Perforation (3) (Explosives Classifications)

Explosives Classifications

Explosives were invented first by the Chinese in the 10th century, then independently by the Arabs in the 13th century. The low explosive, or black powder, was characterized by slow reaction rates, 500 to 1500 m/sec, and relatively low combustion pressure. Much later, in 1846, the first high explosive was discovered by an Italian, Ascanio Sobreto, and then made commercially by Alfred Nobel in 1867 with the development of dynamite, a combination of nitroglycerin and clayey earth. High explosives, unlike the earlier low explosives, detonate at very rapid rates of 5000 to 9000 m/sec and generate tremendous combustion pressures. The terms low and high explosive are still used to characterize chemical explosives.

2.4.1.Low explosives (propellants)

 Are used in modern oilfield applications as power charges for pressure setting assemblies, bullet perforators and sample taker guns as well as for stimulation (high-energy gas fracturing, perf wash, etc.). High explosives are found in shaped charges, the detonating cord and detonators, and blasting caps.

2.4.2.High explosives 

 are further classified by their sensitivity or ease of detonation. 

2.4.2.1. Primary high explosives 
 are very sensitive and easily detonated by shock, friction or heat. For safety reasons, primary high explosives, such as lead azide, are used only in electrical or percussion detonators in Schlumberger gun systems.

2.4.2.2. Secondary high explosives  

are less sensitive and require a high-energy shock wave to initiate detonation (usually provided by a primary high explosive). Secondary high explosives are used in all other elements of the ballistic chain (detonating cord, boosters and shaped charges). PETN, RDX, HMX and HNS are secondary high explosives used in oilwell perforating. The rate of reaction, combustion pressure and sensitivity of chemical explosives are affected by temperature. Consequently, maximum safe operating temperatures are defined for all explosives. Exceeding temperature ratings may result in autodetonation or reduced performance. The table below lists the 1- and 100-hr temperature ratings and uses for the various explosives in gun systems.
 

2.4.3. Effect of temperature

Temperature affects the rate of reaction, combustion pressure and sensitivity of chemical explosives. Consequently, maximum safe operating temperatures are defined for all explosives. Exceeding the optimum temperature rating may result in autodetonation or reduced performance.

The table lists the 1-hr and 100-hrtemperature ratings and uses for the various explosives in schlumberger gun systems.