WO2018106121A1

WO2018106121A1 - Apparatus and method for collecting debris from a wellbore

Info

Publication number: WO2018106121A1
Application number: PCT/NO2017/050315
Authority: WO
Inventors: Bjarte Andreassen
Original assignee: Bri Well Services As
Priority date: 2016-12-06
Filing date: 2017-12-05
Publication date: 2018-06-14
Also published as: NO342058B1; NO20161942A1

Abstract

An apparatus (1) for collecting debris from a wellbore and a method for collecting and bringing debris out from a well, the apparatus (1) comprises a pipe (3) having a first end portion (5) and a second end portion (7) for connecting to a drill pipe string, the first end portion (5) of the pipe being provided with a milling device (9), the apparatus (1) further comprises: - a conduit (11) extending along an outer portion of the pipe (3), the conduit (11) having an inlet (13) for receiving debris, and an outlet (15); - a housing (20) enclosing at least a portion of the conduit (11) and the pipe (3); the housing (20), the pipe (3) and outer portions of the conduit (11) defining a debris collection chamber (25) for receiving debris discharged from the outlet (15) of the conduit (11); and - a strainer (30) for preventing debris exceeding a predetermined size from leaving the debris collection chamber (25), wherein the apparatus (1) is provided with releasable engagement means (40) for selectively engaging and disengaging the housing (20) with respect to the pipe (3), and that the housing (20) is axially displaceable with respect to the pipe (3) when the engagement means (40) has been disen- gaged.

Description

APPARATUS AND METHOD FOR COLLECTING DEBRIS FROM A WELLBORE

The present invention relates to an apparatus and a method for collecting unwanted material in a wellbore. More particularly, the invention relates to an apparatus and a method for collecting debris from a wellbore. The apparatus comprises a pipe having a first end portion and a second end portion for connecting to a drill pipe string. The first end portion of the pipe is provided with a milling device. The apparatus further comprises: a conduit extending along an outer portion of the pipe, the conduit having an inlet for receiving debris passing the milling device, and an outlet; a housing enclosing at least a portion of the conduit and the pipe, the housing, the pipe and outer portions of the conduit defining a debris collection chamber for receiving debris discharged from the outlet of the conduit; and a strainer for preventing debris exceeding a predetermined size from leaving the debris collection chamber.

An apparatus of the above mentioned type is commonly denoted a junk collector. A junk collector is typically used for removing debris in completion and maintenance operations of a well in the oil and gas industry. By the term debris is meant any unwanted loose or fixed removable material or objects within the well that may adversely affect the well.

Publication GB 2 206 508 discloses a junk collector having "shelves" intended to collect junk when a fluid flow is given a centrifugal movement.

Publication US 4 603 739 discloses a junk collector comprising scrapers gliding along a casing wall thereby bringing the collected junk into a chamber in the junk collector. The chamber is closed by valves. By means of these valves, the material is collected in the chamber which can later can be brought up to the surface and emptied.

Further junk collectors are disclosed in the publications US 4 703 804, US 4 838 354 and

US 1 472 213.

Publication GB 2 295 838 B, which is regarded as the closest prior art to the present invention, discloses an apparatus for collecting and bringing up unwanted material from an oil or gas well. The apparatus comprises a grinder or mill and a coating of a wear resistant material along its front and outer surfaces. The mill is secured to a throughgoing drilling pipe having an inner centric liquid channel. An axially leading facing end of the mill comprises a channel extending through the mill and into a junk chamber behind or after the mill. An upper end of the apparatus comprises a strainer allowing penetration of liquid, but restraining the material . A rotation of the apparatus from the throughgoing drilling pipe thereby ensuring that junk is brought into the channel and into the junk chamber.

The apparatus disclosed in GB 2 295 838 B has been utilized by the present applicant for years and has proven suitable for collecting loose and jammed material or objects in both vertical wells and deviated or horizontal wells.

However, the prior art apparatus disclosed in GB 2 295 838 B is encumbered with some drawbacks.

