7 – Shoot and Leave

Quick question: What do wood, plastic, cardboard, cement, paper, steel, glass, and aluminum have in common?

Answer: They were all considered as materials for expendable shaped charge carriers.

Selecting the Best Material

Oilfield services companies knew they had to detonate multiple shaped charges to perforate a formation adequately and enable hydrocarbons to flow into the wellbore. Consequently, design efforts focused on carriers that would hold several charges and survive the trip down the hot wellbore to the desired depth.

Designers had two choices for shaped charge carriers: expendable or retrievable. Both carrier types were considered for cased holes as well as uncased (open hole) wellbores. However, in the early days of oilfield shaped charge development, designers did not know the best material for carriers, especially as it related to the debris from the charge detonations. Several ideas existed for minimizing debris from expendable carriers, and the U.S. Patent Office was a good place to find them.

Patent number 2,779,278 described a design for a “torpedo”—a cylindrical carrier made from wood or plywood (Figure 1).¹ The patent illustrations depicted a carrier containing a stack of several shaped charges connected to a detonating cord.

To ensure the assembly would weigh enough to travel down the wellbore, the patent recommended filling the carrier with “a suitable pourable filling material, such as sand.” The patent also claimed that minimal debris would settle in the wellbore after the charge detonations.

More Choices

In the following years, more patent applications confidently suggested other materials for carriers. A paper carrier was advocated in patent 2,595,960², (Figure 2) and cement was the choice for carrier material in patent 2,669,928³ (Figure 3).

Patent 2,629,325⁴ (Figure 4) suggested enclosing each shaped charge in “a glass material of a type which will be fully disintegrated to a fine powder”. These inventors, and many others, claimed negligible debris in the well after charge detonations.

Dealing With Debris

As oilfield services companies continued testing, results showed that all expendable carriers generated significant amounts of debris. This debris often clogged the wellbore, preventing hydrocarbon flow from the formation. Expensive and time-consuming efforts were then required to clear the wellbores of the debris.

Further recognition of the debris problem came from Val Forsyth, an engineer at the Lane-Wells Company. Forsyth wrote an article in the second quarter 1949 issue of the company publication Tomorrow’s Tools Today.⁵ In the article he recounted that many early shaped charges were placed in expendable carriers. Detonating these charges resulted in large amounts of debris in the well. Damage to casing was also evident, he stated. In a subsequent technical paper that Forsyth submitted to the 1950 American Petroleum Institute Spring Meeting, he re-iterated the reality of debris from expendable carriers and their charges.⁶

Optimism Abounds

These stark observations, though, did not suppress optimism about overcoming the debris problem. W. T. Box, an engineer at the Byron Jackson Company, wrote an article for the June 29, 1950, issue of The Oil and Gas Journal.⁷ His article, “Jet Process of Open Hole Shooting”, proclaimed the successful use of plastic and magnesium as carrier materials for low-pressure, open hole wells. Aluminum and cast iron, according to Box, were the best choice for high-pressure situations because debris from these materials was minimal.

Other optimistic opinions existed. John Gardiner, another engineer at the Lane-Wells Company, proudly announced the sequential progress that his company had made in expendable carriers for open hole shooting. His article in the August 1950 issue of World Oil described the use in 1948 of “boxlike sections built up of thin-gauge aluminum alloy sheet”.⁸ One year later, said Gardiner, the Lane-Wells Company produced a pressure-tight aluminum alloy case that contained the charges.  Gardiner also proclaimed that by May 1950 the company had developed a cast iron “Type G” gun that had “excellent frangibility coupled with good strength characteristics.”

For the moment, then, some of the concerns about debris from expendable carriers subsided. More serious concerns arose when designers focused their efforts on retrievable carriers.

References

1. Klotz, Robert L., Apparatus for Perforating Well Casing , U.S. Patent number 2,779,278. Filed February 19, 1947.↑
2. Lawrence, Robert W., Explosive Device , U.S. Patent number 2,595,960. Filed October 30, 1948.↑
3. Sweetman, William G., Perforating Device for Wells , U.S. Patent number 2,669,928. Filed June 15, 1948.↑
4. Sweetman, William G., Jet Type Perforating Unit , U.S. Patent number 2,629,325. Filed May 28, 1950.↑
5. Forsyth, Val L., “Koneshot Perforating,” Tomorrow’s Tools Today, 2Q 1949. p. 33.↑
6. Forsyth, Val L., A Review of Gun Perforating Methods and Equipment , Technical Paper at 1950 Spring Meeting of the American Petroleum Institute. p. 30.↑
7. Box, W. T., “Jet Process of Open Hole Shooting,” The Oil and Gas Journal, June 29, 1950. p. 86.↑
8. Gardiner, John T., “Use of a Shaped Charge for Open Hole Shooting,” World Oil, August 1950. p. 100.↑

Join the Discussion!

• Do you have any insights into other innovative materials that were tested for shaped charge carriers but did not make it into widespread use?
• Have you encountered any industry discussions or documents from the late 1940s and early 1950s about the challenges of dealing with wellbore debris from shaped charge perforations?

I’d love to hear your perspective. Share your thoughts or answer a question in the comments below!