OIL EXPLORATION | Offshore Drilling Operation| Deilling Rig operation | Types

Υνιτ ΙΙ ΟΦΦΣΗΟΡΕ ΟΙΛ ΟΠΕΡΑΤΙΟΝΣ
1
,
OIL EXPLORATION
By
Gaurav Singh Rajput
School of Engineering, CUSAT
@gauravkrsrajput
ΣΑΦΕΤΨ ΙΝ ΟΝ ΑΝ∆ ΟΦ
ΦΣΗΟΡΕ ∆ΡΙΛΛΙΝΓ

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I - INTRODUCTION
The first offshore oil well was drilled more than 70 years ago off the coast of California,
but the majority of offshore drilling has taken place only in the last 25 years (see figure). Crude
oil is mainly found in certain geological structures such as anticlines, fault traps and salt domes,
which are located by seismic geophysical survey, under different terrains and different climates.
Offshore oil operation involves several activities—
Exploration,
Drilling,
Construction work,
Production,
Maintenance and repair work underwater,
And ultimate transport of oil/gas to refineries.
The location of oil is by seismic geophysical survey. When oil is located, experimental
drilling is carried out to ascertain whether output will be commercially viable. If the
experimental well produces sufficient oil, then production wells are drilled, and the crude oil
and gas are conveyed by pipelines ultimately to refineries on shore.
II - OIL EXPLORATION
Oil is a fossil fuel that can be found in many countries around the world. In this
section, we will discuss how oil is formed and how geologists find it.
Forming Oil
Oil is formed from the remains of tiny plants and animals (plankton) that died in
ancient seas between 10 million and 600 million years ago. After the organisms died, they sank
into the sand and mud at the bottom of the sea.
Oil forms from dead organisms in ancient seas
Over the years, the organisms decayed in the sedimentary layers. In these

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layers, there was little or no oxygen present. So microorganisms broke the remains into
carbon-rich compounds that formed organic layers. The organic material mixed with the
sediments,
forming fine-grained shale, or source rock. As new sedimentary
layers were deposited, they exerted intense pressure and heat on the
source rock. The heat and pressure distilled the organic material into
crude oil and natural gas. The oil flowed from the source rock and
accumulated in thicker, more porous limestone or sandstone, called
reservoir rock. Movements in the Earth trapped the oil and natural gas in the reservoir rocks
between layers of impermeable rock, or cap rock, such as granite or marble.
Oil reservoir rocks (red) and natural gas (blue) can be trapped by folding (left),
faulting (middle) or pinching out (right).
These movements of the Earth include:
• Folding - Horizontal movements press inward and move the rock layers upward into a
fold or anticline.
• Faulting - The layers of rock crack, and one side shifts upward or downward.
• Pinching out - A layer of impermeable rock is squeezed upward into the reservoir
rock.
Finding Oil
The task of finding oil is assigned to geologists, whether employed directly by an oil
Close-up of reservoir
rock (oil is in black)

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company or under contract from a private firm. Their task is to find the right conditions for an
oil trap -- the right source rock, reservoir rock and entrapment. Many years ago, geologists
interpreted surface features, surface rock and soil types, and perhaps some small core samples
obtained by shallow drilling. Modern oil geologists also examine surface rocks and terrain, with
the additional help of satellite images. However, they also use a variety of other methods to
find oil. They can use sensitive gravity meters to measure tiny changes in the Earth's
gravitational field that could indicate flowing oil, as well as sensitive magnetometers to
measure tiny changes in the Earth's magnetic field caused by flowing oil. They can detect the
smell of hydrocarbons using sensitive electronic noses called sniffers. Finally, and most
commonly, they use seismology, creating shock waves that pass through hidden rock layers
and interpreting the waves that are reflected back to the surface.
Searching for oil over water using seismology
In seismic surveys, a shock wave is created by the following:
• Compressed-air gun - shoots pulses of air into the water (for exploration over water)
• Thumper truck - slams heavy plates into the ground (for exploration over land)
• Explosives - drilled into the ground (for exploration over land) or thrown overboard
(for exploration over water), and detonated
The shock waves travel beneath the surface of the Earth and are reflected back by the
various rock layers. The reflections travel at different speeds depending upon the type or
density of rock layers through which they must pass. The reflections of the shock waves are
detected by sensitive microphones or vibration detectors -- hydrophones over water,
seismometers over land. The readings are interpreted by seismologists for signs of oil and
gas traps.
Although modern oil-exploration methods are better than previous ones, they still may
have only a 10-percent success rate for finding new oil fields. Once a prospective oil strike is

