Sub-caliber shaped charge perforator

Abstract

A shaped charge for use in perforating a wellbore that includes a shaped charge case, a liner in the case, and explosive between the liner and case. Detonating the explosive inverts the liner to form a metal jet that forms a perforation in a side wall of the wellbore. The outer diameter of the liner open end is set radially inward from the inner diameter of the case opening to define an annular gap. Providing a gap between the liner and case allows more control of distribution of material of the liner into the jet.

What is claimed is: 
     
         1 . A shaped charge for use in perforating a wellbore comprising:
 a case having an opening;   a liner inserted into a space in the case and having an open end and an apex;   explosive disposed between the liner and case;   a hole in the apex of the liner; and   a gap between an outer diameter of the open end of the liner and inner diameter of the opening in the case.   
     
     
         2 . The shaped charge of  claim 1 , wherein the hole has a diameter that ranges from about 10% to about 82% of an axial length of the liner. 
     
     
         3 . The shaped charge of  claim 1 , wherein an outer diameter of the open end of the liner ranges from about 60% to about 75% of an inner diameter of the opening of the case. 
     
     
         4 . The shaped charge of  claim 1 , wherein the hole ranges from about 7% of the liner outer diameter to about 60% of the liner outer diameter. 
     
     
         5 . The shaped charge of  claim 1 , wherein the shaped charge is selectively retained within a gun tube by a coupling that is provided with the case. 
     
     
         6 . The shaped charge of  claim 1 , wherein the shaped charge is selectively disposed in the wellbore within a perforating string. 
     
     
         7 . The shaped charge of  claim 1 , further comprising a slot on an end of the case opposite the opening that selectively receives a detonating cord, and an initiator in a passage formed through the case between the detonating cord and the explosive. 
     
     
         8 . The shaped charge of  claim 1 , further comprising a protective covering in the gap and over the explosive. 
     
     
         9 . A shaped charge for use in perforating a wellbore comprising:
 a case having an opening;   a liner in the case;   explosive between the liner and case; and   a gap defined by an outer diameter of the open end of the liner and inner diameter of the opening in the case, and having a liner diameter that ranges from about 60% to about 75% of the inner diameter of the opening in the case.   
     
     
         10 . The shaped charge of  claim 9 , further comprising a hole in an apex of the liner. 
     
     
         11 . The shaped charge of  claim 10 , wherein the hole has a diameter that ranges from about 29% to about 82% of a length of the liner. 
     
     
         12 . The shaped charge of  claim 9 , wherein the case is fitted with a coupling to selectively mount the shaped charge in a perforating string, and wherein the perforating string is disposed in the wellbore, and wherein detonating the explosive causes the liner to form a metal jet that penetrates into a formation adjacent the wellbore to form a perforation. 
     
     
         13 . A method of perforating a wellbore comprising:
 a. providing a shaped charge that comprises a case having an opening, a liner inserted in the opening that comprises an apex, a hole in the apex, and an open end with an outer diameter spaced radially inward from an inner diameter of the opening to define an annular gap, and explosive between the liner and the case;   b. installing the shaped charge in a perforating gun;   c. deploying the perforating gun in the wellbore; and   d. detonating the explosive so that a detonation wave is generated that collapses the liner to form a metal jet that penetrates into a wall of the wellbore and perforates the formation.   
     
     
         14 . The method of  claim 13 , wherein the outer diameter of the liner ranges from about 60% to about 75% of the inner diameter of the opening. 
     
     
         15 . The method of  claim 13 , wherein the hole ranges from about 15% of the liner outer diameter to about 44% of the liner outer diameter. 
     
     
         16 . The method of  claim 13 , wherein the perforating gun is part of a perforating string that is deployed on a line, and wherein a detonating signal is transmitted from surface through the line and to perforating gun. 
     
     
         17 . The method of  claim 13 , wherein the shaped charge is mounted into a gun tube that is inserted in the perforating gun.