WO1995012747A1

WO1995012747A1 - Method and system for exploring for and extraction of raw materials, minerals or the like in soft ground

Info

Publication number: WO1995012747A1
Application number: PCT/NL1994/000271
Authority: WO
Inventors: Rüdiger KÖGLER
Original assignee: Nacap Nederland B.V.
Priority date: 1993-11-05
Filing date: 1994-11-04
Publication date: 1995-05-11
Also published as: AU691537B2; AU1123495A; BR9407994A; ZA948719B; NL9301921A; CA2175705A1

Abstract

Method and system for exploring for and extraction of raw materials, minerals or the like in soft ground in not readily accessible or impassable areas. Use is made of a guided horizontal drilling technique for reaching a place where there are deposits. During the drilling a hollow guide drill rod (20) with an open front end is pressed axially into the ground. In another embodiment coaxially around the guide drill rod a hollow wash drill rod (22) with an open front end is pressed into the ground. During the drilling a fluid flow is established through the guide drill rod (20) and in the opposite direction along the outer surface of the guide drill rod (20). The drilling path is used to introduce exploration means (34, 36, 38; 40, 42) and extraction means (52, 56) into the ground.

Description

Method and system for exploring for and extraction of raw materials, minerals or the like in soft ground.

The invention relates to a method and system for exploring for and extraction of raw materials, minerals or the like in soft ground. In this respect, the term "soft" is to be understood as meaning: relatively soft, and soft enough to be able to drill it with the drilling technique used.

According to the prior art, exploring for raw materials, minerals or the like is carried out by geo¬ logical examination, such as visual examination and manual sampling, physical methods, such as taking mud samples and carrying out core drilling and borehole measurements, and geophysical methods, such as seismological, magnetometric and sonar measurements. However, none of these methods is suitable for providing satisfactory results when the locations of the raw materials, minerals or the like lie in not readily accessible or impassable areas, such as surf zones, swamps, river deltas and forest zones, which are often made even more inaccessible through the introduction of more stringent environmental protection laws. Examination of the soil generally occurs in the vertical direction at points which are isolated from each other, so that little or nothing is known of the direct and wider surroundings in the horizontal direction. This is a drawback, since most extractable raw materials, minerals and the like occur in layers extending in the horizontal direction in the ground, for example in the form of deposits.

The object of the invention is in the first place to provide a method for exploring for and extraction of raw materials, minerals and the like, which method is pre¬ eminently suitable for gaining access to relatively shallow deposits extending essentially horizontally in soft ground in not readily accessible or impassable areas. With the conventional essentially vertical drilling techniques (i.e. starting in a vertical direction and essentially relying on the force of gravity to supply drilling pressure on the drilling head) no sufficient pressure can be built up at the drilling head when drilling to a shallow deposit in a more or less horizontal direction, since such pressure cannot be supplied by the relatively short vertically extending drill rod or pipe used.

To reach the object of the invention, the method according to the invention is characterized in that use is made of a guided horizontal drilling technique for reaching a place where there are deposits of raw materials, minerals or the like, following which the drilling path is used for the introduction of exploration or extraction means into the ground.

A guided horizontal drilling technique is known per se - for example from US Patent Specification 3,878,903 - for making a continuous borehole essentially in the horizontal direction in ground, for laying pipelines and cables. However, the invention is based on the surprising realization that a guided horizontal drilling technique can be used advantageously for exploration for and extraction of raw materials, minerals or the like in soft ground. The method according to the invention is pre-eminently suitable for use in essentially horizontally oriented shallow deposits (so called sediment depositions) and makes it possible to drill these selectively, it being possible in principle for the drilling to follow the course of the deposit in any desired direction within certain limits, which are determined by the maximum bend of the drill rods. Contrary to a vertical drilling method, in a horizontal drilling method the drilling machine used can deliver in particular the required pressure on the drilling head.

