یکشنبه ۲۵ شهریور ۰۳ | ۲۰:۲۳ ۸ بازديد
around 4.5 MPa. During production, the pressure will drop further due to
resistance to flow in the reservoir and well.
The mud enters though the drill pipe, passes through the cone and rises in
the uncompleted well. Mud serves several purposes:
• It brings rock shales (fragments of rock) up to the surface
• It cleans and cools the cone
• It lubricates the drill pipe string and cone
• Fibrous particles attach to the well surface to bind solids
• Mud weight should balance the downhole pressure to avoid leakage
of gas and oil. Often, the well will drill though smaller pockets of
hydrocarbons, which may cause a “blow-out" if the mud weight
cannot balance the pressure. The same might happen when drilling
into the main reservoir.
To prevent an uncontrolled blow-out, a subsurface safety valve is often
installed. This valve has enough closing force to seal off the well and cut the
drill string in an uncontrollable blow-out situation. However, unless casing is
already also in place, hydrocarbons may also leave though other cracks
inside the well and rise to the surface through porous or cracked rock. In
addition to fire and pollution hazards, dissolved gas in seawater rising under
a floating structure significantly reduces buoyancy.
The mud mix is a
special brew designed
to match the desired
flow thickness,
lubrication properties
and specific gravity.
Mud is a common name
used for all kinds of
fluids used in drilling
completion and
workover and can be
oil-based, water-based
or synthetic, and
consists of powdered
clays such as bentonite, oil, water and various additives and chemicals such
as caustic soda, barite (sulfurous mineral), lignite (brown coal), polymers and
emulsifiers. Photo: OSHA.gov
A special high-density mud called “kill fluid” is used to shut down a well for
workover.
Mud is recirculated. Coarse rock shales are separated in a shale shaker
before it is passed though finer filters and recalibrated with new additives
before returning to the mud holding tanks.
3.4 The well
Once the well has been drilled, it must be completed. Completing a well
consists of a number of steps, such as installing the well casing, completion,
installing the wellhead, and installing lifting equipment or treating the
formation, if required.
3.4.1 Well casing
Installing the well casing
is an important part of the
drilling and completion
process. Well casing
consists of a series of
metal tubes installed in
the freshly drilled hole.
Casing serves to
strengthen the sides of
the well hole, ensure that
no oil or natural gas
seeps out as it is brought
to the surface, and keep
other fluids or gases from
seeping into the
formation through the
well. A good deal of planning is necessary to ensure that the right casing for
each well is installed. Types of casing used depend on subsurface
characteristics of the well, including the diameter of the well (which is
dependent on the size of the drill bit used) and the pressures and
temperatures experienced. In most wells, the diameter of the well hole
decreases the deeper it is drilled, leading to a conical shape that must be
taken into account when installing casing. The casing is normally cemented
in place. Ill: wikipedia.org
There are five different types of well casing. They include:
• Conductor casing, which is usually no more than 20 to 50 feet (7-
17 m) long, is installed before main drilling to prevent the top of the
well from caving in and to help in the process of circulating the
drilling fluid up from the bottom of the well.
• Surface casing is the next type of casing to be installed. It can be
anywhere from 100 to 400 meters long, and is smaller in diameter to
fit inside the conductor casing. Its primary purpose is to protect fresh
water deposits near the surface of the well from contamination by
leaking hydrocarbons or salt water from deeper underground. It also
serves as a conduit for drilling mud returning to the surface and
helps protect the drill hole from damage during drilling.
• Intermediate casing is usually the longest section of casing found
in a well. Its primary purpose is to minimize the hazards associated
with subsurface formations that may affect the well. These include
abnormal underground pressure zones, underground shales and
formations that might otherwise contaminate the well, such as
underground salt water deposits. Liner strings are sometimes used
instead of intermediate casing. Liner strings are usually just attached
to the previous casing with “hangers” instead of being cemented into
place, and are thus less permanent.
• Production casing, alternatively called the “oil string” or '”long
string,” is installed last and is the deepest section of casing in a well.
This is the casing that provides a conduit from the surface of the well
to the petroleum-producing formation. The size of the production
casing depends on a number of considerations, including the lifting
equipment to be used, the number of completions required, and the
possibility of deepening the well at a later date. For example, if it is
expected that the well will be deepened later, then the production
casing must be wide enough to allow the passage of a drill bit later
on. It is also instrumental in preventing blow-outs, allowing the
formation to be “sealed” from the top should dangerous pressure
levels be reached.
Once the casing is installed, tubing is inserted inside the casing, from the
opening well at the top to the formation at the bottom. The hydrocarbons that
are extracted run up this tubing to the surface. The production casing is
typically 5 to 28 cm (2 -11 in) with most production wells being 6 inches or
more. Production depends on reservoir, bore, pressure, etc., and may be
less than 100 barrels per day to several thousand barrels per day. (5,000
bpd is about 555 liters/minute). A packer is used between casing and tubing
at the bottom of the well.
3.4.2 Completion
Well completion commonly refers to the process of finishing a well so that it
is ready to produce oil or natural gas. In essence, completion consists of
deciding on the characteristics of the intake portion of the well in the targeted
hydrocarbon formation. There are a number of types of completions,
including:
• Open hole completions are the most basic type and are only used
in very competent formations that are unlikely to cave in. An open
hole completion consists of simply running the casing directly down
into the formation, leaving the end of the piping open without any
other protective filter.
• Conventional perforated completions consist of production casing
run through the formation. The sides of this casing are perforated,
with tiny holes along the sides facing the formation, which allows
hydrocarbons to flow into the well hole while still providing a suitable
amount of support and protection for the well hole. In the past, “bullet
perforators” were used. These were essentially small guns lowered
into the well that sent off small bullets to penetrate the casing and
cement. Today, “jet perforating” is preferred. This consists of small,
electrically-fired charges that are lowered into the well. When ignited,
these charges poke tiny holes through to the formation, in the same
manner as bullet perforating.
• Sand exclusion completions are designed for production in an
area that contains a large amount of loose sand. These completions
are designed to allow for the flow of natural gas and oil into the well,
while preventing sand from entering. The most common methods of
keeping sand out of the well hole are screening or filtering systems.
Both of these types of sand barriers can be used in open hole and
perforated completions.
• Permanent completions are those in which the completion and
wellhead are assembled and installed only once. Installing the
casing, cementing, perforating and other completion work is done
with small-diameter tools to ensure the permanent nature of the
completion. Completing a well in this manner can lead to significant
cost savings compared to other types.
• Multiple zone completion is the practice of completing a well such
that hydrocarbons from two or more formations may be produced
simultaneously, without mixing with each other. For example, a well
may be drilled that passes through a number of formations on its
way deeper underground, or it may be more desirable in a horizontal
well to add multiple completions to drain the formation most
effectively. When it is necessary to separate different completions,
hard rubber “packing” instruments are used to maintain separation.
• Drainhole completions are a form of horizontal or slanted drilling.
This type of completion consists of drilling out horizontally into the
formation from a vertical well, essentially providing a drain for the
hydrocarbons to run down into the well. These completions are more
commonly associated with oil wells than with natural gas wells.
3.5 Wellhead
Wellheads can involve dry or subsea completion. Dry completion means that
the well is onshore or on the topside structure on an offshore installation.