The apparatus is assembled by means of a threaded connection arranged in the throughgoing drilling pipe. Thus, in order to open the apparatus for emptying the junk chamber, the apparatus must be disconnected from the drilling string, and rig tongs must be utilized for making and breaking the threaded connection. This is an undesired process both with respect to economy and with respect to a health and safety aspect; to economy because of occupying valuable rig time, and to health and safety because using rig tongs is considered dangerous work for the operator. Further, in order to avoid a weak link within the apparatus, the parts of the drilling pipe provided with the threaded connection, must be provided with an enlarged outer diameter. An enlarged outer diameter pipe will occupy a valuable volume that could otherwise be used for storing collected material within the junk chamber. Still another disadvantage of the apparatus disclosed in GB 2 295 838 B is that the mill is secured to a first drilling pipe, while the housing of the junk chamber is secured to a second drilling pipe which is to be threadedly connected to the first drilling pipe. Because the junk chamber is connected to the second drilling pipe, there is only limited access for cleaning the volume between the drilling pipe and the housing of the junk chamber.

Publication US 6 189 617 discloses a sand-capturing tool comprising tubing segments assembled without treading. The apparatus is lowered into the wellbore on a wire or coiled tubing.

The invention has for its object to remedy or to reduce at least one of the drawbacks of the prior art, or at least to provide a useful alternative to prior art.

The object is achieved through features, which are specified in the description below and in the claims that follow.

The invention is defined by the independent patent claims. The dependent claims define advantageous embodiments of the invention.

According to a first aspect of the present invention, there is provided an apparatus for collecting debris from a wellbore. The apparatus comprises a pipe having a first end portion and a second end portion for connecting to a drill pipe string, the first end portion of the pipe provided with a milling device. The apparatus comprises: a conduit extending along an outer portion of the pipe, the conduit having an inlet for receiving debris, and an outlet; a housing enclosing at least a portion of the conduit and the pipe; the housing, the pipe and outer portions of the conduit defining a debris collection chamber for receiving debris discharged from the outlet of the conduit; and a strainer for preventing debris exceeding a predetermined size from leaving the debris collection chamber. The apparatus is provided with releasable engagement means for selectively engaging and disengaging the housing with respect to the pipe, and the housing is axially displaceable with respect to the pipe when the engagement means has been disengaged.

This has the effect that the only housing is configured for moving with respect to all other parts of the apparatus when the debris collection chamber is to be cleaned or emptied for collected debris. By moving the housing only, there is no need for disconnecting the apparatus from the drilling string. Valuable rig time is therefore saved and dangerous work with rig tongs in so-called "red zone" is avoided. Further, displacing the housing axially with respect to the pipe of the apparatus and the drill string connected to the apparatus, has the positive effect that the housing is not separated from the pipe or drill pipe, only moved axially there along. The operation of the apparatus therefore does not involve any loose parts that may represent a safety risk for personnel involved in the operation of the apparatus.

In order to displace the housing axially onto the drilling pipe connected to the apparatus, the internal diameter of the housing is equal to or larger than a diameter of the drilling pipe.

The releasable engagement means may comprise at least one screw operable through a bore in a wall of the housing. The screw is configured for directly or indirectly engagement with the pipe to prevent rotation and axial displacement of the housing with respect to the rest of the apparatus. Preferably, the bore extends axially with respect to a centre axis of the housing.

The bore in the wall of the housing may comprise an inner bore and an outer bore. The diameter of the outer bore extending from the outer surface of the wall of the housing may be smaller than the diameter of the inner bore extending from the inner surface of the wall. Further, a head of the screw may have a diameter that is larger than the diameter of the bore extending from the outer surface of the wall. This has the effect that the screw is "trapped" in the bore extending from the inner surface of the wall of the housing. In order to release the housing from the rest of the apparatus, the screw must in such an embodiment be screwed inwards, i.e. towards the centre of the pipe, by means of a tool operated through the smaller diameter outer bore extending from the outside of the wall.

In one embodiment, the load bearing capacity of the apparatus is provided by means of the pipe connected at the first and second end portions to the drilling pipe. The connection is provided by means of pin and box connections similar to those used for connecting stands of drilling pipes. This has the effect that the housing may be designed for no axial load bearing capacity, and consequently be relatively thin. However, a thin wall may represent a limited engagement of the engagement means, such as a screw discussed above. Therefore, the bore may be arranged in a portion of the housing having an enlarged thickness with respect to the rest of the housing. In one embodiment, an enlarged thickness of the housing is provided by means of a gauge ring secured to the housing preferably by a welded connection. However, a threaded connection is also conceivable.

