Power-operated Percussive Drill

In this method the rods are lifted and lowered by a walking beam operated by a crank on the engine.

The beam is mounted on steel springs, which give great elasticity and cause a sudden recoil of the boring tool which prevents jamming. The progress of the chisel is followed by controlling the passage of rope through a clamp near the drum. This rope drum is also used to raise the rods from the borehole to change tools, attach the sludger, etc. With this method it is possible to bore a depth equal to the length of one rod without ceasing operations, and as a water flush is incorporated the use of the sludger is minimized. A mixture of mud and water is pumped down the column, which in this case is hollow, and the mixture returns to the surface on the outside of the rods carrying with it a large percentage of the debris.

The rotation of the column is by band by a turning lever clamped to it.

Breakages of Rods

When boreholes become deep, great inconvenience can be caused by rods disconnecting or breaking due to the shock of the heavy column being arrested at the bottom of the hole at every stroke. To minimize this shock, sliding joints are incorporated in the boring column. The effect of such a joint is that the main column can still move downward after the chisel has struck its blow.

When rods break it is difficult to extract the lower part of the column from the borehole, and various tools are used for this purpose.

Rope Boring. Cable Tool System

In this system the rigid rods are replaced by a steel rope to which the boring tools are attached and allowed to fall by their own weight.

Many of the American oil-wells are drilled by this method. The surface "set-up" is practically the same as for rod drilling the difference being in the attachment to the end of the walking beam. The rope passes from a drum over a pulley in the derrick and through a rope clamp, above which is a temper screw which is in turn attached to the walking beam. The temper screw allows the drill to fall to the extent of 4 ft. as the boring proceeds and is then run back and the rope reclamped 4 ft. higher up.

It has been found that no device is necessary with rope boring to give the twist to the chisel in the borehole between- each blow. The lay of the stranded rope accomplishes the work.

As the tools are being raised the торе is in tension and its spiral lay lends to straighten out and stretch, but when the chisel strikes the bottom of the hole the tension is off, the rope assumes its natural spiral and imparts a twist to the chisel.

Rotary Drilling

In the rotary system the cutting tool receives a rapid rotary motion transmitted from an engine situated on the surface, through the boring rods. The drilling is done by abrasion.

The cutting tool may be a hollow bit with the cutting edge set with diamonds or with an annular groove on the cutting edge in which chilled shot revolves, a saw-tooth crown made of finest steel and tipped with a special hard alloy, or a roller bit.

The tool used depends on the strata to be cut.

All rotary bores are equipped with water-flushing systems and their big advantage is that in most cases a complete core is cut from the strata and brought to the surface for examination.

 

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Составьте аннотацию к тексту (2-3 предложения).

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5. Выскажите свое мнение по проблемам, изложенным в тексте:

Обозначение проблемы

Анализ различных мнений по проблеме (С одной стороны…, с другой стороны….)

Выводы (ваше отношение и решение проблемы)

Заключение.

 

Вариант №5

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Diamond System of Drilling

The boring tool, in this case the diamond crown, is a cylindrical cast steel shell having in its lower face a number of small sockets in which pieces of black diamond are set. Half of these are set to the outside to dress the sides of the hole, the others to the inside to dress the core.

The crown is screwed at its upper end into the base of a junction piece joining the crown to the core barrel.

 

The Single-tube Core Barrel

The barrel, screwed to the upper part of the bevel-shell which connects it to the crown, may be anything up to 20 ft. long. A steel coupling-block, with a central passage for the circulating water, is screwed to its upper end and serves tо connectthe barrel to the hollow bore-rods above. A mud bucket is provided above the coupling block...to receive the larger particles of debris which the circulating water fails to carry to the surface.

The junction piece between the barrel and the crown is bevelled and contains a core lifter. This core lifter is a split ring, corrugated on its inner surface, and it does not grip the core. When boring is stopped and the barrel and crown lifted by the rods, the core lifter takes up a lower position, thus tightening on the core. The latter may now be broken off by a twist and raised to the surface.

Lining a Borehole

It is sometimes necessary to line a borehole, especially in the soft strata near the top, to prevent the sides from falling in. This is done by driving steel piping down from the surface.

A special pipe with a cutting edge is driven first and 20-ft. lengths are connected to it. The pipes have screwed joints which are usually flush.

A protection cap is screwed to the top of the pipes to prevent damage and the driving is done by a 500-lb. weight.

Boring Underground

Underground boring is often necessary to prove the position of a coal seam interrupted by a fault, for cementation purposes or when approaching old workings. For holes within a range of 250 ft. a portable diamond core drill can be used, giving a core of 7/8 in. This is a compressed-air drill, and as the rods used are only two feet long. It can be used in restricted spaces. An added advantage is that holes can be bored at any inclination.

When holes are to be bored down deeper the same arrangement is used as for rotary boring on the surface, the main difference being that, in place of the derrick, space is cut out of the roof to allow for the suspension of the lifting gear.

When boring long holes upwards, a hole must be drilled or sunk in the floor to allow the manipulation of long bore-rods.

Surveying of Boreholes

Direct information from a borehole can only be accurate if it is drilled absolutely vertical. If the hole is inclined, the measurement of the thickness of various rock beds will be inaccurate, as will be the position of faults, etc.

Very few holes are drilled vertically, as it is very difficult to maintain vertically when passing through rocks of varying hardness. The drill will deviate and take the line of least resistance. It is therefore essential to survey the borehole to ascertain if there is any deviation, where it takes place, and its direction and amount.

Various methods are used in surveying boreholes, a common one being to lower a phial enclosed in a brass cylinder and containing hot gelatine in which is suspended a plumb line and a magnetic nееdlе. The cylinder is allowed to remain in the hole until the gelatine sets and when withdrawn the positions of the plumb line and the needle give the required information regarding the deviation.