Explosives Applications: The Shaped Charge

One major use for explosives is in the oil and gas industry to complete a well. For a simple well the process is straightforward. The well is drilled, cased and then perforated. This involves inserting a length of tubing with a series of shaped charges along it's length into the cased well and setting off the charges that perforate the casing and the oil and gas bearing strata.

A shaped charge in its simplest form is nothing more than a metal cone surrounded by explosives. The charge is end initiated and the explosive collapses the conical liner into a jet of material that penetrates at very high velocity. The jet penetrates in the same manner as I previously posted about hypervelocity penetration. A model of a simple 65 degree angled shaped charge is shown in the first video. As the detonation proceeds up the charge the cone collapses inward in a symmetrical manner with an upwards momentum. At the collision point the cone coalesces into a jet of material that has a high velocity and has a final form of a long slender rod.

The penetration of a jet into a target is driven mainly by the jet density, the target material density and the standoff as a function of charge diameter from the target.

Shaped Charge Use Scenario.

The relationship between standoff, diameter and penetration can be represented in the following manner. For a given cone angle, cone wall thickness the penetration depth can be represented by:

Penetration/Standoff Relationship for One Geometry.

As you can see the best penetration occurs at a approximately 6 to 7 cone diameters for that given geometry. This relationship is quite uniform for a number of explosive fills and a fairly wide range of cone angles. There are usually space constraints for any shaped charges used in real systems however. One method of maintaining a good standoff while reducing the overall height of the charge is by using a hemi-spherical charge. The jet is more of a projectile shape as opposed to a long rod like the conical charge but it still has a significant penetration capability. A hemi-spherical shaped charge model is shown in the next video.