Chapter 1: Rig Types
Contents
Objectives ................................................................................................................. 1
1.1 Fundamentals ..................................................................................................... 1
1.2 Types of Rigs...................................................................................................... 1
1.3 Land rigs ............................................................................................................. 2
1.4 Offshore Rigs...................................................................................................... 3
1.5 Floating Rigs....................................................................................................... 5
1.5.1 Drillship.................................................................................................................................................... 5
1.5.2 Semisubmersibles...................................................................................................................................... 6
1.6 Stationary Rigs ................................................................................................... 7
1.6.1 Fixed Platforms......................................................................................................................................... 9
1.6.2 Platform Tenders ...................................................................................................................................... 9
1.6.3 Jack-ups .................................................................................................................................................. 11
Submerssible .................................................................................................................................................... 12
Objectives
The main objective of this chapter is to introduce the types of rigs both onshore and
offshore to the trainees. It will also let them know the components of the rig and the
layout as well as basic areas of the offshore rigs.
1.1 Fundamentals
A drilling rig is a device used to drill, case and cement water, oil and gas wells.
The correct procedure for selecting and sizing a drilling rig is as follows:
1. Design the well
2. Establish the various loads to be expected during drilling and testing and
use the highest. This point establishes the DEPTH RATING OF THE RIG.
3. Compare the rating of existing rigs with the design loads
4. Select the appropriate rig and its components.
1.2 Types of Rigs
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Drilling rigs are designed to meet specific operational requirements; therefore,
different rigs have different capabilities. All offshore rigs, however, perform the basic
function of drilling a hole or well in submerged lands by means of rotary drilling. This
procedure provides a method of exploring for or producing oil and/or gas from earth
formations.
Drilling rigs are classified as
•
Land rigs
•
Offshore rigs
1.3 Land rigs
Fig. 1 Land rig
1. Crown Block and Water Table
2. Catline Boom and Hoist Line
3. Drilling Line
4. Monkeyboard
5. Traveling Block
6. Top Drive
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7. Mast
9. Doghouse
11. Water Tank
13. Engine Generator Sets
15. Fuel Tank
17. Mud Pumps
19. Mud Tanks (Pits)
21. Mud-Gas Separator
23. Choke Manifold
25. Pipe Racks
8. Drill Pipe
10. Blowout Preventer
12. Electric Cable Tray
14. Engine Generator Sets
16. Electrical Control House
18. Bulk Mud Component Tanks
20. Reserve Pit
22. Shale Shakers
24. Pipe Ramp
26. Accumulator
1.4 Offshore Rigs
The first successful attempts at offshore drilling occurred between 1910 and 1920. In
the 1920's, the Southern California coast experienced significant offshore drilling
activity. At that time, rigs were often mounted on piers that extended out into the
water. The late 1930's saw the beginning of oil activity in the Gulf of Mexico; at the
present time, the Gulf is the most active offshore drilling area in the United States.
The majority of offshore drilling activity has taken place since the mid 1950's. As
oilmen reached farther out from the shoreline in search of oil, more advanced drilling
techniques and machinery were developed; this advancement continues in today's
oil industry. The first "submersible" drilling rig, the Brenton 40, was basically a drilling
platform mounted on a pontoon stabilized barge. Built in 1949, this rig operated in
the Gulf of Mexico in water depths of up to 22 feet and had a drilling capability of
about 10,000 feet. Approximately twenty of this type of submersible rig were built
between 1949 and 1963. Following the second World War, Navy surplus barges
were utilized and developed as drillships. Jack-up drilling rigs were introduced in the
early 1950's. Modern-type semi-submersible drilling rigs were not developed until
quite recently, Fig. 2.
Fig 2 The Cuss I (circa 1960) Converted from a Navy vessel, its design was based
on research methods and exploratory techniques developed by the Cuss Group," a
joint venture of four oil companies.
Global Marine Drilling Company owns and operates a diversified fleet of offshore
drilling rigs. The services of these rigs are leased, for a fee, to clients-usually oil and
gas companies. The contracting company determines where the well will be drilled
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and the depth of the hole. Having a diversified fleet enables us to offer prospective
customers a rig which will conform to their operational needs.
The purpose of this text is to provide you, the employee, with a general knowledge
of:
• drilling rigs
• departmental responsibilities
• drilling operations
• the drilling department crew
• emergency procedures, and
• your duties as they relate to offshore drilling operations.
In order for you to effectively perform your duties. an understanding of some marine
terminology must be obtained. Fig. 3 will assist in acquainting you with some general
nautical terminology.
Fig. 3 Nautical terminology for direction and movement.
Offshore drilling rigs can be classified into two basic groups: floating and stationary.
Fig. 4 provides illustration of the major types of offshore rigs.
