3. Give English equivalents of the following:

продуктивний об'єкт, тривалість освоєння свердловини, перепад тиску, забруднюватись, властивості колекторів пласту, підвищена водонасиченість, випадання в осад, забивати пори.

3. Translate the following sentences into English using the words and expressions from Text 1.

   1. Відомо багато випадків, коли свердловини, пробурені з дуже високою швидкістю при промиванні прісною водою, були менш продуктивні, ніж свердловини, пробурені із застоуванням високоякісного глинистого розчину.

   2. Часто при випробуванні свердловини одержують інтенсивний притік нафти або газу.

   3. Іноді свердловину взагалі не вдається освоїти.

   4. Під час розбурювання продуктивного пласту у нього з промивальної рідини фільгрується рідка фаза.

   5. Найбільша кількість твердих частинок осідає в порах поблизу стінок свердловини, і саме тут трапляється найбільше погіршення проникності.

4. Pick out from Text 1 all the sentences with adjectives used in different degrees of comparison and translate them.

5. Supply a heading for Text 1.

6. Divide Text 1 into logically complete parts and give each a subtitle.

7. Put questions to each part of Text 1 and retell it in English.

8. Write a summary of Text 1.

Unit 25

The Choice of Mud Fluid for Drilling in the Pay Bed

1. Learn the meaning of the following words, word-combinations and word groups:

quantify, array, contaminate, resort to, hydraulic fracturing, deteriorate, adjust, advance, recovery, drastically, induce, influx, utilization, opening-up, reservoir-bed.

2. Read and translate Text 1:

Text 1

The influence exercised by the mud fluid on the pay bed rock is of an individual nature and depends on man> factors. It is rather difficult to quantify the degree of contamination of a definite pay area by the drilling fluid. But in choosing the mud fluid for drilling over a pay bed two points may be adopted as a guideline.

First, all the drilling muds may be arrayed by the increasing degree of their contaminating action on the reservoir, viz. gaseous agents < oil-base muds < brine-base muds < fresh water-base muds. Weighted muds tend to foul the bed to a greater extent than do non- weighted ones of the same class.

Second, the contaminating action of a mud fluid is the less, the closer its composition and properties of the filtrate approach those of the formation fluid.

The pollution of the productive sand around the well bore zone affects, first and foremost, the time and the amount of labour spent in completing the well and during its initial operation. With a heavy pollution one has to raise the pressure differential, spend more time in pumping out the fluid from the well and remove the filtrate (and sometimes also the mud itseli) from the £irea around the well bore, resort to additional methods of the stimulating action (acid treatment, vibratory action, hydraulic fracturing, etc.).

Not infrequently, because of greatly deteriorated collecting properties of the sands caused by the mud, gross errors are committed in prospecting wells during interpretation of geophysical findings, some of the producing horizons being classified as nonproductive and, therefore, not subjected to testing.

The composition and properties of the mud fluid have a great bearing on the penetration rate (advance). Quite natural are efforts to adjust the composition and properties of the drilling fluid in such a way as to achieve the maximum rate of advance. For example, the application of a water-base mud with a low proportion of clay instead of an oil-base one, or of water in place of a clay mud frequently helps to substantially increase the rate of advance, but this, at the same time, intensifies the contaminating effect on the pay bed. Therefore, in selecting a mud fluid for drilling over a pay bed one should always compare the economy that might be obtained through increasing the speed of the well sinking against losses that are possible as a result of the pay bed pollution and reduction of the production rate, as well as against additional expenses for completing the well.

It is obvious that one has to choose a mud fluid with whose use the savings achieved through a higher drilling rate are greater than the total additional costs of completing the well and its stimulating, as well as the losses due to a reduced recovery during the first period of exploitation. Such a comparison may be made only on the ground of experience in the application of diverse muds in a given district and also in other areas with similar geological and physical conditions specific for the producing zones.

A significant influence on the collecting properties of the productive sands within the zone around the well bore can exercise surfactants applied in the treatment of the mud.

The application of muds treated with properly selected surfactants for drilling in productive strata enables it to minimize their pollution, drastically cut down the time needed for completing the well, reduce pressure differential required for inducing the influx and raise the initial output of the well.

To drill in producing horizons with an abnormality factor, the best oil-base muds are the ones which produce practically no polluting effect on the pay bed. Experience shows that by using such muds the completion of the well and induction of the oil (gas) inflow present no difficulty, while the time spent in completing the well is many times shorter than with utilization of water-base mud fluids. The initial production yielded by wells where drilling in the pay bed was done by using such muds is by far greater (often by as much as 2-5 times) than is the output of neighbouring wells sunk with water-base muds flushing.