Болсуновская Л.М., Абрамова Р.Н., Матвеенко И.А. (ред.) Petroleum engineering. Teachers book. Нефтегазовое дело. Книга для учителя
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All these results are aggregated and studied. Geologists, geophysicists,
petroleum architects, together with drilling, production and reservoir
engineers all supply data to economists and financial planners. By
juggling figures, parameters and probabilities, they seek to work out a
possible strategy for
developing the reservoir in the event of confirmation
of the presence of hydrocarbons.
1. Geophysicist
2. Geologist
Each member of the exploration team has contributed to the performance
of the mission. By collating and comparing their experience, know-h
ow
and findings, their ultimate conclusions are the result of a team effort.
Those conclusions are stated briefly:
• No: the chances of a result are too slim; or...
•
Yes: the "prospect", i.e. this highly promising reservoir, is worth taking
a gamble. The te
am is prepared to "pay to see," making the decision to
drill.
Geologists, geophysicists and reservoir engineers have concluded there is
a "prospect" or possible producing zone. But to find out whether there
really are hydrocarbons trapped in the r
ock, they are going to have to drill
down to that zone.
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1.
Drilling is usually set up
directly over the thickest layer
of hydrocarbons.
Some fields lie at depths equivalent to twelve times the height of the Eiffel
Tower...
The site of the drill rig is determined
based on the existing state of knowledge
of underground conditions and the
topography of the terrain. This is
generally sited vertically above the
thickest part of the stratum thought to
contain hydrocarbons. The drilling team
often operates under difficult conditions.
This narrow-bore hole (with a diameter
of 20–
50 centimeters) is generally sunk to a depth of between 2,000 and
4,000 meters. In a few cases it may go beyond 6,000 meters, and one has
even gone to a depth of 10 kilometers, or 30,000 feet.
1. Well casing
2. Cable retaining the downhole probe
3. Downhole Probe
4. First probe sensor
5. Second probe sensor
6. Third probe sensor
7. Measurements obtained by the sensors
Once a certain depth has been reached, the exploration crew conducts a
series of measurements known as well-logging. An electronic probe is
lowered into the well to measure the physical properties of the rocks
traversed. These actual measurements either confirm or disprove the
hypotheses formulated prior to drilling, and generally provide more
accurate data. The sides of the well are then consolidated by
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means of steel tubes screwed together, and the casing is cemented to the
terrain to keep the strata separate from each other.
1. Coring tool
2. Core sample
3. Indications concerning height of beds
4. Clues concerning type of rock
The cuttings brought up the surface do not supply sufficient information
for a thorough understanding of the rocks traversed: that's where core
sampling comes in. The drill-bit is replaced by a hollow bit called a coring
tool, which extracts a cylindrical sample of rock several meters long.
A study of the resulting core sample yields information about the nature of
the rock, its slope, structure, permeability, porosity, fluid content, fossils
present, etc.
1.
In this example, one hole in five
struck oil
Drilling progresses very gradually, at a speed of a few meters per hour,
slowing to just one meter an hour by the time one is down to 3,000 meters
below the surface. Snags are encountered from time to time,
and the entire
drill-string has to be pulled out regularly for a change of drill-bit.
An exploratory well takes from three to six months to drill. Four wells out
of five, or even six out of seven in pioneer zones, fail to yield
commercially viable quantities of oil or gas. Sometimes, though, the drill-
bit strikes a hydrocarbon-
impregnated rock, in which case the drilling
crew conducts extensive well-logging to find out more.
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1. Economic data
2. Choice of operating methods
3. Geological data
The explorator
y phase has been successful: a reservoir has been identified,
with the prospect of producing profitably. Based on assumptions as to
future oil or gas prices, the next step is to determine whether sales of
products extracted from the reservoir will be suffi
cient to cover the high
cost of studies, development, construction and funding, as well as
production costs proper. The decision to bring a reservoir onstream is a
major one, as the investment outlay can run into several hu
ndred million,
indeed a billion dollars.
The content and images on this page are courtesy of ELF Aquitaine
Exercise 17. Complete the sentences with your own ideas. Use words from
your vocabulary.
(Suggested answers)
1. The hinged beam in this device did not sustain the pressure.
2. Latitude determines the necessity of planetary correction/ variations of
gravity.
3. The astatizing mechanism involves application of labilizing force and
restoring force.
4. The pendulum is used to measure relative gravity .
5. The assumptions should be modified because new data about depth,
shape and density of the subsurface bodies was detected .
6. Discrepancies between two quantities were reduced as a result of field
operations.
7. In our work we give preference to accurate values over plausible
assumptions.
8. A helical spring is suspended from taut horizontal suspension wire.
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Exercise 18. Replace the underlined words or word-combinations with their
synonyms from your active vocabulary. In some instances you have to
change the structure of the sentence.
1. The planetary correction occurs due to variations of gravity with
latitude.
2. The reflection seismology method is commonly applied in petroleum
exploration.
3. Magnetic surveys are usually carried out from the air or from a ship.
4. Air gun arrays are necessary to produce a source energy for seismic
marine survey.