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found, the location is marked by GPS coordinates on land or by marker buoys on water.
III - PREPARING TO DRILL
Once the site has been selected, it must be surveyed to determine its boundaries, and
environmental impact studies may be done. Lease agreements, titles and right-of way accesses
for the land must be obtained and evaluated legally. For off-shore sites, legal jurisdiction must
be determined.
Once the legal issues have been settled, the crew goes about preparing the land:
1. The land is cleared and leveled, and access roads may be built.
2. Because water is used in drilling, there must be a source of water nearby. If there is no
3. natural source, they drill a water well.
4. They dig a reserve pit, which is used to dispose of rock cuttings and drilling mud during
the drilling process, and line it with plastic to protect the environment. If the site is an
ecologically sensitive area, such as a marsh or wilderness, then the cuttings and mud
must be disposed offsite -- trucked away instead of placed in a pit.
Once the land has been prepared, several holes must be dug to make way for the rig and
the main hole. A rectangular pit, called a cellar, is dug around the location of the actual drilling
hole. The cellar provides a work space around the hole, for the workers and drilling accessories.
The crew then begins drilling the main hole, often with a small drill truck rather than the main
rig. The first part of the hole is larger and shallower than the main portion, and is lined with a
large-diameter conductor pipe. Additional holes are dug off to the side to temporarily store
equipment -- when these holes are finished, the rig equipment can be brought in and set up.
Setting Up the Rig
Depending upon
the remoteness of the drill
site and its access,
equipment may be
transported to the site by
truck, helicopter or barge.
Some rigs are built on
ships or barges for work
on inland water where
there is no foundation to
support a rig (as in
marshes or lakes). Once
the equipment is at the
site, the rig is set up. Here

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are the major systems of a land oil rig:
• Power system
 large diesel engines - burn diesel-fuel oil to provide the main source of
power
 electrical generators - powered by the diesel engines to provide electrical
power
• Mechanical system - driven by electric motors
 hoisting system - used for lifting heavy loads; consists of a mechanical winch
(draw works) with a large steel cable spool, a block-and-tackle pulley and a
receiving storage reel for the cable
 turntable - part of the drilling apparatus
• 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
 kelly - four- or six-sided pipe that transfers rotary motion to the turntable and
drill string
 turntable or rotary table - drives the rotating motion using power from
electric motors
 drill string - consists of drill pipe (connected sections of about 30 ft / 10 m)
and drill collars (larger diameter, heavier pipe that fits around the drill pipe and
places weight on the drill bit)
 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 formations
• Casing - large-diameter concrete pipe that lines the drill hole, prevents the hole from
collapsing, and allows drilling mud to circulate
• Circulation system - pumps drilling mud (mixture
of water, clay, weighting material and chemicals, used
to lift rock cuttings from the drill bit to the surface)
under pressure through the kelly, rotary table, drill
pipes and drill collars
 pump - sucks mud from the mud pits and
Anatomy of an oil rig

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pumps it to the drilling apparatus
 pipes and hoses - connects pump to drilling apparatus
 mud-return line - returns mud from hole
 shale shaker - shaker/sieve that separates rock cuttings from the mud
 shale slide - conveys cuttings to the reserve pit
 reserve pit - collects rock cuttings separated from the mud
 mud pits - where drilling mud is mixed and recycled
Mud circulation in the hole
 mud-mixing hopper - where new mud is mixed and then sent to the mud pits
Drill-mud circulation system
• 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)
IV – DRILLING
The crew sets up the rig and starts the drilling
operations. First, from the starter hole, they drill a surface hole
down to a pre-set depth, which is somewhere above where they
think the oil trap is located. There are five basic steps to drilling

