Page 6 - Jacking Systems and Rig Moving Procedures

Petroleum Extension-The University of Texas at Austin
CHAPTER III
MAT-TYPE DRILLING UNITS

GENERAL DESCRIPTION

Mat-type units, having a much larger area cannot be adjusted for a sloping bottom as the
of contact with the sea floor than independent-leg units can. H the sea floor is
independent-leg units, operate with less bear­ not level, it will be necessary to plumb the
ing pressure on bottom, usually in the range of derrick by means of shims beneath the derrick
500 to 600 pounds per square foot. This makes footings so the crown will be vertically over
the mat-type unit the logical choice for soft the rotary. Mat-type units have more drag
mud, provided the bottom is more or less when under tow than independent-leg units;
level. Mat-type units cannot work where the the usual towing speed of a mat-type unit is
sea floor is erratic or covered with coral heads only two and three-fourths to three knots,
or boulders that would damage the bottom of about half the speed of the other type of
the mat. These units are designed to operate drilling unit. Figure 19 shows a mat-type unit
with a bottom slope of 1 ° to 1.5°, and the legs equipped with propulsion gear under tow.

Figure 19. Mat-type drilling unit under tow

19