5. An anomaly can indicate a structural uplift.
6. Different rocks generate local variations in Earth’s magnetic field and
so yield different readings from a magnetometer.
7. A recording truck picks up the data that are transmitted by receivers.
8. The gravity method is based on the measurements of the variations in
the gravitational attraction of the rocks of different density.
Exercise 19. Fill in the blanks with correct prepositions.
1. to, of, with 2. by 3. on 4. on 5. by, in 6. of 7. between, by.
Exercise 20. Translate the following sentences into English.
1. Static gravimeter methods superseded dynamic pendulum methods.
2. Gravity methods are particularly suitable for location of structures in
stratified formations.
3. Terrain correction is calculated from elevation along radial line and
concentric circles around the station.
4. Quantitative interpretation has indirect nature.
5. Pendulum determines not only time but gravity as well.
6. Torsion balance measures gravitational force per unit of horizontal
distance.
Exercise 21. State whether the following sentences are true or false; correct
the false ones.
1. F – gravity too
2. F – the most common
3. T
4. F – using gravimeter
5. F – planetary correction
6. F – north and east
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7. T
8. T
Exercise 22. Match the parts of the sentences.
1. B, 2. F, 3. H, 4. J, 5. G, 6. E, 7. I, 8. C, 9. D, 10. A.
Exercise 25. Remember some facts about pendulums and gravimeters.
Determine their common features and differences.
PENDULUM
GRAVIMETER
Common
1. measure relative gravity
2. are applied for location of subsurface structures in
stratified formations
Different
1) Pendulums are kept as long
as possible in length, so that
variations in period indicate
changes in gravity only.
2) In measurements with
pendulum
gravity can be compared with
chronometer or another
pendulum of nearly equal
period.
1) We should use
corrections.
2) In measurements with
gravimeter gravity is
compared with an elastic
spring force.
3) There are different types
of gravimeters:
Threlfall and Pollock
(a thin horizontal bar
suspended from a horizontal
torsion wire);
Hartley gravimeter
(a horizontal hinged beam
suspended from two helical
springs);
Ising gravimeter
(a vertical quartz rod is
suspended from a taut
horizontal quartz fiber).
Exercise 26.
Listen to a report on new equipment for geophysical
survey. You will hear the text twice. For questions 1–10, choose the correct
answer (A, B or C).
1. C, 2. B, 3. A, 4. C, 5. C, 6. A, 7. C, 8. A, 9.B, 10. A.
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Tapescript
Blue Qube
Based in Houston, Texas and also in Cambridge, England, ARKEX is a
geophysical company that uses proven technology to deliver a whole new
methodology for geological surveying. That system is called BLUE
QUBE (BQ).
BQ is a powerful new imaging tool that can either stand alone or set
alongside seismic and EM (electromagnetics). It provides geophysicists,
geologists and exploration managers with an accurate picture of the
subsurface geology. BQ acquisition includes world leading gravity
gradient imaging instrumentation together with high resolution magnetics,
video and radar. BQ measures the rate of change of rock density in the
form of gravity gradients. The increased band units and higher signal-to-
noise ratio over conventional gravity systems means that smaller or more
deeply buried features can be surveyed and imaged in more detail. The
result is a more accurate Earth’s model than has ever been possible before.
BQ is combined with other technologies to build up a much more detailed
picture of what’s underground.
Standard 2D seismic shows a vertical section into the ground, but no
lateral coverage. In order to get a fuller picture, expensive and often
difficult 3D seismic may have to be carried out. In contrast BQ is
airborne. The airplane flies a crisscross search pattern, measuring gravity
gradients at high resolution quickly and inexpensively with no ground
impact. The resulting data are then carefully processed and interpreted to
give a 3D map like the one you see here. By combining the 2D seismic
data with gravity gradient data, the real decisions can then be made about
whether to lease, where to locate 3D seismic or even where to drill.
Exercise 27.
Listen to the report on new satellite GOCE for measuring
gravity field of the Earth and state if the sentences are true (T) or false (F).
1. T
2. F – rotation of the Earth
3. T
4. T
5. F – by satellite
6. F – less /20 months
7. F – gradiometer
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8. F – low orbit because gravitational signal is stronger when the
satellite is closer to the Earth
Tapescript
Earth’s Gravity Field
When we think of gravity we think of it literally as a force that keeps our
feet on the ground. Although it is invisible, it provides us with the sense of
the horizontal and vertical. Most of us take the Earth’s constant pull of
gravity for granted. But if studied in detail gravity on earth turns out to be
more complex than most people assume. Gravity is not the same all over
the world. It is a force that varies from place to place on the surface of the
planet depending on a number of different factors.
Firstly, the distance between the center of the Earth and its surface is
smaller at the poles than at the equator. This flattening is due to the
Earth’s rotation making the pull of gravity slightly stronger at the poles.
Secondly, the surface of the Earth is not even with high mountains, ocean
trenches causing the value of gravity to vary.
