The permeability of a reservoir rock is a measure of the resistance offered to movement of fluids through its pore spaces. Although the size of the grains composing a sand or sandstone if uniform, does not influence the storage capacity, the size of the pore spaces between grains will determine what fluids may enter and will have a marked effect upon the resistance offered to movement of fluids through the rock. Oil is less readily absorbed by rock pores than water and flows with greater resistance. Natural gas, although entering the rock pores more readily than water, may nevertheless be displaced by the latter in a fine-grained sandstone as a result of capillary action.
Productive Zones. – Frequently a formational interval of considerable thickness perhaps hundreds of feet of oil bearing strata, will be included within the productive formation. Seldom, however, will all the beds so included yield oil to the wells. A productive zone may be made up to lenticular bodies of sand and shale, some component members being productive, others not. Thus, a productive zone may comprise several or many individual reservoirs. Also, there may be several separate zones of production in a given structure, one below another and separated by continuous, impermeable strata, and the several zones do not necessarily have the same lateral expanse.
Impervious Cap Rocks. Cap rocks overlaying productive reservoir rocks are almost invariably argillaceous in nature-clay, shales or marls. Such rocks, in addition to being impervious to oil, do not fracture readily when bent into anticlinal folds. The thickness of the cap rock is often only a few feet, though it must be sufficient, together with the pressure of the overlying rjck masses, to withstand the fluid pressure in the underlying reservoir rock if it is to be effective in retaining oil and gas.
Exercises
I. Переведите на английский язык и ответьте на следующие вопросы:
1. Что такое проницаемость пород?
2. Что поглощают породы лучше – воду или нефть?
3. Из каких пород может быть составлена продуктивная зона?
II. Переведите на русский язык:
1. Oil having higher gravity and viscosity in comparison with water, the latter is more readily absorbed by rock pores.
2. Sands are considered to be the best oil reservoir rocks, most of oil fields being connected with sands.
3. One of the most important problems confronting oil engineers of undersloped oil and gas producing areas is that of determining the number of wells to be drilled to realize maximum profit.
4. Clay, shales and marls being impervious, oil and gas in the underlying strata are trapped and cannot migrate, thus accumulating in pore space of permeable rocks such as sands, sandstones and limestones.
III. Переведите на английский язык:
1. Рассматривая проницаемость пород, нужно заметить, что вода абсорбируется породами скорее, чем нефть.
2. Проницаемость пород зависит от размера пористого пространства между зернами породы.
3. Покрывающие породы вследствие их непроницаемости препятствуют выходу нефти на поверхность.
4. Продуктивная зона часто состоит их нескольких нефтеносных пластов, расположенных один над другим.
5. Покрывающие породы должны быть достаточно мощными, чтобы выдержать давление жидкости в коллекторе и удержать нефть и газ.
IV. Назовите синонимы к следующим словам:
to enter, to effer, although, action, frequency, effect, to yield.
V. Назовите антонимы к следующим словам:
the latter, fine, frequently, considerable, thickness, to include, within, individual, overlie.
VI. Образуйте прилагательные от следующих слов:
permeability, nature, capillarity, consideration, thickness, production, separation, to continue, necessity, addition, anticline.
