GB2231900A - Improved method and apparatus for borehole drilling - Google Patents

Abstract

A cable used to conduct signals from a probe mounted at the leading end of a drill string to instrumentation external of the hole is pre-threaded through a set of drill pipes carried in a magazine.

Description

Improved Method and Apparatus for Borehole Drilling This invention relates to a method and apparatus for borehole drilling and is particularly for use in the drilling of long boreholes. It is also for particular, but not exclusive, use for horizontal and inseam drilling where the borehole is drilled in the plane of a seam for exploration purposes. The invention can also, though, be applied to inclined boreholes or vertical boreholes.

Increasingly in mining operations where a seam of preferred minerals such as coal is to be extracted it is useful to know ahead of the extraction process the state of the strata in the seam ahead of the cutting operation. An increasingly popular method of determining the state of the strata is to bore long holes ahead of the cutting operation into the seam and to insert a probe or probes in the hole to determine electrically the state of the strata.

Currently these holes are drilled by a method which entails first of all, drilling a length of hole, withdrawing the drill and inserting a probe which is fitted with instruments which can measure the position of the hole relative to a boundary of the strata, the inclination of the hole, and the deviation from an optimum course, which the drill is cutting. When the measurements have been taken the probe is withdrawn and the drill reinserted, together with associated drill rods, and a further length of the hole is cut.

It will be appreciated that the constant insertion and withdrawal of the drill and the probe makes the whole business very tedious and it is desirable that the measurement takes place continuously, or in steps, without requiring the drill to be withdrawn. With modern down-hole drilling motors it is now possible to insert the probe behind the drill and to measure in increments as the drilling operation advances. To receive the information from the probe the probe is connected via a cable to instrumentation external of the hole. The presence of this cable presents a problem since fewer rods have to be inserted around it. In order to insert the drill rods the probe itself would have to be withdrawn and another length of drill rod put in and the probe reinserted.Although this saves time, in as much as the drill itself does not have to be withdrawn, it is still very tedious to remove the probe every three metres or so, depending on the length of the drill rods, and then to reinsert it.

It is an object of the present invention to provide a method and apparatus which enables measurements to be taken down-hole successively as the hole advances without the need for the probe to be withdrawn after each measurement.

According to one aspect of the present invention a method of borehole drilling in which a drill member creates a borehole in strata and hollow drill rods are advanced behind the drill member to line the bore, and in which the drill member direction is controlled in response to measurements taken by a down-hole probe connected to instrumentation external of the hole through a cable, is characterised by supplying the drill rods serially to the borehole fran a magazine, through which drill rods a cable connected to the probe has been pre-threaded continuously in the magazine prior to the feeding of the probe into the drill hole.

According to a second aspect of the invention apparatus for use with the method includes a rod magazine having mounting means for a plurality of drill rods, pulley means for guiding a wire sequentially through the rods, and means for dispensing the wire and the rods into a borehole.

For long holes it would be necessary to provide a plurality of magazines with the wire extending from the last rod in the first magazine to the first rod in the successive magazine.

It is convenient if the rods in a magazine are grouped preferably in groups of two, and a convenient number of rods in a group would be of the order of five, making ten in the magazine.

The magazine is preferably fitted with rollers to assist in the dispensing of rods from the magazine in a controlled manner. The magazine also should be fitted with feed and takeoff rollers for the wire to control the feeding of the wire. Mounting brackets which are adjustable preferably hold the feed pulleys for the wire. In order to ensure that the rods are fed as easily as possible from the magazine without the need to turn the rods in a restricted roadway, or other area, the wire may be threaded through the rods in a figure of eight fashion between the two groups of rods.

To allow for different positions of boreholes to be fed from the magazine the magazine is preferably mounted on adjustable legs.

If the drilling operation is one which uses water for flushing and operating a down-hole motor then the feed wire may be fed through a suitable water swivel gland such as is disclosed in our co-pending application (ref 4955)

In order that the invention may be readily understood one example of apparatus, in accordance therewith and using the method thereof, will now be described with reference to the two figures of the accompanying drawings. In the drawings Figure 1 shows a side view, and Figure 2 a plan view of a drill rod support magazine.

The magazine is to be used for supplying drill rods sequentially into a long borehole of up to a thousand metres which is being drilled in a coal seam. The drilling mechanism, which is not shown, is a down-hole fluid operated drill where the cuttings are flushed out by drilling fluid fed through the middle of drill rods, which come back through the annular gap and are discharged at the face of the coal seam. In order to ensure that the drill is correctly positioned in the seam a probe follows the drill and takes measurements at set intervals. These intervals in this example coincide with the length of drill rods.

The probe measures the thickness of coal between the borehole and the edge of the coal seam, with adjacent strata, by using a natural gamma detection arrangement whereby gamma rays are attenuated fram the adjacent strata and the degree of attentuation is noted by instruments in the probe, converted into electric signals, fed back along a connecting wire to instrumentation outside the seam. The probe will also include inclinometers which measures the degree of tilt and roll of the hole, and a mangnetometer to measure azimuth.

