conditions in order to avoid hydrate formation
3. Prevent formation of hydrates by addition of chemicals that lowers the hydrate formation conditions (inhibitors)

The actual philosophy would depend on operational circumstances such as pressure, temperature, type of flow (gas, liquid, presences of water etc.) An inhibitor is a type of effector (biology) that decreases or prevents a chemical reaction. ...

Hydrate inhibitors

When operating within a set of parameters where hydrates could be formed there are still ways to avoid the formation of hydrates. Altering the gas composition by adding chemicals can lower the hydrate formation temperature and / or delay the formation of hydrates. Two options generally exists:

• Thermodynamic inhibitors
• Kinetic inhibitors / anti-agglomerator

The most common thermodynamic inhibitors are, methanol, mono ethylene glycol (MEG) and di-ethylene glycol (DEG) commonly referred to as glycol. All may be recovered and re-circulated, but the economics of methanol recovery will not be favourable in most cases. Methanol, also known as methyl alcohol or wood alcohol, is a chemical compound with chemical formula CH3OH. It is the simplest alcohol, and is a light, volatile, colourless, flammable, poisonous liquid that is used as an antifreeze, solvent, fuel, and as a denaturant for ethyl alcohol. ... Ethylene glycol (monoethylene glycol (MEG), IUPAC name:ethane-1,2-diol) is an alcohol with two -OH groups (a diol), a chemical compound widely used as an automotive antifreeze. ... Ethylene glycol (IUPAC name:ethane-1,2-diol) is a chemical compound widely used as an automotive antifreeze (coolant). ...

Methanol is a colourless volatile liquid fully soluble in water. Synonyms are methyl alcohol, wood alcohol, wood spirits, or curbinol. Methanol is used primarily in anti-freeze compounds, paints, cements, inks, varnishes, shellacs, wood strippers, windshield wiper solvents, gasoline antifreeze and as a solvent in dyes. Methanol is highly toxic and readily absorbed from any routes of exposure. Symptoms include malaise, headache, dizziness, confusion, abdominal cramps with excruciating pain and tenderness, stupor, weakness, and acidosis. When methanol is swallowed, it is metabolized to formaldehyde. This formaldehyde is more toxic than the methanol itself. Blindness and death may occur following ingestion. Methanol, also known as methyl alcohol or wood alcohol, is a chemical compound with chemical formula CH3OH. It is the simplest alcohol, and is a light, volatile, colourless, flammable, poisonous liquid that is used as an antifreeze, solvent, fuel, and as a denaturant for ethyl alcohol. ... Volatile is the name of more than one concept: A financial instrument with high volatility is considered volatile in economics. ... A substance is soluble in a fluid if it dissolves in the fluid. ... Antifreeze is a water-based liquid coolant used in gasoline and diesel engines. ... For information on the U.S. borough, see Paint, Pennsylvania. ... In the general sense, a cement (Latin caementum) is any material with adhesive properties. ... An ink is a liquid containing various pigments and/or dyes used for colouring a surface to render an image or text. ... Varnish is a finish applied to wood or other surfaces in order to provide a clear, hard, durable, protective finish. ... Shellac is a secretion of the lac insect Coccus lacca, found in the forests of Assam and Thailand. ... A dye can generally be described as a coloured substance that has an affinity to the substrate to which it is being applied. ... Malaise is a term used to refer to a general state of discomfort, tiredness, or illness. ... A headache is a condition of mild to severe pain in the head; sometimes upper back or neck pain may also be interpreted as a headache. ... Dizziness (Latin: Vertigo) is the sensation of instability. ... Confusion can have the following meanings: Unclarity, e. ... Categories: Wikipedia articles to be transwikied ... Weakness can mean: The opposite of strength Weakness (medical) This is a disambiguation page — a navigational aid which lists pages that might otherwise share the same title. ... Acidosis is an increased acidity (i. ... The chemical compound formaldehyde (also known as methanal), is a gas with a strong pungent smell. ...