In a preferred embodiment of the method according to the invention, in the guided horizontal drilling technique a hollow drill rod with an open front end is pressed axially into the ground, while a fluid flow is established through the drill rod and in the opposite direction along the outer surface of the drill rod. Alternatively, the hollow drill rod may be a guide drill rod, and in this case coaxially around it a hollow wash drill rod with an open front end is pressed into the ground, while a fluid flow is established through the guide drill rod and in the opposite direction through space between the guide drill rod and the wash drill rod.

If for the horizontal drilling only a drill rod is used, a wash drill rod being absent, in a particularly effective embodiment of the method according to the invention for exploring for raw materials, minerals or the like, the drill rod is provided at its front end with a survey tool and/or a sampling tool for examining characteristics and/or sampling the ground in the area surrounding the survey tool or the sampling tool, the survey tool and/or the sampling tool carrying out ground measurements, the measuring places and corresponding measuring results being recorded, during one or more intervals while pressing the drill rod into the ground and/or during withdrawing the drill rod from the ground.

If for the horizontal drilling a combination of a guide drill rod and a wash drill rod is used, the exploring method preferably comprises the following steps: on reaching the end of the drilling path, the guide drill rod is withdrawn from the wash drill rod; a rod provided at its front end with a measuring instrument for examining characteristics of the ground in the area surrounding the measuring instrument is pressed into the wash drill rod; the wash drill rod is withdrawn; and the rod with the measuring instrument is withdrawn, while the measuring instrument carries out ground measurements, the measuring places and corresponding measuring results being recorded. In order to determine the drilling path as accurately as possible, prior to the introduction of the rod with the measuring instrument into the wash drill rod, a gyroscopic position-measuring instrument is introduced into the wash drill rod until it is near the front end thereof, and said instrument is subsequently withdrawn, while the instrument carries out position measurements, the results of which are recorded.

A preferred embodiment of the method according to the invention for the extraction of raw materials, minerals or the like comprises the following steps: coaxially around the drill rod, an outer production pipe with an open front end is pressed over a predetermined distance into the ground; the drill rod is withdrawn from the outer production pipe; an inner production pipe with an essentially open front end is pressed into the outer - production pipe until the front end of the inner production pipe lies a short distance behind the front end of the outer production pipe; and a fluid flow is established through the inner production pipe and in the opposite direction through the space between the inner production pipe and the outer production pipe. The front ends of the production pipes are, of course, guided to the place where it has been found by means of the exploration that there are deposits of the raw material, mineral or the like which is sought. Deposit material will be entrained in the fluid flow and can be separated above ground in a manner known per se. If the drill rod is a guide drill rod interacting with a wash drill rod, after reaching the end of the drilling path, the wash drill rod is first withdrawn before the outer production pipe is pressed coaxially over the guide drill rod as described above.

In another preferred embodiment of the method according to the invention for the extraction of raw materials, minerals or the like the following steps are carried out: after reaching the end of the drilling path, the guide drill rod is withdrawn from the wash drill rod; an outer production pipe and an inner production pipe are pressed over a predetermined distance into the wash drill rod simultaneously or one after the other, which pipes each have an essentially open front end, the outer production pipe lying coaxially around the inner production pipe, and the front end of the inner production pipe being taken to a short distance behind the front end of the outer production pipe; the wash drill rod is withdrawn completely or to at least behind the front end of the pipes; and a fluid flow is established through the inner production pipe and in the opposite direction through the space between the inner production pipe and the outer production pipe.

By means of the last-mentioned method it is pufcsx_->j_fc. uu press an inner production pipe an outer production pipe, both with a curved front end, simulta¬ neously into the wash drill rod. Due to the curvature at the end of the production pipes, the extraction can be carried out over a considerably greater area by rotating the pipes.