Subsea wellheads are located underwater on a special sea bed template.
The wellhead has equipment
mounted at the opening of the well to
regulate and monitor the extraction of
hydrocarbons from the underground
formation. This also prevents oil or
natural gas leaking out of the well,
and prevents blow-outs due to high
pressure formations. Formations that
are under high pressure typically
require wellheads that can withstand
a great deal of upward pressure from
the escaping gases and liquids.
These must be able to withstand
pressures of up to 140 MPa (1,400
Bar). The wellhead consists of three
components: the casing head, the
tubing head, and the “Christmas tree.”
Photo: Vetco Gray
A typical Christmas tree, composed of
a master gate valve, a pressure
gauge, a wing valve, a swab valve
and a choke is shown above. The
Christmas tree may also have a number of check valves. The functions of
these devices are explained below. Ill: Vetco Gray
At the bottom we find the casing head and casing hangers.
The casing is screwed, bolted or welded to the hanger. Several valves and
plugs are normally fitted to give access to the casing. This permits the casing
Variable flow choke valve. The variable flow choke valve is typically a large
needle valve. Its calibrated opening is adjustable in 1/64 inch increments
(called beans). High-quality steel is used in order to withstand the high-
speed flow of abrasive materials that pass through the choke, usually over
many years, with little damage except to the dart or seat. If a variable choke
is not required, a less expensive positive choke is normally installed on
smaller wells. This has a built-in restriction that limits flow when the wing
valve is fully open.
Vertical tree. Christmas trees can also be horizontal where the master,
wing and choke are on a horizontal axis. This reduces the height and may
allow easier intervention. Horizontal trees are especially used on subsea
wells.
3.5.1 Subsea wells
Subsea wells are essentially the
same as dry completion wells.
Mechanically, however, they are
placed in a subsea structure
(template) that allows the wells to
be drilled and serviced remotely
from the surface, and protected
from damage, e.g., from trawlers.
The wellhead is placed in a slot
in the template where it mates to
the outgoing pipeline as well as
hydraulic and electric control
signals. Ill: Statoil
Control is from the
surface, where a hydraulic
power unit (HPU)
provides power to the
subsea installation via an
umbilical. The umbilical
is a composite cable
containing tension wires,
hydraulic pipes, electrical
power, control and
communication signals. A
control pod with inert gas and/or oil protection contains control electronics,
and operates most equipment via hydraulic switches. More complex subsea
solutions may contain subsea separation/stabilization and electrical
multiphase pumping. This may be necessary if reservoir pressure is low,
offset (distance to main facility) is long or there are flow assurance problems
so that the gas and liquids will not stably flow to the surface.
The product is piped back through pipelines and risers to the surface. The
main choke may be located topside.
3.5.2 Injection
Wells are also divided into production and injection wells. The former are for
production of oil and gas. Injection wells are drilled to inject gas or water into
the reservoir. The purpose of injection is to maintain overall and hydrostatic
reservoir pressure and force the oil toward the production wells. When
injected water reaches the production well, it is called “injected water
breakthrough.” Special logging instruments, often based on radioactive
isotopes added to injection water, are used to detect breakthrough.
Injection wells are fundamentally the same as production wellheads. The
difference is their direction of flow and, therefore, mounting of some
directional components, such as the choke.
3.6 Artificial lift
Production wells are free flowing or lifted. A free flowing oil well has enough
downhole pressure to reach suitable wellhead production pressure and
maintain an acceptable well flow. If the formation pressure is too low, and
water or gas injection cannot maintain pressure or are not suitable, the well
must be artificially lifted. For smaller wells, 0.7 MPa (100 PSI) wellhead
pressure with a standing column of liquid in the tubing is measured, by a rule
of-thumb method, to allow the well to flow. Larger wells will be equipped with
artificial lift to increase production, even at much higher pressures. Some
artificial lift methods are:
3.6.1 Rod pumps
Sucker rod
pumps, also
called donkey
4.4 Oil and gas storage, metering and export
The final stage before the oil and gas leaves the platform consists of
storage, pumps and pipeline terminal equipment.
4.4.1 Fiscal metering
Partners, authorities and customers all calculate invoices, taxes and
payments based on the actual product shipped out. Often, custody transfer
also takes place at this point, which means transfer of responsibility or title
from the producer to a customer, shuttle tanker operator or pipeline operator.
Although some small installations are still operated with a dipstick and
manual records, larger installations have analysis and metering equipment.
To make sure readings are accurate, a fixed or movable prover loop for
calibration is also installed. The illustration shows a full liquid hydrocarbon
(oil and condensate) metering system. The analyzer instruments on the left
provide product data such as density, viscosity and water content. Pressure
and temperature compensation is also included.
Figure 9. Metering system
For liquids, turbine meters with dual pulse outputs are most common.
Alternatives are positive displacement meters (pass a fixed volume per
rotation or stroke) and coriolis mass flow meters. These instruments cannot
cover the full range with sufficient accuracy. Therefore, the metering is split
into several runs, and the number of runs depends on the flow. Each run
employs one meter and several instruments to provide temperature and
pressure correction. Open/close valves allow runs to be selected and control
valves can balance the flow between runs. The instruments and actuators
are monitored and controlled by a flow computer. If the interface is not
digital, dual pulse trains are used to allow direction sensing and fault finding.
To obtain the required accuracy, the meters are calibrated. The most
common method is a prover loop. A prover ball moves though the loop, and
a calibrated volume is provided between the two detectors (Z). When a
meter is to be calibrated, the four-way valve opens to allow oil to flow behind
the ball. The number of pulses from it passes one detector Z to the other and
is counted. After one loop, the four-way valve turns to reverse flow direction
and the ball moves back, providing the same volume in reverse, again
counting the pulses. From the known reference volume, number of pulses,
pressure and temperature the flow computer can calculate the meter factor
and provide accurate flow measurements using formulas from industry
standard organizations such as API MPMS and ISO 5024. The accuracy is
typically ± 0.3% of standard volume.
Gas metering is similar, but instead,
analyzers will measure hydrocarbon
content and energy value (MJ/scm or
BTU, Kcal/scf) as well as pressure
and temperature. The meters are
normally orifice meters or ultrasonic
meters. Orifice plates with a diameter
less than the pipe are mounted in
cassettes. The pressure differential
over the orifice plate as well as
pressure and temperature, is used in
standard formulas (such as AGA 3
and ISO 5024/5167) to calculate normalized flow. Different ranges are
accommodated with different size restrictions.
Orifice plates are sensitive to a buildup of residue and affect the edges of the
hole. Larger new installations therefore prefer ultrasonic gas meters that
work by sending multiple ultrasonic beams across the path and measure the
Doppler effect.
Gas metering is less accurate than liquid, typically ±1.0% of mass. There is
usually no prover loop, the instruments and orifice plates are calibrated in
separate equipment instead.
LNG is often metered
with mass flow meters
that can operate at the
required low temperature.
A three run LNG
metering skid is shown
above.
At various points in the
movement of oil and gas,
similar measurements
are taken, usually in a
more simplified way.
Examples of different gas
types are flare gas, fuel
gas and injected gas, where required accuracy is 2-5% percent.