Rotary workers trip drill pipe
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the surface hole:
1. Place the drill bit, collar and drill pipe in the hole.
2. Attach the kelly and turntable and begin drilling.
3. As drilling progresses, circulate mud through the pipe and out of the bit to float the
rock cuttings out of the hole.
4. Add new sections (joints) of drill pipes as the hole
gets deeper.
5. Remove (trip out) the drill pipe, collar and bit when the pre-set depth (anywhere from a
few hundred to a couple-thousand feet) is reached.
Once they reach the pre-set depth, they must run and cement the casing -- place casing-
pipe sections into the hole to prevent it from collapsing in on itself. The casing pipe has spacers
around the outside to keep it centered in the hole.
The casing crew puts the casing pipe in the hole. The cement crew pumps cement down
the casing pipe using a bottom plug, a cement slurry, a top plug and drill mud. The pressure
from the drill mud causes the cement slurry to move through the casing and fill the space
between the outside of the casing and the hole. Finally, the cement is allowed to harden and
then tested for such properties as hardness, alignment and a proper seal.
Drilling continues in stages: They drill, then run and cement new casings, then drill again.
When the rock cuttings from the mud reveal the oil sand from the reservoir rock, they may
have reached the final depth. At this point, they remove the drilling apparatus from the hole
and perform several tests to confirm this finding:
• Well logging - lowering electrical and gas sensors into the hole to take measurements
of the rock formations there
• Drill-stem testing - lowering a device into the hole to measure the pressures, which
will reveal whether reservoir rock has been reached
• Core samples - taking samples of rock to look for characteristics of reservoir rock
Once they have reached the final depth, the crew completes the well to allow oil to flow
into the casing in a controlled manner. First, they lower a perforating gun into the well to the
production depth. The gun has explosive charges to create holes in the casing through which
oil can flow. After the casing has been perforated, they run a small-diameter pipe (tubing) into
the hole as a conduit for oil and gas to flow up the well. A device called a packer is run down
the outside of the tubing. When the packer is set at the production level, it is expanded to form
a seal around the outside of the tubing. Finally, they connect a multi-valved structure called a
Christmas tree to the top of the tubing and cement it to the top of the casing. The Christmas
tree allows them to control the flow of oil from the well.

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Once the well is completed, they must start the flow of oil into the well. For limestone
reservoir rock, acid is pumped down the well and out the perforations. The acid dissolves
channels in the limestone that lead oil into the well. For sandstone reservoir rock, a specially
blended fluid containing proppants (sand, walnut shells, aluminum pellets) is pumped down
the well and out the perforations. The pressure from this fluid makes small fractures in the
sandstone that allow oil to flow into the well, while the proppants hold these fractures open.
Once the oil is flowing, the oil rig is removed from the site and production equipment is set up
to extract the oil from the well.
OFFSHORE PLATFORMS AND DRILLING VESSELS
The ever increasing demands for oil and gas both for industrial and domestic needs
dictate wider and wider searches for oil either on land or under the ocean floor. At present,
drilling jobs take place mainly within the boundaries of the outer continental shelf, which is the
part of the continental margin that is between the shoreline and the continental slope or, when
there is no noticeable continental slope, a depth of 200 m.
In the USSR, oil is extracted in commercial amounts in the Caspian Sea water area. In
other countries, oil and gas finds have been made in the North Sea, within the continental shelf
of North and South America, and in other regions.
Once oil or gas has been found beneath the seabed and the field is considered to be
worth developing, a platform must be built and then put in place on the field or another base
must be provided to lay out the drilling and production equipment. Depending on the depth of
sea water and the purpose of the wells (producing, explor- -ation, prospecting) the offshore
structures are subdivided into fixed, self-elevating, and semi submersible offshore platforms. In
addition, wildcat wells are sunk with the aid of drilling vessels.
The fixed offshore platforms are used at depths of up to 150 m mainly for drilling
production wells. The design of the fixed platforms is continually being improved and, as a
result, the depths at which they can be used are also continually increasing. The tendency
towards a wider use of fixed offshore structures is accounted for by the possibility of not only
drilling wells, but also operating them under conventional conditions.
Man-made islands are not in wide use, because of the high costs of their
construction. Such islands are too expensive to be constructed even at sea water depths of 10
m. However, in the Soviet Union man made islands are employed in Western Siberia to drill
boreholes in the waterbed of Lake Samotlor. A cluster of 12 wells or more are drilled from
each island. Artificial islands are also used in the Macken zie Delta to support drilling
operations there.
Rig footings of metal piles and large prefabricated concrete blocks are widely used in
the Soviet drilling practice.
Pile type footings are used in shallow waters at depths of up to 8 in as well as in rough
waterbed floors where concrete blocks cannot be utilized.