The pipe within the debris collection chamber may be provided with magnets for retaining any magnetic debris. Any magnetic debris retained by the magnets, may be released therefrom by a scraper or any other suitable device. To facilitate use of said scraper, it is an advantage if the magnets are arranged in indents of the pipe such that an outer surface of the magnets is substantially flush with an outer surface of the pipe.

Because of the housing being axially displaceable with respect to the pipe, easy access to the surface of the pipe portion being a part of the debris collection chamber may be obtained. Such an access facilitates cleaning of for example any magnets.

The outlet of the conduit for leading the debris from the milling device and into the debris collection chamber may be closer to the second end portion of the pipe than to the first end portion of the pipe.

The apparatus may be provided with a fitting for connection to a flushing main. This allows for flushing the debris collection chamber being provided with a limited opening only, a limited axial displacement of the housing, that is. Preferably, the fitting is provided at an end portion of the debris collection chamber.

In a second aspect of the present invention there is provided a method for collecting and bringing debris from a well, the method comprising:

- connecting the apparatus according to the first aspect of the invention to a drill string;

- running the apparatus into the well and collecting debris by pumping through and rotating the drill string;

- bringing the apparatus out of the well ;

- releasing the engagement means to disengage the housing from engagement with the pipe;

- axially displacing the housing with respect to the pipe so that an opening for allowing emptying of the debris collection chamber is provided.

The housing may be displaced axially away from the first end portion of the pipe. The first end portion comprises the milling device which will normally constitute a leading portion of an apparatus when run in a well. Therefore, at a surface of the well, typically on a rig, the first end portion of the apparatus connected to a drill string will be the lower portion of an apparatus. Therefore "rising" the housing with respect to the lower portion of the apparatus will facilitate emptying of the apparatus. The method may further comprise flushing the debris collection chamber.

In the following is described an example of a preferred embodiment illustrated in the accompanying drawings, wherein :

Fig. 1 shows a prior art junk collector disclosed in GB 2 295 838 B;

Fig. 2 shows an apparatus according to the present invention, wherein the apparatus is in a debris collection mode;

Fig. 3a shows in larger scale a detail A shown in fig 2;

Fig. 3b shows in larger scale a detail A1 shown in fig 3a;

Fig. 4 shows the apparatus in fig. 2, but with a housing of the apparatus axially displaced with respect to the rest of the apparatus;

Fig. 5a shows in larger scale detail B shown in fig. 4;

Fig. 5b shows in larger scale a detail B1 shown in fig 5a;

Fig. 6a shows in larger scale a cut through l-l shown in fig. 2;

Fig. 6b shows in larger scale a cut through ll-ll shown in fig. 2;

Fig. 7 shows in larger scale a cut through Ill-Ill shown in fig. 3a;

Fig. 8a shows a plan view of a strainer for use in the apparatus;

Fig. 8b shows a cut through X-X shown in fig. 8a;

Fig. 8c shows a cut through Y-Y shown in fig. 8a; and

Fig. 8d shows a cut through Z-Z shown in fig. 8a.

In figure 1 , the original reference numerals used in GB 2 295 838 B have been added a "P" (P for Prior art) in order to distinguish prior art reference numerals from reference numerals used in figures 2 to 8d showing embodiments of the present invention.

In the figures disclosing the present invention, same or corresponding elements are indicated by same reference numerals. For clarity, some elements may in some of the figures be without reference numerals.

For illustrative reasons, the relative proportions of some of the elements may be somewhat distorted. In what follows, positional specifications, such as for example upper, lower, inner and outer, refer to the positions that are shown in the drawings.

Fig. 1 shows a prior art apparatus, disclosed in GB 2 295 838 B, for collecting and bringing up unwanted material or junk from an oil or gas well. The apparatus comprises a grinder or mill P6 having a coating P8 of a wear resistant material along its front and outer surfaces. The mill P6 is secured to a throughgoing drilling pipe having an inner concentric liquid channel P7. An axially leading face end of the mill P6 comprises a channel P4 extending through the mill P6 and into a junk chamber P3 behind or after the mill P6. The upper end of the apparatus comprises a strainer P2 allowing penetration of liquid, but restraining the material. Rotation of the apparatus is provided by means of rotating the throughgoing drilling pipe. Upon rotation of the apparatus, junk is brought into the channel P4 and from said channel P4 into the junk chamber P3.

