11 – Control the Waves

Companies that offered shaped charge perforation regarded deep perforation depth as crucial for their sales. Some oilfield services companies sought to increase jet penetration to offer a better product than competitors. Determining methods to improve jet penetration became a priority. One way to achieve this goal was to control the explosion blast wave.

In a conventional shaped charge explosion, the blast generates a nearly spherical wave that radiates outward. The expanding wave impacts the liner apex first and proceeds down its length, collapsing it to form the jet.

Shaped charge designers wanted to control the blast wave’s shape and flow direction to increase the jet’s velocity. Patent applications displayed some ideas for exerting better control over the explosion wave.

Steel Shields Delay the Wave

Patent 2,892,407 described the use of a cylindrical steel shield embedded within the charge explosive (Figure 1).¹ When the detonator exploded, it first detonated the thin layer of charge explosive between the shield and the charge casing. The shield delayed detonation of the main charge explosive, which provided enough time for the first explosion wave front to travel around the shield. When this wave front reached the end of the shield, it continued near the base of the conical liner.

The wave front contacted the liner almost perpendicular to its sloped wall at the same moment as the main charge explosion wave impacted the liner. The entire cone collapsed virtually simultaneously, imparting great energy to the jet.

Another patent (3,100,445) displayed a similar idea (Figure 2).² It also placed a small metal shield in the charge explosive, near the detonator. When the detonator exploded, the shield delayed the progress of the central blast wave front. This delay enabled the peripheral blast wave front to converge with the central wave in a circular area at the elliptical liner apex. The converged wave fronts imparted significant pressure on the liner, resulting in a great increase in jet velocity.

Wave Superimposition

In addition to patents, an article in the January 1957 issue of The Petroleum Engineer provided information on a project to increase jet velocity.³ The article described how Poulter Laboratories of the Stanford Research Institute supplied research data to the Jet Research Center (JRC) in Arlington, Texas. JRC then used the data to manufacture shaped charges to test the concept of “wave superimposition”.

In wave superimposition a high-energy wave (a.k.a., “a high-order wave”) overlays a slower, less-powerful “low-order wave,” The overall wave energy becomes much greater than the total of the individual wave fronts.

The article explained that the JRC embedded a steel barrier in the charge explosive above a nearly spherical liner. A small gap separated the barrier from the booster (Figure 3). After the booster detonated, its blast wave front passed through the steel barrier, emerging at a slightly slower speed and energy level. This was the “low-order wave”.

The remaining charge explosive then detonated, yielding a more powerful, “high-order wave”. The combined wave fronts impacted the liner simultaneously and produced a powerful jet capable of making a large entrance hole in the casing wall.

Innovative ideas for improving the jet put to rest, at least initially, concern over insufficient penetration into the formation.

References

1. MacLeod, Norman A., Shaped Cavity Explosive Charge, U.S. Patent number 2,892,407. Filed January 28, 1952.↑
2. Poulter, Thomas C., Shaped Charge and Method of Firing the Same, U.S. Patent number 3,100,445. Filed January 14, 1959.↑
3. Kastrop, J.E., “New Shaped Charge Packs a Bigger Wallop,” The Petroleum Engineer, January 1957. p. B-66.↑

Join the Discussion!

• Have you come across any other historical patents or innovations that aimed to improve the penetration depth of early shaped charges? If so, could you share any details?
• The article mentions the concept of “wave superimposition” to enhance jet velocity. Do you know of any other industries or applications where similar techniques have been used?
• What do you think were the biggest challenges faced by oilfield services companies when implementing shaped charge technology in real-world oilfield conditions?