Mineral oil and natural gas
1.
Mineral oil and natural gas were formed
150 to 400 millions of years ago from
plankton. Dead organisms formed mud at
the bottom of shallow seas. This mud was
later covered by layers of sand and stone
during
geological
processes.
High
temperature and high pressure and the
absence of air promoted the formation of
hydrocarbons
from
the
organic
compounds originally present. Due to the
pressure and higher density of rock strata
oil, gas and water migrated upwards until
stopped by a non-permeable layer.
Upward folding of strata and formation of
faults led to the building of deposits called
traps. There, water, oil and gas are filled
in the rocks’ pores like water in a sponge.
Due to their high energy content hydrocarbons are excellent fuels.
Besides, mineral oil fractions consisting of larger molecules are ideal
lubricants and the black residue called bitumen may be used for paving
roads. Moreover, hydrocarbons are highly suitable as raw materials for
any number of organic syntheses yielding plastics, detergents,
pharmaceuticals, cosmetics, dyes and pigments, solvents, agrochemicals
…………….
That is why man has been exploiting oil and gas deposits for about one
hundred years now. As deposits are running low, engineers and
researchers get more and more inventive in finding out, where oil is and
how it may be brought to the surface.
Oil wells may be found from the earth surface to depths of more than 10
kilometres and they may be below the desert or offshore. They are in
regions with long winters like Alaska or even in the Antarctic. However,
not every oil well merits exploitation.
EROEI “Energy Returned on Energy Invested” is an important factor:
Whether an oil field brings profit or not depends on the quality of oil and
the situation of the field.
mud
shallow
to promote
compound
density
to migrate
permeable
deposit
trap
sponge
slime
chem. Verbindung
to travel
Lagerstätte
Fossil fuels –Information text
fraction
lubricant
residue
detergent
dye
pigment
solvent
to exploit
inventive
to merit
part, portion
Schmiermittel
Farbstoff
ausbeuten
to earn
1/6
Oil rich in gasoline and
diesel that is found on dry
land, in moderate depths
and
in
regions
with
clement climatic conditions
is however no longer an
option. “Peak Oil” means
the maximum in the oil
exploitation
curve.
We
seem to be about to reach
it or might even have
passed it by … That means
that offer and demand of oil are drifting apart rendering the black gold
more and more expensive.
2.
To find oil first of all
geological data are needed.
They are based on satellite
recordings
and
direct
investigation. To get a
geological profile of the
earth surface seismology is
the most important method.
It is based on the reflection
of shock waves from the
rock strata. Regions where
gas and oil traps might
probably be can thus be
designated. Only by drilling
an unambiguous result can
be obtained.
The picture shows a drilling
rig for a rotary drilling
system. This means that the
whole drill string, consisting
of pipes of 10 metres each
is kept rotating during the
drilling process.
gasoline
diesel
moderate
dry land
clement
offer
demand
Festland
Angebot
Nachfrage
Fossil fuels –Information text
investigation
demand
to designate
unambiguous
drilling rig
pipe
drill string
Untersuchung
Bohrgestänge
2/6
The drilling hole needs casing to prevent it from collapsing and besides the
drilling mud must be able to circulate and thus be moved to the surface.
In order to accomplish this and to keep up
constant pressure, water is pumped into the hole.
The derrick is more than 30 metres high. When
the drill string has to be drawn up in order to
exchange the drill, the pipes are stored in units of
three in the derrick.
Oil drilling is performed down to depths of
approximately 10 kilometres now. Depending on
the constitution of the rock layers this process
may take more than a year. Imagine the amount
of work and energy it takes to perform such an
enterprise, when realizing that the overall success
of drilling is less than 20 %!
If drilling is successful additional derricks have to be placed to find out the
size of the field. Modern drilling methods include horizontal drilling
techniques that allow reaching areas unattainable by vertical drilling and
are also more efficient for subsequent extraction.
3.
Oil is a more or less viscous liquid – but
even relatively thin oil is a sticky liquid
more viscous than water. Therefore, only
at the very beginning oil will surface
spontaneously. To extract about 50 % of
the oil in a deposit different techniques
are used:
The most conventional method is using
pumps creating a suction that draws oil
up.
Enhanced oil recovery is brought about
by:
o Injecting gases into the hole to
increase pressure (natural gas or
carbon dioxide are used);
o Injecting
detergents
to
lower
viscosity;
o Injecting hot steam to increase
pressure and lower viscosity by
elevating the temperature;
drilling hole
casing
to collapse
drilling mud
to accomplish
derrick
constitution
to elevate
Gehäuse
Bohrschlamm
to bring about
state, composition
to raise
Fossil fuels –Information text
enterprise
unattainable
subsequent
viscous
spontaneous
suction
to enhance
not to be reached
following
Sog
to heighten
3/6
o
In situ combustion to increase pressure and lower viscosity by
elevating the temperature.
