SAFETY IN PETROLEUM AND

PETROCHEMICAL INDUSTRIES
Subject Code: 19-206-0607(IE)
Lecture 2

By

Dr. Divya P Soman

Assistant Professor
Safety and Fire Engineering
 Module IV
On-Shore and Off-shore drilling
 DRILLING
• Drilling is the process of penetrating through the ground and
extracting rocks from various depths beneath the surface for
confirming the geology beneath and/or providing samples for chemical
analysis.

Onshore drilling Offshore drilling

 TYPES OF DRILLING
• Two types of drilling: Onshore and Offshore drilling
• Onshore drilling is seeking to release resources from beneath the earth's
surface.
• The onshore exploration and drilling process is entirely land-based, or on
the shore. The drilling process begins with the production of a wellbore, a
long and slim vertical hole, that is drilled through layers of rock and
sediment.
• Main types of onshore drilling: the main types of drilling systems
include rotary drilling, percussion drilling, and rotary-percussion drilling.
Rotary drilling involves a rotating drill bit, percussion drilling uses a
hammering action, and rotary-percussion drilling combines both methods to
penetrate various soil and rock conditions.
• Offshore drilling is seeking to release resources from beneath the
ocean's seabed.
• There are two types of off-shore drilling
• These include bottom founded drilling rigs (jackup barges and swamp
barges), combined drilling and production facilities either bottom
founded or floating platforms, and deepwater mobile offshore drilling
units (MODU) including semi-submersibles or drillships.
 Classification of wells

By Produced Fluid
• Wells that produce oil
• Wells that produce oil and natural gas
• Wells that only produce natural gas
By Location

Wells can be located:

• Onshore
• Offshore

Offshore wells can further be subdivided into

• Wells with subsea wellheads, where the top of the well is sitting on the ocean floor
under water, and often connected to a pipeline on the ocean floor.
• Wells with 'dry' wellheads, where the top of the well is above the water on a
platform or jacket, which also often contains processing equipment for the
produced fluid.
By Purpose

Another way to classify oil wells is by their purpose in contributing to the development of a resource.
They can be characterized as:

• wildcat wells are drilled where little or no known geological information is available. The site may
have been selected because of wells drilled some distance from the proposed location but on a terrain
that appeared similar to the proposed site.
• exploration wells are drilled purely for exploratory (information gathering) purposes in a new area,
the site selection is usually based on seismic data, satellite surveys etc. Details gathered in this well
includes the presence of Hydrocarbon in the drilled location, the amount of fluid present and the
depth at which oil or/and gas occurs.
• appraisal wells are used to assess characteristics (such as flow rate, reserve quantity) of a proven
hydrocarbon accumulation. The purpose of this well is to reduce uncertainty about the characteristics
and properties of the hydrocarbon present in the field.
• production wells are drilled primarily for producing oil or gas, once the producing structure and
characteristics are determined.
• development wells are wells drilled for the production of oil or gas already proven by appraisal
drilling to be suitable for exploitation.
• Abandoned well are wells permanently plugged in the drilling phase for technical reasons.
Production wells may be further categorised as-

• oil producers producing predominantly liquid hydrocarbons, but mostly with some
associated gas.
• gas producers producing almost entirely gaseous hydrocarbons.
• water injectors injecting water into the formation to maintain reservoir pressure, or simply
to dispose of water produced with the hydrocarbons because even after treatment, it
would be too oily and too saline to be considered clean for dumping overboard offshore,
let alone into a fresh water resource in the case of onshore wells. Water injection into the
producing zone frequently has an element of reservoir management; however, often
produced water disposal is into shallower zones safely beneath any fresh water zones.
• aquifer producers intentionally producing water for re-injection to manage pressure. If
possible this water will come from the reservoir itself. Using aquifer produced water
rather than water from other sources is to preclude chemical incompatibility that might
lead to reservoir-plugging precipitates. These wells will generally be needed only if
produced water from the oil or gas producers is insufficient for reservoir management
purposes.
• gas injectors injecting gas into the reservoir often as a means of disposal or sequestering
for later production, but also to maintain reservoir pressure
 ONSHORE/OFFSHORE DRILLING
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
 OIL EXPLORATION
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 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).
The various movements of 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 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 found, the location is marked by GPS
coordinates on land or by marker buoys on water
 PREPARING TO DRILL
• Once the legal issues have been settled, the crew goes about preparing the land.
• 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.
Drilling Equipment

Anatomy of an oil rig

 Parts of Drilling Equipment
• 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 - mechanical device on a drilling rig that provides clockwise (as
viewed from above) rotational force to the drill string to facilitate the process
of drilling a borehole.
• 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 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-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)
Top drive rig
 Offshore structures for drilling and production

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
 Fixed platforms
• These platforms are built on concrete or steel legs, or both,
anchored directly onto the seabed, supporting the deck
with space for drilling rigs, production facilities and crew
quarters. Such platforms are, by virtue of their immobility,
designed for very long term use (for instance the Hibernia
platform). Various types of structure are used: steel jacket,
concrete caisson, floating steel, and even floating concrete.
Steel jackets are structural sections made of tubular steel
members, and are usually piled into the seabed
• Concrete caisson structures, pioneered by the Condeep
concept, often have in-built oil storage in tanks below the
sea surface and these tanks were often used as a flotation
capability, allowing them to be built close to shore
(Norwegian fjords and Scottish firths are popular because
they are sheltered and deep enough) and then floated to
their final position where they are sunk to the seabed.
Fixed platforms are economically feasible for installation
in water depths up to about 520 m (1,710 ft)
Compliant towers
These 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 370 to 910 metres (1,210 to 2,990 ft)