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Holes for p are bored in the sea floor from a special ship. A pile (pipe) is lowered and
cemented into each hole. Next, the piles are cut off so that their top ends are at the same level
above the water. The pipe (pile) ends are then connected by flat steel trusses. This done,
wooden flooring is made, a derrick erected and drilling equipment installed. The pile’s height
above sea level must exceed that of the largest waves.
Footings for large prefabricated blocks. Currently, large (pier) prefabricated
concrete blocks are widely utilized in the construction of offshore platforms. Thus, the MOS-1
large module offshore footings are designed for water depths of up to 8 m, MOS-2’-up to 14
m, and MOS-3’up to 22 m.
Once a MOS footing block has been put in place on the sea floor, a hole is drilled
through each of its support tubes. Reinforced concrete piles are then driven in the holes to pin
down the blocks to the sea floor. The above-water portion of the block is furnished with
trusses that are adjustable in height to compensate for bottom irregularities of up to I in. In
deeper areas other types of platforms are used.
In the oil fields situated under the Caspian Sea floor, individual platforms are connected
with one another, sleeping quarters, store houses and workshops by means of connecting piers.
Work in water areas requires much attention be directed toward preventing corrosion
attacks on metallic items. Particularly heavy corrosion, ten times that in air and under water,
occurs in zones alternately wetted and dried. The metal in these zones is given special Coatings.
Gravity offshore platforms. The mass of certain gravity offshore platforms is 300 000
t and more and their tremendous weight precludes the need to secure them to the seabed with
piles. Such structures stand up to any weather. Gravity offshore platforms are built in deep
water close to the shore and have cavities that help them to float. They are then towed by tugs
to the field. After the floating cavities are flooded, the platforms great weight holds them
securely on the seabed. Moreover, such structures generally have a crude oil storage capacity of
500000--600000 in The use of storage tanks allows the platform to continue oil production
even under bad sea conditions, when tankers cannot approach the structure.
Figure shows a steel offshore plat form, type GBS, installed in the North Sea at a
water depth of 160 in. Its total weight is about 400 000 tons. The platform top area is 6 050
mm. It houses all the equipment and materials needed to extract the oil. The base
accommodates storages for 160 000 m of crude oil. The support legs have ballast tanks
containing 75 000 m of water. Up to 40 wells are drilled from such a platform.
In recent years gravity offshore platforms are built more and
more from reinforced concrete as it costs less, resists corrosion
better, and allows the platforms to be built in any depth of water
close to the shore and be floated to the site of drilling.
Illustrated in Fig is the reinforced concrete offshore structure
Condip which is comprised of a foundation consisting of 19
cylindrical concrete oil storages (sections) taper concrete columns
projecting above water, and a steel platform 4 000 m2
area
which is supported by the taper
columns 30 in above the sea level. The Condip structure& weighs

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about 300 thou tons and is designed for a depth of ‘120 m and more. Besides the structures
described above there are other types of gravity structures used in off shore drilling.
Self-elevating off shore plat forms. These are used for drilling wells in water depths
of 30 to 100 m. At present, the self-elevating (jack-up) rigs are used for drilling prospecting
holes. This is because the work of organizing offshore fields is still undergoing theoretical and
experimental research. Besides, the fixed off‘ shore structures are economically more effective
in the drilling and operation of oil wells.
Self-elevating offshore plat forms (jack-up rigs) are barge- like, floating platforms with
legs. The lower ends of the legs are provided with support shoes or are interconnected by a
common plate. After tile plat form has been towed to the field, the legs are lowered to the sea
bottom and the platform is raised or jacked up above tile water as required.
This platform carries the following drilling
equipment: a 45.6 m high derrick with a
load capacity of 4540 kN; draw works, two
three-piston mud pumps and other
equipment for rotary drilling; tanks for
drilling mud, capacity‘2 m containers for
loose mud-making clay, capacity‘ m
storage bins for dry cement, capacity‘ m
diesel fuel tanks, capacity‘75O in a
drinking water tank of 208 m and a
process water tank of 1050 m
Use is also made of three-legged self-
elevating offshore platforms.
Semi submersible floating drilling
platforms (self-propelled and non-self-
propelled) are generally used for drilling
prospecting holes at water depths that are
out of reach of the fixed offshore
platforms and self-elevating offshore platforms.
The most effective are self propelled semi submersible drilling platforms. Semi
submersibles are floating drilling platforms with a buoyant
Substructure, part of which is beneath the surface of the water.
Specifications of a Self‘Elevating Offshore Platform
Water depth m‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘..106.0
Wave height, m‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘19.8
Wave period, s‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘.z.12.0
Maximum wind speed, km/h‘‘‘‘‘‘‘‘‘‘‘‘..‘‘.130
Distance between lower deck and sea surface, m‘‘‘‘‘‘‘..24.6
Penetration of legs into the sea floor, m‘‘‘‘‘‘‘‘‘‘‘15.2
Body dimensions, m:
Length‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘70.9
Steel offshore platform
Self elevating platform

