Interrelationships between Formation Evaluation Methods.
The figure illustrates the formation evaluation picture and the central role of openhole logging and log analysis.
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* VSP – vertical seismic profile (вертикальное сейсмическое профилирование)
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Ex. 6. Decide whether the following statements are True or False, based on the text. Correct the false statements.
Borehole geophysics is an effective method of evaluating formation properties.
Mud logging is performed during drilling.
The core at the surface precisely reflects rock characteristics in the subsurface.
Modern coring tools can provide reliable information about fluid saturation.
There are tools that can obtain core after the wellbore has been cased.
Analysis of core cannot be performed continuously while drilling.
Openhole logging involves many methods.
The correctness of wireline logging analysis largely depends on the analyst.
Gamma radiation is produced by electrons.
Gamma ray log is connected with water saturation.
In SP logging two electrodes are placed in the borehole.
Hydrogen atoms capture neutrons.
The higher the density of the formation, the more gamma rays it absorbs.
The salt content in the formation water plays a role in conductivity of the rock.
The main purpose of acoustic logging is to measure permeability.
Ex. 7. Choose the correct variant.
Important tools of formation evaluation are borehole geophysics, petrology / seismology, and core analysis.
Mud logging is more precisely referred to as hydrocarbon / porosity mud logging.
Conventional cores are cut using a special core bit, and are retrieved in a long core pipe / barrel.
Some coring methods require wireline / logging tools that cut core plugs from the sides of the wellbore.
Continuous coring is impossible for geological / economic reasons.
Geophysical borehole / sidewall measurements allow the continuous determination of rock parameters.
Most wells drilled for hydrocarbons are logged with open-hole logging / mud logging.
Quantitative analysis of well logs provides the analyst with values for porosity and permeability / hydrocarbon content and mineralogy of the rock.
Gamma ray log is measurement of natural radioactivity in formation versus pressure / depth.
GR log reflects sand / shale content.
The SP log records the naturally occurring electrical potential produced by the interaction of formation connate water / hydrocarbon fluids, conductive drilling fluid, and shale.
The Neutron Log is primarily used to evaluate formation porosity / lithology.
Fast neutrons are eventually slowed by collisions with hydrogen / carbon atoms.
Dense formations absorb many electrons / gamma rays, while low-density formations absorb fewer.
Resistivity logs are scaled in units of ohm-meters / ampere-meters.
Acoustic tools measure the speed of neutron movement / sound waves in subsurface formations.
Ex. 8. VOCABULARY. In the text above, find the equivalents to the following words and phrases. (The sequence corresponds to their occurrence in the text.)
применение
размеры
оценка пластовых свойств
скважинная геофизика
петрология, литология
геомеханика
геологическое строение
анализ керна
анализ бурового раствора
буровой шлам
составлять схему, заносить в таблицу
обычный керн (отбираемый керноотборником)
керновое долото
извлекать
керноотборник
претерпевать изменения
усовершенствованный
сохранять
насыщенность флюидом
знание, осведомленность
разрабатывать, изобретать
обсаживать скважину
кабельный инструмент
образец керна
всестороннее
опробование скважины пластоиспытателем
поровый флюид
минеральный состав
толщина слоя
каротаж необсаженной скважины
потенциал самопроизвольной поляризации
удельное сопротивление
проводимость
объемная плотность
индуцированная радиоактивность
эластичные свойства
количественный анализ
гамма-каротаж
электромагнитные волны
испускать
ядро атома (мн.ч. - ядра)
как функция от …
уран
торий
калий
каротаж глинистости
обсаженный ствол скважины
кривая
электрический потенциал
напряжение
связанная вода
проводящий
опорный электрод
показатель
средство корреляции
иметь в виду, не забывать
обнаружить
индуцированное излучение
столкновение
захватывать
плотностной каротаж
поглощать
гамма-лучи
скорость
частица
сталкиваться
уменьшенный
рассеянный
электрический ток
минерализация
измеряться
ом на метр
звуковые волны
вторичная пористость
связь цемента с породой
Ex. 9. From the Vocabulary List, find synonyms to the following words and phrases.
invent, develop
speed
be modified
remember
seize
extract
knowledge
reduced
preserve
reveal
Ex. 10. Match words from Column A to the words from Column B in order to form phrases. Translate the resulting phrases into Russian. Make up five sentences with these phrases.
Column A
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Column B |
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Ex. 11. The Vocabulary List contains a number of useful terms. Reconstruct the definitions putting the phrases in the correct order.
Borehole geophysics – of geophysics / or well / developed around the lowering / the general field / into a boring / of a variety of probes.
Petrology – and classification / the branch of geology / their origin, formation / and mineral composition / that studies rocks.
Core barrel – the core sample / by the drill bit / length of / as it is being cut / designed to receive / steel tube.
Drill stem test – through drill pipe / for testing a formation / procedure.
Bulk density – with the pore volume / of the rock / the density / filled with fluid.
