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7/30/2019 Chapter -2 Offshore & Land Rigs
http://slidepdf.com/reader/full/chapter-2-offshore-land-rigs 1/11
Chapter- 2
Land & Offshore Rigs
7/30/2019 Chapter -2 Offshore & Land Rigs
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2.1 Introduction
Operations proceed in accordance with terms of a permit
issued by the regulatory agency with jurisdiction. Normally, a
drilling location is graded, a conductor pipe is set to support
subsequent casing strings, blowout control equipment is
installed and tested for well safety, the drilling rig and
auxiliary equipment is moved in and set up, and drilling
operations are underway.
2.2 Steps to drilling a well
Before drilling commences, certain arrangements and decisions
have to be made. These may include:
1. Leasing of the land.
2. Building of roads.
3. Moving the equipment in.
4. Drilling method.
5. Depth and size of well.
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2.3 Drill-site selection
The selection of the drill site is based largely on the geological
evidence indicating the possible accumulation of petroleum. The
exploration company will want to drill the well at the most
advantageous location for the discovery of oil or gas. Surface
conditions, however, must also be taken into consideration
when selecting the drill site. There must be a nearly level area
of sufficient size on which to erect the drilling rig, excavate
reserve pits, and provide storage for all of the materials and
equipment that will be required for the drilling program. All of
the required legal matters need to have been attended to, such
as acquiring a drilling permit, surveying of the drill site, and so
on. When all of these matters have been resolved, the work on
site preparation will begin.
2.4 Drill-site preparation
Once the drill site has been selected and surveyed, a
contractor or contractors will move in with equipment to
prepare the location. If necessary, the site will be cleared and
leveled. A large pit will be constructed to contain water for
drilling operations and for the disposal of drill cuttings and
other waste. A large-diameter hole will be drilled to a shallow
depth and lined with conductor pipe.
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A large, rectangular cellar is excavated under the rig floor,
dug before drilling to provide space for equipment at the top
of the wellbore. The cellar serves to collect drainage water andother fluids which are jetted at intervals.
A smaller-diameter hole called a "rat hole" is drilled near the
main bore hole. The rat hole is lined with pipe and is used for
the temporary storage of a piece of drilling equipment called
the "kelly." When all of this work has been completed, the
drilling contractor will move in with the large drilling rig and all
the equipment required for the drilling of the well. After those
actual drilling operations on the well is started. Start of the
actual drilling usually called spud-in. The term is handed down
from cable tool operations in the early days of the oil industry.
2-5 The Rig Crew
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Drilling is usually done by a service company or drilling
contractor . The drilling crew is composed of a toolpusher , a
driller , a derrick man, and several roughnecks. The toolpusher
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manages the drilling operation. The driller operates the rig. The
derrick man helps with the drilling mud and in removing pipe from
the hole. Roughnecks help with the drilling operation and
maintaining the drilling equipment.
2-6 Rotary Drilling rigs
Drilling rig is a machine used to drill a wellbore. In onshore
operations, the rig includes virtually everything except living
quarters. Major components of the rig include the mud tanks,
the mud pumps, the derrick or mast, the drawworks, the rotary
table or topdrive, the drillstring, the power generation
equipment and auxiliary equipment.
Rotary drilling rigs are used for almost all drilling done today.
The hole is drilled by rotating a bit to which a downward force
is applied. The bit is turned by rotating the entire drill string,
which consists of drill pipe and heavy, thick-walled pipe, called
drill collars, which supply the downward force. The cuttingsare lifted to the surface by circulating a fluid down the drill
string, through the bit, and up the annular space between the
hole and the drill string. The cuttings are filtered from the
drilling mud at the surface by a device called a “shale shaker.”
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A blowout prevention system is used to shut in the well in case
of an emergency condition. Most rigs are powered electrically;
diesel engines are used to generate the electrical power.
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Figure 2-1 : Rotary drilling rig
Generally drilling rig classified to two types, onshore and
offshore rigs. Onshore rigs are different tan that offshore
one. Figure 2-2 shows the classifications of rotary drilling rigs.
Figure 2-2: Classifications of rotary drilling rigs
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2.6.1 Land (onshore) Rigs
Figure 2-3 land drilling rig
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2-6-2 Offshore Rigs
Onshore rigs are different tan that offshore one as general
layout. Both types (offshore and onshore) perform the same
principles of operations (hoisting, circulating and rotating. A
power system is required to perform those operations). There
are different types of offshore rigs.
A swamp barge is used in water depths of less than 20 feet.
It is towed to the location and sunk in place.
A jacket rig with tender is also used in shallow waters. The
platform is fixed, and the drilling package is lifted onto the
platform by the tender.
For water depth less than 350 feet, a jack-up rig is often
used. The rig is towed to the location with the legs elevated.
On location, the legs are lowered and the rig is “jacked-up”
above the wave action by means of hydraulic jacks.
For deeper waters, a semi-submersible rig is used. The rig is
towed to the location, and is partially submerged for stability.
The rig is usually anchored over the hole.
Once a large field has been discovered offshore, a large fixed
platform may be employed to drill development wells.
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Drill ships are used to drill in very deep waters. However, they
are limited to areas where wave action is not severe.
Figure 2-4: different types of offshore rigs
Swampbarge
Jacketwith
tender Jack-up
Semi-sub
FixedPlatfor
mDrillship