Semisubmersible floating self-
propelled drilling platform
“Pelican” drilling vessel
Reinforced concrete
offshore structure
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Width‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘64.7
Leg length m‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘157.3
Number of legs‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘..3-4
Well depth m‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘..7620-9144
Body raising rate, m/min‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘.0.3
Structure mass, t‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘..4275
Sleeping quarters‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘ for 78 men
They maintain their position over the borehole by the use of anchors.
Figure shows a semi submersible floating self-propelled
drilling platform with ballast tanks. Platform 1 is secured
to pontoon 2 by special trusses 3 with the aid of locking
devices 4. Tube 5 performs the function of guiding the
drilling and casing strings. The pontoon accommodates
ballast tanks 8, water tank 9, and fuel tank 10. Hinge
devices 7 are used to attach floats 6 to the pontoon. 2 7
When the ballast tanks are filled the platform is floated by
the pontoon. In the oilfield, the platform is raised above
the water to the required height by pumping out the
ballast water. There are other designs of semi submersible floating self-propelled drilling
platforms.
Drilling vessels are used for drilling wells to great water depths. Figure 2.12
schematically shows the layout of working and crew quarters on the drilling ship Pelican which
is known as one of the best vessels of this class. She is equipped with anchor and dynamic
stationing systems for keeping her in place over the hole during drilling operations. The drilling
equipment is designed for drilling wells of up to 5 000 m at a water depth of 600 in. The
ship‘s length is 150 m. The derrick is 73 m high. This drill
ship can operate at sea for three months without
replenishing supplies. The drilling vessels are used only for
sinking extension and stratigraphic test holes.
VI – DRILLING INSTALLATIONS
The search for offshore petroleum has relied upon

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four main types of mobile offshore exploratory drilling installations; i.e.
Submersibles,
Jack-ups,
Semi submersibles and
Drill ships.
The present world fleet of mobile offshore drilling installations numbers approximately
400, of which about 2% are submersibles, 42% are jack-ups, 30% are semi-submersibles, and
26% are drill ships and barges.
Submersible installations are drilling platforms which rest on the sea bed during
operation, but are equipped with a lower column section having sufficient buoyant capacity to
keep the rig afloat when it is moved. About 16 of these submersibles are still in use. They are
designed primarily to work in shallow waters with depths ranging between 15 and 30 m.
Jack-up installations are self-elevating platforms equipped with legs which can be
lowered until they reach the sea bed and support the main section of the drilling platform.
Throughout the drilling process the platform is kept in the raised position above the water
surface. There are around 200 jack-up installations in use today or under construction. These
installations usually operate in water ranging in depth between 30 and 100m.
Semi-submersible installations are floating drilling platforms which, by means of
water ballast, can be submerged to a predetermined depth so that the columns or other
stabilizing devices decrease the influence of wave motion on the installation during operation.
There are approximately 150 semi-submersibles in use today or under construction. These
installations are particularly effective in deeper waters ranging from 120 to 1000 m in depth. It
is expected that semi-submersibles will be able to drill in water over 2000 m deep in the future.
Floating vessels have been used in the offshore petroleum industry as drilling platforms
since the late 1940s. However, as the search for petroleum continues in deeper and deeper
waters, highly sophisticated drill ships are being built to meet the needs of the industry. There
are approximately 100 drill ships active in oil exploration today or under construction, either as
specially designed new ships or as major conversions of older ones. Drill ships operate mostly
in water depths of 120 to 1000 m, although several of the newer ships are capable of drilling in
depths in excess of 2000 m. In addition, there are approximately 20 drilling barges operating
offshore, mostly in water depths ranging from 30-300 m.
In order to exploit petroleum resources discovered offshore, the petroleum industry
has for the past 30 years relied primarily upon fixed steel platforms. In fact, one of the first
steel platforms placed in the Gulf of Mexico 30 years ago is still being used today. These
platforms are constructed by floating out steel jackets which are sunk to the sea floor and then
fixed to the bottom by means of piles driven into the sea bed. The largest steel jacket for a
production platform was recently positioned off the coast of California in 255 m of water. The
various decks and modules necessary for drilling and production are then placed upon the
jacket supports at sea using very large crane barges and work boats.