The most effective action of the fluid flow is obtained if the fluid flow in the inner production pipe is directed away from the front end thereof. If it is ensured that during the drilling for extraction purposes as many deposits of raw materials, minerals or the like as possible are cut through, a high yield can be obtained if the assembly of inner production pipe and outer production pipe is withdrawn along the drilling path during the extraction. If the outer produc¬ tion pipe becomes jammed in the ground in the course of this, a hollow second wash drill rod with an open front end is preferably pressed coaxially over the production pipes into the ground until it is near the end of the production pipes to be able to recover the production pipes.

Thereafter, the second wash pipe is removed from the ground.

For maximization of the extraction yield, it is advantageous if the front ends of the inner production pipe and the outer production pipe can be swung sideways, for example by hydraulic means. This measure ensures that when they are being introduced into the borehole the production pipes can be straight, and during the extraction can cover the greatest possible area near their front ends. A system according to the invention for exploring for or extraction of raw materials, minerals or the like comprises: means for the interconnection and disconnection of coaxial rods or pipes; means for pressing the rods or pipes into the ground and removing them therefrom in an essentially horizontally directed manner for performing a guided horizontal drilling; exploration or extraction means being guided by at least one of said rods or pipes during the introduction of the exploration or extraction means into the ground. If for the horizontal drilling a combination of a guide drill rod and a wash drill rod is used, the system is preferably designed in such a way that the wash drill rod is driven rotatably, and that it is provided at its front end with a tooth system. For a relatively soft soil, such as a sandy soil, a forward projecting tooth system will suffice, while for a harder, coarser soil structure, such as sand-limestone, shingle or gravel, a combination of a forward and laterally outward projecting tooth system may be used. A strong suction action in a fluid flow through the production pipes is achieved if the front end of the outer production pipe is provided with an opening whose cross-section increases in the axial forward direction.

The invention is explained with reference to the drawing, in which:

Figs. 1 and 2 illustrate in cross-section and top view respectively the guided horizontal drilling technique for exploring for and extraction of raw materials, minerals or the like, the scale of Fig. 1 differing from that of Fig. 2;

Fig. 3 shows the end of drill rods during the drilling of a channel by the guided horizontal drilling technique;

Fig. 3a shows on an enlarged scale a detail of the central drill rod of Fig. 3;

Figs. 4, 5, 6, 7 and 8 illustrate different stages of the exploration according to the invention;

Fig. 9 corresponds essentially to Fig. 3;

Figs. 10, 11, 12, 13 and 14 illustrate different stages in the extraction according to the invention;

Fig. 13a shows an embodiment of a central pipe according to Fig. 13;

Figs. 15 and 16 illustrate stages of the movement of pipes in a borehole; and Fig. 17 shows another embodiment of the pipes according to Fig. 14 or 15.

The same reference numbers in the various figures refer to the same parts, or parts with the same function.

Figs. 1 and 2 show a ground profile in a coastal region or at a river bank, at the place where land 2 passes into water 4, the dashed line 5 indicating the level of the water surface. The ground of the land and bed of the water comprise various formations 6, 8, 10 and 12, such as clay, sand, shingle, gravel and the like, or mixtures thereof. A device 14, shown only diagrammatically, is placed on the land 2 near the coastline, for drilling a hole in the direction of the arrow 16 in the ground of the land and bed of the water for exploring for and extraction of raw materials, minerals or the like in the deposits 10, 10a, 10b and 10c. During the exploration, the drilling will be carried out in a manner to be described in greater detail below, for example along the line 16 in the direction of the arrow, then with the same drilling device by moving it to the position of 14a and drilling in the direction of the arrow along the dashed line 16a, then moving the drilling device to the position of 14b and drilling in the direction of the arrow along the dashed line 16b, and so on. When it has been established sufficiently in this way where the deposits sought are situated, a similarly guided horizontal drilling technique can be used to extract the raw materials, minerals or the like, in which case the drilling can be carried out, for example, in the direction of the arrow along the dashed lines 18a or 18b. The exploration according to the invention will be discussed first below with reference to Figs. 3 - 8 and 3a.

