10 – The Liner is the Key

Shaped charge testing programs performed by oilfield services companies revealed several useful facts about liners. Copper or steel liners produced jets that usually achieved the greatest penetration depths. Jets from glass liners did not penetrate as well, but they produced no slugs and smaller amounts of debris.¹

Decreasing the cone angle improved the jet penetration depth, but this approach formed smaller-diameter holes in the formation. Increasing the cone angle slowed the jet velocity, placed more of the liner in the jet, and resulted in smaller slugs. Tests also showed that liner thickness changes as little as 0.0625 inch affected the jet penetration.

The Military Has the Data

Most oilfield services companies, though, lacked the equipment for determining more subtle effects on liners and jet formation. Only the U.S. military had test data with this level of analysis. A U.S. Naval Ordnance Report in August 1950 described the effect of liner and charge assembly defects on the jet and its penetration capability (Figures 1–4 and Table 1).²

This information was classified as Top Secret and not available to oilfield services companies. Companies had to discover these details (and many more) through their own testing efforts.

A Possible Solution for Slugs

As company testing continued, a discovery provided a possible solution to the slug problem: bi-metallic liners. A paper presented at the 1957 Fall Meeting of the Society of Petroleum Engineers described experimental results on eliminating slugs.³

The paper described the details of how a solid copper liner produced a slug. During the jet formation process, the outer layer of the liner, adjacent to the explosive, formed the slug. The liner inner layer became the jet (Figure 5).

Testing indicated If the outer layer of the liner were replaced with a low melting point metal, the temperature and pressure of the explosion would vaporize it, eliminating the slug. The metallic inner layer would then produce a jet with approximately the same penetrating power as the solid copper liner.

The paper stated that considerable testing was performed with lead, zinc, aluminum, and alloy liners. Zinc was favored because testing revealed it produced the smallest slugs.

The thicknesses of the zinc and copper required adjusting to achieve a balance between maximum jet performance and minimum slug weight (Figure 6).

According to the paper, tests showed that the small slug produced by the bi-metallic liner would not enter a perforated hole in downhole conditions.

References

1. Forsyth, Val L., “Koneshot Perforating,” Tomorrow’s Tools Today, 3Q 1949. p. 4.↑
2. Brimmer, Robert A., Manual for Shaped-Charge Design, NAVORD Report #1248. China Lake, California. August 17, 1950. p. 7.↑
3. Delacour, J. et al., A New Approach Toward Elimination of Slug in Shaped Charge Perforating, Technical Paper at 1957 Fall Meeting of the Society of Petroleum Engineers. p. 17.↑

Join the Discussion!

• The U.S. military had advanced testing capabilities and data that were unavailable to oilfield companies. What are your thoughts on how this lack of access may have influenced oilfield perforation technology?
• The testing of liner materials revealed significant effects on jet penetration. Do you have any knowledge or experience with alternative liner materials that were tested later?