13 – Safety is Priority One

A few years after the first commercial use of shaped charges, oilfield services companies directed some of their attention away from product performance and considered an additional topic: safety. An accidental detonation of a shaped charge could damage equipment and the wellbore. Such an event could also be deadly to a field crew.

Oilfield services companies provided few details in industry trade literature about their plans for shaped charge safety. However, patents revealed designs to reduce the danger to field personnel who handled and operated the charges.

Field Crew Safety Assured

In 1953, the Borg-Warner Corporation filed a patent application for tubing string with a heavy-duty, pressure-resistant coupling connected to a casing perforating assembly.¹ During operation, the field crew lowered the string in a well fitted with a completion assembly (a “Christmas tree” and lubricator). After reaching the required depth, the crew would set the tubing in place with a packer. The crew then lowered a small-diameter carrier through tubing. The carrier stopped at a frangible plug (Figure 1).

A command from the surface detonated a small, shaped charge in the carrier. This blast penetrated the plug, detonating the booster charge and the attached Primacord. The other charges then exploded. After a short time lag, the severing charge exploded, causing the perforating assembly to separate from the coupling and fall to the bottom of the well. The crew then retrieved the carrier.

The patent author explained there was no chance of an accidental detonation of the perforating shaped charges because the booster charge could only be set off by a powerful, nearby explosive force. Until the field crew inserted the carrier with its small, shaped charge into the tubing, no detonation was possible.

Through-Tubing Safety

Patents for improving safety in through-tubing perforation also made their debut in the early 1950s. Esso Research and Engineering filed a patent featuring a design that relied on a spring to prevent detonation of the perforating charges until after the assembly passed the end of the tubing.²

When this occurred, two trigger arms expanded slightly, releasing a wedge that had held a firing stem in place. A powerful spring above the stem pushed it down rapidly (Figure 2).

The stem hit a stud, forcing it and the attached piston down and overcoming the resistance of a spring. The firing pin then hit the firing cap, which detonated the powder chamber. This explosion ignited the Primacord that led to the shaped charges.

The patent author stated that the spring above the powder chamber kept the stud and piston away from the firing cap. Only the extreme force of the firing stem could enable the piston to compress the spring.

Patents Promote Safer Charges

Many more patents proposed solutions to accidental firing. The following tables list these patents, in chronological order by their submission dates, up to the mid-1950s.

References

1. Lebourg, Maurice, Method and Apparatus for Detonating Explosive Devices in Bore Holes, U.S. Patent number 2,833,215. Filed June 13, 1953.↑
2. Kanady, William, Automatic Firing Systems for Gun Perforators for Wells, U.S. Patent number 2,705,920. Filed September 11, 1950.↑
3. Griffin, W. H., Method and Apparatus for Completing Wells, U.S. Patent number 2,906,339. Filed March 30, 1954.↑
4. Long, Thomas L., Well Perforating Device, U.S. Patent number 2,859,697. Filed June 7, 1954.↑
5. Castel, Jacques and LeBus, Jake, Perforating Apparatus, U.S. Patent number 3,071,072. Filed August 11, 1954.↑
6. Cirilo, Manuel, Perforator, U.S. Patent number 2,947,253. Filed September 1, 1954.↑
7. Caldwell, Blake, Well Perforating Assembly and Perforating Unit Therefor, U.S. Patent number 3,067,679. Filed October 8, 1954.↑
8. Lebus, Jake, Perforating Device and Method of Perforating Wells, U.S. Patent number 2,927,534. Filed February 6, 1956.↑
9. Caldwell, Blake, Well Perforating Assembly, U.S. Patent number 3,107,611. Filed March 7, 1956.↑
10. Castel, Jacques, Firing System for Jet Type Perforating Gun, U.S. Patent number 2,821,136. Filed April 5, 1951.↑
11. Castel, Jacques, Firing Circuit for Perforating Guns, U.S. Patent number 2,703,053. Filed April 5, 1951.↑
12. Spencer, Lloyd, Gun Perforator and Method of Manufacture, U.S. Patent number 2,833,215. Filed August 18, 1951.↑
13. Houck, Claude, Detonator, U.S. Patent number 2,883,931. Filed December 18, 1953.↑
14. McKee, Donovan, Well Casing Perforator, U.S. Patent number 2,925,775. Filed December 13, 1955.↑

Join the Discussion!

• Could you share any knowledge or experiences about how oilfield service companies first approached the issue of shaped charge safety during field operations?
• Can you recall how early safety designs for shaped charges influenced training or workflow changes for perforating crews? Any details on would be especially helpful.