Turning now to figures 2 to 8d, showing embodiments of the present invention, it will be noted that the present invention has some similarities with the apparatus disclosed in GB 2 295 838 B.

In figures 2 to 8d, the reference numeral 1 discloses an apparatus for collecting debris from a well- bore. The apparatus 1 comprises a pipe 3 having a first end portion 5 and a second end portion 7. Each of the first end portion 5 and the second end portion 7 is provided with a pin and a box, respectively, for threaded connection with complementary box and pin portions of a drill pipe string (not shown).

The first end portion 5 of the pipe 3 is provided with a milling device 9. The milling device 9 is provided with a cutter 1 0 comprising or coated with a material being resistant to wear, such as tungsten carbide known from the coating P8 shown in fig. 1 .

The apparatus 1 comprises a conduit 1 1 extending along an outer portion of the pipe 3. The conduit 1 1 has an inlet 13 for receiving fluid containing any debris passing the milling device 9, i.e. typically torn loose by the milling device 9 when the apparatus 1 is rotated by means of the drill pipe string, and an outlet 15. The fluid containing any debris is urged into the inlet 13 of the conduit 1 1 by means of fluid circulated down the drill pipe string and out of an end portion thereof.

The conduit 1 1 is secured to the pipe 3 by means of a suitable fastening means, such as for example a clamping device or a weld. In a prototype of the apparatus 1 , the conduit 1 1 is fixed by means of a clamping device.

In the embodiment shown, the outlet 15 is deviated with respect to a longitudinal axis L of the apparatus 1 . This is to provide a centrifugal effect to fluid flowing out of the conduit 1 1 . In one embodiment, at least a portion of the conduit 1 1 extends in spiral around the pipe 3.

The apparatus 1 further comprises a housing 20 enclosing the conduit 1 1 and a portion of the pipe 3 being between the milling device 9 and the second end portion 7. Thus, in the embodiment shown, a lower end portion of the housing 20 abuts an upper end portion of the milling device 9. A lower end portion of the housing 20 is therefore located substantially at the inlet 13 of the conduit 1 1 .

A debris collection chamber 25 is formed within portions of the housing 20. In the embodiment shown, the debris collection chamber 25 is defined by the housing 20, outer portions of the conduit 1 1 , the pipe 3, the upper end of the first end portion 5, and a strainer 30 arranged at an upper end portion of the housing 20. The strainer 30 is configured for preventing debris exceeding a predetermined size from leaving the debris collection chamber 25 together with fluid flowing out through openings 32 (see for example fig. 7) of the strainer 30.

In the embodiment shown, the outlet 1 5 of the conduit 1 1 is arranged at an upper portion of the debris collection chamber 25, i.e. closer to the second end portion 7 of the pipe 3 than the first end portion 5 of the pipe 3. In the embodiment shown, the outlet 15 will not be covered by collected debris until a substantial portion of the debris collection chamber 25 has been filled with debris.

In fig. 2, the apparatus 1 is in an operating or debris collection mode. A lower end portion of the housing 20 abuts an upper end of the first end portion 5 and thereby forms a "closed" debris collection chamber 25.

The housing 20 is locked with respect to the pipe 3, and thus the rest of the apparatus 1 , by means of releasable engagement means 40, which in the embodiment shown is cap screws 40 having a longitudinal axis extending radially with respect to the longitudinal axis L of the apparatus 1 . The cap screws 40 are shown in fig. 3a and fig. 3b which show in a larger scale detail A of fig. 2 and detail A1 of fig. 3a, respectively. Although two or more screws 40 are preferred for safety reasons, the apparatus 1 may be provided with only one screw.

As seen in fig. 3b, the at least one screw 40 is operable through a bore 21 , 2Γ in the wall of the housing 20. The bore 21 , 21 ^' consists of an outer bore 21 and an inner bore 21 ^'. A diameter of the outer bore 21 extending from the outer surface of the wall is smaller than the diameter of the inner bore 21 ^' extending from the inner surface of the wall. A head 41 of the screw 40 has a diameter being larger than the outer bore 21 through the outer surface of the wall. Therefore, the screw 40 is "trapped" in the inner bore extending from the inner surface of the wall of the housing 20. In order to release the housing 20 from the rest of the apparatus 1 , the screw 40 must be screwed inwards, i.e. towards the centre of the pipe 3, by means of a tool operated through the smaller diameter outer bore 21 extending from the outside of the wall of the housing 20. Thus, the screws 40 are configured for selective engagement and disengagement of the housing 20 with respect to the pipe 3 as will be apparent from fig. 3 and fig. 5.

