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4 Tell whether each of the following statements is true or false according to the text. Correct the false statements to make them true:

  1. The density of magmatic rocks is, as a rule, smaller than that of sedimentary rocks.

  2. Plasticity depends on the mineral composition of rocks and declines with a higher level of quartz, feldspar and other hard minerals.

  3. For most rocks the yield point: goes down as the three-dimensional compression gains in intensity and the more so the less plastic the rock.

  4. The voids in rocks are tilled either with a dropping fluid (crude oil, water), or with gases under a certain pressure, which subsequently we shall call pore (or formation) pressure, or with some metals.

  5. Gypsum is the most abrasive rock.,

5 Make a written translation of the following:

The abrasive wear-out of metals and hard alloys depends both on the abrasiveness of the rock and also upon a number of other factors, such as the relation between the hardness of rock and metal (alloy), the roughness of friction surfaces, the contact pressure, temperature, sliding speed and the properties of the cooling medium (lubricant). The abrasiveness of a rock is contingent upon the microhardness of mineral grains of which it is composed, their size, shape and the nature of the surface. The abrasiveness of crystalline rocks with regard to chilled steel is proportional to the microhardness of minerals making part of the rocks. By the degree of increasing abrasiveness these rocks the may be arrayed as follows: gypsum < barite < dolomites < limestones < silicious rocks (chalcedony, flint) < magnesioferruginous and feldspar rocks < quartz and quartzites.

PART 2 DRILL BITS

Unit 5

Purpose and! Classification

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

bit, design, disintegration, boring bit, fragmentation, chip, shear, drill, hardness, cut, alternate, layer, viscous, contain, purpose, plane, core, periphery, bottom, enlargement, straightening, casing string, cement.

    1. Read and translate Text 1:

Text 1

The drill bit is intended for breaking up the rock in sinking of Wells. There exist many types of bits each one of which is designed for disintegration of rocks possessing definite mechanical and abrasive properties.

As regards the principle underlying the breaking up of the rock all boring bits may bz classified as follows:

      1. Bits producing fragmentation and chipping (shearing), destined to drill non- abrasive and abrasive rocks of medium hardness, and also hard tough and very tough rocks.

      2. Bits of the cutting-abrasive type of action intended for drilling in rocks of medium hardness and also in alternating layers of high-plastic little viscous rocks and those containing rocks of medium hardness and even hard ones.

As concerns their puipose all the boring bits may also be subdivided into three groups:

  • for full holt; drilling, disintegrating the rock in a single plane or step-wise;

  • for core drilling, breaking up the rock on and along the peri phery of the bottom hole;

  • for special purpose.

At the lower extremity of the drilling shaft is placed the tool which does the actual boring or dril ling of the hole into the formation.

These tools, which are called bits are classified into three general types: drag type, rolling cutter bits, diamond bits and special bits.

Bits for full hole and core drilling are used in sinking wells, while special-purpose bits are designed to operate inside an already drilled well (enlargement and straightening of the well bore) and inside the casing string (drilling out of the cement storie).

Drag bits. Drag bits have rio moving parts and drill by the shoveling action of their blades on (Tie formation. Their water courses are placed so that the drilling fluid is directed on the blades, keeping them clean.

Bits of this type were widely used for drilling soft formations but in recent years they have been replaced by rolling cutter types. Two or three blade bits are used in drilling.

Rolling cutter type. Cutting tools of this type have been improved by using roller bearings on the spindles, on which the cutting elements rotate, and by building them as fully assembled units.

The cutting elements are hard-faced with tungsten carbide to assure long service and high footage. These bits are used in any formations as well as in very hard, abrasive formations.

Sometimes the tooth may be replaced by a peg of hard facing metal. Bits have a nozzle for discharging the drilling fluid. The nozzle sizes vary from 7 to 22 mm.

The unique design of this tool represents a new and revolutionary approach to drilling. This is no ordinary bit, but the result of years of experience, careful engineering and many months of actual drilling to iron out flaws in design. The result is a bit which will offer the driller positive performance in formations and situations where other bits will fail.

The unusual angle-mounted cutter heads produce a rolling - cutting motion which is unexcelled for formation cutting, and the powerful flushing action through the center of the bit insures that the cutting head will always have a clean surface to work on, even in sticky formations.

Diamond bits. Diamond bits are normally used in hard formations and drill by scrapping action of the stones which protrude from a steel matrix. The spiral water ways on the bit serve to channel the drilling fluid around and pick up the cuttings. A bit such as this may contain as much as 900 carats of industrial diamonds. The advantages of these bits are their high penetration capacity and drilling speed.

Core bits. In addition to these tools, which are designed to remove the entire cross-section of the hole with the assistance of the circulating fluid, may be added bits which cut circumferential channels or kerfs, leaving the center as a core to be removed in a properly constructed core barrel.

Core barrels are of three main types: single-tube, double-tube and the swivel type double tube tool. All are hollow tubes which accept the solid cylindrical core of rock cut by the annular-type bit. The drilling rig begins to make hole and as it does the bit, cuts into formation and causes a round portion of it to slide into the core barrel, which is located immediately above the bit. When a specified number of feet are cut, the barrel is brought to the surface and the core is unloaded.

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