8 – Shoot and Retrieve

Clyde Davis was a gifted engineer who worked at the Eastern Laboratory of the E. I. DuPont de Nemours Company (DuPont). During World War II, he and his design group determined optimum values for parameters used in making shaped charge weapons, including the bazooka rocket warhead.¹ The end of the war in 1945, though, did not stop his involvement in shaped charge design. DuPont enlisted his expertise to help design shaped charges for sale to oilfield services companies.

DuPont Offers a Product

Many oilfield services companies bought the DuPont charge assembly (called the “Standard Charge”).² The Standard Charge (Figure 1) contained the explosive material, the liner, and the case. Carrier designs were left to the oilfield services companies, necessitating their expenditure of time and money to develop and test retrievable shaped charge carriers.

These companies were keenly aware of the significant challenges in developing these carriers: damage to the carrier body from the multiple shaped charge explosions, destruction of the carrier ports by the shaped charge jets, and debris left in the wellbore.

Initially, some oilfield services companies were optimistic about designing retrievable carriers. A common belief was that carriers could be designed to deliver shaped charges that detonated without damaging the carrier body or ports. Production of debris was not a significant concern, especially when field crews followed proper procedures.

The procedure to use a retrievable carrier containing several shaped charges was straightforward. A field crew lowered the carrier into the wellbore on a stranded wireline cable. When the carrier reached the required depth, the crew detonated the charges using electrical signals sent from the surface through the wireline. After the explosions, the crew retrieved the carrier, installed new shaped charges, replaced the ports through which the jets had travelled, and lowered the assembly into the wellbore again.

Problems Soon Develop

Field experience, though, quickly showed the challenges of designing retrievable carriers. Damage from the multiple shaped charge explosions or from the jets heavily damaged many carriers after a single run in the well. Thick-walled carriers were considered for withstanding the blasts, but this choice did not prevent damage to the ports. One approach for preventing this damage focused on carrier designs that ensured shaped charge alignment with the ports.

Some carrier designs attached the shaped charges to a cylindrical, non-metallic charge holder. Field crews would insert the holder with its attached charges into the carrier body before sending the assembled device into the wellbore. This design required careful attachment of the shaped charges to the holder and accurate orientation toward the ports in the carrier wall.

Many ideas for shaped charge holders were offered in patents, including one authored by Davis. In 1947, he submitted a patent (2,649,046) that heralded the use of machined channels in the carrier wall (Figure 2).³ Each channel was located directly in line with a shaped charge attached to the carrier by a cylindrical holder.

The machined diameter of the channel, according to Davis, enabled the jet to pass through the carrier without damaging it. His patent also stated the charges could be assembled within a “holding container of paper board, plastic, or other destructible material”.

Field experience showed, however, that many charge holders quickly displayed their unsuitability. An article in the March 1950 issue of World Oil magazine stated that some carriers used cardboard tubes to support and position the shaped charges.⁴ After detonation, the cardboard tended to exit the carrier and litter the well.

Even replacing the cardboard with a phenolic (plastic) charge holder did not eliminate debris. Shaped charge misalignment issues also persisted, resulting in many damaged carriers after the detonations.

Here is a Possible Solution

A technical paper presented in March 1950 at the American Petroleum Institute Spring Meeting described a possible solution to these issues.⁵ The paper, “Review of Gun Perforating Methods and Equipment”, was written by Valoris Forsyth, an engineer at the Lane-Wells Company. The document described the use of threaded ports and charges that the field crew would screw into the carrier body. Jets from the charges could shoot through the ports without blowing debris from the carrier.

Additional patent authors soon realized the wisdom of securing the shaped charges to the carrier wall. The author of one patent advocated attaching the charges to a plastic liner that was inserted snugly into the carrier.⁶ When each charge was oriented over the port, a metal sealing disc and an annular retainer secured the charge to the wall.

Other patents displayed shaped charges in threaded housings that field hands would attach to the carrier body. Patent 2,680,406 described the use of a “loading tool” that inserted each charge into the carrier and secured it to a recessed area with a lock disc (Figure 3).⁷

Another patent (2,734,456) bolted the charges to the carrier body (Figure 4).⁸

During the late 1940s and early 1950s, oilfield services companies worked to develop retrievable shaped charge carriers. Engineers faced challenges such as carrier damage, misalignment, and debris in the wellbore. Despite early setbacks, refinements like secure charge attachments and improved alignment methods helped advance retrievable carrier designs, making them more effective for oilfield perforation.

References

1. Pugh, Emerson, Transactions of the Symposium on Shaped Charges, Aberdeen Proving Ground, Maryland, USA. November 13-16, 1951. p. 387.↑
2. Forsyth, Val L., “Koneshot Perforating,” Tomorrow’s Tools Today, 2Q 1949. p. 33.↑
3. Davis, Clyde O., Explosive Package, U.S. Patent number 2,649,046. Filed May 1, 1947.↑
4. Box, W. T. et al., The Jet Perforating Process, World Oil, March 1950. p. 113.↑
5. Forsyth, Val L., A Review of Gun-perforating Methods and Equipment, Technical Paper at 1950 American Petroleum Institute Spring Meeting.↑
6. Schlumberger, Marcel, Aligning Means for Shaped Charge Perforating Apparatus, U.S. Patent number 2,750,885. Filed November 23, 1949.↑
7. Austin, J. L., Explosive Container for Gun Perforators, U.S. Patent number 2,680,406. Filed March 14, 1949.↑
8. Sweetman, W. G., Gun Perforator, U.S. Patent number 2,734,456. Filed April 21, 1949.↑

Join the Discussion!

• Have you come across any additional historical details or firsthand accounts about the early challenges oilfield companies faced when designing retrievable shaped charge carriers?
• Do you have any insights into how engineers refined shaped charge alignment methods to reduce damage to carrier bodies and ports?