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not always possible for a rig to store all of these provisions on
board and so each rig has a supporting cast of two or three supply
vessels.
The supply vessels, in addition to delivering supplies and
equipment to the rig, perform other important duties. They assist in
the deployment and retrieval of anchors and at least one vessel
stands by the rig at all times in case it must be abandoned. They
sometimes participate in the transfer of personnel to and from the
drilling rig (the crew changes every 3 weeks), although this is
usually handled by helicopters. They tow the rig, when it is not
self-propelled, from one location to the next and in some areas, as
on the Grand Banks, they are required to tow icebergs that may be
drifting into the vicinity of the rig.

Control questions

1. Why do wells sometimes blow out?
2. How is drilling mud used to prevent blowouts?
3. What is the purpose of the casing in the well?
4. Which is more expensive, drilling onshore or offshore?
5. Why did the oil industry start drilling offshore?
6. What are the major differences between drilling offshore and
onshore?
7. What are the main components of the drilling rig?

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