To prevent the screws 40 from an unintentional radial movement outwards, which could result in disengagement of the housing 20 with respect to the pipe 3, each screw 40 may be locked by means of a locking screw 43 arranged in an inclined bore.

The screws 40 are screwed into a bore 34 in a portion of the strainer 30. The bore 34 is best seen in fig. 3b and fig. 8b. The strainer 30 is connected to the pipe 3. Thus, the screws 40 are indirectly connected to the pipe 3.

The bore 21 , 2Γ is provided in an upper portion 20^' of the housing 20 having an enlarged thickness as compared with the rest of the housing 20. The enlarged thickness makes possible a sufficient radial movement of the screws 40 to provide a secure engagement of the head 41 of the screw 40 within the inner bore 21 ^' in the wall of the housing 20.

The upper portion 20^' of the housing 20 is in the embodiment shown as a ring element 20^' that has been securely connected to the rest of the housing 20, typically by means of a weld (not shown). The ring element 20^' is aligned coaxially with the pipe 3 by means of supporting plates 44 arranged spaced apart around the pipe 3. The supporting plates 44 are secured to the pipe 3, typically by means of a weld (not shown).

To facilitate axial movement of the housing 20, the upper portion 20^' of the housing 20 is provided with bores (not shown) for receiving for example shackles used for connecting to a hoisting device.

In fig. 4, a portion of the debris collection chamber 25 has been exposed to the surroundings by displacing the housing 20 axially upwards, for example by means of a hoisting device. This axial displacement has been prepared by screwing the screws 40 inwards as shown in fig. 5a which shows in a larger scale detail B of fig. 4, and in fig. 5b which shows in a larger scale detail B1 of fig. 5a.

The axial displacement of the housing 20 with respect to the rest of the apparatus 1 , and also with respect to the drill pipe string to which the apparatus 1 is connected, is very different from the breaking of the pipe connection P1 1 within the prior art apparatus disclosed in GB 2 295 838. Contrary to the teaching of GB 2 295 838, the axial displacement of the housing 20 with respect to the rest of the apparatus 1 according to the present invention makes possible emptying or cleaning of the debris collection chamber 25 without any rig tongs and without having to disconnect the apparatus 1 from the drill pipe string. By providing a one-piece pipe 3 through the apparatus 1 , there is no threaded pipe connection, cf. P1 1 of GB 2 295 838, representing a possible weak link.

In the embodiment shown in figures 2, 3a, 4, 5a and 5b, an upper portion of the pipe 3 within the debris collection chamber 25 is provided with magnets 50 for retaining any magnetic debris. Although shown only in an upper portion of the pipe 3, it should be clear that in an alternative embodiment other portions of the pipe 3 may be provided with magnets 50. In one embodiment, substantially all of the length of the pipe 3 forming part of the debris collection chamber 25 is provided with magnets 50. In the embodiment shown, the magnets 50 are arranged in indents in the wall of the pipe 3 so that an outer surface of the magnets 50 is substantially flush with an outer surface of the pipe 3. This renders possible easy releasement of magnetic debris retained by the magnets 50. Such a "cleaning" of the magnets may typically be performed by moving a scraper (not shown) along the longitudinal axis L of the apparatus 1 after exposing the debris collection chamber 25 to the surroundings.

Arranging the magnets 50 on or in a portion of the pipe 3, has advantages with respect to arranging the magnets P14 and P15 as suggested in GB 2 295 838 wherein the magnets are arranged in a front or lower area of the collection chamber to an outer wall P5 of the chamber or to the mill P6. In order to prevent magnetic influence to the outside of the wall P5, GB 2 295 838 suggests isolating the magnets P14 from the outer wall P5. Further, arranging the magnets 50 along a portion of the pipe 3 is very advantageous with respect to the working space or "range of operation" of the magnets 50. In the present invention, the magnets 50 may be arranged along the length of the debris collection chamber 25, and especially at or near the outlet 15 of the conduit 1 1 . Thus, at least some magnets 50 will be capable of collecting magnetic debris also after a portion of the debris collection chamber 25 has been filled with debris. Thus, the risk of magnetic debris entering the strainer 30 is reduced. In the prior art apparatus disclosed in GB 2 295 838, the magnets P14 and P15 will be effective only when filling of the chamber P3 commences.