Fig. 3 shows diagrammatically the front end of a hollow guide drill rod 20 and a hollow rotary wash drill rod 22, disposed essentially coaxially with the guide drill rod 20. A control tool 24 is situated near the end in the guide drill rod 20, which tool is connected by means of a communication cable 26 to the device 14, for determining the position of the front end of the guide drill rod 20. As Fig. 3a shows, the guide drill rod 20 is in fact a drill string, made up of different essentially identical sections, which at the ends 21a and 21b are provided with interacting connecting means for producing a screw connection between the sections. The ends 21a and 21b are designed in such a way that a smooth wall without projec- tions is produced on the inside diameter of the guide drill rod 20. The wash drill rod 22 is made up of sections in the same way as the guide drill rod 20, and it is also ensured that the inside wall of the wash drill rod 22 is smooth and without projections. The guide drill rod 20 is provided at its front end with an outlet opening 28 through which fluid under pressure from a pump (not shown) can be forced from the inside of the guide drill rod 20 to the outside. The wash drill rod 22 is provided at the front end with teeth 30 for excavating the ground on the spot.

An exploratory drilling operation with the elements shown in Fig. 3 is carried out in the following manner. From the device 14 (see Fig. 1) the guide drill rod 20 is pressed into the ground, fluid being forced through the guide drill rod 20 and the opening 28. Near the front end of the guide drill rod 20 this causes fluidizationi of the ground, in the course of which bed material is discharged backwards on the outside of the guide drill rod 20. The guide drill rod 20 will consequently be able to move forwards in the direction of arrow 29 when sufficient pressure force is exerted by the device 14. The front end of the guide drill rod 20 is followed at a distance by the rotary wash drill rod 22 in the direction of arrow 31, which increases the diameter of the channel formed by the guide drill rod 20, and the inside of which is also used for discharge of the ground fluidized at the front side of the guide drill rod 20. However, in specific circumstances the wash drill rod may be dispensed with, only a guide drill rod being used for the drilling. Due to the smooth finish of the inside walls of the guide drill rod and the wash drill rod, the hydraulic resistance to the fluid flowing along is as low as possible. However, the smooth finish is not absolutely essential. As Fig. 4 illustrates, on completion of a bore the guide drill rod 20 is withdrawn from the wash drill rod 22 in the direction of the arrow 32.

As Fig. 5 illustrates, a more accurate determina¬ tion of the drilling path covered can be carried out if desired by moving a measuring instrument 34 with a gyro¬ compass 36 through the wash drill rod 22. For this purpose, the measuring instrument is first pumped to the end of the wash drill rod 22, following which the measuring instrument is pulled back out of the wash drill rod on a measuring and pulling cable 38 in the direction of the arrow 39 while carrying out suitable measurements.

Following the removal of the guide drill rod 20 from the wash drill rod 22 according to Fig. 4, or following the measurement of the drilling path according to Fig. 5, a measuring instrument 40 for determining the characteristics of the ground in the area surrounding the measuring instrument is inserted into the wash drill rod 22 by means of a pipe 42 in the direction of arrow 43. As Fig. 7 illustrates, the wash drill rod 22 is then removed from the borehole in the direction of the arrow 44, in order to avoid any influence on the measurement to be made by the measuring instrument 40 through the presence of the usually steel wash drill rod 22. The pipe 42, at the end of which the measuring instrument 40 is disposed, is then withdrawn in the direction of the arrow 46, while the measuring instrument 40 transmits waves 48 in one or more predetermined directions and receives the reflections by the bottom thereof for determining the characteristics of the ground at the spot.

It will be clear that it is also conceivable to drill with a single drill rod which at its front end is provided with a control tool (steering tool) 24, and additionally with a survey tool like the measuring instruments 40 and/or sampling tool for taking ground samples. In this way, both in intervals during drilling and during withdrawal of the drill rod from the ground, measurements may be made for determining the characteristics of the ground surrounding the front end of the drill rod.

