Device and method for enhacning well perforating

Abstract

A perforation enhancement cap for a shaped charge contains a shell and a pack of a solid propellant disposed inside the shell. The shell has a tubular straight section and a rounded cap. The rounded cap has a hole. The propellant pack has a through hole. The straight section, the rounded cap, the hole in the rounded cap, as well as the through hole are disposed about a common longitudinal axis. The through hole has a conical frustum section with its larger base facing the inside of the enhancement cap. The enhancement cap is adapted to receive the shaped charge to-form an enhanced perforation charge assembly for perforation and fracturing the formation.

What is claimed is: 
     
         1 . A perforation enhancement cap for a shaped charge, comprising:
 a shell and a pack of a solid propellant,   wherein the shell comprises a tubular straight section with a first end and a second end, and a rounded cap having a hole,   wherein the rounded cap is connected to the first end of the tubular straight section, the second end of the tubular straight section is adapted to be coupled with a shaped charge,   wherein the propellant pack resides in a cavity formed by the rounded cap and the tubular straight section, and the propellant pack has a through hole in alignment with the hole in the rounded cap, and   wherein the tubular straight section, the rounded cap, the hole in the rounded cap, and the through hole are coaxially aligned.   
     
     
         2 . The perforation enhancement cap of  claim 1 , wherein the through hole in the propellant pack has a conical frustum section connected with an optional straight section, wherein an opening angle of the conical frustum is in the range of 90° to 150°. 
     
     
         3 . The perforation enhancement cap of  claim 2 , wherein the opening angle of the conical frustum is in the range of 90° to 120°. 
     
     
         4 . The perforation enhancement cap of  claim 2 , wherein the opening angle of the conical frustum is in the range of 120° to 150°. 
     
     
         5 . The perforation enhancement cap of  claim 2 , wherein the diameter of the optional straight section equals the diameter of the hole in the rounded cap, and is in the range of 10-40 mm. 
     
     
         6 . The perforated enhancement cap of  claim 2 , wherein the through hole is in the propellant pack is in the shape of a conical frustum, wherein the hole facing the rounded cap is the smaller base in the conical frustum. 
     
     
         7 . The perforation enhancement cap of  claim 1 , wherein the rounded cap is a spherical cap having an inner diameter of 14-80 mm and a height of 10-30 mm. 
     
     
         8 . The perforation enhancement cap of  claim 7 , wherein the tubular straight section has a height in the range of 8-30 mm, an inner diameter in the range of 28-58 mm, and an outer diameter of 30-60 mm. 
     
     
         9 . The perforation enhancement cap of  claim 1 , wherein the propellant pack has a weight in the range of 6-50 grams. 
     
     
         10 . The perforation enhance cap of  claim 2 , wherein the propellant pack is in the shape of a conical frustum without a straight section. 
     
     
         11 . The perforation enhancement cap of  claim 1 , wherein the propellant comprises 30-70 wt % of ammonium perchlorate, 10-30 wt % aluminum powder, 10-15 wt % additive, and 3-5 wt % dioctyl sebacate. 
     
     
         12 . The perforation enhancement cap of  claim 11 , wherein the additive comprises hydroxyl-terminated polybutadiene (HTPB). 
     
     
         13 . The perforation enhancement cap of  claim 12 , wherein the additive is a mixture of HTPB, N, N′-diphenyl-p-phenylenediamine, and toluene di-isocyanate (TDI) at a weight ratio of (2.85-7):(0.05-0.2):(3-7.8). 
     
     
         14 . An enhanced perforation charge assembly for formation perforation, comprising a shaped charge and the perforation enhancement cap of  claim 1  coaxially mounted on a front-face of the shaped charge. 
     
     
         15 . The enhanced perforation charge assembly of  claim 14 , wherein the shaped charge contains an explosive pack having a weight of 6 to 80 grams and the perforation enhancement cap contains a propellant pace having a weight of 6 to 50 grams. 
     
     
         16 . A method for formation perforation, comprising:
 lowering a perforating gun into a borehole, wherein the perforating gun comprises the enhanced perforation charge assembly of  claim 14 ; and   detonating the enhanced shaped charge of  claim 14 .