OIL RIGS

 

OIL RIGS

-       By Akash Deep

-       Batch(2k19), Deptt. of Chemical Engg.

-       BIT Sindri, Dhanbad

Oil Rigs are offshore drilling setup to explore, extract, store, and process petroleum and natural gas stored beneath the seabed. Oil rigs are the most common way to extract large quantity of petroleum in the sea beds rather than onshore. Some of the renowned oil platform includes Hibernia (Largest crude reserve in the world), Canada or Bombay High in India. Oil Rigs installation can be broadly categorised into: –(1) conventional fixed platforms  (2) compliant tower  (3) vertically moored tension leg and mini-tension leg platform (4) spar  (5) semi-submersibles  (6) floating production, storage, and offloading facility; (7) sub-sea completion and tie-back to host facility.

1)Fixed platforms are economically feasible for installation in water depths up to about 520 m (1,710 ft.). Such platforms are, by virtue of their immobility, designed for very long-term use. Ex- Hibernia Oil Reserve.

2) Compliant towers are designed to sustain significant lateral deflections and forces, and are typically used in water depths ranging from 370 to 910 metres (1,210 to 2,990 ft.).

3) Semi-submersibles can be used in water depths from 60 to 6,000 metres (200 to 20,000 ft). They are generally anchored by combinations of chain, wire rope or polyester rope or both.

4) Jack-up drilling rigs are designed to move from place to place, and then anchor themselves by deploying their legs to the ocean bottom.  They are typically used in water depths up to 170 m (560 ft.) depth.

 

5) Tension-leg platform are floating platforms tethered to the seabed in a manner that eliminates most vertical movement of the structure. They are relatively low cost and can be used for water depths between 180 and 1,300 metres.

 

6)Spar platforms have more inherent stability and has the ability, by adjusting the mooring line tensions. The world's deepest platform as of 2011 was the Perdido spar in the Gulf of Mexico, USA floating in 2,438 metres of water.

Basic Process

The process to establish the Rig machine starts with 3D seismic survey of the site they want to drill. In this process, the signals are sent to the ground and the reflected signals are processed. The processed signals detect the presence of Oil and Natural Gas. The identified sites are drilled and Rigs are setup with the help of Cantilever. A derrick is used to drill wells down to a depth from few thousand feets up to a maximum of 20,000 feet. The derrick is made of a collagen-resistant alloy material, which can resist high pressure and temperature, as well as the hydrogen sulphide found at those depths. The wells are connected with pipes which take the Oil and Gas for further separation between Oil, Water and Gas. Sometimes electrical submersible pumps are used to extract from the source.

 

Parts of an Oil Rig

Derrick- It is used to position the drill and to push the drill the pipe into the earth. The other works which includes monitoring gauges, repairing equipment, and checking for problems. The Derrick is the tallest construction of an oil rig setup.

Casing- stabilization and keeping the sides of the well from caving in on them, casing protects the well stream from outside. Casing a well involves running steel pipe down the inside of a recently drilled well. 

Drill String- A drill string on a drilling rig is a column, or string, of drill pipe that transmits drilling fluid (via the mud pumps). The drill string is hollow so that drilling fluid can be pumped down through it and circulated back up the annulus.

Drill Collar - A component of a drill string that provides weight on bit for drilling. As the driller continues to lower the top of the drill string, more and more weight is applied to the bit.

Bit- A tool designed to produce a generally cylindrical hole in the earth’s crust by the rotary drilling method.

Blowout Preventer- A blowout preventer (BOP) is used to seal, control and monitor oil and gas wells to prevent blowouts, the uncontrolled release of crude oil or natural gas from a well. They are usually installed in stacks of other valves.

Challenges faced by an oil rig

Offshore oil and gas production is more challenging than land-based installations due to the remote and harsher environment. The ocean can add several thousand meters or more to the fluid column. This addition increases the equivalent circulating density and downhole pressures in drilling wells, as well as the energy needed to lift produced fluids for separation on the platform. Supplies and waste are transported by ship, and the supply deliveries need to be carefully planned because storage space on the platform is limited. Major Oil leakage may also occur during the process which affects the life of sea creatures. Norilsk oil spill and the Deepwater Horizon Explosion are few such incidents which validates the hazard of offshore oil rigs. The environmental concerns are although increasing and we need to judiciously shift towards non-conventional energy resources.

 

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