Page 4 - Jacking Systems and Rig Moving Procedures

Petroleum Extension-The University of Texas at Austin
CHAPTER I

INTRODUCTION TO JACKING SYSTEMS

HISTORY These docks were Originally deSigned for use
in remote areas where construction equipment
was unavailable or where a dock had to be
Since the early 1950's, the number of immediately installed. Notable examples of
mobile offshore drilling units has steadily Delong docks include those on the Orinoco
increased and today, more than 500 mobile River in Venezuela, the "Texas Towers," built
rigs are in use. By mid-1976 about 150 rigs for radar posts off the U.S. Atlantic seaboard,
using jacking systems will operate in water and the docks at Camranh Bay, Vietnam.
depths up to 350 feet, with future working The barge used in the Delong design is
depths projected to be 400 feet or more. towed to the drilling site with the piles or legs
Figure I shows the history of jackup rigs from drawn above the deck. Upon arriving the legs
1953-69. are lowered through holes in the hull until
The growth of the rig jacking system deve­ they touch the ocean bottom. By means of
loped largely because of economic reasons. air-powered jacks and inflatable tubes which
Offshore contractors realized that construction grip the columns while the jacks are stroking,
costs for a jacking system in 40 feet of water or the barge lifts itself out of the water and
deeper was considerably less than buying a climbs its own legs to the desired elevation.
submersible hull. Because both systems are Later design changes strengthened the legs,
bottom supported, drilling procedures for the added more weight to the jacks, and improved
two are similar, thus facilitating the transition the leg-gripping means. Cylindrical legs gave
from submersibles to jackups for crews exper­ way to a truss-type construction, and mechani­
ienced in offshore exploration. cal slip grips and steel pins replaced the
The design for jacking systems and submer­ pneumatic grip used by Delong. Today, both
sibles calls for the deck of the drilling platform electric and hydraulic jacking systems are
to be stable and the wellhead to be set a fixed available, as are independent-leg and mat­
distance from the rotary. The wellhead and type units. The advantages inherent in both
blowout preventers (BOP's) are usually above systems will be discussed in detail later.
the water, and well pressure control proce­ Most leg deSigns on the jacking systems
dures used at sea are identical to those on include large diameter cans, or spud tanks, to
land. The advantage jacking systems hold is lessen leg penetration in soft bottoms. These
the dual capability of (I) drilling vertical holes cans were originally 10 to 20 feet in diameter
for satellite wells served by a centrally located and 15 to 30 feet high. Modem jackup units
production platform and (2) moving close to a are now provided with leg footings 30 to 40
platform and drilling a number of wells that feet in diameter that have sloping tops to shed
can be serviced and operated from that mud that may accumulate above the can. The
platform. footings are usually 10 to 20 feet high and can
Jackup offshore drilling units evolved from be pulled up into recesses in the hull, thereby
Delong docks, barge hulls which were fitted obtaining minimum water drag when under
with a number of columnar piles for legs. tow.

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