Crude oil has to be transported to a refinery in order to separate its
components and transform them to the desired products.
This is done by tank ships or pipelines.
4.
At the refinery crude oil is separated into fractions containing compounds
of similar boiling
points. This is done
by distillation. The
oil is heated to a
temperature
of
approximately
350°C so that most
of it evaporates.
The hot steam rises
through a chimneylike
construction
(called
the
distillation
–
column) that has
sieve–bottoms in it,
where the portions
that liquefy due to
the
decrease
in
temperature collect
and may be drawn. The most important fractions are: gasoline, kerosene,
diesel and fuel oil. Crude oil contains also substantial amounts of dissolved
natural gas that collects at the top of the column. The residue is distilled a
second time under reduced pressure (vacuum distillation) so that boiling
points decrease. The main fraction of this second distillation is called
vacuum gas oil. It’s a valuable raw material for gaining additional gasoline
by cracking. The residue of the vacuum distillation process is bitumen.
The compounds composing the fractions differ in the size of the
molecules: Small hydrocarbons with short chains (few carbon atoms) have
low boiling points. The boiling points increase with increasing size of the
molecules.
combustion
crude oil
refinery
boiling point
to evaporate
sieve
burning
verdampfen
Fossil fuels –Information text
to liquefy
fuel oil
substantial
to dissolve
raw material
size
make/get liquid
important
lösen
4/6
5.
The fractions of mineral oil have then to be purified e. g. to be
desulphurized.
Afterwards chemical conversion is performed. The most important
processes are cracking and reforming. While the former helps to increase
the amount of gasoline that can be derived from crude oil the latter
increases the quality of gasoline (octane number).
Cracking indicates a process where long hydrocarbon chains consisting of
15 to 20 carbon atoms (and – of course – the necessary hydrogen atoms
as well) are broken to chains of about half the original length. To obtain
saturated hydrocarbons hydrogen has to be added. That is why this
process is called hydro-cracking.
Otherwise unsaturated hydrocarbons are obtained:
Unsaturated
hydrocarbons are very
important
raw
materials
of
the
petroleum processing
industry, e. g. for the
synthesis of polymers
like polyethene – but
they are undesirable
in fuels.
Reforming is done to improve the quality of gasoline with respect to its
ability to withstand self-ignition.
Self-ignition is called knocking. It happens prematurely, before the piston
in the cylinder has reached the top dead centre, i. e. the maximum
compression. Normally, ignition is caused by the spark plug at the top of
each cylinder. Knocking reduces the engines output and de-synchronises
the cylinders of the engine – thus causing a characteristic sound that has
given its name to the phenomenon.
Branched and cyclic hydrocarbons are less prone to knocking than simple
chains. Reforming is a process to rearrange molecules so that the number
of branched and cyclic molecules increases.
to purify
to desulphurize
conversion
to indicate
saturated
to withstand
self-ignition
anti-knock-quality
polymers
make free of sulphur
to mean, to denote
gesättigt
Klopffestigkeit
Fossil fuels –Information text
prematurely
piston
dead centre
spark plug
output
prone
to rearrange
petroleum processing
undesirable
early
Totpunkt
geneigt, anfällig
umlagern
Erdölverarbeitung
not wanted
5/6
2,2,4-Trimethylpentane, called iso-octane is the
compound with the highest anti-knock quality of
all saturated hydrocarbons in gasoline. It has
given its name to the octane number that is a
measure for the anti-knock-quality of gasoline.
Pure iso-octane has an octane number of 100.
If the desired octane-number cannot be reached by reforming, anti knock
additives are added.
There are many other additives in gasoline and diesel that are all
synthesized at the refinery.
Tasks:




Add the missing expressions in the word tables at the end of each
page! Look for other words you don’t understand!
Treat each section separately by studying it carefully and condensing
its content to 3 - 4 sentences!
Look for technical expressions that are not contained in the word
tables and make sure you know their meaning. (Consult the key word
tables!)
Together with a partner a) draft a dialogue between a journalist and
an expert about the benefits of oil and the problems ahead as
supplies are running low or b) write an article for a newspaper about
our oil dependent world.
additive
to condense
benefit
supplies
to run low
Vorräte
advantage
Fossil fuels –Information text
6/6