Read and translate the text. In order to be able to forecast the result of drilling in respect of penetration rate, hole quality

In order to be able to forecast the result of drilling in respect of penetration rate, hole quality, drillsteel costs, etc., we must be able to make a correct appraisal of the rock concerned. In doing so we distinguish between microscopic and macroscopic properties. A rock is composed of grains of various minerals, and among the microscopic properties are mineral composition, grain size, the form and distribution of the grains. Taken together, these factors decide important properties of the rock, such as hardness, abrasiveness, compressive strength and density. These properties, in their turn, determine the penetration rate that can be achieved and how heavy the tool wear will be.

The drillability of a rock depends on among other things, the hardness of its constituent minerals and on the grain size and crystal form. Quartz is one of the commonest minerals in rocks. Since quartz is a very hard material, high quartz content makes the rock very hard to drill and causes heavy wear particularly on the drill bits. We say that the rock is abrasive. Conversely, a rock with a high content of calcite is easy to drill and causes little wear on the drill bits. The effects of rock hardness and abrasiveness on rate of penetration require care in bit selection. Such features as cone offset and hard-facing should be chosen to enhance drilling capability and endurance so that tripping time and bit replacement costs can be kept to a minimum.

As regards crystal form, minerals with high symmetry, e.g. cubic are easier to drill than minerals with low symmetry, e.g. fibrous.

A coarse-grained structure is easier to drill in and causes less wear than a fine-grain structure. Consequently, rocks with essentially the same mineral content may be quite different as regards drillability. For example, quartzite may be fine-grained (grain size 0,5-1 mm) or dense (grain size 0,05 mm), while a granite may be coarse-grained (grain size > 5 mm), medium-grained (grain size 1-5 mm) or fine-grained (grain size 0,5-1 mm).

A rock's compressive strengthis its ability to resist the geophysical stresses imposed upon it. In hard formations, weight on bit must be sufficient to overcome compressive strength so that the rock will fail under the applied stress of the drilling mechanism. Compressive strength generally increases with depth, since pressure from the overburden,the strata above the formation being drilled, increases.

Formation zones that are porous-characterizedby the presence of small openings, or pores,in the rock structure drill faster than nonporous areas. Porosity usually means lower compressive strength, and the rock structure more readily fails when it is drilled. In formations that are permeable,having a network of porous zones that allow fluid to flow, hydrostatic and formation pressures tend to equalize. This reduced differential pressure, which decreases chip hold-down, contributes to faster drilling.

Among the macroscopic properties are slatiness, fissuring, contact zones, layering, veining and inclination. These factors are often оf great significance in drilling. For example, cracks or inclined and layered formations can cause hole deviation and can occasionally cause drilling tools to get stuck. Soft rocks make it difficult to achieve a good hole quality, since the walls often cave in and in extreme cases the flushing air disappears into cracks in the rock without reaching the surface.

The reaction of a formation material as it comes in contact with drilling mud can reduce the drilling rate. For example, when water-base muds are used, some clay and shale formations tend to form a sticky mixture that can make bottomhole cleaning difficult and ball up the bit.

4. Give the adequate Russian variants for the following word combinations:

To make a correct appraisal of the rock concerned; the form and distribution of the grains; to determine how heavy the tool wear will be; the hardness of rock’s constituent minerals; to cause heavy wear on the drill bits; to enhance drilling capability and endurance; bit replacement costs; rocks with essentially the same mineral content; to be quite different as regards drillability; to fail under the applied stress of the drilling mechanism; pressure from the overburden; inclined and layered formations; to cause drilling tools to get stuck; the reaction of a formation material as it comes in contact with drilling mud; water-base muds.

5. Find the English equivalents for the following words and word combinations:

Прогнозировать результаты бурения; определять скорость проходки; износ долота; буримость породы; увеличить производительность бурения; сократить время спускоподъемных операций; вызывать большой/незначительный износ оборудования; большое содержание минерала; сопротивляться геофизическим нагрузкам; нагрузка на долото; перепад давления; способствовать быстрому бурению; покрывающий слой; пористость; проницаемая горная порода; искривление скважины; застревать; очистка забоя; образовывать сальник на долоте.

6. Match the words with their definitions and give their Russian equivalents:

1. aquifer	a. the most frequently occurring fine-grained sedimentary rock composed of consolidated silt and clay or mud.
2. formation fluid	b. a loosely arranged, apparently unstratified section of rock.
3. shale	c. the difference between two fluid pressures; e.g. the difference between the pressure in a reservoir and in a wellbore drilled in the reservoir.
4. unconsolidated formation	d. fluid (such as gas, oil, or water) that exists in a subsurface rock formation.
5. differential pressure	e. a layer of rock or sand under the ground that contains water and allows water to pass through it.