SE541084C2 - Drill pipe and drill string - Google Patents

Abstract

The present invention relates to a drill pipe (1) comprising at least a central portion (2), a first end piece (3) and a second end piece (4), where the end pieces (3, 4) permit interconnection with mating parts of another drill pipe (1), said central portion (2) comprising a cylindrical tube, wherein said central portion (2) is arranged with an inner pipe (5) arranged at an inner wall (20) of said central portion (2) and having a wall thickness (t) which reduces the volume (V) of the void inside the central portion (2) with at least 10 %, more preferred at least 25 % and most preferred at least 50 %.

Description

DRILL PIPE AND DRILL STRING TECHNICAL FIELD The present invention relates to a drill pipe comprising at least a central portion, a first end piece and a second end piece, where the end piece permits interconnection with mating parts of another drill pipe, said central portion comprising a cylindrical tube.

STATE OF THE ART Drilling is an activity that humans have used for a long, long time. The Egyptians were drilling in stone already around 5,000 years ago and the Chinese drilled for oil in 300 AD. To make straight, deep and stable holes in land and rock, drilling is quite clearly the best technique. There are several drilling methods you can use to get underground.

Drilling into rock is performed to extract oil, heat, water and other natural materials deep underground and it is also possible to drill holes to build tunnels or lay pipes and cables. Since these structures can be several kilometers deep and long depending on what method is used, drilling offers great opportunities.

Drilling is also an alternative for laying pipes and cables in cities and densely populated areas where trenching, digging and blasting rock would be too expensive, noisy and extensive. Without creating major disturbances, a drilling operation can be performed from the same start and finish hole by drilling down into the earth.

A drilling operation requires a drill string and depending on the method used different accessories are required. A drill string comprises at least a drilling rig, a drill bit and a drill pipe. A drill pipe is a high strength steel pipe and depending on the drilling method and purpose of drilling, pipes come in different thickness and length with the most common lengths being 1 - 12 meters. Drill pipes are joined together one by one as the drill progresses deeper into the bedrock. Together, the pipes form a drill string which can extend several kilometers down into the ground. Some problems associated with drilling is that a lot of diesel is consumed to run the compressor that builds up the pressure in the drill string, which is bad from both environmental and economic perspectives.

It is previously known a drill pipe that is arranged with an inner pipe of steel, where the inner pipe is fixed to the end pieces of the drill pipe and thereby creating a double-pipe system in order to reduce the air volume. However, this pipe does not fulfil the demands set.

BRIEF DESCRIPTION OF THE INVENTION It is an object of the present invention to eliminate or at least minimize the above mentioned problems, which is achieved by means of a drill pipe according to the invention.

Thanks to the invention, a drill pipe with an inner pipe is provided where the inner pipe fills a portion of the void within said drill pipe and reduces the volume, giving the advantage that appropriate pressure of air is reached quicker inside the drill pipe.

According to one aspect of the invention, said inner pipe reduces the volume inside the drill pipe and since it requires less air to fill up the drill pipe less fuel is consumed. This offers great advantages both environmentally, economically and in a time saving perspective.

According to another aspect of the invention, the inner pipe has an outer diameter that is adapted to an inner diameter of a central portion of said drill pipe, in such a way that the outer side of the inner pipe is in a tight abutment to the inner side of said central portion, to fill up as much space as possible. Also, any water that may leak into the pipe will not be stuck in the space between the drill pipe and the inner pipe, which may cause damage to the pipes as the water may freeze. The water can flow down and out of the drill string and the compressed air will contribute to transporting the water during operation. The problem with known devices of increased weight due to accumulated water is avoided or at least minimized.

According to a further aspect of the invention, the inner pipe has an inner diameter that is arranged to be about the same as an inner diameter of an end piece of the drill pipe to not throttle the air flow, which is the case if the inner pipe has a smaller inner diameter than the end piece.

According to yet another aspect of the invention, the inner pipe comprises a lightweight and impermeable material which is an advantage since there are weight restrictions in those cases where the drill pipes are fed manually. Also, water absorption in the inner pipe material is avoided, which otherwise would increase the weight and possibly damage the inner pipe when freezing.