4.4.2 Storage
On most production
sites, oil and gas are
piped directly to a
refinery or tanker
terminal. Gas is
difficult to store
locally, but
occasionally
underground mines,
caverns or salt
deposits can be used
to store gas.
On platforms without
a pipeline, oil is stored in onboard storage tanks to be transported by shuttle
tanker. The oil is stored in storage cells around the shafts on concrete
platforms, and in tanks on floating units. On some floaters, a separate
storage tanker is used. Ballast handling is very important in both cases to
balance the buoyancy when oil volume varies. For onshore, fixed roof tanks
are used for crude, floating roof for condensate. Rock caves are also used
for storage
Special tank gauging systems such as level radars, pressure or float are
used to measure the level in storage tanks, cells and caves. The level
measurement is converted to volume via tank strapping tables (depending
on tank geometry) and compensated for temperature to provide standard
volume. Float gauges can also calculate density, and so mass can be
established.
A tank farm consists of 10-100 tanks of varying volume for a typical total
capacity in the area of 1-50 million barrels. Storage or shuttle tankers
normally store up to two weeks of production, one week for normal cycle and
one extra week for delays, e.g., bad weather. This can amount to several
million barrels.
Accurate records of volumes and history are kept to document what is
received and dispatched. For installations that serve multiple production
sites, different qualities and product blending must also be handled. Another
planning task is forecasting for future received and delivered products. This
is for stock control and warehousing requirements. A tank farm management
system keeps track of all stock movements and logs all transport operations
that take place.
4.4.3 Marine loading
Loading systems consist of one or
more loading arms/jetties, pumps,
valves and a metering system.
Tanker loading systems are complex,
both because of the volume involved,
and because several loading arms will
normally interact with the tanker's
ballast system to control the loading
operation. The tanks must be filled in
a certain sequence; otherwise the
tanker's structure might be damaged
due to uneven stresses. It is the
responsibility of the tanker's ballast
system to signal data to the loading
system and to operate the different
valves and monitor the tanks on
board the ship. Photo: Statoil
5 Midstream facilities
Raw natural gas from the well consists of methane as well as many other
smaller fractions of heavier hydrocarbons, and various other components.
The gas has to be separated into marketable fractions and treated to trade
specifications and to protect equipment from contaminants.
5.1 Gathering
Many upstream facilities include the gathering system in the processing
plant. However, for distributed gas production systems with many (often
small) producers, there is little processing at each location and gas
production from thousands of wells over an area instead feed into a
distributed gathering system. This system in general is composed of:
• Flowlines: A line connecting the wellpad with a field gathering station
(FGS), in general equipped with a fixed or mobile type pig launcher.
• FGS is a system allowing gathering of several flowlines and permits
transmission of the combined stream to the central processing facility
(CPF) and measures the oil/water/gas ratio. Each FGS is composed of:
o Pig receiver (fixed/mobile)
o Production header where all flowlines are connected
o Test header where a single flow line is routed for analysis
purposes (GOR Gas to oil ratio, water cut)
o Test system (mainly test separator or multiphase flow meter)
o Pig trap launcher
• Trunk line – pipeline connecting the FGS with the CPF. Equipped with a
pig receiver at the end.
5.2 Gas plants
5.2.1 Gas composition
When gas is exported, many gas trains include additional equipment for
further gas processing to remove unwanted components such as hydrogen
sulfide and carbon dioxide. These gases are called acids and
sweetening/acid removal is the process of removing them.
Natural gas sweetening methods include absorption processes, cryogenic
processes, adsorption processes (PSA, TSA and iron sponge) and
membranes. Often hybrid combinations are used, such as cryogenic and
membranes.
Gas treatment may also include calibration. If the delivery specification is for
a specific calorific value (BTU per scf or MJ per scm), gas with higher values
can be adjusted by adding an inert gas, such as nitrogen. This is often done
at a common point such as a pipeline gathering system or a pipeline onshore
terminal.
Raw natural gas from the well consists of methane as well, as many other
smaller fractions of heavier hydrocarbons and various other components.
Component Chemical
Formula
Boiling Point
at 101 kPa
Vapor pressure
at 20 °C approx.
Methane CH 4 -161,6 °C Tcri t−82.6 °C
@ 4,6 MPa
Ethane C 2H 6 -88.6 °C 4200 kPa
Propane C 3H 8 -42.1 °C 890 kPa
Butane n-C 4H 10 −0.5 °C 210 kPa
Higher order HC
Alkenes
Aromatics
C nH 2n
e.g. C 6H 6
Acid gases
Carbon dioxide
Hydrogen sulfide
Mercaptans ex.
Methanethiol
Ethanethiol
CO 2
H 2S
CH 3SH
C 2H 5SH
−78 °C
-60.2 °C
5.95 °C
35 °C
5500 kPa
Other Gases
Nitrogen
Helium
N 2
He
-195.79 °C
-268.93 °C
Water H2O 0 °C
Trace pollutants
Mercury
Chlorides
Data source: Wikipedia, Air Liquide Gas Encyclopedia
Natural gas is characterized in several ways dependent on the content of
these components:
o Wet gas is raw gas with a methane content of less than 85%.
o Dry gas is raw or treated natural gas that contains less than 15 liters
of condensate per 1,000 SM 3
. (0.1 gallon per 1000 scf).
o Sour gas is raw gas with a content of more than 5.7 mg hydrogen
sulfide (H 2S) per scm (0.25 grains per 100 scf); this is about 4 ppm.
o Acid gas has a high content of acidic gases such as carbon dioxide
(CO 2) or H 2St. Pipeline natural gas specification is typically less than
2% CO2. Acid gas fields with up to 90% CO 2 exist, but the normal
range for sour raw gas is 20-40%.
o Condensates are a mixture of hydrocarbons and other components
in the above table. These are normally gaseous from the well but
condense out as liquid during the production process (see previous
chapter). This is a refinery and petrochemical feedstock.
Raw gas is processed into various products or fractions:
o Natural gas in its marketable form has been processed for a
specific composition of hydrocarbons, sour and acid components,
etc., and energy content. Content is typically 90% methane, with
10% other light alkenes.
o Natural gas liquids (NGL) is a processed purified product
consisting of ethane, propane, butane or some higher alkenes
separately, or in a blend. It is primarily a raw material for
petrochemical industry and is often processed from the condensate.
o Liquefied petroleum gas (LPG) refers to propane or butane or a
mixture of these that has been compressed to liquid at room
temperature (200 to 900 kPa depending on composition). LPG is
filled in bottles for consumer domestic use as fuel, and is also used
as aerosol propellant (in spray cans) and refrigerant (e.g., in air
conditioners). Energy to volume ratio is 74% of gasoline.
o Liquefied natural gas (LNG) is natural gas that is refrigerated and
liquefied at below -162 °C, for storage and transport. It is stored at
close to atmospheric pressure, typically less than 125 kPa. As a
liquid, LNG takes up 1/600 of the volume of the gas at room
temperature. Energy to volume ratio is 66% of gasoline. After
transport and storage it is reheated/vaporized and compressed for
pipeline transport.
o Compressed natural gas (CNG) is natural gas that is compressed
at 2-2,2 MPa to less than 1% of volume at atmospheric pressure.
