Drilling vessels

Drilling Vessels 1357. Marine Riser Systems. 1359. Casing Programs 1361. Well Control 1363. 

Offshore drilling vessels are classified as either bottom-supported or floating-type vessels. Water depth is generally the governing factor as to which type of vessel is employed. 

Drilling barges, commonly employed in inland waters and marshes, can be used where water depths do not exceed about 25 ft. These self-contained vessels provide the least expensive drilling vessel, but have limited applicability because of water depth limitations. 

Drillships and semisubmersible rigs are the two types of floating drilling vessels. 

In ocean drilling, hydrated sediment cores are often obtained. Because the cores frequently traverse warm waters for periods of about 1 h, hydrated cores dissociate and release gas, to yield higher pressures. When core liners are retrieved on the deck of a drilling vessel, frequently the warm weather can cause additional hydrate dissolution, resulting in further pressure increases. The modeling of this dissociation has been done by Wright et al. (2005) and by Davies et al. (2006). 

In offshore drilling, the equipment allows drilling from a floating vessel and the completion of oil wells on the ocean floor is accomplished by remote control from the surface. The drilling vessel uses an automatic pilot to keep it in position while drilling. 

The drilling vessel and consequently the drill pipe will tend to experience a cyclic loading because of the nature of open water operations. To reduce this cyclic load effect, heave compensators are utilized as discussed earlier. Unfortunately, heave compensators do not... 

These include blowouts (22 deaths on the C.P. Baker catamaran drilling vessel in 1964), helicopter crashes (eleven in one crash in 1966) , a near-miss crash of a Louisiana Air National Guard jet on an ODECO rig, Santa Barbara oil spill following a blowout at Union Oil s Platform A-21 in 1969 and another blowout in 1970 at Chevron s Platform C in Main Pass block 41. For more discussion on these incidents, see MMS, History of Offshore Vol. I, pp. 145-146. 

For deeper water depths a dedicated drilling vessel is required. See Figure B.l 1. 

The disadvantages of these systems are the shallow penetrations and often small diameter of samples. However, under certain circumstances (such as unavailability of drilling vessels or jack-ups) this might be the only option to collect seabed samples. 

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