An odometer is provided on a winch for the wire to measure the distance of the probe along the hole. The wire connecting the probe is a steel stranded wire wound about a copper conductor. The steel strands take the tension while the copper strand conducts the signals.

For a hole with a maximum depth expected of a thousand metres the whole of the cable will be wound on a drum and fed off by a cable winch not shown. The borehole is lined with wire line drill tubes and these are shown as items (1) in Figure 1 in dotted line. The drill tubes are mounted in a frame (2) of a magazine and are mounted in two vertical groups of five sets of tubes with two tubes in each line. The tubes have a tapered front end (3) which is designed to fit into the rear socket end of a mating tube.

The frame (2) is constituted by four legs (4) which are adjustable by means of a telescopic part (5) secured by bolts (6) into a lower support socket. The legs (4) carry a rectangular base (7) which has upright side supports (8) and at each end a double roller arrangement (9) (10). Wire line drill tubes (1) are to be fed off the magazine in the direction of the arrow (A) and a guide roller (11) is situated at the end nearer the face and it is mounted on a plate (12) in an adjustable manner, as is indicated by virtue of the releasable bolt and slot arrangement (13) on the plate (12).

At the other end a feed pulley (14) is mounted on a bracket (15) on a plate (16) by a similar adjustable arrangement (17). The pulley (14) takes the wire which is fed from the winch via a pulley into the magazine. The remote end of the wire is connected to instrumentation, and control mechanisms, not shown, for processing the signals received from the probe and reacting to them.

In operation the magazine is set up adjacent to a borehole in a seam and the adjustable legs (4) of the frame are set to the correct height for optimum feeding in of the wire line drill tubes. The magazine has to be pre-loaded with the tubes (1) and as can be seen in Figure (1) there are two rods on each layer of the group of rods. The wire is fed in a figure of eight manner as is indicated by the line (20) in Figure 2, around the rollers (9) and (10), and through the rods. As the drill hole is advanced by the length of one rod the drill is stopped and the first of the rods (1) is fed over the roller (11) into the drill hole where its end engages with the end of the previous drill rod already in the hole. The drill rod is then pushed into the hole and forces the rest of the drill rods along the hole. The probe is then advanced and this draws the cable with it.Since the cable is threaded through all the rods in the magazine it advances around the rollers (9) (10) readily and follows its path through the remaining rods.

The measurements are now taken by the probe and drilling continues. When drilling has advanced sufficiently for the next rod to be inserted, this is taken off the top of the adjacent group of rods, and the wire (20) follows the probe further into the hole without there being any risk of kinking.

The winch feeds the wire in as is required.

The whole system is repeated feeding rods alternately from each group until the magazine is exhausted. If the magazine has now supplied enough rods for the whole length of the hole then the drilling operation is complete. However, if more rods are required, a second magazine would have been connected by threading the wire through the rods in that second magazine in advance with the operation, and the second magazine would then be moved into position to replace the first magazine.The whole operation would then be repeated until the whole length of the hole had been lined with drill rods and been measured by the probe.

There will be seen that the present invention enables the hole to be continually fed with rods and to be measured continuously, while only withdrawing the probe at intervals of drilling depths based on the total number of drill rods in the rack. The reduction in time which is saved by fewer pump downs and withdrawals of the probe is substantial and consequentially gives a large saving in cost in a mining operation.

Although the magazine shown carries the rods in two groups of five it would be appreciated that magazines using the same principle can be devised which carry a different number of rods and in different groupings. It is essential though that the wire is led through the rods in a manner which enables the rods to be pulled off sequentially and without causing any entanglement of the wire or need to reverse rods in a confined space.

By the use of an adjustably positioned roller (11) the rods can be fed off into the borehole without the need to alter the position of the frame. Similarly, the adjustable feed pulley (14), enables the position of the feed wire to be correctly located with regard to the end of the rods and also with regard to a winch.

Claims (9)

1. A method of borehole drilling in which a drill member creates a borehole in strata and hollow drill rods are advanced behind the drill member to line the bore, and in which the drill member direction is controlled in response to measurements taken by a down-hole probe connected to instrumentation external of the hole through a cable, characterised by supplying the drill rods serially to the borehole from a magazine, through which drill rods a cable connected to the probe has been pre-threaded continuously in the magazine prior to the feeding of the probe into the drill hole.

2. A method of borehole drilling substantially as hereinbefore described with reference to the accompanying drawings.

3. Apparatus for use with the method according to claim 1 or 2 including a drill rod magazine having mounting means for a plurality of drill rods, pulley means for guiding a cable sequentially through the rods, and means for dispensing the cable and the rods into a borehole.

4. Apparatus according to claim 3 in which the means for dispensing the cables and the rods into a borehole comprise rollers.

5. Apparatus according to claim 4 in which the position of the rollers is adjustable.

6. Apparatus according to any one of claims 3,4 or 5 in which the magazine includes a frame mounted on adjustable legs.

7. Apparatus according to any one of the preceding claims 3 to 6 in which the frame is adapted to accanmodate two vertical groups of drill rods.

8. Apparatus according to claim 7 in which in use the cable is threaded sequentially through the rods in a figure of eight pattern.

9. Apparatus substantially as hereinbefore described with reference to the accompanying drawings.