Unlike higher alkenes, methane cannot be kept liquid by high
pressure at normal ambient temperatures because of a low critical
temperature. CNG is used as a less costly alternative to LNG for
lower capacity and medium distance transport. Methane for vehicle
fuel is also stored as CNG. Energy to volume ratio is typically 25% of
processes than end products, as each product may require multiple steps,
so an exhaustive list would not fit within this book. Instead, we will focus on
the main chains, properties and uses of the most important compounds and
a few key processes for this overview.
Many of these processes are based on polymerization, which means that it
is based on processes that first form monomers then let these bind together
to form polymers as long chains or a three dimensional network. Compounds
whose names start with “poly” are generally polymers, but many other trade
names, such as nylon which is a generic name for a family of polyamides,
are polymers.
Petrochemicals are often made in clusters of plants in the same area. These
plants are often operated by separate companies, and this concept is known
as integrated manufacturing. Groups of related materials are often used in
adjacent manufacturing plants, to use common infrastructure and minimize
transport.
WST - Exxon Singapore Petrochemical Complex
7.1 Aromatics
Aromatics, so called because of their distinctive perfumed smell, are a group
of hydrocarbons that include benzene, toluene and the xylenes. These are
basic chemicals used as starting materials for a wide range of consumer
products. Almost all aromatics come from crude oil, although small quantities
are made from coal.
7.1.1 Xylene and polyester chain
Figure 24. Aromatics – xylene and polyester chain, derivatives
One of the forms of xylene, paraxylene, is used to make polyesters which
have applications in clothing, packaging and plastic bottles.
The most widely-used polyester is polyethylene terephthalate (PET), used in
lightweight, recyclable soft drink bottles (30% of production), as fibers in
clothing (60% of production), as a filling for anoraks and duvets, in car tire
cords and conveyor belts. It can also be made into a film that is used in
video and audiotapes and X-ray films. Polyester makes up about 18% of
world polymer production and is the third most-produced polymer;
polyethylene (PE) and polypropylene (PP) are first and second, respectively.
Metaxylene is an isomer of mixed xylene. It is used as an intermediate in the
manufacture of polyesters for coatings, inks, reinforced plastics and
packaging applications.
Unsaturated polyester is used over a broad spread of industries, mainly the
construction, boat building, automotive and electrical industries. In most
applications, they are reinforced with small glass fibers. Hence, these
plastics are commonly referred to as glass reinforced plastics (GRP).
Initially a liquid, the resin becomes solid by cross-linking chains. A curative
or hardener creates free radicals at unsaturated bonds, which propagate in a
chain reaction to adjacent molecules, linking them in the process. Styrene is
often used to lower viscosity and evaporates during hardening, where the
cross linking releases heat.
Orthoxylene is an isomer of mixed xylene. It is primarily used in plasticizers
(primarily in flexible polyvinyl chloride (PVC) material to make it more
flexible), medicines and dyes.
Alkyd resins are a group of sticky synthetic resins used in protective coatings
and paints.
7.1.2 Toluene, benzene, polyurethane and phenolic
chain
Figure 25, Aromatics – toluene and benzene, polyurethane and
phenolic chain
Tolune diisocyanate (TDI) is an isocyanate used in the production of
polyurethanes for flexible foam applications, ranging from furniture, bedding,
and carpet underlay to transportation and packaging. TDI is also used in the
manufacture of coatings, sealants, adhesives and elastomers.
Nylon is a generic designation for a family of synthetic polymers known
generically as aliphatic polyamides derived from benzene, first produced in
1935 by DuPont. Nylon can be used to form fibers, filaments, bristles, or
sheets to be manufactured into yarn, fabric, and cordage; and it can be
formed into molded products. Nylon is tough, elastic and strong, and it has
high resistance to wear, heat, and chemicals. It is generally used in the form
of fine filaments in such articles as hosiery and sports equipment, e.g.,
parachutes; but its applications also include engineering plastics for cars,
toys, healthcare products, carpets, roller-blade wheels and ship sails.
There are many varieties of nylon that have their own characteristic
properties. Nylon plastics are used for making such products as combs,
brushes and gears. Nylon yarns, on the other hand, are used for making
nylon fabrics. When talking about nylon textile, there are two types that are
mostly prevalent in the market: nylon 6-6 (also written as nylon 6,6) and
nylon 6.
Phenol is an aromatic alcohol, mainly used as an intermediate in organic
synthesis. Essentially, it serves as a raw material for the production of
bisphenol A, phenolic resins, alkylphenols and caprolactam. It is a
poisonous, acidic compound obtained from coal tar or benzene and used
mainly as a disinfectant or antiseptic, carbolic acid; any hydroxyl derivative of
benzene.
Phenolic resins are manufactured from phenol. They are used in wood
products and molding powders applications, and also have a wide range of
applications on the electrical, mechanical and decorative markets, in the
automotive industry, in building and construction, in thermal insulation
products and in foundry industry products.
Epoxy resin is a flexible resin made using phenols and used chiefly in
coatings, adhesives, electrical laminants and composites for its excellent
adhesion, strength and chemical resistance.
Polycarbonates are a particular group of thermoplastics. They are easily
worked, molded, and thermoformed; as such, these plastics are very widely
used in modern manufacturing. Polycarbonate is becoming more common in
housewares, as well as laboratories and in industry. It is often used to create
protective features, for example, in banks as well as vandal-proof windows
and lighting lenses for many buildings.
7.1.3 Benzene and styrenic chain, derivatives
Polystyrene is solid plastic made from polymerized styrene. It is the second
most common plastic and used in a wide variety of everyday applications,
from coffee cups to CD jewel boxes. It is a thermoplastic polymer in a solid
“glassy” state at room temperature, but flows if heated above about 100 °C.
It becomes solid again when cooled. This allows polystyrene to be extruded,
molded and vacuum-formed in molds with fine detail and high finish.
Figure 26. Aromatics – benzene and styrenic chain, derivatives
Styrene-acrylonitrile (SAN) is like polystyrene but offers higher thermal
resistance and is therefore used mainly in the automotive, electrical and
electronics industry, as well as in household applications and building
products.
Acrylonitrile-butadiene-styrene (ABS) is a tough, heat-resistant and impact-
resistant thermoplastic, with the acrylonitrile providing heat resistance and
the styrene units offering rigidity. It is widely used for appliance and
telephone housings, luggage, sporting helmets, pipe fittings and automotive
parts.
Styrene-butadiene rubber (SBR) is a rubber manufactured from styrene.
Because of its excellent abrasion resistance, it is widely used in automobile
and truck tires, as well as for carpet backing and paper coating. About 50%
of a car tire is made from SBR. Other applications are in belting, flooring,
wire and cable insulation and footwear.
7.2 Olefins
Olefins are petrochemical derivatives produced by cracking feed stocks from
raw materials such as natural gas and crude oil. Lower olefins have short
chains with only two, three or four carbon atoms, and the simplest one is
ethylene. The higher olefins have chains of up to twenty or more carbon
atoms. The main olefin products are ethylene, propylene, butadiene and C4
derivatives. They are used to produce plastics, as chemical intermediates,
and, in some cases, as industrial solvents.