Ethylene glycol is a colourless, odourless, involatile, hygroscopic liquid. It is characterised by two hydroxyl groups, which contribute to its high water solubility, hygroscopic and reactivity with many organic compounds. Major applications for ethylene glycol are as an intermediate for the manufacture of polyester resins, fibres and surface coatings, as well as antifreeze in the automotive industry. Mono-, di- and triethylene glycols (MEG, DEG and TEG) are the first three members of a homologous series of dihydroxyalcohols. They are colourless, essentially odourless stable liquids with low viscosities and high boiling points that are poisonous when ingested. Ingestion may result in depres-sion followed by respiratory and cardiac failure, kidney damage and brain damage. (Mono) ethylene glycol is by far the largest volume of the glycol products and is used in a variety of applications. Ethylene glycol (monoethylene glycol (MEG), IUPAC name:ethane-1,2-diol) is an alcohol with two -OH groups (a diol), a chemical compound widely used as an automotive antifreeze. ... A hygroscopic or hydroscopic substance is a substance that absorbs water readily from its surroundings. ... Hydroxide is a functional group consisting of oxygen and hydrogen: -O−H It has a charge of 1-. The term hydroxyl group is used when the functional group -OH is counted as a substituent of an organic compound. ... Meg refers to: A given name, Meg. ... DEG may stand for: diethylene glycol a shortcut for degree (angular degree, temperature degree, degree symbol, or degree of curvature) This is a disambiguation page — a navigational aid which lists pages that might otherwise share the same title. ... Diethylene glycol (DEG, 3-oxa-1,5-pentanediol, diglycol, ethylene diglycol, or dihydroxy diethyl ether) is a diol, an alcohol with two -OH groups, a dimer of ethylene glycol. ...

Methanol, mono ethylene glycol and di-ethylene glycol could all three be used as a hydrate inhibitor. Methanol would currently be the cheapest solution and the solutions preferred by most for applications where the inhibitor is not expected to be reused.

MEG is preferred over DEG for applications where the temperature is expected to be –10ºC or lower due to high viscosity at low temperatures. TEG has too low vapour pressure to be suited as an inhibitor injected into a gas stream.

More methanol will be lost in the gas phase when compared to MEG or DEG.

The use of kinetic inhibitors and anti-agglomerators in actual field operations is a new and evolving technology. The use requires extensive tests and optimisation to the actual system. Kinetic inhibitors might be interesting because of the lower volumes associated with the use of this type of inhibitor.

Natural Gas Hydrate

a short note of warning by Russell E University of Birmingham UK

Natural gas hydrates are extremely common on continental margins where there is a sufficient source of methane (biogenic or thermogenic), where the sea tempeature is sufficiently cold, geothermal temperature sufficiently low, and hydrostatic pressure sufficiently large to allow hydrate to be stable. Methane gas generated by deep biospheres / gas reservoirs and decomposition migrate into areas where conditions are suitable for gas hydrate formation. The methane is surrounded by water molecules forming an ice like substance within the pore spaces of sediments. Approximately 50% of the natural carbon on Earth is locked up in gas hydrates; oil accounts for approximately 25%.

Seismic sections in regions containing gas hydrate show a clear boundary between free gas (gas because the geothermal temperature is too high) trapped and under pressure beneath sediment whose pores are occupied by solid hydrate, this zone of stability is called the hydrate stability zone. The boundary is marked on seismic sections by a BSR (Bottom Simulating Reflector) an effect caused by the change in seismic velocity between the stability zone and the free gas zone (it has a negative impedance contrast).

If sea temperatures are increased through climatic changes, such as in interglacial periods or through anthropogenic means, sediment containing solid hydrate may become overpressured and under-cemented as the hydrate returns to gas. Fresh water from the hydrate is released into the pore space altering the geochemistry. Electrostatic bonds between clay particles are weakened. Increased overpressure caused by the gas in a critical system can result in submarine slope failure on a massive scale.

The largest known underwater landslide on Earth is the Storegga Slide it occured in an area containing significant volumes of natural gas hydrate. It is located off the western coast of Norway and happened at the end of the last ice age. A series of retrogressive events over a period from 8200 to 5500 years before present caused a series of large tsunamis. Run up heights in the Shetlands and Norway are in excess of 20 meters; northern Scotland 3-6 meters. During such an event massive volumes of methane are released into the water column (Bermuda Triangle scenario) and eventually into the atmosphere. Methane is four times more potent a greehouse gas than carbon dioxide!

If global temperatures continue to rise the natural gas hydrate switch could be suddenly turned on. In theory one gas release, through continental slope failure, in one area of the globe could potentially put enough methane into the atmosphere to increase global temperatures further causing more natural gas hydrate to dissociate (turn to gas) and more submarine failures. A chain reaction or positive feedback loop is created. Rapid warming driven by natural gas hydrate dissociation via continental slope failure could explain the sharp warming events identifiable just before an ice age.