GB2179124A - Explosive cutting device - Google Patents

Abstract

A cutting device for cutting tubulars comprises a tubular casing 1, containing a pack of explosives made up from a number of explosive pellets 2. A first detonator 3 is mounted at one end of the casing 1 and is connected by a first fuse 6 to a second detonator 4 adjacent the nearer end of the explosive pack and connected by a second fuse 7 to a third detonator 5 adjacent the opposite end of the explosive pack. The first and second fuses 6 and 7 are of equal length with one of the fuses being flexible to conform to relative movement between the second and third detonators. <IMAGE>

Description

SPECIFICATION Cutting device This invention relates to a cutting device.

During oil drilling operations the drill string, due to a variety of reasons, may become stuck in the drilled bore. Initially, it is normal to attempt to free the pipe mechanically. However, should this fail an explosive charge may be lowered into the pipe and exploded above the point where the pipe is stuck. The explosion cuts the pipe and allows the operator to retrieve a substantial amount of downhole apparatus which would otherwise have been lost.

According to the present invention there is provided a cutting device for cutting tubulars comprising a casing containing an explosive charge, first detonating means connected by a first fuse to a second detonating means adjacent a first end portion of the explosive charge and connected by a second fuse to a third detonating means adjacent a second end portion of the explosive charge, the first and second fuses being of equal length and at least one of the fuses being flexible along its length so as to conform to any relative movement between the second and third detonating means.

Preferably, the explosive charge comprises a plurality of cylindrical pellets of explosive material selected according to the magnitude of explosive force required.

Preferably also, a fuse assembly, accommodating the first fuse, is located at an end portion of the casing, the fuse assembly being provided with a first clamp at one end portion and a second clamp at a second end portion, the first and second detonating means being mounted in the first and second clamps respectively.

Preferably also, the third detonating means is mounted in a clamp located at the opposite end portion of the casing to the fuse assembly.

Preferably also, the second and third detonating means are located on the central longitudinal axis of the explosive charge.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a sectional side view of a first embodiment of a cutting device of the present invention; Figure 2 is an end view of a third booster clamp of the cutting device of Fig. 1; Figure 3 is a sectional side view of the fuse assembly of the cutting device of Fig. 1; Figure 4 is an end view of a booster clamp of the cutting device of Fig. 1; Figure 5 is an end view of the booster clamp of Fig. 4 showing the hidden detail; Figure 6 is an end view of an explosive pellet of a cutting device of the present invention; Figure 7 is a side view of the explosive pellet of Fig. 6; and Figure 8 is a sectional side view of a second embodiment of a cutting device of the present invention.

Referring to Figs. 1 to 7 of the drawings, a cutting device for cutting pipes or tubulars comprises a tubular casing 1, shown by broken lines, containing a pack of explosives made up from a number of explosive pellets 2, detonating means in the form of a first booster 3 at one end of the casing 1 connected by a first fuse 6 to detonating means in the form of a second booster 4 adjacent the nearer end of the explosive pack and connected by a second fuse 7 to detonating means in the form of a third booster 5 adjacent the opposite end of the explosive pack.

The first and second fuses 6 and 7 are of equal length and the second fuse 7 is contained within an armoured flexible cable 8.

A cylindrical fuse assembly 9 is located within the casing 1 and contains the first fuse 6. A disc shaped clamp 10 is provided at one end of the assembly 9 and has a central stepped through bore 11 (Fig. 3).

The larger diameter portion of the stepped bore 11 is occupied by the R.D.X. filled first booster 3. The ends of the fuses, 6 and 7, run from the fuse assembly 9 through the smaller diameter portion of the bore 11 to the booster 3.

Another through bore 12 is provided towards the outer edge of the clamp 10 and contains the end of the armoured cable 8.

The cable 8 is secured in the bore 12 by two socket headed screws (not shown) which are located in two threaded holes 1 5 provided in the clamp 10.

From the clamp 10 the first fuse 6 extends, in the form of a helical coii, through the sylguard potting filled fuse assembly 9 to a second clamp 13 at the opposite end of the fuse assembly 9.

The second clamp 13 is similar to the first clamp 10 and is provided with a stepped through bore 16 and a through bore 17 towards the outer edge of the clamp 13.

The first fuse 6 passes from the fuse assembly 9 through the smaller diameter portion of the stepped bore 16 into the R.D.X. filled second booster 4.