7.2.1 Ethylene, derivatives
Figure 27. Olefins – ethylene, derivatives
Polyester and polyester resins is described under the Aromatics chain
(Chapter 7.1.1).
Ethanol, also known as ethyl alcohol (common alcohol), is manufactured by
synthesis from ethylene. It is an oxygenated hydrocarbon used in a wide
variety of high performance solvent applications (toiletries and cosmetics,
paints, lacquer thinners, printing inks, dyes, detergents, disinfectants and
pharmaceuticals), as a chemical raw material for the production of a range of
monomers and solvents, and is essential in pharmaceutical purification. In
transportation, ethanol is used as a vehicle fuel by itself, blended with
gasoline, or as a gasoline octane enhancer and oxygenate.
Ethanolamines are prepared by the reaction of ammonia and ethylene oxide.
They include monoethanolamine (MEA), diethanolamine (DEA) and
triethanolamine (TEA). The three are widely used in industry, principally as
absorbents for acidic components of natural gas and of petroleum-refinery
gas streams. It is also used to make detergents, metalworking fluids, and as
gas sweetening. TEA is used in detergents and cosmetics applications and
as a cement additive.
Polyethylene (PE), with a world production around 80 million tons, is the
most common plastic (and polymer). It is a polymer of ethylene, especially
any of various lightweight thermoplastics that are resistant to chemicals and
moisture, and has good insulating properties. Its primary use is in packaging
(plastic bags, plastic films, geomembranes, containers including bottles,
etc.).
Many kinds of polyethylene are known, with most having the chemical
formula (C 2H4) nH 2. It has many different trade varieties, and the most
common are:
High-density polyethylene (HDPE) is used predominantly in the
manufacture of blow-molded bottles for milk and household cleaners
and injection-molded pails, bottle caps, appliance housings and toys.
Low-density polyethylene (LDPE) is used in film applications due
to its toughness, flexibility and relative transparency. Typically,
LDPE is used to manufacture flexible films such as those used for
plastic retail bags. LDPE is also used to flexible lids and bottles, in
wire and cable applications for its stable electrical properties and
processing characteristics.
Linear low-density polyethylene (LLDPE) is used predominantly in
film applications due to its toughness, flexibility and relative
transparency. LLDPE is the preferred resin for injection molding
because of its superior toughness
Polyvinyl chloride (PVC). A polymer of vinyl chloride is used to make a
diverse range of cost-effective products with various levels of technical
performance suited to a wide range of applications. Many of these PVC
products are used every day and include everything from medical devices
such as medical tubing and blood bags, to footwear, electrical cables,
packaging, stationery and toys.
7.2.2 Propylene, derivatives
Polypropylenes (PP) are various thermoplastic plastics or fibers that are
polymers of propylene. Polypropylene can be made into fibers, where it is a
major constituent in fabrics for home furnishings such as upholstery and
carpets. Numerous industrial end uses include rope and cordage, disposable
non-woven fabrics for diapers and medical applications. As a plastic,
polypropylene is molded into bottles for foods and personal care products,
appliance housings, dishwasher-proof food containers, toys, automobile
battery casings and outdoor furniture.
Polyurethanes are used to make the foam in furniture, mattresses, car
seats, building insulation, and coatings for floors, furniture and refrigerators.
They are also used in artificial sports tracks, jogging shoes, and in roller
blade wheels. (See also, Chapter 7.1.2.)
Figure 28. Olefins – propylene, derivatives
Acrylonitrile-butadiene-styrene (ABS) (see chapter 7.1.3).
Polyacrylonitrile (PAN) is a semi-crystalline polymer resin. Though it is
thermoplastic, it does not melt under normal conditions. It degrades before
melting. It is used to produce large variety of products including ultra-filtration
membranes, hollow fibers for reverse osmosis, fibers for textiles, and PAN
fibers that are the chemical precursor of carbon fiber.
Cumene is an aromatic derived from benzene and is used in turn to produce
polycarbonates, phenolic resins and essential healthcare products such as
aspirin and penicillin.
Methyl methacrylate (MMA). The principal application of methyl
methacrylate is the production of polymethyl methacrylate (PMMA) acrylic
plastics. Also, MMA is used for the production of the co-polymer methyl
methacrylate butadiene-styrene (MBS), used as a modifier for PVC. MMA
polymers and copolymers are used for waterborne coatings, such latex
house paint.
7.2.3 Butadiene, butylenes, and pygas, derivatives
Pygas, or pyrolysis gasoline, is a naphtha-range product with a high
aromatic content, used either for gasoline blending or as a feedstock for a
BTX extraction unit. Pygas is produced in an ethylene plant that processes
butane, naphtha or gasoil.
Figure 29. Olefins – butadiene, butylene, and pygas, derivatives
Styrene-butadiene (rubber) (SBR) (see Chapter 7.1.3.)
Methyl methacrylate (MMA) (see chapter 7.2.2
Polybutadiene is a synthetic rubber that is a polymer formed from the
polymerization of the monomer 1,3-butadiene. It has a high resistance to
PSD and can be handled with less strict requirements.
These actions are handled by the emergency shut down system (ESD) and
process shut down system (PSD) according to functional safety
requirements and standards. Thus, a typical ESD function might require a
SIL 3 or even SIL 4 level, while PSD loops could be SIL 2 or SIL 3.
Smaller ESD systems, e.g., on wellhead platforms, can be hydraulic or
hardwired (non-programmable).
8.1.3 Fire and gas system
The fire and gas system is not generally
related to any particular process.
Instead, it divides into fire areas by
geographical location. Each fire area
should be designed to be self-contained,
in that it should detect fire and gas by
several types of sensors, and control fire
protection and firefighting devices to
contain and fight fire within the fire area.
In the event of fire, the area will be
partially shut off through closure of
ventilation fire dampers. A fire area
protection data sheet typically shows what detection exists for each fire area,
and which fire protection action should be taken in case of an incident.
The type and number of the detection, protection and fighting devices
depends on the type of equipment and size of the fire area and will vary for
different process areas, e.g., electrical rooms and accommodation rooms.
Fire detection:
• Gas detection: Combustible and toxic gas, electro-catalytic or
optical (IR) detector
• Flame detection: Ultraviolet (UV) or infra red (IR) optical detectors
• Fire detection: Heat and ionic smoke detectors
• Manual pushbuttons
Firefighting, protection:
• Gas-based firefighting, such as CO 2
• Foam-based firefighting
• Water-based firefighting: sprinklers, mist (water spray) and deluge
• Protection: Interface to emergency shutdown and HVAC fire dampers.
• Warning and escape: PA systems, beacons/lights, fire door and
damper release
A separate package related to fire and gas is the diesel- or electrically-driven
fire water pumps for the sprinkler and deluge ring systems.
For fire detection, coincidence and logic are often used to identify false
alarms. In such schemes, several detectors in the same area are required to
detect a fire condition or gas leakage for automatic reaction. This will include
different detection principles, e.g., a fire, but not welding or lightning strike.
Action is controlled by a fire and
gas system (F&G). Like the ESD
system, F&G action is specified
in a cause and action chart
called the Fire Area Protection
Datasheet. This chart shows all
detectors and fire protection
systems in a fire area and how
the system will operate.
