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A typical shaped charge consists of a high explosive into which a cone shaped cavity is pressed  The cavity is fitted with a metal conical liner, often made from copper, or copper alloys.  The entire assembly fits in a metal housing, usually steel or aluminum.  When the high explosive is detonated, the metal liner is compressed and squeezed forward, forming a jet of metal particles with a tip velocity in excess of 20,000 feet per second.  The lined shaped charge was originally developed for warfare, but ironically they are now used extensively to disarm landmines in war torn countries around the world.  But the biggest use of lined shaped charges is in the oil and gas industry as perforators.  Interestingly, when the liner is pressed into the high explosive, there are occasional accidental detonations; while these episodes are hard on the presses, special press construction and the use of blast shields makes the press operator's job a safe one.

The liner may be a pressed powdered metal liner (PML), used in most high performance deep penetrating charges, and which technological advance has the advantage of not forming a solid "carrot" in the perforation tunnel.  It may be a wrapped metal liner (WML) cut and wrapped from thin sheet metal.  Or it may be a coined metal liner (CML) formed by stamping.  The solid metal liners (WML and CML) are considered more dangerous than powdered metal lined charges.  A large solid metal lined charge can make a hole in half inch steel plate at thirty feet, a powdered metal lined charge will not.  Today, most commercial jet charges use powdered metal liners because of the improved performance offered under most circumstances, but the solid metal liners are still used in certain "big hole" charges.

The outer metal housing of the charge may be designed to be used in a hollow steel carrier, or it may constitute its own water and pressure tight housing (the latter often called capsule charges).  The hollow steel carrier is merely a steel tube with pressure tight fittings that close both ends.  Reusable hollow steel carriers employ replaceable "port plugs" that the charge shoots through.  Expendable carriers are used only once and discarded; these are sometimes called throw away guns (TAG).  Expendable guns may be a smooth "slickwall" tube or may be "scalloped", thus providing a thinned area for jet penetration.  Small diameter expendable carriers (often scalloped) designed for use in tubing are sometimes called retrievable tubing guns (RTG).  There are many different kinds of capsule or exposed charges.  These include link jets, stick jets, strap jets, strip jets, bi-wire jets, formed wire jets, etc.  The huge variety of lined shaped charge jet perforators, and associated delivery systems would comprise a book; such a catalog is beyond the scope of this meager effort.

See our The Life Cycle of Lined Shaped Charge Perforators for what happens when perforating charges are shot.  Also see our Brief History of Lined Shaped Charge Perforators for the  fascinating story of how it all got started.

The major domestic manufacturers of lined shaped charges available to independents are:

JRC (Halliburton)                                Owen                                Titan (Shaped Charge Specialists)

The American Petroleum Institute (API) publishes RP 19B, Recommended Practices for Evaluation of Well Perforators(formerly RP 43), which standard is supposed to give us an impartial and unbiased basis for comparing various perforating products.  There were persistent rumors of cheating, but no real proof under the old RP 43 procedures, but RP 19B provides for witnessing among other changes.  API now publishes the results of the tests here:  API Perforator Tests.

In shallow stripper well country, we were sold on the old 90 gram "frac" capsule shot (it has gone by several trade names).  It was touted as producing a hole almost 0.7 inches in diameter, and almost 19 inches deep (some manufactures claimed a little less).  In fact, the charge was more on the order of 65 grams, not 90, and perforation depth figures were undoubtedly exaggerated (no current RP 19B data is available for the 90's).  It was also notorious for carrot formation with its solid liner construction.  The idea was that you could shoot these monsters in old wells, even open hole completions, and rejuvenate the well.  The problem is that the alleged rejuvenation seldom improved production.  There is alternative rejuvenation technology which should be considered in such situations.

In recent years, incredible advances have been made in lined shaped charge design.  Part of the progress is attributable to computer aided design (CAD).  Heck, it was not until the 1970s that modeling codes could even predict with any accuracy how a shaped charge would behave.  Premium charges capable of penetrating 36 or even 48 inches are now available.  Might these deep penetrating charges be useful for well rejuvenation, perhaps producing new flow paths out beyond near well bore damage?  These charges are relatively expensive, hence little field work has been done in this regard.  In 1995, we proposed testing this hypothesis as a project to DOE, but their evaluation contractor, BDM-Oklahoma, Inc., was not moved.  There are reports of good results in a few newly drilled open hole completions where the only stimulation has been shooting with the new deep penetrating charges.

In general, many of our wireline customers have reported very good luck with the premium deep penetrating charges in conventional applications.  Many of their customers are happy to bear the increased cost for what they perceive as a superior completion.

Exercise extreme caution when working with explosives.  Stay alert and THINK; complacency kills!  Follow the guidelines in the American Petroleum Institute (API) Recommended Practices for Oilfield Explosives Safety, RP 67.

11-06-00
Last 09-23-05