BRIEF DESCRIPTION OF FIGURES In the following, the invention will be described in greater detail with reference to the attached figures of the drawings, in which: Fig. 1 illustrates a drill pipe according to the invention, seen from the side, and Fig. 2 illustrates a cross sectional view of a drill pipe according to the invention, seen from the side.

DETAILED DESCRIPTION OF FIGURES The following detailed description and the examples contained therein, are provided for the purpose of describing and illustrating certain embodiments of the invention only, and are not intended to limit the scope of the invention in any way.

In DTH (down the hole) drilling a hammer is situated down the hole in direct contact with the drill bit. The hammer piston strikes the drill bit, resulting in an efficient transmission of the impact energy and insignificant power losses with the hole depth.

In rotary drilling, rotation is provided by a gearbox called a rotary head that moves up and down the tower via a feed system, generating the pulldown required to give sufficient weight on the bit. Flushing of drill cuttings between the wall of the hole and the drill rod is normally done with compressed air.

In a drilling operation a diesel-powered compressor builds up pressure in the drill pipe and a drill tool driven by the high air pressure strikes frequent strokes on a drill bit which simultaneously rotates. As the drill bit works its way down into the ground, the compressed air is immersed down to the rotary hammer through the drill pipe.

A drill string comprises a bottom hole assembly (BHA), which is the portion closest to the bit, a drilling rig and drill pipes that connect the surface equipment to the lowest part of the drill string.

In the following description is referred to air and compressed air and it shall be understood that both terms refers to compressed gaseous media unless otherwise indicated.

A drill pipe consists of three parts, a central portion and two end pieces. The end piece contains either a male or a female thread, which permits interconnection of two drill pipes. The three parts are usually welded together, although other methods of joining the parts, such as gluing or screwing, which allow rotation of the drill string and provide an airtight joint are of course conceivable.

Figure 1 shows a side view of a drill pipe 1 according to the invention. The drill pipe 1 comprises at least three parts, a central portion 2, a first end piece 3 and a second end piece 4. The first end piece 3 comprises female threads and the second end piece 4 comprises male threads, which permit interconnection with mating parts of another drill pipe 1 in a conventional manner. Any of the ends, i.e. the first end piece 3 and the second end piece 4, may be the leading end and be directed downwards in the hole. Both procedures occur. In a preferred embodiment, the central portion 2 is preferably a cylindrical tube and has an outer diameter Di which is adapted to the application. The diameter Di is normally in the interval 30 - 500 mm, preferably in the interval 40 - 300 mm and more preferred in the interval 50 - 100 mm. In the illustrated example the outer diameter Di is 70 mm and the effective length L of the drill pipe 1 (an outer part 41 of the second end piece 4 which comprises the male threads that will be threaded into a first end piece 3 with female threads excluded) is 3 m, but the skilled person realizes and knows that drill pipes are available in all sort of lengths within a range of 1 - 12 m. The central portion 2 has a length L’ that is 2692 mm in this described example. The three parts, the central portion 2, the first end piece 3 and the second end piece 4 are welded together at a first joint 6 and a second joint 7. For this purpose, the first end piece 3 and the second end piece 4 comprise a respective cylindrical tube section 30, 40 having the same diameter and wall thickness as the tube of the central portion 2, although the skilled person understands that the cylindrical section may be omitted. The first end piece 3 and the second end piece 4 may comprise wrench flats 43, 44 used when the pipes are dismantled.

Figure 2 illustrates a cross sectional view of a drill pipe 1 according to the invention in a longitudinal direction. The central portion 2 has a wall thickness T which is adapted to the application. The wall thickness T is normally in the interval 3 - 40 mm, preferably in the interval 3 - 25 mm and more preferred in the interval 4 - 16 mm. In this described example the wall thickness T is 4 mm. When assembling the drill pipe 1, one of the end pieces is first welded to the central portion 2. Thereafter, an inner pipe 5 is arranged inside the central portion 2 and finally the other end piece is welded to the central portion 2.

The outer diameter of the end pieces 3, 4 are preferably the same. The inner diameter D4of the male end piece 4 is smaller than the inner diameter D3of the female end piece 3, which is a requisite for this particular design of the end pieces as the strength in the threaded portion of the male piece would otherwise be too low.

