SE1750921A1 - Drill pipe - 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 TECHNICAL FIELD The present invention relates to a drill pipe comprising at least a central portion, a firstend piece and a second end piece, Where the end piece perrnits 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 Weredrilling in stone already around 5,000 years ago and the Chinese drilled for oil in 300AD. 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 materialsdeep underground and it is also possible to drill holes to build tunnels or lay pipes andcables. Since these structures can be several kilometers deep and long depending on What method is used, drilling offers great opportunities.

Drilling is also an altemative for laying pipes and cables in cities and densely populatedareas Where trenching, digging and blasting rock Would be too expensive, noisy andextensive. 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 differentaccessories are required. A drill string comprises at least a drilling rig, a drill bit and adrill pipe. A drill pipe is a high strength steel pipe and depending on the drilling methodand purpose of drilling, pipes come in different thickness and length With the mostcommon lengths being l - 12 meters. Drill pipes are joined together one by one as thedrill progresses deeper into the bedrock. Together, the pipes form a drill string Whichcan eXtend several kilometers down into the ground. Some problems associated Withdrilling is that a lot of diesel is consumed to run the compressor that builds up thepressure 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 theinner pipe is fixed to the end pieces of the drill pipe and thereby creating a double-pipesystem 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 abovementioned 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 pipefills 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 thedrill pipe and since it requires less air to fill up the drill pipe less fuel is consumed. Thisoffers 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 isadapted to an inner diameter of a central portion of said drill pipe, in such a way that theouter 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 notbe stuck in the space between the drill pipe and the inner pipe, which may cause damageto the pipes as the water may freeze. The water can flow down and out of the drill stringand 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 thatis arranged to be about the same as an inner diameter of an end piece of the drill pipe tonot 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 lightweightand imperrneable 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 forthe 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 contactwith 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 upand down the tower via a feed system, generating the pulldown required to givesufficient weight on the bit. Flushing of drill cuttings between the wall of the hole and the drill rod is norrnally done with compres sed air.

In a drilling operation a diesel-powered compressor builds up pressure in the drill pipeand a drill tool driven by the high air pressure strikes frequent strokes on a drill bitwhich 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 tothe bit, a drilling rig and drill pipes that connect the surface equipment to the lowest partof the drill string.

In the following description is referred to air and compressed air and it shall beunderstood 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 piececontains either a male or a female thread, which permits interconnection of two drillpipes. The three parts are usually welded together, although other methods of joiningthe 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 1comprises at least three parts, a central portion 2, a first end piece 3 and a second endpiece 4. The first end piece 3 comprises female threads and the second end piece 4comprises male threads, which permit interconnection with mating parts of another drillpipe 1 in a conventional manner. Any of the ends, i.e. the first end piece 3 and thesecond 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 acylindrical tube and has an outer diameter D1 which is adapted to the application. Thediameter D1 is norrnally in the interval 30 - 500 mm, preferably in the interval 40 - 300mm and more preferred in the interval 50 - 100 mm. In the illustrated example the outerdiameter D1 is 70 mm and the effective length L of the drill pipe 1 (an outer part 41 ofthe second end piece 4 which comprises the male threads that will be threaded into afirst end piece 3 with female threads excluded) is 3 m, but the skilled person realizesand 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. Thethree parts, the central portion 2, the first end piece 3 and the second end piece 4 arewelded together at a first joint 6 and a second joint 7. For this purpose, the first endpiece 3 and the second end piece 4 comprise a respective cylindrical tube section 30, 40having 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. Thefirst 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 alongitudinal direction. The central portion 2 has a wall thickness T which is adapted tothe application. The wall thickness T is normally in the interval 3 - 40 mm, preferablyin 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 isarranged 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 D3 of 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. ln the preferred embodiment, the inner pipe 5 preferably has a length l that is shorterthan the length L” of the central portion 2, in order to not be damaged by the heat ofwelding. In the preferred embodiment, the inner pipe 5 has a length l that is 80 - 95 %of the length L” of said central portion 2. In this described example the inner pipe 5 hasa length l that is 2680 mm. The skilled person realizes that said inner pipe 5 may have alength l that is as long as or even longer than said central portion 2. This may be thecase if the first end piece 3 and the second end piece 4 comprise a respective cylindricaltube section 30, 40. The skilled person also understands that the inner pipe maycomprise 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 requiredvolume of air according to the inventive concept. However, the inner diameter d” shallnot 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 theinner pipe 5 such that the inner diameter d” of the inner pipe 5 is about the same as theinner diameter D4 of the male end piece 4 or slightly wider. The wall thickness is in theinterval l - 100 mm, preferably in the interval 3 - 30 mm and more preferred in theinterval 5 - 15 mm. In this described example the inner pipe 5 has a wall thickness t thatis 10 mm. In the preferred embodiment, said inner pipe (5) is unfixedly arranged insidethe central portion 2. The outer diameter d of the inner pipe 5 is preferably arrangedsuch that when the inner pipe 5 is pressed into the central portion 2 the outer side of theinner 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 endwhen the final welding is performed, in order to protect the inner pipe 5 against the heatfrom the weldin g. 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. ln this described example the outer diameter d is 60 mm.

