Page 5 - Jacking Systems and Rig Moving Procedures

Petroleum Extension-The University of Texas at Austin
CHAPTER II

INDEPENDENT-LEG DRILLING UNITS

GENERAL DESCRIPTION

Mobile offshore jacking rigs which employ The independent-leg drilling unit performs
cans or spud tanks are known as independent­ best in firm, uneven bottoms such as coral,
leg drilling units. The tanks are fabricated to limestone, or boulders. In soft mud where
the lower end of the legs and allow 3500 to penetration may be 60 feet maximum, the legs
5500 pounds per square foot of bearing load, sometimes cannot obtain the necessary bear­
depending on tank size and the weight of the ing to support the weight of the unit, and thus
drilling unit. Most cans contain water jets and cannot sufficiently jack itself out of the water.
piping for the washing of material which may Because of this, independent-leg drilling units
accumulate on top of the can, and drain valves are preloaded, that is, for stability they take on
and vents to allow free-flooding capability. more weight than will actually be used during
Figure 3 is an illustration of footing configura­ the drilling operation.
tions for various tanks.

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MR. LOUIE OFFSHORE OFFSHORE MR. CAP JULIE ANN ,
NO, 52 NO. 54 SCORPION a
VI NEGAROON
Q
46'

T !; 1'1
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j 31' ': : I ,;1 2I,Lr~t I
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PENROD 53 a PE NROD 55 TR ITON
OCE AN MASTER I

Figure 3. Footing configurations

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