In the preferred embodiment, the inner pipe 5 preferably has a length 1 that is shorter than the length L’ of the central portion 2, in order to not be damaged by the heat of welding. In the preferred embodiment, the inner pipe 5 has a length 1 that is 80 - 95 % of the length L’ of said central portion 2. In this described example the inner pipe 5 has a length 1 that is 2680 mm. The skilled person realizes that said inner pipe 5 may have a length 1 that is as long as or even longer than said central portion 2. This may be the case if the first end piece 3 and the second end piece 4 comprise a respective cylindrical tube section 30, 40. The skilled person also understands that the inner pipe may comprise several pipe sections placed one after the other in the central portion 2 until appropriate length is obtained.

The inner diameter d’ of the inner pipe 5 shall be small in order to reduce the required volume of air according to the inventive concept. However, the inner diameter d’ shall not be too small as the pressure loss will affect the drilling operation. For this reason, the inner pipe 5 has a wall thickness t, which is adapted to the inner diameter d’ of the inner pipe 5 such that the inner diameter d’ of the inner pipe 5 is about the same as the inner diameter D4of the male end piece 4 or slightly wider. The wall thickness is in the interval 1 - 100 mm, preferably in the interval 3 - 30 mm and more preferred in the interval 5 - 15 mm. In this described example the inner pipe 5 has a wall thickness t that is 10 mm. In the preferred embodiment, said inner pipe (5) is unfixedly arranged inside the central portion 2. The outer diameter d of the inner pipe 5 is preferably arranged such that when the inner pipe 5 is pressed into the central portion 2 the outer side of the inner pipe 5 is in a tight abutment to the inner side of the central portion 2. However, preferably not tighter than that the inner pipe 5 may be moved towards the opposite end when the final welding is performed, in order to protect the inner pipe 5 against the heat from the welding. The inner pipe 5 preferably has an outer diameter d in the interval 30 - 500 mm, preferably in the interval 40 - 300 mm and more preferred in the interval 50 - 100 mm. In this described example the outer diameter d is 60 mm.

The inner pipe 5 preferably consists of a material with resistance to compression up to 45 bars and impermeability of liquid. An example of such material is plastics. Plastics also give the advantage such as light weight. The inner pipe 5 fills a portion of the void within the central portion 2 and reduces the volume that needs to be filled with compressed air. In the preferred embodiment, the inner pipe 5 has a wall thickness t, which reduces the volume V of the void inside the central portion 2 with at least 10 %, more preferred 25 % and most preferred at least 50 %. This gives the advantage that the appropriate pressure of the air is reached quicker inside the drill pipe 1. In the described example, about 4 liters of air is required when the drill pipe 1 is arranged with the inner pipe 5, while about 10 liters of air is required to fill up the drill pipe 1 if the inner pipe 5 is excluded.

Another advantage is that since less air is required to fill up the drill pipe 1 less fuel is consumed. Instead of 2 liters of diesel per meter drilled, it takes 1.5 liters of diesel per meter drilled. This offers great advantages both environmentally and economically. Since less air is required to fill up the drill pipe 1 the filling is quicker and the required pressure to start the hammer is obtained faster.

Yet another advantage is obtained in the step of mounting the drill pipes to the drill string during the progress of the drilling. Since the amount of pressurized air inside the drill string is significantly reduced the release of the pressure becomes safer and also in this step a significant time reduction is achieved.

It is also advantageous that the inner pipe 5 is made of a lightweight material, such as plastics, since there are weight restrictions in those cases where the drill pipes 1 are fed manually.

Other advantages of having an inner pipe that fills the volume within the central portion 2 is that, when the volume is smaller, more pressure is generated to the hammer. The inner pipe 5 also absorbs vibrations which mutes the sound.

When drilling at high altitudes, such as in mines at high altitudes, there is a problem of compressing air and getting it forward to the hammer. Thanks to the drill pipe 1 according to the invention having a smaller volume to fill this problem is reduced.

