Hydrates were first discovered by Sir Humphrey Davy in 1810 but remained a scientific curiosity until Hammerschmidt reported in 1934 that they could form in natural gas pipelines leading to blockages and reduced or zero gas flow. The initial work by Hammerschmidt motivated considerable research activity into the formation of hydrates and their prevention in pipelines and led to the development of the first hydrate prediction methods and inhibition techniques.
Gas hydrates are crystalline ice-like solids formed from water and a range of lower molecular weight molecules, typically methane, ethane, propane, hydrogen sulphide and carbon dioxide. The structures of the crystals fall into the class of clathrates with the water molecules forming a hydrogen-bonded cage-like structure which is stabilized by 'guest' molecules located within the lattice. For more detail please refer to our recent paper on hydrates.
To date there are three known hydrate structures referred to as structures I, II and H. The figure below presents schematics of the three different structures together with a picture of a pure crystal
Although the most common form of hydrate is structure II, the others may form under certain circumstances. For example, structure I may form in a gas-water system where the gas is rich in methane. Maximus is able to predict the dissociation curve of all three hydrate structures and so allow engineers to select operating envelopes that avoid the formation of these solids. An example phase diagram is provided below:
