Apparatus for cutting a drill collar

Abstract

 Apparatus 1 for cutting a drill collar of a well casing, com. prising a housing 2 for an explosive charge to be located in a well casing adjacent a drill collar and means 3 to centralize the apparatus 1 in a well casing 4 over varying diameters thereof. Variations in casing diameter are shown at x and y.

Description

[0001] The invention relates to apparatus for cutting a drill collar.

[0002] Wells such as sub-sea wells for the extraction of fossil fuel deposits such as oil and/or gas, are often drilled and subsequerrtly are closed down as they prove uneconomic. In such a case it is often necessary to sever a drill collar of the well, so that there is no underwater debris proud of the sea-bed. However, such drill collars can be u^p to 9½ inches (about 24 cms) thick. Severing such a structure in an often hostile environment can present grave problems, not least of which is that of satisfying the need to locate a cutter, usually an explosive charge, accurately within a well casing which can have varying internal diameters.

[0003] It is accordingly among the objects of the invention to seek to mitigate these disadvantages.

[0004] According to the invention there is provided apparatus for cutting a drill collar of a well casing, comprising a housing for an explosive charge, the housing being adapted for insertion in a cylindrical well casing adjacent a drill collar thereof, and means connectible with an end of the casing substantially to cent.ralize the housing in the well casing.

[0005] Using the invention it is possible to locate the apparatus by a wireline system downhole.

[0006] The centralizing means may comprise resilient means adapted to flex radially whereby to accommodate variations in diameter of a well casing.

[0007] There may be two resilient means, a first being at one end of the housing and a second at an axially opposite end of the housing, whereby the two resilient. means may be spaced apart axially of the apparatus.

[0008] The or each resilient means may comprise spaced bowed strip spring means carried by an elongate member.

[0009] The first resilient means may comprise two pairs of bowed strip means, and the pairs may be on opposite diametral sides of the elongate member, the opposite ends of the spring means being secured to respective rings encircling the elongate member, one of the rings being fixed and the other slidable on the elongate member.

[0010] The slidable ring may be between two further fixed rings, and a coil spring may encircle the elongate member between one of the further rings and the slidable ring, and a coil spring may encircle the elongate member between the other of the further rings and the slidable ring.

[0011] The bowed strip spring means may be pivotally secured to the respective rings.

[0012] The bowed strip spring means may be secured by a spring band means encircling the fixed ring.

[0013] The second resilient means may comprise two pairs of bowed strip spring means, the pairs being on opposite diametral sides of the elongate member, the opposite ends of the spring means being secured to respective rings encircling the elongate menber, one of the rings being fixed and the other slidable on the elongate member, and means on the elongate member to adjust the initial position of the slidable ring whereby to set the maximum lateral extent of the bowed strip means.

[0014] The adjusting means may comprise a ring having locking means whereby the ring can be locked in any desired position along the length of the elongate menber.

[0015] The ends of the bowed spring means may be secured to the fixed ring by crimping.

[0016] The elongate member may comprise a mandrel which carries electrical connections of the apparatus.

[0017] The mandrel may comprise a steel body with an internal elongate brass rod electrically insulated therefrom.

[0018] The brass rod may be coaxial with the steel body.

[0019] There may be plug means connecting the housing with the respective elongate members of the first and second centralizing means, and each plug means may have two cylindrical parts of different diameters whereby to provide plug and socket connections with the centralizing means and housing.

[0020] The apparatus may comprise crossover means for connecting the apparatus with a wireline suspension system.

[0021] The crossover means may be mounted at an end of the mandrel remote from the housing.

[0022] There may be an elongate extension member intermediate the housing and the mandrel, the extension member housing a detonator.

[0023] The plug means may connect the housing and the first centralizing means may include one or more vents whereby pressure waves and/or water in the well casing can be dispersed on detonation of the explosive charge.

[0024] Apparatus for cutting a drill collar is hereinafter described, by way of example, with reference to the accompanying drawings.

[0025] 

Figure 1 is a schematic elevational view of one embodiment of drill collar cutting apparatus according to the invention;

Figure 2 is, to an enlarged scale, a side elevational view of a first centralizing means of the apparatus;

Figure 3 is a part longitudinal sectional view of a first, or bottom, plug of the apparatus of Figure 1, and to a larger scale;

Figure 4 is a side elevational view, partly in longitudinal section, of a housing of the apparatus of Figure 1, and to a larger scale with the bottom plug and a top plug, in position;

Figure 5 is a side elevational view; partly in longitudinal section, of a second, or top, plug of the apparatus, and as shown in Figure 4;

Figure 6 is a side elevational view, partly in longitudinal section, of a mandrel of the apparatus of Figure 1, and to a larger scale than that Figure;

Figure 7 is a side elevational view, partly in longitudinal section, of a crossover body for use in the apparatus of Figure 1, and to a larger scale than that Figure;

Figure 8 is a side elevational view of a second centralizing means of the apparatus of Figure 1, and to a larger scale than t.hat Figure;

Figure 9 is a side elevational view, partly in longitudinal section, of a keystone for use in the apparatus of Figure 1 and to a larger scale than that Figure 1; and

Figure 10 is a side elevational view, partly in longitudinal section, of a modified appratus according to the invention.

[0026] Referring to the drawings, there is shown apparatus 1 for cutting a drill collar of a well casing, comprising a housing 2 for an explosive charge to be located in a well casing adjacent a drill collar and means 3 to centralize the apparatus 1 in a well casing 4 over varying diameters thereof. Variations in casing diameter are shown at x and y in Figure 1.

[0027] The centralizing means 3 in the embodiment illustrated comprises two resilient means spaced apart by the housing 2, the first or bottom (in use) resilient means 5 being connected to the housing by a first or bottom (in use) plug 6 at one end of the housing 2, which is tubular, and the second or top resilient means 7 being connected with the housing 2 at the opposite (or top in use) end by a second or top plug 8. The second resilient means 7 is mounted on a mandrel 9, which itself carries a crossover body or tool 10 of the apparatus 1.

[0028] The apparatus 1 thus includes in series, starting from the bottom (in use) end, the first resilient means 5, the bottom plug 6, the housing 2, the top plug 8, the mandrel 9 with the second resilient means 7 and the crossover body 10. The crossover body 10 connects the apparatus with a wireline system (not shown), which can be of any standard kind, for locating the apparatus 1 downhole, that is down an oil or gas well, for example.

[0029] There is also a keystone 11 including a fuse or detonator, in the housing adjacent the top plug 8 (Figure 9). The keystone 11 is effectively an electrical bayonet connection from piece to piece of the apparatus, so providing an earth return through the body of the apparatus.

[0030] The bottom resilient means 5 (Figure 2) comprises a central rod 12¹ on which are secured three spaced apart rings 12, 13 and 14 and a movable ring 15. Two spaced apart spring means, each in the form of a pair of outwardly bowed leaf springs 16, are pivotally secured between the rings 12 and 15. There is a coil spring 17 encircling the rod between the rings 13 and 15 and another coil spring 18 encircling the rod 12' between the rings 15 and 14. The rings and the rod are made of a suitable material such as steel.

[0031] The bottom plug (Figure 3) is made of a suitable material such as steel and has a body with a frusto-conical nose portion 19 and a generally cylindrical portion 20 with transverse tapped holes 21 which are aligned with holes in the housing when the cylindrical portion of the plug is inserted therein with a shoulder 22 abutting the free lower end of the housing. Screws or like securing means can then be inserted and screwed home to secure the plug 6 and housing 2 together. Likewise, the frusto-conical nose 19 has a splined bore 23 for receiving a splined end 24 of the rod 12, there being a transverse hole 25 for a fixing means such as a screw. The end 24 of the rod 12 butts against an inclined shoulder 26 in the bore 23, which leads to a bore part 27 of smaller diameter, which itself leads to a conical part 28, the nose of which leads to a bleed hole 29 extending along the longitudinal axis of the plug to a surface 30 of the portion 20. The bleed hole 29 communicates via the bore parts 28 and 27 with a bleed hole 31 extending from the external surface 32 of the frusto-conical nose 19 to the splined part of the bore. As the bore is splined, there is always fluid passage between the surface 30 and the surface 32. The plug is generally cylindrical below a shoulder, except for two flats 33 which assist in insertion of the plug in the housing.

[0032] The top plug 8 (Figure 5) is a hollow bar of suitable material such as steel. It has an end 34 for insertion into the upper in use end with a shoulder 35 for abutting against the free upper end of the housing 2 and diametrically opposed tapped holes 36 for receiving securing means such as screws inserted through holes in the housing 2 aligned with the holes 34 when the housing 2 and top plug 8 are assembled.

[0033] The opposite end of the top plug has an internal configuration for receiving the keystone 11 (Figure 9), which includes a fuse, and an external configuration for receiving a lower, in use, end of a mandrel 9, the main function of which is to carry the top centraliser and to provide an outer face between the crossover body 10 and the cutting tool (the housing 2 and its contents) part of the apparatus.

[0034] The mandrel 9 has an internal configuration 37 at one end to fit round the top plug 8 and keystone 11, and a configuration 38 at the other end to accommodate the crossover 10 (Figure 7). The mandrel 9 comprises a steel tube with a central brass rod insulated from the tube and thereby effecting electrical connection from the crossover body 10 to the keystone 11 and explosive charge. Mounted on the external surface of the mandrel is the second resilient means, or top centralizer 7 (Figure 8). This comprises two opposite spring means, each in the form of two substantially parallel leaf springs 39 which are bowed outwardly. The springs 39 are secured at one end by screws 43 to a ring 40 abutting a ring or collar 41 on the mandrel and at the opposite end by screws 44 to a collar 42 which is slidable on the mandrel 9. The ring 42 is adjustable in position longitudinally on mandrel 9. The collar 41 has a hole 45 for receiving a securing means such as an Allen screw. The collar 41 is slid along the mandrel to the correct axial position to give the correct length for correct outside diameter (O.D.) or lateral extent of the springs 39 for the particular bore hole inside diameter (I.D.) and locked in this position using the Allen keys. The springs 39, ring 40 and collar 41 can then slide up, away from each other, but not towards each other, and can thus go to smaller O.D. 's but not to too great an O.D. and thus cannot get stuck downhole, as described hereinafter.

[0035] The apparatus 1 is thus essentially a series of aligned members essentially secured together by plug and socket connections, symmetrical about a common longitudinal axis, which makes for a coherent, integral in-line structure.

[0036] The farthest lateral extent of the leaf springs 16 and 39 (which are symmetrically arranged about the axis of the apparatus) is such that they can brace against the interior surface of the well casing 4 to centralize the apparatus therein particularly at a position aligned with the drill collar (not shown). Further, as the apparatus 1 is being lowered into the well casing 4, the centralizers 5 and 7 contract and expand so that the apparatus 1 can pass through the narrowest part of the bore whilst still being centralized therein. This contraction and expansion is allowed by the rings 15, 40 and 42, which slide along the respective rod 12' or mandrel 9 as the leaf springs 16 or 39 are pressed inwardly, towards the axis of the apparatus, to accommodate the inward flexing of the springs when the springs encounter a narrowing of the well bore. When the narrow part is passed, the springs 16 and 39 flex outwardly again owing to their inherent resilience, and assisted in the case of the lower centralizer by the coil springs 17 and 18.

[0037] The apparatus 1 can thus pass through the narrowest bore of the well casing, but is always centralized in the bore, even at the widest part thereof. This ensures that when the explosive charge is detonated, the force of the explosion is distributed evenly round the apparatus transversely of a well casing to sever that casing. An apparatus embodying the invention can sever a drill collar up to 91 inches (about 24 cms) thick. The bleed bore 29 of the lower plug allows venting of fluid such as sea-water on explosion so seeking to obviate back pressure build up on explosion.

[0038] Referring to Figure 10, the apparatus 100 is similar to the apparatus 1, and functions in a similar manner. It has however an extension member 101 between housing 2 and top plug 8, which is itself connected in turn to the mandrel 9, and houses the keystone 11. The keystone 11 is connected by a hot wire 102 to a detonator 103 housed in the extension member 101, the detonator being housed in the hollow interior of the extension member 101. The extension member 101 has a reduced diameter "plug" 104 housing a fuse cap 105 for priming the fuse and detonating the charge in housing 2. The earth wire 106 is connected to the extension member 101 for the detonator 103.

[0039] Other modifications can, it will be understood, be incorporated. For example, in the lower centralizer 5, the springs 16 can be secured to the ring 12 in a different manner to the screws shown. Thus the ring can instead have a groove for the end of each spring 16 with a circumferential spring band holding the springs 16 in position. Moreover, the springs 39 can be secured to the rings 40 by providing longitudinal grooves in the rings 110, receiving the ends of the springs 39 on the grooves and upsetting the edges of the springs and grooves, by crimping over for example, to hold the springs physically in position.

