High Explosive

A high explosive in oil and gas operations is a chemical compound or mixture that, when initiated by heat, shock, or an initiating detonator, undergoes rapid detonation — a supersonic exothermic decomposition that produces a shock wave and high-pressure gas expansion at velocities exceeding the speed of sound in the material — used in perforating guns, well abandonment charges, pipe-cutting tools, and seismic energy sources where the energy density and detonation performance of high explosives are required to achieve the intended downhole effect.

Key Takeaways

High explosives used in perforating guns are primarily RDX (cyclotrimethylenetrinitramine), HMX (cyclotetramethylenetetranitramine), and PYX (pyrolytic explosives rated for HTHP service), selected based on the required temperature rating, detonation pressure, and regulatory requirements for the specific well application.
The detonation velocity (VOD) of high explosives used in perforating charges typically ranges from 7,000 to 9,000 metres per second, generating the shaped charge jet that penetrates casing, cement, and formation to create the perforation tunnel.
Temperature rating is the critical selection criterion for downhole high explosives: RDX is rated to approximately 150 to 170 degrees C, HMX to approximately 177 to 204 degrees C, and HTHP grades such as PYX or CL-20 compounds to 260 degrees C or higher for HPHT well applications.
High explosives are classified as Class 1 Division 1 (or Class 1.1) under UN hazardous materials transport regulations and require licensed handlers, specialized transport, secure storage in licensed explosive magazines, and site-specific blasting permits in most jurisdictions.
Deflagration (subsonic burning) of a high explosive without detonation produces different — often far less effective and potentially hazardous — results than detonation; ensuring proper initiation through a correctly rated, fully assembled detonating cord and detonator train is essential to achieve the intended downhole effect safely.

Fast Facts

RDX (Research Department Explosive, or cyclonite) is the most widely used high explosive in oilfield perforating, accounting for the majority of shaped charges used in conventional wells globally. It was originally developed for military applications in World War II and adapted for oilfield use in the 1950s. A typical oilfield shaped charge contains 10 to 50 grams of high explosive in a shaped metal liner and case assembly, with the charge geometry (standoff, case material, liner metal and shape) optimized to maximize penetration depth and entrance hole diameter in the formation. The total explosive load of a fully loaded perforating gun string for a 100-metre interval can be several kilograms — requiring careful transport and handling procedures.

What Is a High Explosive in Oil and Gas?

Explosives are broadly categorized as low explosives (which deflagrate — burn rapidly but subsonically) and high explosives (which detonate — decompose supersonically with a characteristic shock wave). In oil and gas, the term high explosive refers specifically to materials capable of detonation: RDX, HMX, PETN, TNT, and related compounds and formulations used in downhole tools, seismic sources, and well intervention devices.

The primary application of high explosives in oilfield operations is perforating — creating tunnels through steel casing, cement, and reservoir rock to establish hydraulic communication between the wellbore and the formation. Perforating charges use the shaped charge principle, in which the high explosive's detonation energy is directed by a concave metal liner that collapses under the explosive pressure, forming a high-velocity metal jet that penetrates the casing and formation to depths of 10 to 120 centimetres depending on charge design, shot density, and formation conditions.

Other oilfield applications of high explosives include explosive-driven pipe cutters for downhole pipe cutting during fishing and well abandonment, explosive release mechanisms in downhole tools, and specialized seismic sources for borehole seismic surveys.

High Explosive Selection for Perforating

The dominant selection criterion for high explosives in perforating is temperature rating — the maximum sustained temperature at which the explosive maintains its detonation properties without significant self-decomposition over the duration of the gun's deployment in the wellbore. Self-decomposition at elevated temperature can reduce the explosive's detonation velocity and energy output, degrading perforation performance, or in severe cases can cause premature initiation through thermal runaway.

RDX is the workhorse high explosive for temperatures below approximately 150 degrees C. For HTHP applications above this threshold, HMX — a closely related compound with higher melting point and better thermal stability — is used up to approximately 200 degrees C. For ultra-HTHP wells above 200 to 230 degrees C, specialty explosives including PYX (pyridinyloxy xenon, or more correctly 2,6-bis(picrylamino)-3,5-dinitropyridine), TATB (triaminotrinitrobenzene), or newer HTHP-rated formulations developed for specific applications are required.

Detonation velocity and charge performance are also considered: the penetration depth and hole diameter produced by a given shaped charge depend on the VOD of the explosive, the liner metal and geometry, the charge case, and the standoff from the casing wall. API RP 19B (Recommended Practice for Evaluation of Well Perforators) provides standardized test procedures for measuring shaped charge penetration depth and entrance hole diameter, enabling objective comparison between competing charge designs.

