Offshore Gas Production

Total annual natural gas production in 2015 was 3,500 billion m ³ , (CEDIGAZ, 2016) of which around 20% was produced offshore. In terms of primary energy, natural gas production represented 3.1 Gtoe (Giga tonnes of oil equivalent) in 2015, as much as three-quarters of the primary energy supplied by oil (4.3 Gtoe). Natural gas is often contrasted with oil, which is just as natural, even though these two energy sources have many points in common. Oil and natural gas are most often found together. Some fields are exploited solely for the production of natural gas, but a significant proportion of natural gas production - around half - comes from the separation into a gas phase and a liquid phase (or oil) of production from the same field.

Generally speaking, gas, which is much less easy to store than oil, was valued in January 2017 in the United States (Henry hub) at a price three times lower than that of oil, on the basis of the same quantity of heat produced. However, it is important to distinguish between different markets in different consumption zones: since 2015, gas prices at the Henry hub in the United States have remained less than half those in Japan, the world's leading consumer. In the absence of a consumption basin, some gas deposits are not large enough and may remain unexploited (stranded gas).

In the offshore sector, the following distinct activities are considered:

• field production of wet gas and condensate;

• gas production associated with oil production ;

• floating liquefaction trains, which, like floating production, storage and offloading (FPSO) units for oil, reduce infrastructure costs for gas;

• interconnections between producers and consumers via large-diameter pipelines of the order of 1 m (42 to 48 inches), with the gas generally being dry, dehydrated gas.

Natural gas is both a raw material for the petrochemical industry and a fuel. As a fuel, it produces CO ₂ but around 25% less than oil for the same calorific energy produced. What's more, because of its flexibility of use, natural gas power plants can quickly take over from intermittent renewable energies.

Natural gas mainly contains methane, itself a gas with a high greenhouse effect: its release into the atmosphere must be avoided.

Due to the low density of the gas, the hydrostatic head of the gas column in the well is low, and wellhead pressures are commonly 100 to 200 bar, and can go much higher. On gas fields with shallow water depths, it is not uncommon to find 7-1/16...