[0040] The apparatus illustrated and described with reference to the drawings is thus able to withstand very great temperatures and pressure, while closely matchin performance to target thickness, that is the diameter of the drill collar to be cut.

[0041] It will be understood that the apparatus extends to a set of parts comprising the individual components hereinbefore described.

Claims

₁. Apparatus for cutting a drill collar for a well casing, characterised by a housing (2) for an explosive charge, by the housing (2) being adapted for insertion in a cylindrical well casing (4) adjacent a drill collar thereof, and by means (3) connectible with an end of the casing (2) substantially to centralize the housing (2) in the well casing (4).

2. Apparatus according to Claim 1, characterised by the centralizing means (3) comprising resilient means (5,7) adapted to flex radially whereby to accommodate variations in diameter of the well casing (4).

3. Apparatus according to Claim 2, characterised by a first resilient means (5) at one end of the housing (2) and by a second resilient means (7) at an axially opposite end of the housing (2).

4. Apparatus according to Claim 3, characterised by the resilient means (5) comprising spaced bowed strip spring means (16) carried by an elongate member (12') and by the resilient means (7) comprising spaced bowed strip spring means (39) carried by an elongate member (9).

5. Apparatus according to Claim 4, characterised by the first resilient means (5) comprising two pairs of bowed strip spring means (16), by the pairs (16) being on opposite diametral sides of the elongate member (12), by opposite ends of the spring means (16) being secured to respective rings (12,15) encircling the elongate member (12'), by one of the rings (12) being fixed to the elongate member (12'), and by the other of the rings (15) being slidable on the elongate member (12').

6. Apparatus according to Claim 5, characterised by the slidable ring (15) being between two further rings (13,14), by a coil spring (17) encircling the elongate member (12') and being between one of the further rings (13) and the slidable ring (15), and by a coil spring (18) encircling the elongate member (12') and being between the slidable ring (15) and the other of the further rings (14).

7. Apparatus according to Claim 6, characterised by the bowed strip spring means (16) being pivotally secured at their respective opposite ends to the respective rings (12,15).

.8. Apparatus according to Claim 6, characterised by the bowed strip spring means (16) being secured by a spring band means encircling the fixed ring (12).

9. Apparatus according to any of claims 4 to 8, characterised by the second resilient means (7) comprising two pairs of bowed strip spring means (39), by the pairs (39) being on opposite diametral sides of the elongate member (9), by the opposite ends of the spring means (39) being secured to respective rings (40, 42) encircling the elongate member (9), by the ring (42) being fixed, by the ring (40) being slidable on the elongate member (9), and by means (41) on the elongate member (9) to adjust the initial position of the slidable ring (4) whereby to set the maximum lateral extent of the bowed strip means (39).

10. Apparatus according to Claim 9, characterised by the adjusting means comprising a ring (41), and by the locking ring (41) having locking means (45) whereby the ring (41) can be locked in any desired position along the length of the elongate member (9).

11. Apparatus according to Claim 9 or Claim 10, characterised by the ends of the bowed spring means (39) being secured to the fixed ring (42) by crimping.

12. Apparatus according to any of Claims 9 to 11, characterised by the elongate member (9) comprising a mandrel which carries electrical connections of the apparatus (1), and by the mandrel (9) comprising a steel body with an internal elongate brass rod electrically insulated therefrom.

13. Apparatus according to any preceding claim, characterised by plug means (6,8) connecting the housing (2) with respective elongate members (9, 12') of the first and second centralizing means (5,7), and by each plug means having two cylindrical parts of different diameters whereby to provide plug and socket connections with the centralizing means (5,7) and housing (2).

14. Apparatus according to any preceding claim, characterised by crossover means (10), for connecting the apparatus (1) with a wireline suspension system, mounted at an end of the mandrel (9) remote from the housing (2).

15. Apparatus according to any of Claims 3 to 14, characterised by an elongate extension member (100) intermediate the housing (2) and the mandrel (9), and by a detonator (103) in the extension member (100).

16. Apparatus according to any of Claims 13 to 15, characterised by the plug means (6) having vent means (29) whereby pressure waves and/or water in the well casing (4) are dispersed on detonation of the explosive charge.

Drawing