The extraction of raw materials, minerals or the like will be discussed below with reference to Figs. 9 - 17 and 13a.

Fig. 9 illustrates the making of a borehole by a guided horizontal drilling technique, as already explained above with reference to Fig. 3.

As Fig. 10 illustrates, the wash drill rod 22 is withdrawn from the borehole in the direction of arrow 50 on completion of the predetermined drilling path. The guide drill rod 20 remains behind in the borehole. Of course, it is also possible in the horizontal drilling to use only a drill rod and no wash drill rod. In that case, the same situation will result. As Fig. 11 illustrates, a hollow outer production pipe 52 is then pushed through the borehole in the direction of arrow 53 over the guide drill rod 20 until it is near the front end thereof. The guide drill rod 20 acts as a guide in this case. As Fig. 12 illustrates, after the outer production pipe 52 has been inserted into the borehole, the guide drill rod 20 is withdrawn in the direction of arrow 54 from the outer production pipe 52, which thereby remains in place in the borehole. As Fig. 13 illustrates, after the removal of the guide drill rod 20 a hollow inner production pipe 56 is pushed into the outer production pipe 52 in the direction of arrow 57 until the front end of the inner production pipe 56 is situated at a predetermined distance behind the front end of the outer production pipe 52. The front end of the inner production pipe 56 is provided with a grate 58. Fig. 13 indicates the way in which a screw connection is used between sections of the inner production pipe 56 in order to fix them to each other. In particular, it can be seen from this figure that both the inside surface and the outside surface of the inner production pipe are smooth and without projections, although this is not absolutely essential. It is pointed out that the couplings of sections of the outer production pipe are, for example, formed as shown in Fig. 3a, in order to obtain an inside diameter which is smooth and without projections.

As illustrated in Fig. 14, raw materials, minerals or the like are extracted by pumping by means of a pump (not shown) a fluid in the direction of the arrows into the space 60 bounded by the inside wall of the outer production pipe 52 and the outside wall of the inner production pipe 56, and at the same time creating a partial vacuum inside the inner production pipe 56. The fluid supplied through the space 60 will reverse its direction of movement between the front ends of the inner production pipe 52 and outer production pipe 56 and be discharged through the inner production pipe 56. In this case fluidized material from the ground in front of the front end of the outer produc- tion pipe 52 will be sucked in through the opening 52a thereof and will be entrained into the inner production pipe. The grate 58 stops coarser material.

It is possible that during the extraction the outer production pipe 52 will become jammed in the ground. This is undesirable, since it must be possible to move the front end of the outer production pipe 52 backwards through the borehole in order to extract as much bed material 62 as possible. As Fig. 15 illustrates, the outer production pipe 52 can be drilled out by means of a hollow drill rod 66 which is provided with teeth 68 and can be moved in the direction of arrow 64, following which the assembly of outer production pipe 52 and inner production pipe 56 can be moved in the direction of arrow 70. As Fig. 16 illustrates, prior to that the drill rod 66 is withdrawn from the borehole in the direction of arrow 72, in any case at least so far that the front end of the drill rod 66 lies behind the front end of the outer production pipe 52. The drill rod 66 can also be removed entirely from the borehole first, before the production pipes 52 and 56 are moved. The inner and outer production pipes can also be placed in a different way from that shown in Figs. 9 - 13. If from the starting position shown in Fig. 9 the wash drill rod 22 is left in its place and the guide drill rod 20 is withdrawn from it, and the outer production pipe 52 is then pushed into the wash drill rod 22 and thereafter or simultaneously the inner production pipe 56 inside the outer production pipe 52 is moved into the borehole, the wash drill rod 22 can subsequently be withdrawn over some distance or fully from the borehole. This latter method of setting up the production pipes 52 and 56 in the borehole has advantages if, as Fig. 17 shows, the front ends of the production pipes 52 and 56 are curved. Such a curvature is advantageous, because in this way a larger area in the sur- roundings of the front ends of the production pipes 52 and 56 can be covered without the production pipes having to be moved in their lengthwise direction. The curvature of the production pipes shown can also be achieved by means of a suitable, for example hydraulically operated articulation of the drill rods.