High Explosives Across International Jurisdictions

Canada (NRCan / PWGSC / AER): High explosives used in oil and gas operations in Canada are regulated under the Explosives Act (federal, administered by Natural Resources Canada's Explosives Regulatory Division) and provincial occupational health and safety regulations. Handling, storage, and use of high explosives requires a federal explosives license and adherence to NRCan's Explosives Safety and Security Branch regulations. AER and BCOGC require that perforating operations be conducted by licensed explosives personnel and documented in well completion reports. Transport of Class 1 explosives on Canadian roads requires compliance with Transportation of Dangerous Goods (TDG) regulations.

United States (ATF / BSEE): The Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) regulates acquisition, storage, and transfer of high explosives under the Safe Explosives Act. Users and service companies handling oilfield explosives require federal explosives licenses from the ATF. BSEE offshore operations require that all explosive perforating operations be conducted by licensed personnel with explosives use records maintained in the well file. OSHA standards (29 CFR Part 1926 Subpart U) govern safe handling and use of explosives at construction and industrial sites including oilfield locations.

Norway (Sodir / DSB): The Norwegian Directorate for Civil Protection (DSB) regulates explosives handling in Norway, including oilfield applications on the NCS. Equinor and service companies conducting perforating or explosive pipe-cutting operations on NCS wells must comply with DSB licensing requirements and explosion protection regulations. Environmental and safety data sheets for explosives used offshore must be filed with Sodir as part of the chemical safety documentation for the well.

Middle East (Saudi Aramco): Saudi Aramco's explosives handling regulations govern the acquisition, transport, storage, and use of perforating explosives for Aramco well operations. All explosive components used in Aramco wells must meet Aramco's approved products list requirements, including temperature ratings verified against the BHST of the intended completion interval. Saudi Arabia's national explosives regulations require that all explosive use be conducted by licensed personnel under Ministry of Interior oversight.

High explosives in oilfield use are also called perforating explosives, shaped charge explosives, or downhole explosives. Related terms include perforating, shaped charge, detonator, detonating cord, RDX, HMX, and API RP 19B. Low explosives (gunpowder, propellants) and blasting agents (ANFO, emulsions) are distinct categories that deflagrate rather than detonate and are not used for perforating applications requiring the shaped charge jet.

Tip: When specifying high explosives for a perforating program in an HTHP well, add a minimum 20 degree C temperature safety margin above the confirmed BHST when selecting the explosive temperature rating. Downhole tools may be stationary for several hours before perforating (waiting for wellbore conditions to stabilize), during which the explosive equilibrates to formation temperature. The BHST rating should not be the limit — it should be well within the explosive's continuous service temperature. Always verify the explosive's temperature rating from the manufacturer's data sheet against the specific combination of maximum temperature and maximum exposure time anticipated for the completion operation, not just the well's rated temperature.

FAQ

What is the difference between detonation and deflagration for oilfield explosives?
Detonation is a supersonic exothermic decomposition in which a shock wave propagates through the explosive material at velocities typically between 6,000 and 9,000 metres per second. The shock wave generates an extremely high instantaneous pressure (typically 10 to 40 GPa in the explosive) that drives the shaped charge liner at high velocity to form the penetrating jet. Deflagration is a subsonic rapid burning (velocities of 1 to 100 metres per second) that produces high-pressure gas without the shock wave characteristic of detonation. If a high explosive deflagrates rather than detonates (due to insufficient initiator energy, temperature degradation, or mechanical damage), the perforating charge may produce a partial effect or fail entirely — the liner does not form a coherent jet and penetration is greatly reduced. Ensuring that the complete detonating train (detonator to detonating cord to charge) functions as designed to guarantee full detonation is the principal quality control requirement for perforating operations.

How are unexploded high explosives managed if a perforating run misfires?
A perforating misfire — where a gun is run, attempted to be fired, and returns to surface without detonating — is one of the most hazardous situations in oilfield explosives management because the gun contains armed high explosives in an unknown state. Standard procedures require that the gun be isolated at surface (not opened or disassembled) while awaiting assessment by licensed explosives personnel. The misfired gun must be held in a safe location away from personnel and ignition sources while the disposal procedure is determined. In most jurisdictions, only licensed explosive shot firers may handle misfired explosive tools, and disposal options include controlled detonation, soaking in water to desensitize the detonator before disassembly, or return to the manufacturer.

Why High Explosives Matter

High explosives are the technical foundation of well completion perforating — the operation that physically connects the wellbore to the reservoir and initiates production. The performance of the perforating charges (penetration depth, entrance hole diameter, perforation density) directly determines the productivity index of the completion and therefore the economic value of the well. Selection of the appropriate high explosive for the temperature and pressure conditions of each well, combined with rigorous explosives safety and regulatory compliance, is a core technical competency for completion engineers and wireline service companies that shapes the outcome of every perforated completion globally.