What are the features of offshore production

admin 2016-06-02 16:20

What are the features of offshore production?

Natural gas fields occur not only on land. There are also offshore deposits: oil and gas are occasionally encountered in the subsurface covered with water.

Shore and shelf

Geologists survey both onshore and offshore areas. If a field is close to the shore, in a coastal area, then directional wells are drilled from the shore towards the sea. Fields that are farther away from the shore belong to the shelf area. Underwater continental edge having the same structure as the shore is called “shelf” and its boundary is the crest – a steep difference in depth. Floating platforms and rigs are used for such fields, or simply high piles from which they drill if the depth is shallow.

Three main types of floating rigs – special platforms – are used for hydrocarbons production at offshore fields: gravity-based, semi-submersible, and self-elevating.

At greater depths

Semi-submersible platforms are used at great depths. Platforms are not elevated above the water but float over the drilling site held by heavy anchors.

Gravity-based drilling platforms are most stable as they have a thick concrete base supported by the seabed. Drill strings, storage tanks, and pipelines are integrated with this base, while the rig is located above the base. Dozens and even hundreds of workers can live on such platforms.

Offshore production in Russia

Since the world’s largest shelf with many deposits belongs to Russia, the development of the offshore production is very promising for the oil and gas industry. Sakhalin Energy started to drill first Russian offshore wells for gas production at the Lunskoye field offshore Sakhalin in 2007. Production of gas at the Lunskaya-A platform started in 2009. Today, the Sakhalin-2 project is one of the major projects implemented by Gazprom. Two of three gravity-based platforms installed on the shelf of Sakhalin are the heaviest offshore structures in the entire history of the international oil and gas industry.

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What are the features of offshore production