Pre-fragmented shaped charge

Abstract

The present invention provides an apparatus and method for controlling the debris generated by shaped charges during perforating. The controlled debris perforating system comprises a pre-fragmented shaped charge having a charge case and an explosive material.

Description

FIELD OF THE INVENTION

[0001] The subject matter of the present invention relates to a pre-fragmented shaped charge for use in perforating operations. More specifically, the subject matter of the present invention relates to controlling the debris generated by the shaped charges during perforating.

BACKGROUND OF THE INVENTION

[0002] In drilling operations, the drilled hole is often lined with a casing to prevent the earth from filling the hole. In order for the surrounding fluid to enter the drilled hole, the well casing must be perforated. Such operation is typically performed by a perforating gun loaded with one or more shaped charges.

[0003] Conventional shaped charges produce significant debris upon detonation. If small enough, the generated debris can exit the gun carrier and enter the well fluid and become entrained in the well fluid. The exit of the debris can occur both during detonation and during the retrieval process of the carrier to the surface. As the debris is carried by the well fluid, it can complicate down stream processing of the well fluids by clogging filters and jamming pumps, for example.

[0004] There exists, therefore, a need for controlling the size of debris generated during perforating operations.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] FIG. 1 is a cross-sectional view of a typical shaped charge, loading tube, and hollow carrier.

[0006] FIG. 2 is a perspective view of a typical shaped charge and loading tube.

[0007] FIG. 3 is a perspective view of a loading tube being inserted into a hollow carrier.

[0008] FIG. 4 illustrates an embodiment of the pre-fragmented shaped charge.

[0009] FIG. 5 provides a top view of an embodiment of the pre-fragmented charge case having 6 slots.

[0010] FIG. 6 provides a top view of an embodiment of the pre-fragmented charge case having 2 slots.

[0011] FIG. 7 provides a top view of an embodiment of the pre-fragmented charge case having 4 slots.

[0012] FIG. 8 illustrates an embodiment of the pre-fragmented charge casing having V-notch slots.

[0013] FIG. 9 illustrates an embodiment of the pre-fragmented charge casing having U-notch slots.

[0014] FIG. 10 illustrates an embodiment of the pre-fragmented charge case having internal slots.

[0015] FIG. 11 illustrates an embodiment of the pre-fragmented charge case having circumferential slots.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0016] FIG. 1 provides an illustration of a typical shaped charge, indicated generally as 1, used for perforating a well casing. Typical shaped charges for use in perforating guns are discussed in U.S. Pat. No. 4,724,767 to Astatine issued Feb. 16, 1988; U.S. Pat. No. 5,413,048 to Warner et al. issued May 9, 1995; U.S. Pat. No. 4,669,384 to Chawla et al. issued Jun. 2, 1987; and again in U.S. Pat. No. 5,597,974 to Voreck, Jr. et al. issued Jan. 28, 1997. Each of the above mentioned disclosures are incorporated by reference into this specification.

[0017] A typical shaped charge 1 includes a case 10, a main body of explosive material 12, which in the past has been, for example, RDX, HMX, PYX, or HNS packed against the inner wall of the case 10, a primer 13 disposed adjacent the main body of explosive 12 that is adapted to detonate the main body of explosive 12 when the primer 13 is detonated, and a liner 14 lining the primer 13 and the main body of explosive material 12. The liner 14 acts to maintain the shape of the explosive to assure proper propagation of the detonation. A detonating cord 20 contacts the case 10 of the shaped charge 1 at a point nearest the apex of the liner 14 of the charge. When a detonation wave propagates within the detonating cord 20, the detonation wave will detonate the primer 13. When the primer 13 is detonated, the detonation of the primer 13 will further detonate the main body of explosive 12 of the charge 1. In response to the detonation of the main body of explosive 12, the liner 14 will form a jet that will propagate along a longitudinal axis of the shaped charge 1. The jet will perforate a formation penetrated by the wellbore.

[0018] One or more shaped charges 1 are housed within a loading tube 22 for transport. The loading tube 22 can house the shaped charges 1 at desired orientations, or in a linear fashion. A jacket 24 is used to both secure the shaped charges 1 to the loading tube 22 and to maintain the orientation of the shaped charges 1. Once the loading tube 22 is ready for delivery downhole, a hollow carrier 30 is used to carry the loading tube 22 and housed shaped charges 1.

[0019] In one conventional use shown in FIGS. 2 and 3, the shaped charges 1 and jackets 24 are inserted into the loading tube 22 until the jackets 24 shoulder against the loading tube shoulders 23. Once all of the shaped charges 1 are secured, the loading tube 22 is inserted into the interior of the hollow carrier 30. The hollow carrier 30 then transports the shaped charges 1 downhole to the desired depth of perforation.