Induced radioactivity – with charged particles / by bombarding a substance / radioactivity / with neutrons / in a reactor or / produced by particle accelerators / that is created.
Connate water – in the same zone / the water / occupied by oil and gas / present in a petroleum reservoir.
Ex. 12. Insert appropriate items from the box into the following sentences. Sometimes you will have to change the form of the word.
a) lithology |
e) coring |
i) pore fluid |
m) induced radiation |
b) self-potential |
f) gamma rays |
j) electric current |
n) wireline logging |
c) cuttings |
g) conventional core |
k) conductive |
o) voltage |
d) collide |
h) versus |
l) resistivity |
p) salinity |
A low __________ indicates a material that readily allows the movement of electrical charge.
Diamond __________ can be carried out to depth of 2000m using conventional mineral exploration drilling equipment.
__________ once was approximately synonymous with petrography, but in current usage, it is a subdivision of petrology focusing on macroscopic hand-sample or outcrop-scale description of rocks.
__________ is an ecological factor of considerable importance, influencing the types of organisms that live in a body of water.
Non- __________ materials lack mobile charges, and so resist the flow of electric current, generating heat.
Two points in an electric circuit that are connected by an "ideal conductor," that is, a conductor without resistance, have a __________ difference of zero.
In __________, measurements are recorded continuously even though the probe is moving.
When a metal wire is subjected to electric force applied on its opposite ends, these free electrons rush in the direction of the force, thus forming an __________.
During mud logging, rock __________ circulated to the surface in drilling mud are sampled and analyzed.
The logging procedure consists of lowering a 'logging tool' on the end of a wireline into an oil well to measure the rock and __________ properties of the formation.
Using a special core bit, a solid cylinder of rock, called __________, approximately 4” – 5” in diameter, is extracted from a well.
When neutrons __________ with hydrogen atoms, they slow down and get captured.
Only through open-hole logging can a continuous record of measurement __________ depth be made of so many formation properties.
The Neutron Log can be summarized as the continuous measurement of the __________ from the formations penetrated by the borehole.
The __________log works by measuring small electric potentials between depths in the borehole and a grounded voltage at the surface.
Unlike __________, neutrons are particles with a mass which is very nearly that of a hydrogen atom.
Ex. 13. Translate the following sentences into English, using vocabulary from the text. (The items are underlined.)
Для изучения пластовых свойств используются такие дисциплины, как скважинная геофизика, петрология, геомеханика.
Эта геофизическая компания успешно применяет методики для отбора керна из стенок скважин приборами на кабеле.
Приборы для анализа бурового раствора позволяют определять минеральный состав пород, плотность и пористость пород по шламу и керну.
Образцы керна забираются керноотборником в относительно неповреждённом состоянии, но претерпевают изменения, когда извлекаются на поверхность.
Электрический каротаж позволяет определить насыщенность флюидом.
Считается, что каротаж необсаженной скважины имеет повышенный уровень риска.
Естественный электрический потенциал в скважине измеряется с помощью двух электродов, один из которых опускается в необсаженную скважину.
Форма каротажных кривых показывает, что интенсивность захвата нейтронов меняется в зависимости от глубины.
Распространенным методом исследования скважин является метод естественной радиоактивности, основанный на присутствии в породе урана и тория, а также радиоактивного изотопа калия.
Сопротивление глинистого коллектора зависит от объемного содержания и удельного сопротивления связанной пластовой воды.
Величина гамма-излучения определяется в основном электронной плотностью среды, окружающей каротажный прибор, пропорциональной объемной плотности.
Возможности нейтронного каротажа определяются минерализацией связанной воды в нефтеносной части пласта.
Карбонатные породы характеризуются отрицательными значениями ПС, высокими сопротивлениями (сотни и даже тысячи ом*метров) у плотных пород.
Данные акустического каротажа позволили определить низкую вторичную пористость этой глинистой породы.
Особенно сильно скорость движения нейтронов уменьшается под воздействием ядер атома водорода, входящего в состав молекул воды, минералов и углеводородов.
Ex. 14. Read the text and discuss the following issues in class.
Does it sound rather like written or oral speech?
In what situation do you think this text could be presented?
What is the target audience?
What techniques does the author use to make himself understood?
Note down particular ways of simplifying complex ideas: examples, comparisons, vocabulary, sentence structures, and ways of interaction with the listeners / readers.
Paraphrase the underlined sentences or phrases in your own words.
Logging a well does not mean a two by four between the eyes
So what is a reserve? Can we wander into a meeting with one of them Eastern banker types wave a fistful of geological maps under his/her nose and get them to cough up $100 million so that we can go drill a hole in the back 40? Well not exactly. There is a fundamental definition that says that a proven reserve can only be counted where there is no "reasonable doubt of uncertainty" in the estimate of the oil/gas in place. And how do you overcome that doubt, why by drilling a hole down into the reservoir and starting to produce the oil.