VII. Переведите на русский язык:
1. Cap rocks
2. Oil bearing strata
3. Anticlinal folds
4. Overlying reservoir rock
5. Fluid pressure
LESSON SIX
Выучите следующие слова и выражения к тексту:
above – свыше, над
advice – совет, советовать
advantage – преимущество
alternation – чередование
aside – в стороне, отдельно
concerning – относительно (чего-либо)
crest – сводная часть складки, хребет
deciphere – расшифровывать, разбирать
dome – свод, купол
especially – особенно
estimate – оценивать
exploration – разведка
further – дальнейший
gasoline – бензин
log – буровой журнал, каротажная диаграмма
occurance – залегание, местонахождение
odour – запах
operation – 1) действие; 2) разработка, эксплуатация
penetrate – проникать
previous – предыдущий
primarily – первоначальный
promise – обещать
prospector – разведчик, поисковик
saturate – насыщать
select – выбирать, отбирать
sign – знак
significant – значительный
stage – стадия, уровень
stratify – напластовывать, наслаивать
strive (strove, striven) – стараться, прилагать усилия
trace – след
value – ценность, величина, значение
vapour – пар
to be in doubt – сомневаться
at somedody’s best – на высоте
of course – конечно
LOCATING TEST WELLS
The subsurface structural relationships have been deciphered and a decision has been reached that conditions seem sufficiently favourable to justify the drilling of a test well, it will next be the task of the exploration geologist to select the most promising position for the well. In locating test wells the geologist will be primarily influenced by structural conditions.
Structure being the primary consideration, the geologist will strive to locate the test well as to secure the maximum advantages that the structure affords. In locating test wells on dome and anticlinal structure, the prospector should aim at penetrating the petroliferous stratum at its structural crest. Here nature’s forces are concentrated the gas pressure is greatest, and the possibilities of high and long-continued production are at their best. A well drilled in any other location, if unproductive, would still leave in doubt the presence and absence of oil in the formation.
During the drilling of a test well there are occurences that may be significant in indicating the proximity or presence of petroleum. Knowing and observing these occurances the geologist can advise those in charge of drilling operations concerning the prospects for further drilling. Even when the surface signs are unmistakable, the exidence to be obtained from the log of the well during the drilling stage will be of great value in checking previous estimates and also in the subsequent development of the field through the drilling of additional wells.
Oil-saturated sand or even traces of oil in the pulverized material from the well are, of course, direct evidence and usually justify a production test of the stratum from which they come. Flows of hydrocarbon gases from a drilling well are always favourable evidence, especially if they contain gasoline vapours or if they have a petroleum odour. Many sedimentary formations produce march gas/methane/which, if dry/ i.e. without hydrocarbons of higher molecular weight, is often formed in the absence of petroleum, and therefore it is not necessarily indicative of the presence of oil.
Aside from the more direct indications of petroleum mentioned above, it should be pointed out that mere alternation of stratified porous and impervious beds in horizons known to be petroliferous is in itself a favourable indication.
Exercises
I. Ответьте на следующие вопросы:
1. What is the task of an exploration geologist when the conditions are favourable for the drilling of a test well?
2. Why should the prospector aim at penetrating the petroliferous stratum at its structural crest?
3. What may serve as an evidence for presence of oil during the drilling of a test well?
II. Переведите на русский язык:
1. The subsurface structural relationship having been found favourable for oil accumulation, the geologist should select a proper place for a test well.
2. The presence of methane, if dry, not always proves to be indicative for the presence of oil since the former is often formed in the absence of petroleum.
3. Natural gas associated with petroleum in nature is a mixture of hydrocarbon and other gases, its composition varying widely in different fields.
III. Переведите на английский язык:
1. Нужно заметить, что добыча нефти в сильной степени зависит от правильного расположения скважин на месторождении.
2. Как сообщалось, скважина, расположенная на хребте структуры, дает наибольшее количество нефти.
3. Если бы нам пришлось бурить испытательную скважину, мы изучили бы структурные условия данного района.
4. Кроме данных, собранных геологами, мы имеем данные каротажа, полученные во время бурения разведывательной скважины.
IV. Назовите синонимы к следующим словам:
underground, proof, to obtain, to decide, to reach, to select, primarily, concerning, prospector, petroliferous, force, possibility, proximity, occurences.
V. Образуйте существительные от следующих слов:
to decide, to explore, to select, to promise, to influence, to penetrate, to occur, to know, to observe, to operate, to advise, to develop, to add, to relate, to consider.
VI. Переведите на английский язык:
1) расположение скважин 4) давление газа в пласте
2) структурные условия 5) месторождения нефти
3) проходка пластов