Offshore Platforms

useful for offshore studies.

1. OFFSHORE PLATFORMS
BY
ABHISHEK KUMAR
Indian Maritime University
Visakhapatnam Campus

2. WHAT IS AN OFFSHORE
PLATFORM?
A large structure at sea used to house crew and mechinery for
exploration and/ or production of natural resouces such as fossil fuels
from under the ocean bed.
Normally located in the continental shelf, but could be in deeper waters.
Could be fixed to sea bed or floating.
Could be dumb or mobile.

3. WHERE ARE OFFSHORE
PLATFORMS?
Around 6,500 offshore oil and gas installations distributed in
some 53 countries
US Gulf of Mexico: 4,000; Asia: 950; Middle East: 700; Europe,
North Sea and North East Atlantic: 490; West Africa coast:
380; and South America: 340

4. TYPES OF OFFSHORE
PLATFORMS
Fixed Platforms
 Compliant towers
 Jack-up Platforms
Semi-submersible Platforms
 Drillships
Tension-leg platforms
 SPAR Platforms
 Normally unmanned installations
Floating production systems

5. FIXED OFFSHORE
PLATFORMS
Superstructure: 'topsides' supported on a
deck mounted on jacket structure. Has
modules which house drilling equipment,
production equipment, power generating
sets, pumps, compressors, a gas flare stack,
revolving cranes, survival craft, helicopter
pad and living quarters with hotel and
catering facilities. Weight - up to 40,000
tonnes.
Substructure: (a) steel tubular jacket or
(b)pre-stressed concrete structure.

6. FIXED OFFSHORE
PLATFORMS(CONTD.)
Long term use production platform
Shallow depth installations (from 5m to 500 feet)
Load on platform depends on jacket length and can be very
severe

7. A TYPICAL STEEL JACKET
PLATFORM

8. A steel jacket structure A concrete gravity platform

9. A typical concrete platform.

10. FIXED CONCRETE
PLATFORM
(TROLL A PLATFORM, NS,
NORWAY)

11. FIXED CONCRETE
PLATFORM
(TROLL A PLATFORM, NS,
NORWAY)

12. OFFSHORE STRUCTURES
– COMPLIANT TOWERS
Narrow, flexible towers on a piled foundation
supporting a conventional deck for drilling and
production operations.
With the use of flex elements such as flex legs or
axial tubes, resonance is reduced and wave forces
are de-amplified.
Used for conventional oil production from much
greater depth upto 900m.
MAIN ATTRACTION: Due to its flexibility, the
compliant tower system is strong enough to
withstand wind and sea, even hurricane conditions.

13. COMPLIANT TOWERS -
RECENT EXAMPLES

14. COMPLIANT TOWERS
PETRONIUS, GULF OF
MEXICO, USA

15. OFFSHORE STRUCTURES
– JACK-UP RIGS
Self-contained drilling rig on a floating barge, fitted
with long support legs that can be raised or lowered
independently of each other.
The rig is towed onto location by a supply vessel with
its legs elevated and the barge section floating on
the water.
 Upon arrival at the drilling location, three legs are
jacked down to the seabed, raising the entire barge
slowly above water, to a predetermined height.
Used for exploration and production upto a depth of
100m, even upto 130m or 400 feet

16. A TYPICAL JACK-UP
PLATFORM

17. SELF ELEVATING
PLATFORM JB-109/JB-110,
SINGAPORE

18. FLOATING PLATFORMS

19. SEMI-SUBMERSIBLE
PLATFORMS
Two or more submerged Hulls
Four or six pillars or legs
Platform about 100 feet above water
Remains afloat by weight and buoyancy balance
Height above water can be varied by buoyancy adjustment in
tanks

20. SEMI-SUBMERSIBLE
PLATFORMS (CONTD.)
Can be moved from place to place
Remains in position by multi-point anchoring to sea bed and
Dynamic positioning system
Can be operated inshallow as well as deep waters upto 5000
feet depth

21. A TYPICAL SEMI-SUBMERSIBLE
PLATFORM

22. SEMI-SUBMERSIBLE
PLATFORM THUNDER
HORSE, USA

23. DRILL SHIPS
It is a ship equipped with a drilling rig and station-keeping equipment such as
anchor chains and/ or a DP system
They carry larger payloads than semi-submersible rigs and due to their
mobility and ability to carry large amounts of drilling equipment, drill-ships are
well suited to operate in remote and deep oceans

24. A TYPICAL DRILL SHIP

25. DRILL SHIP, CHIKYU,
JAPAN

26. TENSION LEG PLATFORM
Semi-submersible construction with submerged hulls, four or
six pillars and a platform
Vertical tethers hold the TLP to the sea floor and these are in
tension always
Tension in tethers =
buoyancy - weight

27. TENSION LEG
PLATFORM(CONTD.)
Vertical motion of structure restricted
Can be used in very deep waters upto 2000m
depth

28. TENSION-LEG PLATFORM

29. FUNCTIONAL SCHEMATIC OF A
TYPICAL TLP

30. TENSION-LEG PLATFORM:
MARS, USA

31. MINI TLP

32. SPAR PLATFORMS
Single cylindrical strucures moored to sea bed holding a
production platform above water
Moored to the seabed conventional mooring lines.
Three configurations: Conventional SPAR - one-piece
cylindrical hull; Truss SPAR - where the midsection is
composed of truss elements and Cell SPAR - which is
built from multiple vertical cylinders.
SPAR is more economical to build for small and medium
sized rigs than the TLP, and has more inherent stability
than a TLP.

33. SCHEMATIC OF A SPAR
PLATFORM

34. DEPTH SCHEMATIC OF
TYPICAL SPAR PLATFORMS

35. GENESIS SPAR PLATFORM, NEW
ORLEANS, USA

36. OFFSHORE PLATFORMS –
UNMANNED INSTALLATION (UI)
Offshore facility designed to be operated
remotely without the constant presence of
personnel.
Small size with a helipad on top. These are
easy to build and maintain, while avoiding
the high operating costs of a full production
platform.
Used only in shallower water, where
constructing many small UIs is a relatively
easy and cheap option as compared to the
cost of using subsea wells.

37. A TYPICAL UNMANNED
INSTALLATION

38. SLEIPNER UNMANNED
INSTALLATION, NORWAY

39. FLOATING PRODUCTION
SYSTEMS
Large ships equipped with processing facilities and
moored to a location for a long period.
FPSs: FPSO (floating production, storage, and
offloading system), FSO (floating storage and
offloading system), and FSU (floating storage unit).
FPSO is a "unit" or a "system“ of floating tanks
designed to take all of the oil or gas produced from
itself and/ or nearby platforms, process and store it.
From FPSO oil or gas is offloaded onto waiting
tankers, or sent through a pipeline.
FSO is a similar system, but without facility for
production and processing of the oil or gas.

40. FLOATING PRODUCTION
SYSTEMS
(CONTD.)
FPSOs are effective in remote or deepwater
locations where seabed pipelines are not
cost effective.
FPSOs are economical in smaller oil fields
which can be exhausted in a few years and
do not justify the expense of installing a fixed
oil platform. Once the field is depleted, the
FPSO can be moved to a new location
Large tankers have been converted to work
as FPSO or FSO

41. SOME TYPICAL FLOATING
PRODUCTION SYSTEMS

42. A TYPICAL SHUTTLE TANKER

43. SCHEMATIC OF A
TYPICAL FPSO

44. FUNCTIONAL SCHEMATIC OF A
TYPICAL FPSO

45. FPSO, MODEC V II

46. THANK YOU