WO2000055469A1

WO2000055469A1 - Method and apparatus for underground drilling

Info

Publication number: WO2000055469A1
Application number: PCT/FI2000/000212
Authority: WO
Inventors: Risto Välisalo
Original assignee: Rd Trenchless Ltd Oy
Priority date: 1999-03-16
Filing date: 2000-03-16
Publication date: 2000-09-21
Also published as: AU3436000A; FI990589A0; FI990589A

Abstract

In a method for underground drilling, an impact tool (2) advancing in the ground is used to ream a previously formed hole (11), and a medium is supplied to the apparatus to produce the impactive movement of the impact tool (2) and for flushing drill cuttings out of the drilling point. By means of the medium, the drill cuttings are simultaneously carried in the drilling direction along a previously formed hole. The flushing medium intended for removing drill cuttings is introduced to the drilling point along a different channel (1a) than the working medium intended for producing the impactive movement is introduced into the impact tool (2). The flushing medium is a liquid or a flowing mixture, especially a liquid or mixture more viscous than water, such as drilling mud, and at least part of the flushing medium is led back opposite to the supply direction after it has flushed the drilling point.

Description

Method and apparatus for underground drilling

The invention relates to a method for underground drilling, in which an impact tool advancing in the ground is used to ream a previously formed hole, and a medium is supplied to the apparatus to produce the impactive movement of the impact tool and for flushing drill cuttings out of the drilling point, and simultaneously the impact tool is pulled in the drilling direction and the impacting drill bit assembly is rotated. The invention also relates to an apparatus comprising an impact tool equipped with a drill bit assembly, wherein the drill bit assembly is arranged to ream a previously formed hole, the apparatus further comprising a channel for conveying a medium to the impact tool and, in front of the drill bit assembly, a pulling means for pulling the impact tool and a means for rotating the drill bit assembly.

Solutions are known in which drill cuttings are discharged through a hole already existing on the front side of the drilling apparatus in the drilling direction, such as by means of a helical screw placed within pipes installed in a pilot hole (US Patent 4,024,721), or by means of a helical screw brought along a sewer pipe or the like to be renovated (US Patent 5,791 ,419 by the applicant). In the latter case, the drilling device is an impact tool.

It is also known to drill a hole in the ground by arranging a drilling appa- ratus to advance in the ground, to which a medium is brought for drilling power as well as for flushing the drilling point and for discharging the drill cuttings. Such a drilling device reams a hole of a smaller diameter formed previously in the ground and determining the drilling direction, a so-called pilot hole, larger, and simultaneously the produced drill cuttings are discharged with the medium. The device can be used as a pipe-laying device, wherein pipes are placed after it, or the walls of the reamed hole can be left free after the drilling device.

At present, so-called rotary blades are used in drilling devices to ream a pilot hole, which blades are slow under hard earth conditions and require very great tractive forces to function properly. Such a rotary blade is presented in the above-mentioned US Patent 4,024,721 , in which, however, a mechanical solution is used to convey the drill cuttings away.

The invention relates particularly to directional drilling, wherein a so- called pilot hole is reamed to a certain extent for the installation of the final pipe. In the technology, to which the invention relates, no helical screws are used for flushing or cleaning the hole, but the material is discharged forward in the space between a pulling rod used in the drilling and the inner wall of the hole, by the transferring capacity of air.

Air is a popular medium in drilling, because it is abundantly available, it can be well conveyed, its possible leakage in different parts of the apparatus will cause no damage, and it can be safely discharged back to the environment. It is thus self-evident to use air both as a working medium (the energy required by the drill bit) and as a flushing medium. It is difficult to control flushing in such apparatuses, and moreover, the method has certain limitations with certain soil types.

It is an aim of the invention to eliminate the drawbacks of prior art and to present a novel method and apparatus for underground drilling. To achieve this aim, the method is primarily characterized in that the medium intended for discharging the drill cuttings is introduced to the drilling point along a different channel than the working medium intended for providing the impactive movement. Thanks to this, the flows of the flushing medium and the working medium to be introduced from the outside to the impact tool can be separated, and it is possible to use media which are precisely suitable for the use. At least one of the media is introduced preferably from the drilling direction, from the front. If the flushing medium is introduced from the front, it can be led along relatively short channels to the drilling point. The drill cuttings can be discharged forward to the direction of advancing of the drilling in the space between the supply channel of the flushing medium and the previously formed hole, i.e. the pilot hole, by means of the transfer effect of the medium. By adjusting the quantity of the flushing medium, the flushing capacity can be adjusted independently without affecting the drilling capacity. However, it has been found that air as such is not a sufficiently good medium for discharging the drilling material from the hole, because in a horizontal hole, the material tends to drop to the bottom of the hole, wherein it cannot be sufficiently well removed by air. The situation can, however, be facilitated by increasing the quantity of the air, but particularly in soil material with a tendency to collapse, the speed of the air will tend to break the walls of the previously formed pilot hole. Thus, in an advantageous embodiment, the flushing medium introduced separately from the working medium is a liquid or a flowing mixture, particularly a liquid or mixture more viscous than water, such as drilling mud. A substance more viscous than water, for example so-called drilling mud, has a better material transfer capacity than air. Because a liquid or a flowing mixture has a better material transfer capacity than air, its speed does not need to be high. Further, the flow is laminar. Thus, the risk of collapsing of the hole is reduced. The drilling mud used can be e.g. a mixture of bentonite clay and water in a suitable ratio.

