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connection. After the next conductor joint is stabbed and made up
to the joint in the rotary table, the pad eyes are cut off and the
casing is lowered to the next set of pad eyes. Thirty-in. casing
elevators are sometimes used in lieu of the pad eyes as a means of
handling the 30-in. conductor.
After the casing string is made up to the 30-in. housing
joint, the conductor string assembly is lowered through the rotary
table and landed in the PGS, which has already been set on the
spider or moonpool beams below the rotary floor and through
which the 30-in. casing joint has been lowered. The 30-in. housing
joint is handled using a housing running tool. Lockdown is
accomplished by bolting down a split lock plate that secures the
30-in. housing to the PGS. The four vertical posts on the
permanent guide structure guide subsequent tools and stabilize
equipment for the BOP stack when it is run and landed on the
subsea wellhead.
Once a casing string is run and landed in place, circulation
is established to clean the hole. Then cement slurry is pumped,
under pressure, down through the casing, through the casing shoe,
and up into the casing/hole annulus. The liquid cement inside the
casing string is displaced with a calculated volume of water or
drilling fluid to place the cement in the correct position where it
sets (becomes solid) in approximately three to four hours. Usually
the 30-in. and 20-in. casing/hole annulus is cemented back up to
the mud line. Besides sealing off the upper formation zones, the
cement provides a strong pile section to support the heavy weight
of the BOP stack when it is attached to the wellhead.
If formation conditions are favorable, the 13% in., 9% in.,
and 7-in. casing annuli may be cemented up only a few hundred
feet inside the shoe of the previous casing string. This, of course,
increases the amount of recoverable casing when and if the well is
abandoned. The composition and formation pressures of the
various zones encountered, as well as government regulations,
determine exactly how much cement is set in each annulus.
The set cement seals each annulus to prevent migration of
gases or fluids to other zones of the subsoil geologic structure.
Cement is also used to shut off highly permeable zones (potential
lost-circulation zones), high-pressure zones, or other problem
zones. Because of these possible problems, the weight of the
cement slurry must be controlled closely to avoid placing large
hydrostatic loads on the formation. Cementing protects the casing

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