Semi-submersible platform
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 and 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 and/or
production operations, though they can also be
kept in place by the use of dynamic positioning.
Semi-submersibles can be used in water depths
from 60 to 3,000 metres (200 to 10,000 ft)
Jack-up drilling rigs

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. These MODUs (Mobile
Offshore Drilling Units) are typically used in water depths up to 120 metres (390
ft), although some designs can go to 170 m (560 ft) depth. They are designed to
move from place to place, and then anchor themselves by deploying their legs to the
ocean bottom using a rack and pinion gear system on each leg.
Drillships

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 3,700 m (12,100 ft).
Floating production, storage, and offloading system (FPSO)
The main types of floating production systems are FPSO (floating
production, storage, and offloading system). FPSOs consist of large
monohull structures, generally (but not always) ship shaped, equipped
with processing facilities. These platforms are moored to a location for
extended periods, and do not actually drill for oil or gas. Some variants
of these applications, called FSO (floating storage and offloading
system) or FSU (floating storage unit), are used exclusively for storage
purposes, and host very little process equipment. This is one of the best
sources for having floating production.
Spar platforms

Spars are moored to the seabed like TLPs, but whereas

a TLP has vertical tension tethers, a spar has more
conventional mooring lines. Spars have to-date been
designed in three configurations: the "conventional"
one-piece cylindrical hull; the "truss spar", in which
the midsection is composed of truss elements
connecting the upper buoyant hull (called a hard tank)
with the bottom soft tank containing permanent ballast;
and the "cell spar", which is built from multiple
vertical cylinders. The spar has more inherent stability
than a TLP since it has a large counterweight at the
bottom and does not depend on the mooring to hold it
upright. It also has the ability, by adjusting the mooring
line tensions (using chain-jacks attached to the
mooring lines), to move horizontally and to position
itself over wells at some distance from the main
platform location. The first production spar was Kerr-
McGee's Neptune, anchored in 590 m (1,940 ft) in the
Gulf of Mexico; however, spars (such as Brent Spar)
were previously used as FSOs.

Devils tower
 Well Killing
• A well kill is the operation of placing a column of special fluids of the
required density into a well bore in order to prevent the flow of
reservoir fluids without the need for pressure control equipment at the
surface.
• Methods:
• Reverse Circulation
• Bullheading
• Forward Circulation
• Lubricate and bleed
 Well kick

A kick is a well control problem in which the pressure found within the
drilled rock is higher than the mud hydrostatic pressure acting on the
borehole or rock face. When this occurs, the greater formation pressure
has a tendency to force formation fluids into the wellbore. This forced
fluid flow is called a kick. If the flow is successfully controlled, the kick
is considered to have been killed. An uncontrolled kick that increases in
severity may result in what is known as a “blowout.”
 Blow out

A blowout is the uncontrolled release of crude oil and/or natural gas

from an oil well or gas well after pressure control systems have failed.
Modern wells have blowout preventers intended to prevent such an
occurrence. An accidental spark during a blowout can lead to a
catastrophic oil or gas fire.

Prior to the advent of pressure control equipment in the 1920s, the

uncontrolled release of oil and gas from a well while drilling was
common and was known as an oil gusher, gusher or wild well.
“Anything that can go
wrong will go wrong”
Categories of oil well control
There are basically three types of oil well control which are: primary oil well control, secondary oil well
control, and tertiary oil well control. Those types are explained below.
Primary Oil Well Control
• Primary oil well control is the process which maintains a hydrostatic pressure in the wellbore greater
than the pressure of the fluids in the formation being drilled, but less than formation fracture pressure.
It uses the mud weight to provide sufficient pressure to prevent an influx of formation fluid into the
wellbore. If hydrostatic pressure is less than formation pressure, then formation fluids will enter the
wellbore. If the hydrostatic pressure of the fluid in the wellbore exceeds the fracture pressure of the
formation, then the fluid in the well could be lost. In an extreme case of lost circulation, the formation
pressure may exceed hydrostatic pressure, allowing formation fluids to enter into the well.
Secondary Oil Well Control
• Secondary oil well control is done after the Primary oil well control has failed to prevent formation
fluids entering the wellbore. This process is stopped using a “blow out preventer”, a BOP, to prevent
the escape of wellbore fluids from the well. As the rams and choke of the BOP remain closed, a
pressure built up test is carried out and a kill mud weight calculated and pumped inside the well to kill
the kick and circulate it out.
Tertiary (or shearing) Oil Well Control
• Tertiary oil well control describes the third line of defence, where the formation cannot be controlled
by primary or secondary well control (hydrostatic and equipment). This happens in underground
blowout situations. The following are examples of tertiary well control:
• Drill a relief well to hit an adjacent well that is flowing and kill the well with heavy mud
• Rapid pumping of heavy mud to control the well with equivalent circulating density
• Pump barite or heavy weighting agents to plug the wellbore in order to stop flowing
Secondary Oil Well Control
 Kill Mud weight (KMW)
• Kill Mud weight is the density of the mud required to balance formation pressure during kill operation. The Kill
Weight Mud can be calculated by:

KWM = SIDPP/(0.052 × TVD) + OWM

where

• KWM = kill weight mud (ppg)

• SIDPP = shut-in drillpipe pressure (psi)
• TVD = true vertical depth (ft)
• OWM = original weight mud (ppg)
• But when the formation pressure can be determined from data sources such as bottom hole pressure, then KWM
can be calculated as follows:

• KWM = FP / 0.052 × TVD

• where FP = Formation pressure