The F&G system often provides
supervisory functions, either in
the F&G or the information
management system (IMS) to
handle such tasks as
maintenance, calibration or
replacement and hot work
permits, e.g., welding. Such
actions may require that one or
more fire and gas detectors or
systems are overridden or
bypassed. Specific work
procedures should be enforced,
such as a placing fire guards on duty, to make sure all devices are re-
enabled when the work permit expires or work is complete.
8.1.4 Control and safety configuration
Piping and instrumentation diagrams (P&ID) show the process. Additional
information is needed for the specification of the process control and safety
systems design and their control logic. These include: Loop diagram,
Instrument datasheet, Cable schedule and Termination list.
The illustration shows one typical format. This is the common format for the
NORSOK SCD standard. (Example for the Njord Separator 1 and 2 systems
control diagram). Essentially, the P&ID mechanical information has been
removed, and control loops and safety interlocks drawn in with references to
typical loops.
8.1.5 Telemetry/SCADA
Supervisory control and data acquisition (SCADA) is normally associated
with telemetry and wide area communications, for data gathering and control
over large production sites, pipelines, or corporate data from multiple
facilities. With telemetry, the bandwidth is often quite low and based on
telephone or local radio systems. SCADA systems are often optimized for
efficient use of the available bandwidth. Wide area communication operates
with wideband services, such as optical fibers and broadband internet.
Figure 32. SCADA system topology (typical)
Remote terminal units (RTU) or local controls systems on wells, wellhead
platforms, compressor and pump stations, are connected to the SCADA
system by means of the available communication media. SCADA systems
have many of the same functions as the control system, and the difference
between them is mainly their data architecture and use of communications.
8.2 Digital oilfield
In the oil and gas industry digital oilfield (DOF) is a generic term for new
solutions and technologies for operation, work processes and methods that
are being made possible by adopting innovations in information technology.
Other names such as Integrated Operations (IO), E-Field, Smart Fields, i-
Field and Integrated Asset Management are used for the same concept.
Intelligent Energy is a general umbrella term adopted by Society of
Petroleum Engineers (SPE).
Central to this concept is collaboration between people; where data,
information, knowledge shared between a number of parties in digital form.
This often supported by technologies such as video conferencing and
augmented reality for personnel in remote locations or in the field. In this
environment we add solutions for optimal performance, security,
maintenance.
Figure 33. Digital Oilfield
Optimal production targets and maximum utilization of production resources
are achieved through the use of several sources of information, such as
reservoir mass balance calculations and depletion strategies, well test
results and use of simulation models. This is made possible by linking skills,
data and tools together in real time – independent of location.
Some of the enabler technology areas are:
1. A system and communication IT infrastructure
2. Applications for remote operations and remote operations support
3. Reservoir management and drilling operations
4. Production optimization
5. Information management systems
6. Operation support and maintenance
8.2.1 Reservoir management and drilling operations
Solution for data acquisition, modeling
and visualization between facility
operators and central company experts
to provide:
• Drilling simulation and
visualization, automatic
diagnostics and decision
support, real-time measurements
while drilling in order to locate the best targets
• Reservoir models based on real-time reservoir data, analysis of 4D
seismic, in-situ measurements of changes. On-line integration with
well-serviced company data
• Optimization models for increased production, based on in-reservoir
properties during production, with decision support incorporated to
improve productivity
8.2.2 Production optimization
Optimizing the production or improving productivity is a complex problem. In
addition to the production optimization of the downhole, subsea and topside
process, one has to consider operational costs, hardware damage, reservoir
performance, environmental requirements and operational difficulties within
each well and/or topside. To further complicate optimization, the individual
challenges will change over time, e.g., reservoir behavior changes as an
effect of depletion, shutdown of wells due to slugging, failed sensors and the
change of efficiencies within the topside process system. Some of the
applications included in production optimization are:
• Flowline control to stabilize multiphase flow in gathering systems,
risers and flow lines.
• Well control that will stabilize and optimize gas lift and naturally
flowing wells. This application should prevent flow and pressure
surges while maintaining minimal backpressure and maintain
maximum production as well as continuing production at the
optimum lift gas rate.
• Gas-lift optimization is provided to ensure the best possible
distribution of lift-gas between gas lifted wells.
• Slug management helps mitigate variations in inflow impact. The
separation and hydrocarbon processing during startup, upset and
normal operation.
• Well monitoring systems (WMS) are used to estimate the flow rates
of oil, gas and water from all the individual wells in an oil field. The
real-time evaluation is based on data from available sensors in the
wells and flow lines.
• Hydrate prediction tools help to avoid hydrate formation, which may
occur if a subsea gathering system is allowed to cool down too much
before the necessary hydrate preventive actions are performed.
• Optimal operation is defined by a set of constraints in the wells and
production facilities. A constraint monitoring tool monitors the
closeness to all constraints. This provides decision support for
corrective actions needed to move current operation closer to its true
potential.
• Advanced control and optimization solutions to improve the
performance of product quality control, while adhering to operating
constraints. This is typically done with two technologies: model
predictive control to drive the process closer to operating targets,
and inferential measurement to increase the frequency of product
quality feedback information.
• Tuning tools are designed to optimize and properly maintain the
optimal setting of control loops in the process automation system.
8.2.3 Asset optimization and maintenance support
An asset optimization (AO) system reduces costly production disruptions by
enabling predictive maintenance. It records the maintenance history of an
asset and identifies potential problems to avert unscheduled shutdowns,
maximize up-time and operate closer to plant production prognoses. This
functionality supports maintenance workflow as the AO system
communicates with a maintenance system, often denoted as a computerized
maintenance management system (CMMS).
Figure 34. Computerized maintenance management system
Condition monitoring includes both structural monitoring and condition
monitoring for process equipment such as valves and rotating machinery.
For structural monitoring, the devices are corrosion meters (essentially
plates that corrode, so that corrosion may be metered), tension force meters
and free swinging strings. These statistics are logged to a central structure
condition monitoring system, to show what forces are acting against the
installation, and the effect those forces are having.
Condition monitoring of machinery is generally used for large rotating
apparatus, such as turbines, compressors, generators and large pumps.
Input devices are vibration meters, temperature (bearing, exhaust gases,
etc.), as well as the number of start/stops, running time, lubrication intervals
and over-current trip-outs. For other process equipment, such as valves, the
system can register closing times, flow and torque. A valve that exhibits a
negative trend in closing time or torque ("stiction") can be diagnosed. The
maintenance trigger is the mechanism whereby field device or equipment
monitor resident information, in the form of digital status signals or other
Asset Monitor
Maintenance Management
Create work order
Work order history
Maintenance status
Preventive maintenance,…
Operator
Heat Exchanger
Actuator/
Valve
Diagnosis
and
Status Data
Messenger CMMS*CMMS*
Service staff
extern
Maximize the utilization of
plant assets over their lifecycle
Asset
Condition
Document
ERP-System
numerical or computed variables are interpreted to trigger a maintenance
request. A work order procedure is then automatically initiated in the CMMS.
Maintenance support functionality will plan maintenance, based on input
from condition monitoring systems, and a periodic maintenance plan. This
will allow the system to schedule personnel for such tasks as lubrication or
cleaning, and plan larger tasks such as turbine and compressor periodic
maintenance.