Part of the flushing medium can be directed to the rear, past the impact tool, into the reamed hole. It can thus be used as a lubricant to facilitate the movement of the impact tool in the reamed hole. If the method in question is used for laying pipes in the reamed hole, the medium thus led to the rear can also be used as a lubricant between the pipe fed behind and the wall of the reamed hole. In a method, where no pipes are laid and the hole is left free after the impact tool, the quantity of the flushing medium can be adjusted to achieve a situation in which the reamed hole is full of the heavy viscous medium and it will not tend to collapse inwards so easily. In the drilling mud or water, it is also possible to add polymers reinforcing particularly the wall of the reamed hole.

The medium used to produce the impactive movement of the impact tool, i.e. the working medium, is preferably air, and it can be introduced to the impact tool from behind, or also from the front. The supply channel of the working medium is coupled at its initial end to a device for supplying the working medium, such as an air compressor, known as such. Another advantage of the invention is that it is not intended to mix the air, which produces the impactive movement of the drilling apparatus, with the flushing medium, in which case it would possibly tend to damage the drilled hole. It should be kept in mind, however, that when a hole is being drilled in sound rock or in another firm soil type, there is practically no risk of collapse, wherein it is also possible to lead air as an aid to the liquid flushing, that is, in practice, part of the air used as the working medium is led there. In this case, both air and liquid are led forward in the space between the pulling means and the inner wall of the pilot hole to remove the drill cuttings.

The apparatus according to the invention is equipped with a channel system to introduce the working medium to achieve the impactive movement of the drill bit assembly of the drilling apparatus, as well as with a second channel system to introduce flushing medium to convey the material away. Either of the channel systems is preferably led from the front of the drilling apparatus along a drill string (pulling means). Thus, the apparatus has a channel system, through which a medium is supplied solely for the above-mentioned purpose of flushing and conveying, and it can be used to introduce air, or preferably a liquid or a flowing mixture, particularly the above-mentioned viscous liquid or mixture.

In the following, the invention will be described with reference to the appended drawings, in which

Fig. 1 shows a longitudinal section of a pilot hole and a reamed hole, and also shows the apparatus located therein in a partial longitudinal section,

Fig. 2 shows a longitudinal section, as in Fig. 1 , of another embodiment of the invention.

In the apparatus of Fig. 1 , a drill string, i.e. a pulling rod 1 is introduced along a pilot hole 11 to an impact tool 2 used as the drilling device, i.e. a hammer. The pulling rod is provided with a channel system 1 a, along which a flushing medium is introduced to a drill bit assembly to be distributed radially e.g. on its outer periphery and from there towards the centre along grooves formed on the front surface of the drill bit assembly. The flow channel 1a of the flushing medium extends parallelly to the pulling rod, inside the same, and at the initial end it is connected to a device for feeding the flushing medium. In Fig. 1 , the channel 1a is introduced centrally through the drill bit assembly into the drill bit assembly, and there are channels 9 extending radially inside the bit towards the outer surface of the drill bit assembly. From the channels 9, the flushing medium is discharged to the front side of the drill bit assembly to flush the drill cuttings produced by the impacting bit away from the drilling point and to carry them further in the annular space between the hole 11 and the drill string 1 forward towards a rotating/pulling device at the other end of the pilot hole, by means of which the pulling rod 1 and through the latter the impact tool 2 is pulled and rotated, as a result of which also the drill bit assembly rotates around an axis parallel to the drilling direction.