The inner pipe 5 preferably consists of a material With resistance to compression up to45 bars and imperrneability of liquid. An example of such material is plastics. Plasticsalso give the advantage such as light Weight. The inner pipe 5 fills a portion of the voidWithin the central portion 2 and reduces the volume that needs to be filled Withcompressed 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 theappropriate pressure of the air is reached quicker inside the drill pipe 1. In the describedexample, about 4 liters of air is required When the drill pipe 1 is arranged With the innerpipe 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 isconsumed. Instead of 2 liters of diesel per meter drilled, it takes 1.5 liters of diesel permeter 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 drillstring during the progress of the drilling. Since the amount of pressurized air inside thedrill 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 asplastics, 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 portion2 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 ofcompressing 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 innerpipe 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 EMBODHVIENTS The invention is not limited to the embodiment described above. In a variant of theinvention, the inner pipe eXtends into the end pieces 3, 4 and the inner pipe”s ends areforrned to follow the inner wall of the bridging portion between the cylindrical tubesection and thicker wall portion of the end pieces 3, 4. This may be advantageous inorder to avoid or at least reduce turbulence and pressure loss due to variations in thediameter of the air channel in the portions before and after the inner pipe”s ends. In thisvariant it may be advantageous to arrange a recess at the outside of wall of the innertube 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 innerpipe 5, several pipes with gradually increasing diameter may be arranged outside oneanother in order to form a body. The pipes may be manufactured from differentmaterials such that a layered structure may be obtained which fulfill a combination ofproperties otherwise difficult to obtain. For example, polyurethane foam may resistpressure up to 45 bar and to some extent is imperrneable. However, any water that mayleak into the pipe may damage the ends of a polyurethane pipe when freezing. Also, airbumps occurring inside the drill string may damage the ends and fragments ofpolyurethane may fall off and damage the function of hammer. The ends are preferablyencapsulated in order to prevent this. Polyurethane may also be arranged as a centrallightweight 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 innerpipe applies to all kinds of drill pipes and not just the variant described above, theinventive idea comprises drill pipes of different materials and with different threadconnections. Also, it is realized that in some applications the inner diameter d” of theinner pipe 5 may be smaller than the diameter D4 of the end piece although that maythrottle 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 (1)

1. l. Drill pipe (l) comprising at least a central portion (2), a first end piece (3) and asecond end piece (4), Where the end pieces (3, 4) perrnit interconnection Withmating parts of another drill pipe (l), said central portion (2) comprising acylindrical tube, characterized in that said central portion (2) is arranged Withan inner pipe (5) arranged in connection With an inner Wall (20) of said centralportion (2) and having a Wall thickness (t) Which reduces the volume (V) of thevoid inside the central portion (2), Wherein the inner pipe (5) has an outerdiameter in the interval 30 - 500 mm and the Wall thickness (t) is in the interval1-100 mm. Drill pipe according to claim 1, characterízed in that said inner pipe (5) has anouter diameter (d) that is adapted to an inner diameter (Dg) of said centralportion (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). Drill pipe according to claim l or 2, characterízed in that said inner pipe (5)has an inner diameter (d”) that is the same as an inner diameter (D4) of said second end piece (4) or slightly Wider. Drill pipe according to any of preceding claims, characterized in that said inner pipe (5) comprises a lightWeight and impermeable material, preferably plastics. Drill pipe according to claim 1, characterízed in that the inner pipe (5 ) eXtend into said end pieces (3, 4). Drill pipe according to claim 5, characterízed in that the outer side of the innerpipe”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). Drill pipe according to any of preceding claims, characterized in that the innerpipe (5) comprises a layered structure having several pipes With gradually increasing diameter arranged outside one another. 5 8. Drill pipe according to claim 6, characterized in that said inner pipe (5) has acentral li ghtwei ght layer Which is sandwiched between an inner and outer layer of impermeable material. 9. Drill pipe according to any of preceding claims, characterized in that said inner pipe (5) comprises several pipe sections placed one after the other. 10. Drill pipe according to any of preceding claims, characterized in that said inner pipe (5) is unfiXedly arranged inside said central portion (2).