8.2.4 Information management systems (IMS)
A specific information management system (IMS) can be used to provide
information about the operation and production of the facility. This can be a
separate system, or an integral part of the control system or SCADA system.
Synthesis gas can also be created from natural gas by lean combustion or
steam reforming:
CH 4 + 1/2O 2 → CO + 2H 2 Lean combustion
CH 4 + H 2O → CO + 3H 2 Steam reforming
This can be fed to the water shift reaction and to the F-T process. This
process, together with the following application, are often called gas to
liquids (GTL) processes.
An alternative use of the synthesis gases (CO and H 2) is production of
methanol and synthetic gasoline:
2 H 2 + CO → CH 3OH Methanol synthesis
Then, the methanol is converted to synthetic gasoline in the Mobil process.
2 CH 3OH → CH 3OCH 3 + H 2O Dehydration to dimethyl ether
The second stage further dehydrates the ether with ceolite catalyst to yield a
synthetic gasoline with 80% carbon number 5 and above.
9.1.6 Methane hydrates
Methane hydrates are the most recent form of
unconventional natural gas to be discovered
and researched. These formations are made
up of a lattice of frozen water, which forms a
sort of cage around molecules of methane.
Hydrates were first discovered in permafrost
regions of the Arctic and have been found in
most of the deepwater continental shelves
tested. The methane originates from organic
decay.
At the sea bottom, under high pressure and low temperatures, the hydrate is
heavier than water and cannot escape. Research has revealed that this form
of methane may be much more plentiful than first expected. Estimates range
anywhere from 180 to over 5800 trillion scm.
The US Geological Survey estimates that methane hydrates may contain
more organic carbon than all the world's coal, oil, and conventional natural
gas – combined. However, research into methane hydrates is still in its
infancy.
9.1.7 Biofuels
Biofuels are produced from specially-grown products such as oilseeds or
sugars, and organic waste, e.g., from the forest industry. These fuels are
called carbon neutral, because the carbon dioxide (CO 2) released during
burning is offset by the CO2 used by the plant when growing.
Ethanol alcohol (C 2H 5OH) is distilled from fermented sugars and/or starch
(e.g., wood, sugar cane or beets, corn (maize) or grain) to produce ethanol
that can be burned alone with retuning of the engine, or mixed with ordinary
gasoline.
Biodiesel is made from oils from crops such as rapeseed, soy, sesame, palm
or sunflower. The vegetable oil (lipid) is significantly different from mineral
(crude) oil, and is composed of triglycerides. In these molecules, three fatty
acids are bound to a glycerol molecule shown in the following picture (The
wiggly line represents the carbon chain with a carbon atom at each knee
with single or double bonds and two or one hydrogen atoms respectively):
Figure 38, Vegetable Oil structure
The glycerol backbone on the left is bound (ester OH binding) to three fatty
acids, shown here with palmitic acid, oleic acid and alpha-linolenic acid and
a total carbon number of 55.
This molecule is broken down to individual alkyl esters through a chemical
process called transesterification, whereby the glycerin is separated from the
fatty acids. Methanol (CH 3OH) is added to the lipids and heated. Any strong
base capable of deprotonating the alcohol, such as NaOH or KOH is used as
catalyst.
The process leaves behind methyl esters (with a CH 3 group on the ester
binding) and glycerin (a valuable byproduct used in soaps, explosives and
other products).
Figure 39. Transesterification
Biodiesel contains no petroleum, but it can be blended at any level with
petroleum diesel to create a biodiesel blend. It can be used in compression-
ignition (diesel) engines with little or no modification. Biodiesel is simple to
use, biodegradable, non-toxic, and essentially free of sulfur and aromatics.
Although biofuel is carbon-neutral, concern has been raised about diverting
agricultural areas away from food production. Recently, research has shown
potential for growing certain strains in arid regions that could not otherwise
be used for producing human food.
An alternative to the above process that is still at the research stage is
genetically modified E. coli bacteria. E. coli can produce enzymes to break
down cellulose to sugar, which can then be used to produce biodiesel. This
method allows use of general biological waste and limit competition with
human food resources.
9.1.8 Hydrogen
Although not a hydrocarbon resource, hydrogen can be used in place of or
as a complement to traditional hydrocarbon-based fuels. As an "energy
carrier,” hydrogen is clean burning, which means that when hydrogen reacts
with oxygen, either in a conventional engine or a fuel cell, water vapor is the
only emission. (Combustion with air at high temperatures will also form
nitrous oxides).
Hydrogen can be produced either from hydrocarbons (natural gas, ethanol,
etc.) or by electrolysis. Production from natural gas is often done via syngas
(see chapter 9.1.5) with up to 75-80% efficiency. Its advantage over
methane gas is that carbon dioxide can be removed and handled at a central
location rather than by each consumer, providing a cleaner energy carrier.
Hydrogen is also produced from water by electrolysis with an efficiency of
about 25% at normal conditions, to about 50% in high temperature, high
pressure processes, or in various recycling processes in the chemical
industry. (e.g., hydrochloric acid recycled in the polyurethane process). The
energy supply can then come from a renewable source such as
hydroelectric, solar, wind, wave, or tidal, where hydrogen acts as an energy
carrier replacing batteries, to form a fully clean, renewable energy source
supply chain.
In both cases, the main problem is overall economy, distribution and storage.
Hydrogen cannot easily be compressed to small volumes, and requires quite
bulky gas tanks for storage. Also, hydrogen produced from electricity
currently has an end-to-end efficiency that does not compare well with
gasoline or electrical battery vehicles.
9.2 Emissions and environmental effects
The production, distribution and consumption of hydrocarbons as fuel or
feedstock are globally the largest source of emissions into the environment.
The total annual world energy supply of 11,000 million TOE is based 81% on
fossil fuels, and releases some 26,000 million tons of carbon dioxide plus
other gases, e.g., methane into the atmosphere.
The most serious effect of these emissions is global climate change. The
Intergovernmental Panel on Climate Change (often called the UN Climate
Panel) predicts that these emissions will cause the global temperature to rise
from between 1.4 to 6.4 ºC by the end of the 21 st century, depending on
models and global scenarios.
9.2.1 Indigenous emissions
Emissions from the industry can be divided into several types.
Discharge: Mud, shale, silt, produced water with traces of
hydrocarbons. Ballast water, polluted wastewater with
detergent, sewage, etc.
Accidental spills: Blowout, shipwreck cargo and bunker oil, pipeline
leakage, other chemicals, traces of low level
radioactive isotopes.
Emissions: CO2, methane, nitrous oxides (NO x) and sulfur from
power plants and flaring
Exposure: Toxic and/or carcinogenic chemicals
Locally, these emissions are tightly controlled in most countries by national
and international regulations, and during normal operations, emission targets
can be reached with the systems and equipment described earlier in this
document. However, there is continuing concern and research into the
environmental impact of trace levels of hydrocarbons and other chemicals on
the reproductive cycle and health of wildlife in the vicinity of oil and gas
installations.
The major short-term environmental impact is from spills associated with
accidents. These spills can have dramatic short-term effects on the local
environment, with damage to marine and wildlife. However, the effects
seldom last for more than a few years outside Arctic regions.
