Unit 2 - Offshore Platforms and Vessels

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Working on a Rig

Unit 2

Offshore platforms and Vessels



Unit Objective

A high proportion of oil and gas explorationand production is carried out offshore.Platform construction has developed over

time to become better adapted to deal withphysical challenges of different offshorelocations. This unit focuses on vocabularywhich will help you to describe in English thedifferent offshore platforms and vessels onwhich you or employees of your companywork.



Focused reading1. The right platform

Study the table describing the different platforms and vessels used for drilling

offshore.

Type of platform/vessel Description

Drilling barge A flat-bottomed rig used in shallow waters.

Jack-up rig A rig which has two hulls and at least three vertical legs

through the hulls

Semi-submersible rig A rectangular-shaped platform floated with pontoons

below the surface of the water.

Drillship A ship with a drilling rig mounted in the center.

Gravity-base fixed

production platform

A platform with a steel-reinforced concrete base, held

to the seabed by gravity

Steel-jacket platform A platform which has steel legs that sit on the seabed,

held by concrete piles

Tension-leg platform A platform held in position by heavy weights connected

to hollow steel tubes

Compliant platform A light platform designed to sway with the wind, waves

and currents



Drilling barge



Jack-up rig

Jack-up Mobile Drilling Units (or jack-ups), as the name suggests, are rigs that can be

jacked up above the sea using legs that can be lowered, much like jacks. These MODU's-

Mobile Offshore Drilling Units are typically used in water depths up to 400 feet (120 m),

although some designs can go to 550 ft (170 m) depth. They are designed to move from

place to place, and then anchor themselves by deploying the legs to the ocean bottom

using a rack and pinion gear system on each leg.



1. Derrick Load-bearing tower like framework

over an oil/gas well which holds the hoisting

and lowering equipment.

2. Drawworks Hoisting mechanism on a

drilling rig which spools off or takes in the

drilling line and thus raises or lowers the drill

string and bit.

3. Drill Floor Foundation on which the

derrick and engines sit. Contains space for

storage and well control equipment.

4. Drill pipe Steel pipe, in approximately 30-

foot (9-meter) lengths, screwed together to

form a continuous pipe extending from the

drilling rig to the drilling bit at the bottom of

the hole. Rotation of the drill pipe and bitcauses the bit to bore through the rock.

5. Drill String String of individual joints of pipe

that extends from the bit to the kelly and

carries the mud down to, and rotates, the bit.



Semi-submersible rig

These platforms have hulls (columns and pontoons) of

sufficient buoyancy to cause the structure to float, but of weight

sufficient to keep the structure upright. Semi-submersible

platforms can be moved from place to place; can be ballasted up

or down by altering the amount of flooding in buoyancy tanks;they are generally anchored by combinations of chain, wire rope

or polyester rope, or both, during drilling or production

operations, or both, though they can also be kept in place by the

use of dynamic positioning. Semi-submersibles can be used in

water depths from 200 to 10,000 feet (60 to 3,000 m).



Drillship

A drillship is a maritime vessel that has been fitted with drilling apparatus. It is most

often used for exploratory drilling of new oil or gas wells in deep water but can also be

used for scientific drilling. Early versions were built on a modified tanker hull, but

purpose-built designs are used today. Most drillships are outfitted with a dynamic

positioning system to maintain position over the well. They can drill in water depths up

to 12,000 ft (3,700 m).[7]



Drillship



Gravity-base fixed production platform

These GBS can either be steel or concrete. It is anchored directly onto the seabed. For

steel GBS, it is predominantly used when there is no or limited availability of crane

barge to install conventional fixed offshore platform, for example in the Caspian Sea.

There are several steel GBS in the world today (i.e. offshore Turkmenistan Waters

(Caspian Sea) and offshore New Zealand). Steel GBS does not provide storage capability.

It is mainly installed by pulling it off the yard, by either wet-tow or/and dry-tow, and

self-installing by controlled-ballasting of the compartments with sea water. To better

position the GBS during installation, the GBS shall be connected with either atransportation barge or any other barge (provided it is big enough to support the GBS)

using strand jacks. The jacks shall be released bit by bit whilst the GBS is ballasted to

ensure that the GBS does not sway too much from target location.



Steel-jacket platform

The steel jacket type platform on apile foundation is by far the mostcommon kind of offshorestructure and they existworldwide. The "substructure" or"jacket" is fabricated from steelwelded pipes and is pinned to the

sea floor with steel piles, whichare driven through piles guides onthe outer members of the

jacket.The piles are thick steelpipes of 1 to 2 meters diameterand can penetrate as much as 100m into the sea bed. The jacket can

weigh up to 20,000 tones.To ensure that the installation will last

for the required service life,maintenance must be carried outincluding the cathodic protectionused to prevent corrosion.



Tension-leg platform

TLPs are floating platforms tethered to the seabed in a manner that eliminates most

vertical movement of the structure. TLPs are used in water depths up to about 6,000 feet

(2,000 m). The "conventional" TLP is a 4-column design which looks similar to a

semisubmersible. Proprietary versions include the Seastar and MOSES mini TLPs; they are

relatively low cost, used in water depths between 600 and 4,300 feet (180 and 1,300 m).

