Home Page Home Page
Advanced Search  Site Map  
What's NewMedia CentreIndustry IssuesAbout UKOOAEducation

Britain's Offshore Oil and Gas Index Britain's Offshore Oil and Gas Index Next Section Next

BRITAIN'S OFFSHORE OIL & GAS

*Production Wells


F93: Drilling and perforating a production well

To develop offshore fields as economically as possible, numerous directional wells radiate out from a single platform to drain a large area of reservoir (F94). For directional drilling special weighted drill collars are used with a 'bent sub' to deflect the drill bit at a certain angle in the required direction (F93). Wells which deviate at more than 65 degrees from the vertical and reach out horizontally more than twice their vertical depth are known as extended reach wells. In order for the driller to guide the deviated well to a specific target zone in the reservoir a monitoring-while-drilling (MWD) 'directional sub' is run above the bit to relay information back to the surface on the bit location and inclination. This information can be transmitted to the surface using a mud-pulse telemetry system or recorded in the directional sub and recovered when the bit is changed.

As the angle of deviation from the vertical increases, the friction of the rotating drillstring becomes excessive. Also, as drilling becomes slower the risk of sticking the drilling assembly against swelling shales rapidly increases. Environmental restrictions limit the use of friction-reducing oil-based muds in many areas, so that oil-contaminated cuttings from wells need to be shipped back for onshore disposal. The alternate is water-based which needs additives to reduce its frictional effects, and to inhibit its chemical reactivity with the clays drilled.

F92: Designing a horizontal well in a 3D immersive visualisation system to optimise oil production

Deviated wells which exceed 80 degrees from the vertical are known as horizontal wells (F92) and the horizontal section of the well is maintained in the reservoirs to give the highest production rate possible. Horizontal wells are used when the reservoir permeability is low, or the reservoir interval is very thin or the oil and gas is being produced from vertical fractures in the rock. The flow from a horizontal well may be over 5 times the flow from a normal vertical well. The higher flow rates more than offset the higher cost of drilling a horizontal well.

F94: Deviated wells in a North sea oilfield    F95: The well system above superimposed on central London

More than one horizontal section can be drilled in one well as a multilateral well (F96). This technique is used to reduce drilling costs and to maximise the number of wells that can be drilled from small platforms.



Britain's Offshore Oil and Gas Index Britain's Offshore Oil and Gas Index Next Section Next

Home What's New Media Centre Industry Issues About UKOOA Education

© 2002 United Kingdom Offshore Operators Association
London: Tel 020 7802 2400  Fax 020 7802 2401    Aberdeen: Tel 01224 577 250  Fax 01224 577 251
Email info@ukooa.co.uk  Web http://www.oilandgas.org.uk/

Legal and Copyright Issues and Privacy Statement