1. Floating rigs
1. Semisubmersible
2. Drillships
2. Bottom-supported rigs: There are three types:
1. Jack-ups
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2. Platform
3. submesrsible
4. Barge
Fig. 4 Basic types of drilling rigs
1.5 Floating Rigs
1.5.1 Drillship
Drillships are normally used to drill single exploratory wells. The two basic types of
drillships are the barge type and the self-propelled type. Barge type, or non-selfpropelled drillships must be towed into position above drilling sites. Self-propelled
type drillships are capable of movement under their own power and do not require
towing. Drillships have the advantage of deep water drilling capabilities. The
operating depth is usually between 100 and 600 feet; however, several drilling
operations have been conducted in water depths greater than 1,000 feet. Other
advantages of drillship rigs include economical operation, large storage capacities,
and rapid mobility between drilling locations, Fig. 5.
Drillships employ two basic methods of station keeping to maintain their position
above drilling sites, Drillships that employ a conventional anchoring system utilize a
series of anchors that fan out from the bow and stern of the ship and are set into the
sea floor, Fig. 6. Ships using this type of system are restricted to operating depths of
1,500 feet or less. Drillships that are dynamically positioned keep their position
above the drill sites by using bow and stern thrusters that are computer controlled,
These drillships are capable of operating in water depths of over 2,000 feet.
Dynamically positioned drillships do not have to employ the conventional anchoring
system, but do on occasion in order to achieve better performance.
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Fig. 5 Drillship
Fig. 6 Diagram of drillship showing basic areas
1.5.2 Semisubmersibles
Semis, as they are called, are also used to drill single exploratory wells. The majority
of semis are towed to their drilling locations, although some of the more recent
models are self-propelled. The basic deck configurations range from triangular to
pentagonal and utilize anywhere from three to over ten legs for support. The legs are
attached to hulls or pontoons that can be flooded. The primary advantage of semis
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over drillships is their high degree of stability in rough weather. For instance, in
swells of 15 feet, some large semis have experienced vertical movement of as little
as 12 inches. Semis utilize a spread anchoring system of radially spaced anchors to
hold their position, The spread of the anchors is dependent upon anticipated wind
and sea conditions, This anchoring system restricts semis to water depths of 200 to
1,500 feet. Some semi-submersibles are capable of setting on the sea floor, in the
same manner as submersibles, Figs. 7 and 8.
Fig. 7 Semi-submerssible rig
1.6 Stationary Rigs
Stationary drilling rigs, as defined by their name, are affixed to the ocean floor by
means of some type of legs. Some stationary rigs are moveable; however, during
drilling operations, they do not encounter the ocean's movement because their
drilling platforms are' positioned above the water line. Stationary rigs are used both
for exploration and production of oil and gas fields.
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Fig. 8 Diagram for semi-submerssible
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1.6.1 Fixed Platforms
Fixed platforms are normally used in developmental drilling. The first platforms were
constructed on top of jetties that extended out from the shore, with connecting
roadways supporting the drilling operations. This type of structure is still used in
many areas of the world. A large percentage of offshore oil is obtained from fixed
platform drilling operations. Several wells can be drilled from the same platform
through multiple conductors within the steel jacket that supports the platform. A
template system is common procedure for drilling from multi-well platforms and the
use of directional drilling methods is common. Presently, most fixed platform
operations are conducted in water depths of 450 to 600 feet; however, a number of
platforms in the Southern California coastal area are set in waters 800 feet deep,
with plans for new structures to sit in water depths of 1 ,000 to 1 ,500 feet., Fig. 9
Fig. 9 Fixed platform
1.6.2 Platform Tenders
Platform tenders, as the name implies, serve to sup port a fixed platform drilling
operation. Unlike a full scale platform operation, the support equipment such as the
mud pumps, bulk material storage containers and crew quarters are located aboard
the tender rather than mounted onboard the platform. Physical connection between
the platform and the tender is maintained by means of a bow ramp. Tubular goods
such as drill pipe and casing are stored aboard the tender and transferred as needed
to the platform. Pedestal cranes are provided aboard the tender for this purpose as
well as for personnel transfer. Particular attention and care by personnel working
aboard platform tenders must be paid whenever moving from the tender to the
platform because the bow ramp is constantly in motion due to the wave action. The
bow ramp area is particularly hazardous during periods of rough weather or heavy
sea conditions as the" movement of the ramp is greatly increased, Figs 10 and 11.
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Fig. 10 Platform-tender
Fig. 11 Diagram showing basic areas of a platform-tender
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1.6.3 Jack-ups
Normally, a jack-up drilling rig is used to drill single exploratory wells in waters from
50 to 350 feet deep. The water depth is dependent upon the specifications of each
individual rig as well as the bottom conditions, Figs 12 ad 13.
Fig. 12 Jack-up rig
Fig. 13 Diagram showing basic areas of a jack-up rig
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A jack-up rig provides a stable platform from which a well can be drilled, with the
added advantage of mobility to new locations when desirable. Most jack-up rigs have
the capability of skidding, or cantilevering the derrick structure away from the main
vessel for workover capability.
Submerssible
Submesrssible rigs, also suitable for shallow water, are like jack-up rigs in that they
come in contact with the ocean or lake floor, Fig. 14.
These rigs consist of platforms with two hulls positioned on top of one another. The
upper hull contains the living quarters for the crew, as well as the actual drilling
platform. The lower hull works much like the outer hull in a submarine
Fig 14 Submerssible
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