Field of the Invention
The present invention relates to devices and methods for energetically coupling a detonator cord to one or more shaped charges.
Description of the Related Art
Hydrocarbons, such as oil and gas, are produced from cased wellbores intersecting one or more hydrocarbon reservoirs in a formation. These hydrocarbons flow into the wellbore through perforations in the cased wellbore. Perforations are usually made using a perforating gun loaded with shaped charges. The gun is lowered into the wellbore on electric wireline, slickline, tubing, coiled tubing, or other conveyance device until it is adjacent to the hydrocarbon producing formation. Thereafter, a surface signal actuates a firing head associated with the perforating gun, which then detonates the shaped charges. Projectiles or jets formed by the explosion of the shaped charges penetrate the casing to thereby allow formation fluids to flow through the perforations and into a production string.
Referring now to FIG. 1A, there is shown a conventional perforating gun 10. The gun 10 includes a charge strip or tube 12, concentrically positioned in a carrier tube 14. Fixed within the charge tube 12 are shaped charges 16. Typically, the charge tube 12 is oriented in the carrier tube 14 such that the shaped charges 16 on each charge strip (not shown) align with weakened portions or scallops 18 formed in the carrier tube 14. A detonator cord 20 runs through suitable bores (not shown) in the perforating gun 10. Referring now to FIG. 1B, there is shown a cross-sectional view of the FIG. 1A perforating gun 10. Conventionally, the detonator cord 20 is coupled to the shaped charge 16 with an external clip 28. As is known, the shaped charge 16 may not detonate if the detonator cord 20 is not held firmly within a groove 30 formed in a post 31 extending from the rear of the shaped charge 16. Thus, in a typical assembly sequence, the shaped charges 16 are fixed within the charge tube 12 and then the detonator cord 20 is run through the grooves 30 of the shaped charges 16. Thereafter, the external clips 28 are snapped over the grooves 30 to retain the detonator cord 20 within the grooves 30. Next, the charge tube 12 is slid into the carrier tube 14. It should be noted that the annular clearance space 32 separating the charge tube 12 and the carrier tube 14 is relatively small in the region of the groove 30 and external clip 28. It should be noted that conventionally, the external clip 28 lies radially outward of the post 31 formed on the shaped charge 16. Disadvantageously, during installation of the charge tube 12 in the carrier tube 14, the external clip 28 sometimes hangs up with, gets caught by, and/or scrapes against the carrier tube 14 and becomes dislodged or damaged. If the external clip 28 is so damaged, the detonator cord 20 can fall out of the groove 30, in which case the shaped charge 16 may not detonate. An incomplete detonation of the shaped charges 16 can impair the effectiveness of the perforating activity and necessitate remedial work.
Thus, what is needed is a perforating gun that can be assembled without impairing the ballistic coupling of the detonator cord to the shaped charges. The present invention addresses these and other disadvantages of the prior art.