INTRODUCTION TO OFFSHORE STRUCTURE INTRODUCTION TO OFFSHORE STRUCTURE
Jul 16, 2015
INTRODUCTION TO OFFSHORE STRUCTUREINTRODUCTION TO OFFSHORE STRUCTURE
Searching for oil over water using seismology
ANATOMY OF OIL RIG
MAJOR SYSTEMS OF LAND OIL RIG
Power system
electrical generators
large diesel engines
Mechanical system
hoisting system
turntable
Rotating equipment
Hoisting System: The hoisting system is used to raise and lower pipe in and out of the hole and to support the drill string to control the weight on the drill bit during drilling. It also acts as an elaborate pulley to lift the travelling block and remove the drill pipe.
Rotating equipment - used for rotary drilling
swivel - large handle that holds the weight of the drill string; allows the string to rotate and makes a pressure-tight seal on the hole
drill string - consists of drill pipe (connected sections of about 30 feet (10 meters) and drill collars (larger diameter, heavier pipe that fits around the drill pipe and places weight on the drill bit)
turntable or rotary table - drives the rotating motion using power from electric motors
drill bit(s) - end of the drill that actually cuts up the rock; comes in many shapes and materials (tungsten carbide steel, diamond) that are specialized for various drilling tasks and rock
Casing - large-diameter concrete pipe that lines the drill hole, prevents the hole from collapsing, and allows drilling mud to circulate
Drilling mud:
used to stabilize the excess pressure created due to fluid in the
formation
used to cool drill bit
remove rock chips
Derrick - support structure that holds the drilling apparatus; tall enough to allow new sections of drill pipe to be added to the drilling apparatus as drilling progresses
Blowout preventer - high-pressure valves (located under the land rig or on the sea floor) that seal the high-pressure drill lines and relieve pressure when necessary to prevent a blowout (uncontrolled gush of gas or oil to the surface, often associated with fire)
DRILLING PLATFORMS
Types of offshore drilling platforms:
Movable drilling rig-(MODU-mobile offshore drilling unit)
exploration purposes
Eg, drilling barge, jack-up barges, ,submersibles ,semi-submersibles ,FPSO (floating, production, storage and offloading systems), drill ships
Permanent drilling rig-
extraction and production
Eg, jacket platform, gravity platform
Complaint platform:
tension leg platform
guy towers
articulated towers
Questions
1.Petroleum and natural gas deposits are found in -------- rocks in sea bed.
2.Oil and gas are made up of --------.
3.When was 1st offshore drilling began and where.
4Name one active location where many platforms exist
5.What is derrick?
6.List some functions of drilling mud.
7.Write few movable drilling platform names and draw free sketch of one
GRAVITY PLATFORM:Hibernia oil platform
GRAVITY PLATFORMS
The Hibernia Gravity Base Structure is the world's largest offshore oil platform
Caisson: void spaces used as storage compartment for crude oil or filled
with permanant Fe ore ballast
importance:
to provide buoyancy during construction/towing and later serve as oil storage space
Skirts:
improve foundation stability
act erosion resistance feature
provides transverse resistance to platform sliding
Troll A platform (condeep )
GRAVITY PLATFORM
GBS: gravity based structure-concrete, steel
Condeep (concrete deep water structure) :gravity base structure for oil platforms developed
and fabricated by Norwegian Contractors in Stavanger, Norway .
The Condeep is used for a series of production platforms introduced for crude oil and natural gas production in the North Sea and Norwegian continental shelf
Design: production
: large reinforced concrete bottom mounted structure
:uses its weight to resist environmental loads. If it fails ,it fails severely
:generally built in soft soil like Gulf of Mexico
Depth : medium--- up to 350m
Advantages
Support large deck loads
Possible reuse
Construction and testing may be completed before floating and towing to site
Large field , long term production
May have large storage capacity
More tolerant to overloading and sea water exposure .
Disadvantages
Cost increases exponentially with depth
Foundation settlement (sea-bed profile increases due to geological disturbances)
Subject to seafloor scour
May require more steel than steel jacket structure
Questions
1.Draw a neat sketch of one of gravity platform and mark the parts
2.What are CONDEEP.
3.What are essential features of gravity platform.
4.Give one field example of gravity platform.
5.What is the key word of gravity platform.
6.What is a caisson.
7.What is the use of skirts.
8.Give essential features of gravity platforms.
9.What are exclusive advantage of gravity platform.
10.State few demerits.
11.Show in sketch possible failure modes of foundation of gravity platforms
FIXED PLATFORM
Two main components:
substructure
superstructure (topside)
JACKET PLATFORM
Sketch of jacket platform
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Superstructure:
supported on jacket structure
consist of drilling equipment, production equipment, gas turbine ,generating sets, gas flare stations
it weighs up to 40,000 tonnes
Substructure:
Jacket-tubular platform support structure
- It serves as guides for driving of piles –called template structure
- It supports and protects well conductors,
pumps, risers etc
- Suitable for water depths:150-250m
- Soil condition: clay-penetrable- because of piles
Most common: steel jacket platform
Substructure and jacket is fabricated from steel welded pipes and is pinned through to sea floor with steel piles which are driven through pile guides on outer members of jacket
The piles are thick steel pipes of 1 to 2m diameter and can penetrate as much as 100m into sea-bed
The jacket can weigh up to 20,000 tonnes
PARTS OF JACKET PLATFORM
Transition piece: connects topsides and jacket structure
Conductors: long hollow straight or curved tubes that embed into sea- bed and through which drilling for oil, gas or both is performed
Risers: long slender tubes that carry the crude or partially processed oil/gas to another location for further processing either to a land based facility or to another platform
Boat landing, Barge bumper and riser guard:
-for berthing of supply vessels
-for smooth berthing to facilitate a reduced vessel impact on the structure
Riser guard:Another protective structure that protects the oil/gas carrying risers.
They are designed for accidental vessel impacts
Launch truss:are provided on one side of jacket to facilitate the loading out on to the barge
Mud mat: bottom most framing of platform that helps resist natural forces of nature towards stability of platform before piles are driven through legs
ADVANTAGES
Support large deck loadsConstruction and testing may be
completed before floating and towing to site
Large field , long term productionPiles result in good stabilityLittle effect from sea floor scour
DISADVANTAGES
Cost increase exponentially with depth High initial and maintenance cost
Not reusable
Steel structure member subject to corrosion
Corrosion severe near the SWL
Questions
1.List the purpose for building an offshore structure2.What are the two main components of a fixed
platform3.Describe important features of jacket platform4.Draw a line diagram of jacket platform and mark
the parts5.What do you understand by the term template
structure6.What is the most suitable soil condition for a jacket
platform 7.What is the typical weight of a jacket platform in
tonnes8.Write a brief note on flare boom
QUESTIONS
1.Give advantages of jacket platform.
2.Give some demerits of jacket platform
3.Generally top-sides are connected to jackets by-----
4.Which component of the platform helps them from skidding from barge
5.What do you understand by mud mats.
6.With neat sketches ,show installation steps of jackets.
7.Jacket structure have high maintenance cost .Why?