9.2.2 Greenhouse emissions
The most effective greenhouse gas is water vapor. Water naturally
evaporates from the sea and spreads out, and can amplify or suppress the
other effects because of its reflective and absorbing capability.
The two most potent emitted greenhouse gases emitted are CO 2 and
methane. Because of its heat-trapping properties and lifespan in the
atmosphere, methane's effect on global warming is 22-25 times higher than
CO 2 per kilo released to atmosphere. By order of importance to greenhouse
effects, CO2 emissions contribute 72-77%, methane 14-18%, nitrous oxides
8-9% and other gases less than 1%. (sources: Wikipedia, UNEP)
The main source of carbon dioxide emissions is burning of hydrocarbons.
Out of 29 billion tons (many publications use teragram (Tg) = million tons) of
CO 2 emitted in 2008, 18 billion tons or about 60% of the total comes from oil
and gas, the remainder is coal, peat and renewable bioenergy, such as
firewood. 11% or 3.2 billion tons comes from the oil and gas industry itself in
the form of losses, local heating, power generation, etc.
The annual emissions are about 1% of total atmospheric CO 2, which is in
balance with about 50 times more carbon dioxide dissolved in seawater. This
balance is dependent on sea temperature: Ocean CO 2 storage is reduced as
temperature increases, but increases with the partial pressure of CO2 in the
atmosphere. Short term, the net effect is that about half the CO 2 emitted to
air contributes to an increase of atmospheric CO 2 by about 1.5 ppm annually.
For methane, the largest source of human activity-related methane
emissions to atmosphere is from rice paddies and enteric fermentation in
ruminant animals (dung and compost) from 1.4 billion cows and buffalos.
These emissions are estimated at 78.5 Tg/year (source: FAO) out of a total
of 200 Tg, which is equivalent to about 5,000 Tg of CO 2. Methane from the
oil and gas industry accounts for around 30% of emissions, mainly from
losses in transmission and distribution pipelines and systems for natural gas.
Figure 40. Greenhouse emissions Source: Wikipedia Commons
There are many mechanisms affecting the overall balance of greenhouse
gases in the atmosphere. CO2 has been measured both directly and in ice
cores, and has increased from a pre-industrial value of around 250 ppm to
385 ppm today. Methane has increased from 1732 to 1774 ppb (parts per
billion).
There is no full model that describes the net effect of these changes. It is
well accepted that without CO2, methane and water vapor, the global
average temperature would be about 30 ºC colder. The current data
correlates well with a current global average temperature increase from a
pre-industrial global average of 13.7 ºC to 14.4 ºC today. The atmosphere
and seas have large heat trapping capacity, which makes their temperatures
rise. These temperature rises lag behind greenhouse gas temperature
increases. It is therefore predicted that the temperature will continue to rise
by about 1ºC even if there were no further increase in levels of CO 2 and
methane.
The heat capacity of the atmosphere and seas also means that when the
temperature increases, there will be more energy stored in the atmosphere,
which is expected to drive more violent weather systems.
Figure 41. Carbon cycle
Volcanoes release
Erosion & Sediments
Organic Sediments
Oil, Gas Coal -------------------------
Carbonates
Absorbtion
The main contribution to sea level change in the short-to-medium term is
thermal expansion of the oceans, currently predicted to have reached about
0.15 m over pre-industrial standards, and currently rising some 3 mm/year.
Although the melting of inland ice in Greenland and Antarctica is reported,
this will mainly have local effects, as this ice will possibly take 15-20,000
years to have any significant contribution to sea levels. However, polar
glaciation and sea ice is an important indicator of global warming, and in
particular, Arctic summer temperatures have risen and sea ice has been
significantly reduced in area and thickness.
9.2.3 Carbon capture and sequestration
Due to these effects and the long-term concerns, it will be a high priority to
reduce the amount of carbon dioxide and methane released into the
atmosphere, and to develop more sustainable energy sources. The main
problem is that as much as one third of all emissions come from planes, cars
and ships, which account for about 45% of emissions from hydrocarbon fuels
that are not replaceable by other known energy sources at this time.
There are three main problem areas:
• There are losses in production: Only about 70% of hydrocarbons
extracted from the ground reach the private or industrial consumer.
The rest is lost from production systems, transportation and through
the refining and distribution of oil and gas.
• There are losses in consumption: Much of the oil and gas is
converted to work with an efficiency of 30% in cars, for example, to
60% in the best power plants.
• Better methods for capturing and storing emissions must also be
found.
Efficiency will be improved by maintaining and operating facilities to reduce
losses, and by converting to more efficient systems. For example, it can be
argued that conversion to electrically-driven equipment in place of gas
turbine-driven equipment could reduce CO 2 emissions by more than 50%,
even if power is generated by a gas turbine and steam combined cycle unit.
This also moves the emissions to a centralized unit rather than distributing to
a larger number of smaller gas turbines.
To reduce overall emissions, carbon will have to be separated from other
emitted gases (such as water vapor) and stored. Current plans call for re-
injection into empty reservoirs, or reservoirs that need pressure assistance
for oil extraction.
Capturing CO2 can be done at large point sites, such as large fossil fuel or
biomass energy facilities, industries with major CO2 emissions, natural gas
processing, synthetic fuel plants and fossil fuel-based hydrogen production
plants:
Overall there are three types of processes:
• Pre-combustion systems, where the fuel is gasified and processed
before combustion, and carbon dioxide can be removed from a
relatively pure exhaust stream.
• Post-combustion systems, where carbon dioxide is extracted from
the flue gas, e.g., using an amine process.
• Oxyfuel consumption, where fuel is burned as relatively pure
oxygen, so the hydrocarbon is burned in oxygen instead of air. This
produces a flue gas consisting of only carbon dioxide and water
vapor, which is cooled and condensed.
For storage:
• A system to store, transport and inject gas into existing reservoirs.
This is done by a pipeline, which is generally the cheapest form of
transport, or by ship if pipelines are not available.
• Alternatives to storage include carbonatization, deep sea deposit,
and planting of photosynthetic plants in otherwise infertile areas.
Currently these processes could remove around 90% of CO 2 at a cost of
$35-90 per ton, including injection and storage in a reservoir. This is about 2-
3 times the long-term expected emission quota cost
Figure 35. Information management system topology
wear and is used especially in the manufacture of tires. It has also been
used to coat or encapsulate electronic assemblies offering extremely high
electrical resistivity.
Polyisobutylene is a synthetic rubber, or elastomer. It is special because it
is the only rubber that is gas impermeable; it is the only rubber which can
hold air for long periods of time. Polyisobutylene, sometimes called buty
gasoline.
5.3 Gas processing
Raw natural gas must be processed to meet the trading specifications of
pipeline and gas distribution companies. As part of the purification other
components such as NGL is produced, and pollutants extracted.
The diagram shows an overview of a typical gas plant. Marketable products
are listed in blue and the production process is shown in grey as it is not
considered part of the gas plant.
Figure 10. Typical gas plant
5.3.1 Acid gas removal
Acid gases such as carbon dioxide and hydrogen sulfide form acids when
reacting with water, and must be removed to prevent corrosive damage to
equipment and pipeline
or beam
pumps, are the
most common
artificial lift
system used in
land-based
operations
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