In the case shown in the figure, the pressurized medium producing the reciprocating impactive movement, i.e. the working medium, is supplied to the impact tool 2 from behind along a feeding conduit 5. The drill bit assembly, directly impacting the material to be drilled, consists of a drill bit 3 with a larger diameter and a drill bit 4 drilling the centre hole, as shown in the figure. The drill bit assembly is placed foremost in the body of the impact tool 2 to be movable in a reciprocating manner with respect to the body, and it is also capable of moving in the axial direction in comparison with the drill string 1 , as in the sewer refurbishing device known from US Patent 5,791 ,419 by the applicant. The channel 1a is, in spite of the movement of the drill bit, continuously in contact with the channel system 9 extending inside the drill bit, by means of an opening in the wall of the rod which opens inside the drill bit to an expansion extending parallel to the impactive movement on the inner surface of the drill bit. By changing the central drill bit shown in the figure, the apparatus can be fitted in pilot holes of various sizes, and it is aimed at limiting the particle size of the drill cuttings to prevent too large material particles from blocking the space between the hole 11 and the drill string 1.

Part of the flushing medium can be let past the drill bit assembly 3, 4, wherein it can fill the space between the outer mantle of the impact tool 2 and the wall of the reamed hole 10, supporting the newly reamed hole and also acting as a lubricant at the same time. The medium can also fill, at least on part of the length, the whole inner volume of the reamed hole 10 behind the impact tool 2. It can thus be absorbed in the wall of the reamed hole 10 or, if the flushing medium contains such polymers which reinforce the wall of the hole and simultaneously make it impermeable, it can be left in the hole. The flushing medium left in the hole can be removed by suction or, when laying a pipe in the hole later on, also by displacement. The distribution of the flushing medium to the front and rear sides of the drill bit assembly 3, 4 can be adjusted with the rate of feeding the medium introduced along the channel 1a. In the outer edge of the drill bit assembly, there can naturally be points at which the medium can be passed behind more easily.

In the case shown in the figure, the exhaust air of the impact tool 2 is led along a channel system 8 in the drill bit assembly 3, 4 backwards in the inner volume of the mantle 7 of the impact tool to a third channel 6, a return duct, in such a way that it is not connected to the reamed hole 10 and could not possibly damage the reamed larger hole 10. If there is no such risk (hard soil material), instead of having a closed return duct 6 the air can be left to discharge freely backwards.

Depending on the conditions as well as the needs, the pressurized medium used by the hammer can also be led, by changing the channel system 8, to make the flushing of the hole in the space between the drill string 1 and the hole 11 more effective; that is, part of the return air is led forward. In this case, the channel system 8 is led as a channelling separate from the channel system 9 inside the drill bit assembly 3, 4 to the front side of the drill bit, wherein it opens as separate openings onto the front surface of the drill bit assembly and mixes the air at the drilling point to the flushing medium in the form of a liquid or a flowing mixture. If necessary, the device can also install a pipe in the way shown in Fig. 2, wherein the pipe can be coupled to the drill bit assembly in a way known as such or, as shown in Fig. 2, the pipe 12 is connected behind the impact tool 2. The pipe can also be pushed from the rear end while the impact tool advances. In other respects the same reference numbers are used to indicate the same parts in Fig. 2. In this embodiment, however, channels 9a are branched off backwards from the flushing medium channel system 9 inside the drill bit assembly. The channels 9a open on the rear side of the drill bit assembly in such a way that they direct part of the flushing medium into a space between the mantle 7 of the impact tool and the hole 10, wherein the flushing medium, in the form of a liquid or a flowing mixture, can enter this space and further into the space between the pipe 12 to be placed in the hole and the wall of the hole 10, facilitating the installation of the pipe in the hole. In the embodiment of Fig. 2, the drill bit assembly is integrated, consisting of one drill bit piece 4.

Because there is a drill string used as a pulling means and a rotating means in the apparatus, it is used for introducing at least one of the media, normally at least the flushing medium. In some cases, the drill string 1 could also be a so-called double-wall pipe with two concentric channels in the longitudinal direction of the rod 1. The second channel thus formed parallelly to the flushing medium channel 1a can be used for supplying the working medium, either so that it makes it possible to lead the pressurized medium required by the impact tool to the impact tool, or so that it is part of the channel system 8 for removing used pressurized medium away from the impact tool, that is, in this case, along the rod 1 in the drilling direction, wherein in the latter case, the working medium is introduced to the impact tool 2 from behind.

Upon drilling sound earth, wherein there is practically no risk of collapse of the hole, also pressurized air can be supplied along the flushing medium channel system 1a, wherein it is arranged to flush the hole together with or separately from the pressurized medium enabling the impactive movement. Although the media can be the same, their supply channels are still separated. Because the pressurized medium (working medium) is separated from the flushing medium, it is also possible to make an arrangement which prevents the drilled material from penetrating into the impact tool 2, particularly when no pressurized medium is supplied to it, since the flushing is independent of the supply of the pressurized medium. The arrangement can be made with an appropriate flushing medium channel system in the impact tool in such a way that it prevents foreign material from entering into the impact tool in case the supply of the pressurized medium, i.e. the working medium, is temporarily cut off due to some work stage in drilling.

