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]    [0005]FIG. 1 is a cross-sectional view of a typical shaped charge, loading tube, and hollow carrier.  
         [0006]    [0006]FIG. 2 is a perspective view of a typical shaped charge and loading tube.  
         [0007]    [0007]FIG. 3 is a perspective view of a loading tube being inserted into a hollow carrier.  
         [0008]    [0008]FIG. 4 illustrates an embodiment of the pre-fragmented shaped charge.  
         [0009]    [0009]FIG. 5 provides a top view of an embodiment of the pre-fragmented charge case having 6 slots.  
         [0010]    [0010]FIG. 6 provides a top view of an embodiment of the pre-fragmented charge case having 2 slots.  
         [0011]    [0011]FIG. 7 provides a top view of an embodiment of the pre-fragmented charge case having 4 slots.  
         [0012]    [0012]FIG. 8 illustrates an embodiment of the pre-fragmented charge casing having V-notch slots.  
         [0013]    [0013]FIG. 9 illustrates an embodiment of the pre-fragmented charge casing having U-notch slots.  
         [0014]    [0014]FIG. 10 illustrates an embodiment of the pre-fragmented charge case having internal slots.  
         [0015]    [0015]FIG. 11 illustrates an embodiment of the pre-fragmented charge case having circumferential slots. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0016]    [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]    [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.