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The special conditions of the North Sea have encouraged the recent development of
vast reinforced concrete gravity platforms which are constructed on and near shore and then
floated out to the field in a more completed state. These gravity structures provide very large
deck areas and load capacities, and may also provide integral oil storage facilities. A concrete
platform has been constructed for use on the Ninian Field in 168 m of water. Steel gravity
structures have also recently been placed in waters off the coast of Africa.
In future more reliance will be placed on the development and refinement of new
offshore production methods, for example floating platforms, sub-sea completions and
tethered platforms. These new methods are available today and are in fact already being tested
and used. Sub-sea well completions have been used in many areas, including the North Sea, off
the coast of Gabon and in the Gulf of Mexico. The semi-submersible drilling installation
Transworld 58 has been converted into a production platform for the Argyll field in the North
Sea.
On And Offshore Oil Production

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VII - OFFSHORE CONSTRUCTION OF INSTALLATIONS
Offshore mobile drilling installations
Offshore mobile drilling installations are generally constructed in similar fashion to
ships at onshore construction sites.
Steel jacket production platforms
The construction of steel jacket production platforms takes place in two basic stages.
There is the initial construction stage, which takes place onshore where the steel jacket is
fabricated. This process is similar to shipbuilding. It is followed by a second stage, in which the
steel jacket is provided with temporary flotation equipment or placed on a barge and towed out
to the offshore petroleum field. It is then up ended, usually using a remote controlled ballasting
system, and manoeuvred into position. At this point the jacket is only a few feet from the
bottom. When it is in position the flotation equipment is further ballasted to set it on the sea
bed, and then over-ballasted to provide the necessary weight to achieve penetration of the
supports into the sea bed.
Throughout this towing out and positioning process there are usually no workers on
board the jacket. Therefore, the occupational safety and health problems are limited to workers
on the various service boats and derrick barges involved in the operations.
However, once the jacket has been positioned, piles must be driven into the sea bed in
order to provide the necessary footing to support the installation in the face of wind and
waves. This early part of offshore construction activity is particularly hazardous. The
construction workers are accommodated on the work barges anchored near the jacket and
must be transferred from the work boat by means of cradle lifts and hoists to the jacket
support, often in difficult weather conditions. The work surfaces are uncovered and often
dangerously slippery.
After the jacket has been secured to the sea bed, large crane ships or barges are used to
place the deck and modules on the jacket support. These modules are very heavy, weighing up
to 2400 tones and it is necessary to carry out these heavy-lift activities under almost perfect
weather conditions.
The situation improves once the platform has been sufficiently completed to allow the
workers to live on board. Throughout the construction period, however, they are faced with
many safety hazards, including fire, explosion, bad weather, working in confined areas, falls,
lifting, noise and vibration. In other words, many of the hazards are the same as those faced by
construction workers on land, with the additional difficulties created by offshore operations.
Some of these additional difficulties include the crucial factor of emergency evacuation
measures to allow the workers to abandon the platform safely and rapidly in case of serious
hazard. This requires special provisions for life-rafts, life-preservers, escape ladders or nets, and
alarm systems, during all phases of construction, as well as when the platform is completed and
certified. In addition, the attending vessels during the early construction phases should have all
the necessary safety equipment available, including life-rafts and rescue boats, life-preservers
and fire-fighting equipment.

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An additional factor is that many of the Construction workers find it particularly
difficult to adapt to the isolation and hardships of life at sea. The effect of working 12 h a day
for 7 to 21 days (and sometimes even more) while living in a relatively confined environment
has created difficulties for some construction workers. Problems of insomnia are often
reported, which may be aggravated by the relatively high levels of noise and vibration on
platforms.
Reinforced concrete gravity platforms
The construction of reinforced concrete gravity platforms is a relatively new
development which has evolved out of offshore petroleum activities in the North Sea. Many of
the safety and health problems which occur during the construction period are very similar to
those which exist during onshore building and civil engineering work.
One of the special advantages of the gravity platforms is that the decks and modules
can be attached to the platform while it is near shore in protected waters. This greatly decreases
the risks involved in carrying out the required heavy lifts.
However, once the platform has been completed it must be towed out to the field.
During the towing of these gigantic structures there are significant risks. The platforms are
floating with the decks and modules very high out of the water, sometimes over 75 m, and the
problems that this creates for emergency evacuation may require the use of helicopters. With
this in mind, the number of personnel on board the platform during the towing and
positioning process should be limited to the absolute minimum.
New types of offshore construction activities
In the Canadian Arctic, artificial islands have been constructed to be used as drilling
platforms and underground caverns and tunnels have been dug where the drilling and
production facilities are protected from the severe ice and weather conditions.
VIII - OFFSHORE PIPELINE CONSTRUCTION
There are at present only two major methods of transporting offshore petroleum
resources to onshore processing facilities: the construction of offshore pipelines and the use of
tankers receiving oil through mooring systems located near the offshore production facility.
An offshore pipe-laying activity is one of the major technological challenges in the
offshore petroleum industry. Nowadays giant barges, ships and semi submersibles are able to
lay pipes of increasingly large diameter.
Weather has a particularly strong influence on the activities of offshore pipe-laying
barges, especially in areas such as the North Sea. The combination of high winds, waves and
cold severely limits the activities of pipe-laying and also prevents the pipe haul boats from
supplying the lay barges with pipe and other equipment. Pipe is delivered to lay barges usually
in 12- or 24-m lengths.
The transfer of loads from a supply ship which is rolling and pitching with the waves
alongside the barge is a difficult and dangerous job. The crane operator must be able to judge
the movements of the supply craft and the barge so as to allow the lifting of the supplies at the