Another advantage is obtained in the manufacturing process. As the length of the inner pipe 5 is easily adapted, e.g. by cutting, to any length of the central pipe section 2, the drill pipe may be manufactured in various lengths.

ALTERNATIVE EMBODIMENTS The invention is not limited to the embodiment described above. In a variant of the invention, the inner pipe extends into the end pieces 3, 4 and the inner pipe’s ends are formed to follow the inner wall of the bridging portion between the cylindrical tube section and thicker wall portion of the end pieces 3, 4. This may be advantageous in order to avoid or at least reduce turbulence and pressure loss due to variations in the diameter of the air channel in the portions before and after the inner pipe’s ends. In this variant it may be advantageous to arrange a recess at the outside of wall of the inner tube 5 in the area where the joint (e.g. weld) between the central portion 2 and the respective end pieces 3, 4 in order to avoid damage during the joining procedure.

It is also understood that in order to obtain desired thickness of the wall of the inner pipe 5, several pipes with gradually increasing diameter may be arranged outside one another in order to form a body. The pipes may be manufactured from different materials such that a layered structure may be obtained which fulfill a combination of properties otherwise difficult to obtain. For example, polyurethane foam may resist pressure up to 45 bar and to some extent is impermeable. However, any water that may leak into the pipe may damage the ends of a polyurethane pipe when freezing. Also, air bumps occurring inside the drill string may damage the ends and fragments of polyurethane may fall off and damage the function of hammer. The ends are preferably encapsulated in order to prevent this. Polyurethane may also be arranged as a central lightweight layer which is sandwiched between an inner and outer layer of plastics or other more impermeable material.

The skilled person also realizes that the inventive idea to fill a drill pipe with an inner pipe applies to all kinds of drill pipes and not just the variant described above, the inventive idea comprises drill pipes of different materials and with different thread connections. Also, it is realized that in some applications the inner diameter d’ of the inner pipe 5 may be smaller than the diameter D4of the end piece although that may throttle the air. The end pieces may be designed in other ways, several variants are known, and the invention is not limited to the variants described herein.

Claims (10)

1. Drill pipe (1) adapted to be connected to a compressor that builds up air pressure in the drill pipe (1), wherein the drill pipe (1) comprising at least a central portion (2), a first end piece (3) and a second end piece (4), where the end pieces (3, 4) permit interconnection with mating parts of another drill pipe (1), said central portion (2) comprising a cylindrical tube, characterized in that said central portion (2) is arranged with an inner pipe (5) arranged in connection with an inner wall (20) of said central portion (2) and having a wall thickness (t) which reduces the volume (V) of the void inside the central portion (2) with at least 10 %, and in that) said drill pipe (1) is adapted to be connected to a drill tool, driven by the air pressure, that strikes frequent strokes on a drill bit which simultaneously rotates.

2. Drill pipe according to claim 1, characterized in that said inner pipe (5) has an outer diameter (d) that is adapted to an inner diameter (D2) of said central portion (2), in such a way that the outer side of said inner pipe (5) is in a tight abutment to the inner side of said central portion (2).

3. Drill pipe according to any of preceding claims, characterized in that said inner pipe (5) comprises a lightweight and impermeable material, preferably plastics.

4. Drill pipe according to claim 1, characterized in that the inner pipe (5) extend into said end pieces (3, 4).

5. Drill pipe according to claim 4, characterized in that the outer side of the inner pipe’s end is formed to closely abut the inner side of a bridging portion between the central section (2) and said end piece (3, 4).

6. Drill pipe according to any of preceding claims, characterized in that the inner pipe (5) comprises a layered structure having several pipes with gradually increasing diameter arranged outside one another.

7. Drill pipe according to claim 5, characterized in that said inner pipe (5) has a central lightweight layer which is sandwiched between an inner and outer layer of impermeable material.

8. Drill pipe according to any of preceding claims, characterized in that said inner pipe (5) comprises several pipe sections placed one after the other.

9. Drill pipe according to any of preceding claims, characterized in that said inner pipe (5) is unfixedly arranged inside said central portion (2).

10. A drill string comprising at least a drilling rig, a drill bit and a drill pipe (1), wherein the drill pipe (1) is a drill pipe (1) according to any one of claims 1-9.