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
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
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.
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
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
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
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
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.
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.
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