Thirdly, the material composition inside the Earth varies and matter is not
even distributed, all of which affect gravitational pull. Even smaller
changes in topography such as ice-sheet movements, sea-level changes,
volcanic eruptions and erection of large buildings can certainly affect the
local gravity field. All these factors taken together form a gravity field
that is very different from the smooth globe we traditionally think of the
Earth. Right at satellite era gravity had not been measured accurately
across the world. What we had looked is a fragmented world map of the
gravity field of uneven quality. GOCE satellite due to be launched in 2006
is the first easier satellite solely dedicated to measuring the Earth’s
gravity. It will make uniform high accuracy measurements of gravity field
once rotating round the Earth at particularly low orbit height of only two
hundred and fifty kilometers. During its twenty months mission GOCE
will build detailed and precise picture of the earth’s gravitational field
using an incredibly sensitive new instrument called a gradiometer.
GOCE has been designed to fly in low orbit of two hundred and fifty
kilometers because the gravitational signal is stronger closer to the Earth.
However, the remaining atmosphere in low altitudes creates a demanding
environment for the satellite, presents a real challenge for its design.
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Exercise 28. Using the diagram describe the general principle of gravity
survey.
Suggested answer
The diagram shows how the force of gravity affects the weight suspended
from a coiled spring. The length of a coiled spring varies with the force of
gravity exerted by the rocks beneath. In cases B and C we observe that
differences in density of rocks affect the normal gravimetric readings.
Dense igneous rocks in case B cause high readings from the gravimeter,
low density salt dome brings about low readings. As a consequence, if we
analyze the readings received from the gravimeters and know
relationships between the gravity value and properties of the rocks, we can
make conclusions about what type of geological formation is located
beneath the surface.
Exercise 29. Work in groups and answer the questions given below. Give
your explanations.
1. Let's ignore the physics and imagine that, one day, the planet's gravity
turned off, and suddenly there was no force of gravity on planet Earth.
This would turn out to be a pretty bad day. We depend on gravity to hold
so many things down – cars, people, furniture, pencils and papers on
your desk, and so on. Everything not stuck in place would suddenly have
no reason to stay down, it would start floating. But it's not just furniture
and the like that would start to float. Two of the more important things
held on the ground by gravity are the atmosphere and the water in the
oceans, lakes and rivers. Without gravity, the air in the atmosphere has no
reason to hang around, and it would immediately leap into space. This is
the problem the moon has – the moon doesn't have enough gravity to keep
an atmosphere around it, so it's in a near vacuum. Without an atmosphere,
any living thing would die immediately and anything liquid would boil
away into space. In other words, no one would last long if the planet didn't
have gravity.
2. Gravity is one of those things we take completely for granted. And
there are two things about it that we take for granted: the fact that it is
always there, and the fact that it never changes. If the Earth's gravity were
ever to change significantly, it would have a huge effect on nearly
everything because so many things are designed around the current state
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of gravity. Before looking at changes in gravity however, it is helpful to
first understand what gravity is. Gravity is an attractive force between any
two atoms. Let's say you take two golf balls and place them on a table.
There will be an incredibly slight gravitational attraction between the
atoms in those two golf balls. If you use two massive pieces of lead and
some amazingly precise instruments, you can actually measure an
infinitesimal attraction between them. It is only when you get an gigantic
number of atoms together, as in the case of the planet Earth, that the force
of gravitational attraction is significant. The reason why gravity on Earth
never changes is because the mass of the Earth never changes. The only
way to suddenly change the gravity on Earth would be to change the mass
of the planet. A change in mass great enough to result in a change in
gravity isn't going to happen anytime soon.
3. If gravity were to suddenly double, It would be almost as bad, because
everything would be twice as heavy. There would be big problems with
anything structural. Houses, bridges, skyscrapers, table legs, support
columns and so on are all sized for normal gravity. Most structures would
collapse fairly quickly if you doubled the load on them. Trees and plants
would have problems. Power lines would have problems. The air pressure
would double and that would have a big effect on the Earth’s surface.
4. Measuring Earth's weight is derived from the gravitational attraction
that the Earth has for objects near it.
It would be more proper to ask, "What is the mass of planet Earth?"
1
The
quick answer to that is: approximately 6,000,000,000,000,000,000,000,000
(6E+24) kilograms.
The interesting sub-question is, "How did anyone figure that out?" It's not
like the planet steps onto the scale each morning before it takes a shower.
The measurement of the planet's weight is derived from the gravitational
attraction
that the Earth has for objects near it.
It turns out that any two masses have a gravitational attraction for one
another. If you put two bowling balls near each other, they will attract one
another gravitationally. The attraction is extremely slight, but if your
instruments are sensitive enough you can measure the gravitational
attraction that two bowling balls have on one another. From that
measurement, you could determine the mass of the two objects. The same
is true for two golf balls, but the attraction is even slighter because the
amount of gravitational force depends on mass of the objects.
Newton showed that, for spherical objects, you can make the simplifying
assumption that all of the object's mass is concentrated at the center of the