17
critical moment when the supply boat reaches its highest point in the wave cycle.
After the load has been safely lifted, however, the deck crew must assist in positioning
it properly on the deck. These operations are also complicated by the problems of motion, and
in wet weather the deck is often slippery. The deck crew also sometimes suffers from the cold,
which is aggravated by the wind-chill factor, especially during night transfers. Therefore it is
not surprising that the principal victims of accidents on offshore pipe-laying barges are the
deck crews.
Another occupational safety and health problem on the pipe-laying barges appears to
be the noise level. It has been reported that it may reach 110 dB in some mechanics shops on
board, and at the anchor-raising positions levels of 105 dB have been recorded.
Another area where safety problems appear to exist on board pipe-laying barges is in the
welding operation.
There are of course numerous activities in the diving area related to the laying of
offshore pipelines.
IX - MAINTENANCE AND REPAIR ACTIVITIES
There are two basic types of maintenance and repair activities: those carried out as a
result of an immediate problem or failure of equipment (corrective maintenance) and
preventive maintenance. In the offshore petroleum industry the role of the latter is especially
important and has received considerable attention from the industry. The substantial
investments involved in offshore petroleum installations, their relative isolation, and their
location in unknown or difficult environmental conditions have created a situation where any
failure of equipment is very expensive and critical in terms of possible risks to the crews on
board the installation. Particular problems appear to exist regarding corrosion.
There are three key elements to a successful offshore preventive maintenance and
repair programme: planning, inspection and record keeping.
Planning takes on a particularly important role in maintenance activities in cold areas as
a result of the so called weather window, or the period during the year when the weather
conditions are safe enough for many major maintenance and repair tasks to be completed.
Long-range planning therefore is required.
Planning also requires the establishment of a master schedule for the routine inspection
and replacement of equipment on board the installation.
The inspection programmes for fixed offshore installations are carried out mainly by
diving crews or submersibles, which visually and mechanically inspect the condition of the
jacket or installation at various intervals to ascertain its over-all state.
The third aspect of preventive maintenance is comprehensive record keeping. Careful
records for all equipment must be kept, which include the date of installation, inspection,
testing results and defect reporting. In addition, there should be available on the installation, if
practicable, documentation indicating the procedures for removal, replacement, and testing,
etc., if emergency repairs are necessary.
X- HOURS OF WORK