Claims

1. Method for exploring for or extraction of raw materials, minerals or the like in shallow deposits in soft ground in not readily accessible or impassable areas, characterized in that a guided horizontal drilling technique is used for reaching a place (10, 10a, 10b, 10c) where there are deposits of raw materials, minerals or the like, following which the drilling path is used for the introduction and removal of exploration means (34, 36, 38; 40, 42) or extraction means (52, 56) into or from the ground.

2. Method according to claim 1, characterized in that in the guided horizontal drilling technique a hollow drill rod (20) with an open front end is pressed axially into the ground, while a fluid flow is established through the drill rod and in the opposite direction along the outer surface of the drill rod.

3. Method according to claim 2, characterized in that the hollow drill rod is a guide drill rod (20) and coaxial¬ ly around it a hollow wash drill rod (22) with an open front end is pressed into the ground, while a fluid flow is established through the guide drill rod and in the opposite direction through space between the guide drill rod and the wash drill rod.

4. Method according to claim 2 for exploring for raw materials, minerals or the like, characterized in that the drill rod (20) is provided at its front end with a survey tool and/or a sampling tool for examining characteristics and/or sampling the ground in the area surrounding the survey tool or the sampling tool, the survey tool and/or the sampling tool carrying out ground measurements, the measuring places and corresponding measuring results being recorded, during one or more intervals while pressing the drill rod into the ground, and/or during withdrawing the drill rod from the ground. 5. Method according to claim 3 for exploring for raw materials, minerals or the like, characterized by the following steps: on reaching the end of the drilling path, the guide drill rod (20) is withdrawn from the wash drill rod (22); a rod (42) provided at its front end with a measuring instrument (40) for examining characteristics of the ground in the area surrounding the measuring instrument is pressed into the wash drill rod (22) ; the wash drill rod (22) is withdrawn; and the rod (42) with the measuring instrument (40) is withdrawn, while the measuring instrument carries out ground measurements, the measuring places and corresponding measuring results being recorded.

6. Method according to claim 5, characterized in that prior to the introduction of the rod (42) with the measuring instrument (40) into the wash drill rod (22) , the course of the drilling path is determined by introducing a gyroscopic position-measuring instrument (34) into the wash drill rod until it is near the front end thereof, and subsequently withdrawing the instrument, while the instrument carries out position measurements, the results of which are recorded.

7. Method according to claim 2 for the extraction of raw materials, minerals or the like, characterized by the following steps: coaxially around the drill rod (20) , an outer production pipe (52) with an open front end is pressed over a predetermined distance into the ground; the drill rod is withdrawn from the outer production pipe (52) ; an inner production pipe (56) with an essentially open front end is pressed into the outer production pipe (52) until the front end of the inner production pipe (56) lies a short distance behind the front end of the outer production pipe (52) ; and a fluid flow is established through the inner production pipe (56) and in the opposite direction through space (60) between the inner production pipe (56) and the outer production pipe (52) . 8. Method according to claim 3 for the extraction of raw materials, minerals or the like, characterized by the following steps: after reaching the end of the drilling path, the wash drill rod (22) is withdrawn; coaxially around the guide drill rod (20) , an outer production pipe (52) with an open front end is pressed over a predetermined distance into the ground; the guide drill rod (20) is withdrawn from the outer production pipe (52) ; an inner production pipe (56) with an essentially open front end is pressed into the outer production pipe (52) until the front end of the inner production pipe (56) lies a short distance behind the front end of the outer production pipe (52) ; and a fluid flow is established through the inner production pipe (56) and in the opposite direction through space (60) between the inner production pipe (56) and the outer production pipe (52) . 9. Method according to claim 3 for the extraction of raw materials, minerals or the like, characterized by the following steps: after reaching the end of the drilling path, the guide drill rod (20) is withdrawn from the wash drill rod (22); an outer production pipe (52) and an inner production pipe (56) are pressed over a predetermined distance into the wash drill rod (22) simultaneously or one after the other, which pipes (52, 56) each have an essentially open front end, the outer production pipe (52) lying coaxially around the inner production pipe (56) , and the front end of the inner production pipe (56) being taken to a short distance behind the front end of the outer production pipe (52) ; the wash drill rod (22) is withdrawn completely or to at least behind the front end of the pipes (52, 56); and a fluid flow is established through the inner production pipe (56) and in the opposite direction through the space between the inner production pipe (56) and the outer production pipe (52) .