The invention is not limited solely to what is presented in the figures and in the description. The flushing medium can be introduced to the drilling point from the front also in such a way that the channel system opens in front of the drill bit assembly, e.g. directly from the inside of the drill string. The flushing medium will thereby not pass through the channel system in the drill bit assembly. Also in this case, it is possible to utilize the return flow of the working medium led to the front side of the drill bit assembly as an aid in the flushing of the drilling point. Moreover, the invention is not strictly limited to the direction in which the flushing medium and the drill cuttings are led from the drilling point in front of the impacting drill bit assembly; i.e., it can be conveyed by suitable arrangements also backwards opposite to the incoming direction of the impact tool.

The invention is suitable for use in directional drilling, particularly in horizontal directional drilling, which are methods using a pilot hole. The invention can also be used in connection with refurbishing underground pipes, such as sewers, wherein a pipe to be drilled off is used as a kind of pilot hole. In such a case, the invention suits particularly well for cases in which the pipe to be removed has such a small inner diameter (e.g. a maximum of 150 mm) that a helical screw to remove the waste does not fit into the pipe. The pipe to be removed can also be so large that it is not expedient to manufacture a conveyor screw with a large diameter for that particular purpose. Furthermore, the invention is suitable for use in such sites where problems of dusting can occur and in which the liquid or the flowing mixture used as the flushing medium will also bind dust.

Claims

Claims:

1. A method for underground drilling, in which an impact tool (2) advancing in the ground is used to ream a previously formed hole (11), and a medium is supplied to the tool to produce the impactive movement of the impact tool (2) and for flushing drill cuttings out of the drilling point, and simultaneously the impact tool is pulled in the drilling direction and an impacting drill bit assembly is rotated, characterized in that a flushing medium intended for removing drill cuttings is introduced to the drilling point along a different channel (1a) than a working medium intended for producing the impactive movement is introduced into the impact tool (2).

2. The method according to claim 1 , characterized in that at least one of the media is introduced from the front to the drilling point.

3. The method according to claim 2, characterized in that at least the flushing medium is introduced from the front to the drilling point.

4. The method according to any of the preceding claims, characterized in that the flushing medium is a liquid or a flowing mixture, particularly a liquid or mixture more viscous than water, such as drilling mud, and at least part of the flushing medium is led back opposite to the supply direction after it has flushed the drilling point.

5. The method according to any of the preceding claims, characterized in that the working medium is pressurized air.

6. The method according to claim 4 or 5, characterized in that part of the flushing medium is allowed to pass to the rear between the reamed hole (10) and the impact tool (2).

7. The method according to claim 6, characterized in that the flushing medium is used to fill the space between the impact tool (2) and the reamed hole (10).

8. The method according to any of the preceding claims 4 to 7, characterized in that the flushing medium is a liquid or a flowing mixture, especially a liquid or mixture more viscous than water, such as drilling mud, the working medium is pressurized air, and part of the working medium is introduced to mix with the flushing medium in the drilling point.

9. The method according to any of the preceding claims, characterized in that it is used in horizontal directional drilling.

10. An apparatus for underground drilling, comprising a impact tool (2) equipped with a drill bit assembly (3, 4), arranged to ream a previously formed hole (11), the apparatus further comprising a channel (5) for supplying a medium to the impact tool (2), and a pulling means (1) in front of the drill bit assembly (3, 4) to pull the impact tool (2) in the drilling direction and means for rotating the drill bit assembly (3, 4), characterized in that the apparatus is equipped with a channel system for introducing a working medium to produce the impactive movement of the drill bit assembly (3, 4), as well as a second, separate channel system (1a) for introducing a flushing medium for conveying material away.

11. The apparatus according to claim 10, characterized in that said second channel system (1a) for the flushing medium is introduced from the front of the drilling device (2) along the pulling means (1 ).

12. The apparatus according to claim 11 , characterized in that the channel system (1a) is introduced inside the drill bit assembly (3, 4) where it forms a separate channel system (9) to distribute flushing medium to the front side of the drill bit assembly.

13. The apparatus according to any of the claims 10 to 12, characterized in that the channel system (1a) for the flushing medium is connected to a source of a liquid or a flowing mixture, particularly a liquid or flowing mixture more viscous than water, such as drilling mud, and to pumping means for supplying said medium along the channel system (1a).