Mini TLPs can also be used as utility, satellite or early production platforms for larger

deepwater discoveries.



Compliant platformThese platforms consist of slender flexible towers and a pile foundation supporting a

conventional deck for drilling and production operations. Compliant towers are

designed to sustain significant lateral deflections and forces, and are typically used in

water depths ranging from 1,500 to 3,000 feet (460 to 910 m).



1, 2) conventional fixed platforms; 3) compliant tower; 4, 5) vertically

moored tension leg and mini-tension leg platform; 6) Spar ; 7,8) Semi-

submersibles ; 9) Floating production, storage, and offloading facility; 10)

sub-sea completion and tie-back to host facility.[6]



Focused reading

� Which of these are:

1. easy to move from one place to another?

drilling barge, jack-up rig, semi-submersiblerig, drillship , compliant platform

2. probably fixed in one place for a long period

of time?gravity-based fixed production platform,

steel-jacket platform, tension-leg platform



Focused reading

3. designed for use in shallow water?

drilling barge, gravity-based fixed

production platform, steel-jacket platform,tension-leg platform

4. designed for use in deep water?

jack-up rig, semi-submersible rig, drillship,compliant platform



Focused reading

2. Construction types

Some of these construction are shown in thepictures. Read the descriptions again and see

if you can match them.

1. jack-up rig

2. tension-leg platform

3. semi-submersible rig4. drillship

5. drilling barge



Focused reading

3. Support vessels

frequently oil companies use other support

vessels attached to existing rigs. an exampleof this is a Floating Production, Storage and

Offloading vessel. (FPSO). Study the diagram

and read the following description of FPSO.

Why do oil companies use FPSO vessels?



The Floating Production, Storage and Offloading vessel is atype of floating tank system designed to take all of the oiland gas produced from a nearby platform or platforms,process it and store it until the oil and gas can be offloaded

onto waiting tankers, or sent through a pipeline. Suchvessels are particularly effective in remote or deep-waterlocations where seabed pipelines are not cost-effective.FPSOs eliminate the need to lay expensive long-distancepipelines from the oil well to an onshore terminal. Theycan also be used economically in smaller oilfields which can

be exhausted in a few years and do not justify the expenseof installing a fixed oil platform. Once the field is depleted,the FPSO can be moved to a new location



Why do oil companies use FPSO

vessels?

� to store oil and then transfer it to tankers or

pipelines. They are more economical in smallfields or where the lifetime of a field is

expected to be short.



Vocabulary-building activities

1. This is where the helicopter, bringing crew and supplies tothe platform, lands and takes off.

heli-deck

2. These are used for lifting heavy equipment onto the rig.

service cranes3. Supplies are kept here until they are needed.

store areas

1. The features of a rig

Using words from the box below, label the features visible in the

photograph, (not all of the features given in the box are shown

jacket piles accommodation modules derrick drilling rig flare stack

pontoon service cranes drilling pipe deck heli-deck store areas

ballast tanks barge hull



4. Waste emissions are burnt off through these.flare stack

4. These are filled with water to submerse the platform.

ballast tanks

6. This structure supports the crown block and strings of a drilling rig.

derrick

7. This is the legs and structure that support theplatform

jacket

8. These are used to secure the platform to the seabed.

piles






9. This is used to pull the platform into position.

barge

10.This is where the crew sleep and relax when

they are off-dutyaccommodation modules

11. This is equipment used for drilling.

drilling rig

12. This is where the sections of the drillstring arestored.

drilling pipe deck






3. Know your rig1. An FPSO vessel is a small drilling rig.

False. it is a support vessel for a drilling rig.

2. The FPSO can offload oil or gas to either a tanker or a pipeline.

True

3. It can store oil produced on several different platforms.

True

4. It is useful in shallow waters just off the coast.

False. It is useful in remote or deep-water locations

5. It is used as a replacement for seabed pipelines.

True

6. It saves a lot of money in certain situations.

True

7. It works well in fields where oil or gas is expected to last a long time.False. it works well in fields which can be exhausted in a few years.

8. It is more cost-effective than a fixed platform in some situations.

True

9. It is very mobile and flexible

False



4. Attraction of opposites

a. This is where the helicopter lands.

takes-off

b. This type of rig is suitable for deep water.shallow

c. The crew are on-duty 12 hours per day.

off-duty

d. This is a heavy type of platform.

lighte. The offloading vessel is a fixed system.

floating

f. First, the ballast tanks are emptied.

filled

g. It is a horizontal construction.vertical

h. It is a solid cylinder made of steel.

hollow

i. We want the equipment to sink.

float



2. make a negative word using in

and un

� economical uneconomical

� effective ineffective

�

expected unexpected� expensive inexpensive

� flexible unflexible

� necessary unnecessary� suitable unsuitable

Unit 2 - Offshore Platforms and Vessels

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