But here's the thing, let's say I buried a container of soda in a sandbox and just left a straw sticking out of the sand. How do you know, short of digging it up, or fully draining it, whether I buried a soda can, a liter bottle or a full barrel's worth? That is the problem that you face when you finally drill to the bottom of an oil well and find that the cuttings that come to the surface are all nice and oily. And the answer is that you can place a special coring bit on the end of the drill string and take out a cored cylinder of rock all the way down through the pay zone, or you must log the well, and often you will do both.
This is one of the techie talks that turn up on this site on intermittent weekends. It tries to provide some basic information on topics that relate to oil and gas production and you are asked to bear in mind that it is a very simplified explanation, so that you can grasp the basics.
Taking the core of rock is useful. It allows a visual inspection and real measurement of porosity and permeability. But it is expensive, and does not give a lot of information on what conditions are really like at the bottom of the well. Logging the well is usually carried out by an oilwell service company. Schlumberger was one of the earliest in the business, and has a fairly good site that explains a lot of the terms with illustrations, so I may pinch some of their materials in what follows.
What do we need to know? Basically how much oil is there, and how fast can we get it out. To calculate the former number we need to know how porous the rock is, as an initial number. If a rock has a porosity of 20% and it is 200 ft thick and the area to be extracted in 1000 ft long and 1000 ft wide then the total volume of the rock is 200 x 1000 x 1000 = 200 million cubic feet. The total available space for oil to be in is 20% of that or 40 million cubic feet. Were this all oil it would be equivalent to about 6.8 million barrels of oil. Unfortunately it likely won't be and this is, in part, why we have the hole logged.
The operation is carried out after the well is drilled, but before you spend the money to put in a proper completion and wellhead connection. (There is after all no point in spending that money if it is not going to be worth it. Plus it is easier to measure the rock properties while the hole is still open and before it is cased). The company will bring out a logging truck that will run a wireline down the well, at the bottom of this line is a pod, called a sonde, that contains the various logging tools that will be used to take measurements. Typically it can be anywhere from 30 to 90 ft long and will contain a number of instruments. Each will give a different number that will collectively help with the estimate of the amount of oil that is there, and the condition of the hole itself. Generally the sonde is lowered to the bottom of the hole and then drawn back up the hole recording the information as it goes. The sonde will probably measure the density of the rock, and indirectly measure the porosity and the resistivity of the rock using electrical acoustic and the trace levels of radioactivity that can be found in some rocks. The signals are continuously sent back to the logging truck, and continuously recorded against the depth of the hole, on thin strips of paper that form the well log. The borehole diameter can also be measured up the hole at the same time using a caliper tool. Along the way cores can also be drilled into the side of the well.
The first thing to know is the porosity, since this will tell if there is enough space for an economic amount of oil. A reservoir rock will have porosity somewhere between 6 and 30%. This can be calculated from the measurement of the rock density, or by using a neutron porosity tool that is calibrated to give a trace of porosity percentage as the sonde travels up. The porosity can also be found using a sonic log that measures the speed of sound through the rock. By correlating the value against known standards the type of rock, and its porosity can be found.
Apart from the oil in the rock, there is likely to be some water. Some of this can be bound to the rock, particularly if has some shale in it, and this has to be deducted from the porosity so that we are left with the effective porosity – which is the combined volume of water and oil that there. A Gamma Ray (GR) trace will give an indication of how much shale there is in the rock,
So we then need to know how much water and how much oil are present. It is a little difficult to measure the oil directly, but one can measure water content, since this controls the resistance of the rock to the passage of an electric current. And so by measuring resistivity one can see how much water is there, and where the interface between an oil layer, and the underlying water can be found.
There is an additional tool that measures the immediate resistivity between electrodes on a pad that pushes against the rock as the sonde moves up, and this can give an additional measure of the rock permeability. This also has found a use in tracking conditions as the bit is still drilling.
Running a measurement of the well diameter can also tell a number of things. Many oil bearing rocks are weak, and can be crushed around the edge of the hole, after it is made, by the surrounding rock pressure. On the other hand very permeable rocks will have soaked up some of the water from the drilling mud, leaving a thicker cake on the wall, reducing the diameter. Finding these zones ahead of time can make it easier to plan to deal with them when the well is completed. Provided, of course, that when these logs are run, that they show that there is enough oil in that rock to justify the investment. After all if the resistivity log shows that the layer has about 80% water in those pores, that will only leave 20% of the space filled with oil – or, in this case, perhaps only 1 million barrels or so. And life being the way it is, we may only be able to produce about 35% of that oil, or 350,000 bbl. So how much did you say that completion was going to cost?
Incidentally, by comparing the logs run in your well, with those nearby it is possible to get a much better picture of the rock structure in the whole area and this helps in deciding if it would be worth drilling infield wells between the existing ones.
Ex. 15. Now, choose one or two passages of the text above and practice reading it out loud with effective intonation, as if you were giving an oral presentation in front of your class. You can also prepare some visual aids to help you demonstrate important points.
Ex. 16. Make up five questions on the basis of the text above and ask them your partner.
Grammar
Ex. 17. Study the following information.