In a prototype of the apparatus 1 , magnets 50 having a diameter of 20 mm and 90N force were used.

Fig. 6a is a cut through l-l in fig. 2 and shows a possible configuration of the conduit 1 1 which is connected to the pipe 3. In the embodiment shown, a portion of an outer surface of the pipe 3 forms a portion of the conduit 1 1 . The housing 20 encloses the conduit 1 1 and the pipe 3. The debris collection chamber 25 is defined between the housing 20, the pipe 3 and radially extending walls 1 1 ^' of the conduit 1 1 .

In an alternative embodiment (not shown), the conduit 1 1 is formed by means of the radially extending walls 1 1 ^' only, together with an inner surface of the housing 20, i.e. without an outer wall 1 1 ^" of the conduit 1 1 as in the embodiment shown in fig. 6a. This alternative embodiment may be advantageous if any debris is stuck within the conduit 1 1 ; access to the internal of the conduit 1 1 is easily obtained by displacing the housing 20 axially with respect to the rest of the apparatus 1 , including the radially extending walls 1 1 ^'.

Fig. 6b is a cut through ll-ll in fig. 2 and shows an embodiment of the milling device 9 enclosing a portion of the pipe 3 at the first end portion 5 of the apparatus 1 . The milling device 9 comprises cutters 10. The cutters 10 are aligned with the inlet 13 of the conduit 1 1 . The cutters 10 typically comprise a wear resistant material such as for example tungsten carbide. It should be noted that the cutters 10 extend also in the longitudinal direction of the apparatus 1 , as indicated in fig. 2.

Fig. 7 is a view through Ill-Ill in fig. 3a and shows the strainer 30 arranged within an upper portion 20^' of the housing 20. The strainer 30 is provided with a plurality of holes 32, and is arranged at a distal end portion of the four supporting plates 44 shown.

The strainer 30 may further be provided with a fitting such as a hose coupling 33 for connecting a fluid line to the apparatus 1 . Thus, the debris collection chamber 25 may be flushed for example by means of water or air. Such a flushing may be performed with the housing 20 only slightly displaced axially towards the second end portion 7 of the apparatus 1 . By the term slightly is meant a few centimeters, for example 10 cm. A positive effect of having a small discharge opening in the debris collection chamber 25 is that debris can be collected in a very controlled manner at the lower end portion of the apparatus 1 . This again has a positive effect with respect to health and safety for operators emptying the debris collection chamber 25.

Details of the strainer 30 is shown in figures 8a to 8d. Fig. 8a is a plan view of the strainer 30.

Fig. 8b is a cut through X-X in fig. 8a and shows radially extending bores 34 in the strainer 30. Each of the two bores 34 shown are provided with a threaded portion 35 for engaging with a threaded portion of the screw 40 shown for example in fig. 3b, and a head receiving portion 36 configured for receiving substantially the entire head of the screw 40. Thus, the screw 40 can be screwed into the strainer 30 and disengaged from the housing 20.

Figures 8c and 8d are cuts through Y-Y and Z-Z, respectively, in fig. 8a and show that the holes 32 extend inclined with respect to the longitudinal axis L of the apparatus 1 between an inner face facing the debris collection chamber 25, and an outer face facing the second end portion 7 of the apparatus 1 . The purpose of the inclination of the holes 32 is to reduce the risk for debris clogging the holes or flowing through the holes.

Now turning now back to fig. 3a, it should be noted that the upper portion 20^' of the housing 20 extends downstream of the strainer 30, i.e. beyond that side of the strainer 30 which faces the second end portion 7 of the apparatus 1 . The purpose of such a configuration is inter alia to provide a so- called boot basked capable of collecting any loose junk or debris during the trip out of the drill pipe string with the apparatus 1 .

