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punch through the reservoir a high pressure builds up due to the
presence of gases, to prevent our system from blowing out high
viscosity mud is used to lower the pressure. When the mud returns
from the BOP and goes to shale shaker assembly, it is called low
pressure mud system.

Figure 1.11 -- Mud system
Listings this year (2010) total 381 jackup units, a net
decrease of five from last year. Transocean dropped five rigs;
Rowan and Arabdrill one each. For additions, Ensco announced a
newbuilding, and Nabors picked up a unit from Transocean that
was last listed in 2001. The listing excludes shallow-water units
working in inland water, and those in non-drilling/workover
modes, e.g., tender assist, production and accommodation. This
year has not seen the corporate ownership changes that
consolidated many of the jackup listings last year. These primarily
involved. Transocean, which incorporated the R&B Falcon and
Sedco Forex companies. GlobalSantaFe consolidated two previous
companies. Schlumberger Drilling Services no longer lists jackups.
Transocean is the largest jackup owner, with 50 units, down six
from its last year’s listing. The next largest owners are:
GlobalSantaFe (46), ENSCO (44), Noble (38), Pride (32) and
Rowan (24). Nabors and Diamond Offshore list 16 and 14 rigs
each. International owners with significant fleets include: Maersk
(11), National Drilling Co. of Abu Dhabi and China Oilfield

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