Introduction – Types of rigs
To start drilling for oil, surveys will be conducted of the proposed drilling area using specialist vessels to see if there is any oil or gas in underground reservoirs. If the results are positive, the company will hire drilling oil rigs, or possibly a drillship to drill some exploration wells. If these wells prove to contain oil or gas, the company will develop the field with the drilling unit before constructing and placing on site a production platform, depending on the size of the reservoir, the company will choose the types of rigs to be used.Here are different types of rigs:
Production Platform
- Production platforms are the largest type of North Sea oil rigs
- They are permanent oil rigs
- They are immobile structures built on steel or concrete legs that are fixed directly onto the seabed
- Single platform will gather oil and gas from a number of outlying wells
- Platform will pump the oil out of the ground into a pipeline to shore, or to an oil tanker directly which then takes the oil to its final destination
- Semi-submersible platforms or rigs are floating structures used for drilling for oil and natural gas
- Number of pontoons and/or columns that are flooded with seawater, causing the oil rigs to sit very low in the water
- The oil rigs are fixed in position with very large mooring anchors and are moved from location to location by tugs
- These types of installation can drill in very deep, rough water due to their excellent stability
- A Jack-up oil rig is a self-contained combination drilling rig and floating barge
- fitted with long legs that are raised when moving and lowered to the sea bed
- Limited to operating in shallower water depths
- Like the semi-submersible it is moved from location to location by tugs
- This type of rig is basically a hull, usually triangular, supported by 3 legs with a drilling package on top
- The legs pass through the hull of the rig and are ‘jacked’ up and down using very large motors
- When the rig needs to be moved, the legs are jacked up
- A Drill ship is a maritime vessel that has been fitted with drilling equipment
- They can move under their own power and, though not as stable as semi-submersible platforms, they can drill in deep water
- A drill ship is held in position over the well by a combination of its own engines turning powerful screws in the hull and global positioning satellite (GPS) technology
- A FPSO is a type of floating tank system
- They are often converted oil tankers – although increasingly they are purpose built
- The oil is then offloaded to another tanker for transport to the refinery
- They are particularly used for production from small reservoirs where it would be too expensive to build a production platform
- Flotels are literally floating accommodation units
- They are quite often converted from different types of rigs
- These are then moored alongside a production platform or other type of oil rig, and connected to them via a long gangway
- This is one way of keeping the accommodation, leisure and catering facilities remote from the working areas which is a legal requirement in the North Sea
- This is used to make extremely heavy lifts
- To lay underwater pipelines
- Derrick barges can be either self-propelled or towed