10. Method according to claim 9, characterized in that the inner production pipe (56) and the outer production pipe (52) are curved near the front end thereof and are pressed simultaneously into the wash drill rod (22) .

11. Method according to any of claims 7 - 10, characterized in that the fluid flow in the inner production pipe (56) is directed away from the front end thereof. 12. Method according to any of claims 7 - 11, characterized in that the assembly of inner production pipe (56) and outer production pipe (52) is withdrawn along the drilling path during the extraction.

13. Method according to claim 12, characterized in that prior to the withdrawal of the assembly of inner production pipe (56) and outer production pipe (52) a hollow second wash drill rod (66) with an open front end is pressed coaxially over the production pipes (52, 56) into the ground until it is near the end of the production pipes (52, 56) .

14. System for carrying out the method according to any of the preceding claims, comprising: means (21a, 21b) for the interconnection and disconnection of coaxial rods or pipes (20, 22) ; means for pressing the rods or pipes (20, 22) into the ground and removing them therefrom in an essentially horizontally directed manner for performing a guided horizontal drilling; and exploration means (34, 36, 38; 40, 42) or extraction means (52, 56) being guided by at least one of said rods or pipes (20, 22) during the introduction of the exploration or extraction means into the ground.

15. System according to claim 14, characterized in that said rods or pipes comprise a hollow drill rod (20) with an open front end, the system further comprising means for establishing a fluid flow through the drill rod and in the opposite direction along the outer surface of the drill rod.

16. System according to claim 14, characterized in

production pipe (52).

22. System according to claim 16 or 17, characterized in that the extraction means comprise an outer (52) and an inner (56) production pipe with an open front end, the outer production pipe (52) being adapted to be pressed coaxially around the guide drill rod (20) into the ground, the inner production pipe (56) being adapted to be pressed into the outer production pipe (52) when the guide drill rod (20) has been removed from it, the system further comprising means for establishing a fluid flow through the inner production pipe (56) and in the opposite direction through space between the inner production pipe (56) and the outer production pipe (52) .

23. System according to claim 16 or 17, characterized in that the extraction means comprise an outer (52) and an inner (56) production pipe with an open front end, the outer production pipe (52) being adapted to lie coaxially around the inner production pipe (56) , and being adapted to be pressed into the wash drill rod (22) , the system further comprising means for establishing a fluid flow through the inner production pipe (56) and in the opposite direction through space between the inner production pipe (56) and the outer production pipe (52) .

24. System according to claim 21, 22 or 23, characterized in that the front end of the outer production pipe (52) is provided with an opening (52a) whose cross- section increases in the axial forward direction.

25. System according to claim 23 or 24, characterized in that the inner production pipe (56) and the outer production pipe (52) are curved near the front end thereof.

26. System according to any of claims 21 - 24, characterized in that the front ends of the inner production pipe (56) and the outer production pipe (52) can be swung sideways.