In the embodiment shown in fig. 2, only one apparatus 1 is shown. However, it should be clear that two or more apparatuses 1 according to the present invention may be arranged in series. For example, a first end portion 5 of one apparatus 1 , may be connected to a second end portion 7 of another apparatus 1 according to the present invention, so that two apparatuses 1 are arranged in tandem. In such a tandem arrangement, a milling device 9 of a leading part of the apparatus 1 , may have an operating diameter being less than a milling device 9 of a trailing part of the apparatus 1 , i.e. the "second" apparatus in the tandem arrangement. This has the effect that the smaller diameter milling device 9 of the leading apparatus 1 scrapes one radial portion of the wellbore, while the larger diameter milling device 9 of the trailing apparatus 1 scrapes the rest of the radial portion of the wellbore. Thus, a longer distance of the wellbore may be cleaned in one trip of the apparatus 1 . Again, emptying or cleaning of the apparatus 1 may be performed without having to break any parts of the apparatus 1 or drill pipe string. The apparatus 1 according to the present invention is very effective and very safe compared with the prior art apparatus disclosed in

GB 2 295 838.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim . Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

C l a i m s

1 . An apparatus (1 ) for collecting debris from a wellbore, the apparatus (1 ) comprises a pipe (3) having a first end portion (5) and a second end portion (7) for connecting to a drill pipe string, the first end portion (5) of the pipe (3) being provided with a milling device (9), the apparatus (1 ) further comprises:

- a conduit (1 1 ) extending along an outer portion of the pipe (3), the conduit (1 1 ) having an inlet (13) for receiving debris, and an outlet (1 5) ;

- a housing (20) enclosing at least a portion of the conduit (1 1 ) and the pipe (3); the housing (20), the pipe (3) and outer portions of the conduit (1 1 ) defining a debris collection chamber (25) for receiving debris discharged from the outlet (15) of the conduit (1 1 ); and

- a strainer (30) for preventing debris exceeding a predetermined size from leaving the debris collection chamber (25),

c h a r a c t e r i s e d i n that the apparatus (1 ) is provided with releasable engagement means (40) for selectively engaging and disengaging the housing (20) with respect to the pipe (3), and that the housing (20) is axially displaceable with respect to the pipe (3) when the engagement means (40) has been disengaged.

2. The apparatus (1 ) according to claim 1 , wherein the releasable engagement means comprises at least one screw (40) operable through a bore (21 , 21 ^') in a wall of the housing (20).

3. The apparatus (1 ) according to claim 2, wherein the bore (21 , 21 ^') comprises an inner bore (21 ') and an outer bore (21 ), the diameter of the outer bore (21 ) extending from the outer surface of the wall, is smaller than the diameter of the inner bore (21 ^') extending from the inner surface of the wall, and wherein a head (41 ) of the screw (40) has a diameter being larger than the bore (21 ) at the outer surface of the wall.

4. The apparatus (1 ) according to claim 2 or 3, wherein the bore (21 , 21 ^') is arranged in a portion of the housing (20) having an enlarged thickness.

5. The apparatus (1 ) according to any one of the preceding claims, wherein the pipe (3) within the debris collection chamber (25) is provided with magnets (50).

6. The apparatus (1 ) according to claim 1 , wherein the outlet (15) of the conduit (1 1 ) is closer to the second end portion (7) of the pipe (3) than to the first end portion (5) of the pipe (3).

7. The apparatus (1 ) according to any of the preceding claims, wherein the apparatus (1 ) is further provided with a fitting (33) for connecting to a flushing main.

8. A method for collecting and bringing debris out from a wellbore, the method comprising:

- connecting the apparatus (1 ) according to any one of the preceding claims to a drill string;

- running the apparatus (1 ) into the well and collecting debris by pumping through and rotating the drill string;

- bringing the apparatus (1 ) out of the well, c h a r a c t e r i s e d i n that the method further comprises the following steps:

- releasing the engagement means (40) to disengage the housing (20) from engagement with the pipe (3);

- axially displacing the housing (20) with respect to the pipe (3) so that an opening for allowing emptying of the debris collection chamber (25) is provided.

9. The method according to claim 8, wherein the housing (20) is displaced axially away from the first end portion (5) of the pipe (3).

10. The method according to claim 8 or 9, the method further comprising flushing the debris collection chamber (25).