The cable 8 passes through and is secured in position in the other through bore 17.

The cable 8 which contains the second fuse 7, extends from the first clamp 10 through the fuse assembly 9 and the second clamp 13. From the second clamp 13 the cable 8 passes along an outer edge of the explosive pack to a third clamp 18. The cable 8 passes through a notch 19 in the clamp 18 and turns to the centre of the clamp 18 where a stepped bore 20 is provided.

The larger portion of the bore 20 contains the R.D.X. filled third booster 5. The second fuse 7 extends from the end of the cable 8 and passes through the smaller portion of the bore 20 into the booster 5.

The dotted lines of Fig. 1 represent the clamp 18 in the in use position.

The explosive charge is made up from a number of cylindrical explosive pellets 2. The pellets 2 are located in the casing 1 between the second and third clamps 13 and 18. A longitudinal notch 21 is provided in each of the pellets 2 to accommodate the cable 8 which carries the second fuse 7.

When the device is to be used to cut a pipe, for example, an operator must first decide what size of explosive charge is required.

When this has been calculated the number of pellets 2 necessary to produce this size of charge is placed in the casing 1. The third clamp 18 is then placed in the casing 1 such that the pellets 2 are tightly packed in the casing between the second and third clamps 13 and 18.

The device may then be lowered down the bore of a drill string which has become jammed against removal to just above the point where jamming has occurred.

An initiation signal is then applied to the first booster 3 from where signals travel along the first and second fuses 6 and 7, to the second and third boosters, 4 and 5, causing simultaneous detonation of the opposite ends of the explosive charge. Thus, the full explosive force is developed in the lateral plane at the centre of the charge and the pipe is parted by the force of the explosion.

The flexible nature of the cable 8 allows the operator to fit a different number of pellets 2 into the device without major modification of the device.

Referring now to Fig. 8, a second embodiment of a cutting device has a tubular casing 100 which contains an explosive charge (not shown). One end portion of the casing 100 is occupied by a cylindrical fuse assembly 109 which contains a first fuse 106 and is provided with a first booster 103 and clamp 110 at one end and a second booster 104 and clamp 111 at the opposite end.

The first fuse 106 is helically wound and connects the first booster 103 to the second booster 104.

The opposite end portion of the casing is provided with a third booster 105 mounted in a clamp 118. The first booster 103 is connected to the third booster by a second fuse 107 which is contained within a flexible stainless steel Bowden cable 108. The first and second fuses, 106 and 107, are of equal length.

The explosive charge used in the device is made up from explosive pellets 2 as shown in Figs. 6 and 7.

When the device is to be assembled the fuse assembly 109 is taken out of the casing 100 and the number of pellets 2 required are placed in the casing 100. The fuse assembly 109 is then replaced in the casing 100 which has previously been cut to the desired length, the flexible second fuse 107 being bent to suit the length of the casing 100.

A retainer 115 is placed in the casing 100 to hold the fuse assembly 109 in place.

By activating a detonator assembly 120 adjacent the first booster 103 the explosive charge may be exploded.

Modifications and improvements may be made without departing from the scope of the invention.

Claims (6)

1. A cutting device for cutting tubulars comprising a casing containing an explosive charge, first detonating means connected by a first fuse to a second detonating means adjacent a first end portion of the explosive charge and connected by a second fuse to a third detonating means adjacent a second end portion of the explosive charge, the first and second fuses being of equal length and at least one of the fuses being flexible along its length so as to conform to any relative movement between the second and third detonating means.

2. A cutting device as claimed in Claim 1 wherein the explosive charge comprises a plurality of cylindrical pellets of explosive material.

3. A cutting device as claimed in Claim 1 or 2, wherein a fuse assembly, accommodating the first fuse, is located at an end portion of the casing, the fuse assembly being provided with a first clamp at one end portion and a second clamp at a second end portion, the first and second detonating means being mounted in the first and second clamps respectively.

4. A cutting device as claimed in Claim 3 wherein the third detonating means is mounted in a clamp located at the opposite end portion of the casing to the fuse assembly.

5. A cutting device as claimed in any one of the preceding Claims wherein the second and third detonating means are located on the central longitudinal axis of the explosive charge.

6. A cutting device substantially as hereinbefore described and with reference to the accompanying drawings.