[0020] It should be noted that the above description of the convention shaped charges 1 is intended for illustration only and not intended to limit the scope of the present invention. The present invention is equally applicable for use in alternate shaped charges and carriers. For example, the present invention can be used with equal applicability with jacket-less shaped charges.

[0021] FIG. 4 illustrates one embodiment of the pre-fragmented shaped charge, indicated generally as 40, of the present invention. Slots, or grooves, 42 are cut into the charge case 44 to weaken the case 44 according to a certain pattern or design. Upon detonation of the pre-fragmented shaped charge 40, the case material is subject to explosion forces and will undergo stretching in its hoop direction. Because the slots 42 are cut in the axial direction orthogonal to the hoop stretching, the slots 42 define weakening lines along the stretching direction. As a result, the charge case 44 will fracture along these lines of weakness. In this manner, the pre-fragmented shaped charge 40 can be used to control the size and shape of the debris generated by the charge case 44 during perforating operations. The slots 42 in the pre-fragmented shaped charge 40 can also be used to channel the explosion energy in certain directions. Such channeling of explosive energy improves the survivability of the gun carrier 30.

[0022] As shown in FIGS. 5-7, the pre-fragmented shaped charge 40 can be designed with any number of slots 42. As examples, FIG. 5 displays a charge case 44 having 6 slots 42, FIG. 6 displays a charge case 44 having 2 slots 42, and FIG. 7 displays a charge case 44 having 4 slots 42. It should be understood that any number of slots 42 can be cut into the charge case 44 depending upon the application. Because the distance between the slots 42 controls the size of the generated debris, for applications in which it is desired to make the debris larger than the exit hole in the hollow carrier 30 (shown in FIG. 3), the pre-fragmented shaped charge 40 may have fewer slots 42. Conversely, when it is desired to make the debris very small, such as when the shaped charge 40 is used for spiral or strip guns, the charge case 44 may have many slots 42.

[0023] In addition to variances in the number of slots 42, the slots 42 cut into the charge case 44 can be of multiple shapes and sizes. FIGS. 8 and 9 illustrate two example slot 42 designs. In FIG. 8, the slot 42 cut into the wall of the case 44 is a V-notch groove, while in FIG. 9, the slot 42 cut into the wall of the case 44 is a U-notch groove. The shape and depth of the slot 42 controls the timing of the breakup of the charge case 44.

[0024] Another embodiment of the pre-fragmented shaped charge 40 is illustrated in FIG. 10. In this embodiment, the slots 42 are cut on the internal surface of the charge case 40.

[0025] Yet another embodiment of the pre-fragmented shaped charge 40 is illustrated in FIG. 11. In this embodiment, the slots 42 are oriented circumferentially around the charge case 40. The circumferential slots 42 can be internal or external.

[0026] The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such are intended to be included within the scope of the following non-limiting claims.

Claims

1. A controlled debris perforating system, comprising: a pre-fragmented shaped charge having a charge case and an explosive material.

2. The controlled debris perforating system of claim 1, wherein the charge case defines at least one slot.

3. The controlled debris perforating system of claim 2, wherein the at least one slot is axially oriented.

4. The controlled debris perforating system of claim 2, wherein the at least one slot is circumferentially oriented.

5. The controlled debris perforating system of claim 2, wherein the at least one slot is a U-notched groove.

6. The controlled debris perforating system of claim 2, wherein the at least one slot is a V-notched groove.

7. The controlled debris perforating system of claim 2, wherein the at least one slot is an external slot.

8. The controlled debris perforating system of claim 2, wherein the at least one slot is an internal slot.

9. A method of controlling the debris during perforating, comprising: providing a pre-fragmented shaped charge having a charge case defining a plurality of grooves.

10. The method of claim 9, wherein the plurality of grooves are axially oriented.

11. The method of claim 9, wherein the plurality of grooves are circumferentially oriented.

12. A shaped charge made by a process, comprising: inserting an explosive into a case; inserting a liner over the main body of explosive; and machining a plurality of slots in the case.

13. The shaped charge made by the process of claim 12, wherein the plurality of slots are U-notched grooves.

14. The shaped charge made by the process of claim 12, wherein the plurality of slots are V-notched grooves.

15. The shaped charge made by the process of claim 12, wherein the plurality of slots are machined externally.

16. The shaped charge made by the process of claim 12, wherein the plurality of slots are machined internally.

17. A method of using one or more pre-fragmented shaped charges in a well, comprising: providing a perforating string having one or more pre-fragmented shaped charges; and conveying the perforating string into the well.

18. The method of claim 17, wherein the perforating string comprises a loading tube and carrier.

19. The method of claim 17, wherein the perforating string comprises a spiral gun.

20. The method of claim 17, wherein the perforating string comprises a strip gun.