18
All persons engaged on continuous operations work according to the system of two 12-
h shifts, which requires the presence of two complete teams on the installation. The same
applies where there are two 6-h shifts each day, alternating with two periods of 6 h of rest, as in
the case of staff engaged on offshore prospecting in Argentina. As for those not employed on
shift work, they generally work for 12 h and then have 12 h off.
The general practice on all offshore petroleum installations is to alternate a period of
work offshore with an equal period of rest on land. There can be a rotation covering 7 days of
work and 7 days of leave or 14 days of work and 14 days of rest or even longer periods—a
practice that is usually justified on the grounds of problems of organization and of the cost of
transport between the coast and exceptionally remote installations. There may also be other
arrangements, depending on the undertaking and local conditions.
XI - HAZARDS
There are a number of hazards characteristic of all offshore work, as well as specific
hazards inherent in particular jobs such as diving or in the materials handled, such as chemicals.
Etc.
Stress
Mental stress of men working on offshore drilling rigs and platforms is recognized as a
factor contributing to illnesses, accidents and low output. Its causes are long hours, the fast
pace of work, lack of proper rest, various environmental factors such as noise, vibration, heat,
cold, poor lighting, etc., domestic worries, and constant fear of hazards, injury and disease. The
effects are cumulative. The signs of stress are unusual irritability, frequent insomnia (2%)
requiring tranquilizers, psychosis and depressive psychosis. Stress may also lead to excessive
smoking, alcoholism, and even drug addictions. Fraternization among workers and more
frequent leaves onshore may reduce the build-up of tension.
Geographical and climatic factors
Geographic and climatic conditions materially affect the health of workers, particularly
with regard to divers. In certain areas the water deep down may be extremely cold. In the
North Sea it was found that the temperature at depths greater than 50 m is below -10 C. Such
conditions require the circulation of warm water inside the diver—s suit. Progressive
hypothermia in divers produces cardiac irregularities followed by confusion and finally
unconsciousness; divers may die of syncopal attack. In the Persian Gulf the climate is hot and
humid (up to 40 C in the shade with 90-100% humidity). Heat exhaustion and heat stroke may
occur unless light clothing, sun helmets, air conditioning of living and rest rooms together with
careful medical surveillance are provided.
Rough seas make large numbers of people sick, and increase the risk of drowning
during transfer of men from boat to ship or barges. Storms may also increase the hazards of
drilling and construction work both on rigs and under the sea and have been responsible for
the collapse of rigs and platforms with large numbers of fatalities.

19
XII – SAFETY AND HEALTH MEASURES
Offshore work is dangerous at all stages. The men to be employed in this work should
be carefully chosen and trained. They should be examined both physically and psychologically.
Men physically handicapped, those with a history or evidence of pulmonary, cardiovascular or
neurological disease, epilepsy or diabetes, those with a personal or family history of
psychological disturbances or with a history of alcohol or drug addiction should not be
accepted. Periodical six-monthly medical examinations are advisable.
Emergency medical services on offshore drilling and production installations should
include the presence of a certified medical doctor or nurse on board. The installations should
be equipped with small dispensaries. The distance from regular medical services is what
distinguishes offshore needs from other industrial situations. The rapid removal of a sick or
injured worker may be carried out by helicopter to a hospital in many cases but even this can
be delayed by weather. Alternatively, a doctor might travel by helicopter to the installation or
talk by radio with the medical orderly or nurse on board to advice on possible special
emergency treatment.
When offshore work is in mid-ocean and there are many workers, a hospital ship with
doctors on shift duty is essential. Such a ship has been provided recently in the North Sea.
Formerly, in case of sickness or accident a medical report was sent by radio to the shore
hospital (at Aberdeen) and instructions were radioed back. An injured man or an emergency
medical case was transferred to hospital by helicopter, but bad weather often delayed transport.
Cases dealt with by radio were many, as the doctor often could not be brought from the shore
in time. With the provision of the hospital ship, medical help and relief is more readily available
and the number of accident cases dealt with by radio has been nearly halved.
In addition to the regular medical services required on board, continuing attention must
be given to the need for complete and careful medical examinations of workers, both in
advance of their work offshore and periodically during their employment. The special rigours
and stresses of offshore life and work required that they be given the best possible preventive
health care.
Safety training of offshore workers is essential. Panic, inadequate training and
foolhardiness are often cited as the cause of many avoidable accidents. Safety meetings should
be held and attendance enforced. Safety drills, fire drills and survival drills should be organised.
Men should be encouraged to wear protective clothing. Those being transferred by boat from
shore to rigs should wear life jackets. Helicopters are now being employed more and more
frequently in offshore drilling. Travel time is reduced and the inconveniences of rough seas are
avoided, and the cost is therefore competitive. But helicopter accidents, with or without loss of
life, are not uncommon. Passengers should therefore wear survival suits.
The US Occupational Safety and Health Administration (OSHA) have issued detailed
regulations for the safety of offshore workers. Its diving regulations require a drilling contractor
to make a medical and psychological evaluation of the state of the diver before each dive: he
should not be permitted to dive or be otherwise exposed to hyperbaric conditions for the
duration of any known temporary impairment such as cold, alcoholic intoxication, influence of
drugs, respiratory diseases, skin or external ear infections, excessive fatigue, or emotional

20
distress. The OSHA has also laid down regulations for the operation of helicopters.
Statutory regulations covering operational safety, health and welfare of the offshore
installations, emergency procedures, life-saving appliances and diving operations have been
enacted in the United Kingdom between 1974 and 1976. Recent legislation has also been issued
in Norway.
At the international level, the reader is referred to the ILO code of practice on safety
and health in the construction of fixed offshore installations.

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