Explosive thermal stability is an important topic for oilfield perforating operations and impacts perforating system performance and safety. Explosives have time dependent temperature limits which can lead to thermal decomposition when exceeded and, under some circumstances, can result in performance losses and safety hazards. Explosive thermal stability information is currently provided by perforating system manufacturers through time versus temperature plots. While these plots have proved useful for many years, this review of current industry thermal stability data and practices aims to highlight a need for improvement and expanded testing representative of the energetic materials as used in actual well environments. More specifically, this review discusses the potential economic impact on well performance and operational safety when thermal stability limits are exceeded. When using currently available time versus temperature plots, operators sometimes must select lower performing explosives which are thermally stable at higher temperatures especially for high temperature well environments. As a result, operators risk optimal well inflow performance with significant economic impact. Furthermore, exceeding the time dependent temperature limits can lead to thermal decomposition. Off-gassing from thermal decomposition can trap pressure inside of gun carriers creating safety hazards during misruns. This review includes a reference to a known occurrence where overexposure to temperature led to thermal runaway and a surface explosion of a recovered perforating system. Additionally, this review discusses shortcomings in thermal stability test methods and related API recommended practices. Current methods assessing thermal stability, including vacuum thermal stability, ampule, and ODTX (One Dimensional Time to Explosion) tests tend to use unrealistic test conditions. The API recommended practices do not directly assess thermal decomposition which is important in developing safe practices for recovered perforating systems which may have been exposed to temperatures exceeding thermal stability limits. This review concludes with recommendations for future work to better understand thermal stability in oilfield explosives. More suitable thermal stability tests which evaluate oilfield explosives in well environment conditions will lead to improved safety recommendations and has the potential for significant economic impact on well productivity through enhanced understanding of the time dependent temperature limits. Finally, this paper draws on the urgent requirements of the Operator community, the experience of the manufacturing community and the advanced technical support of a US National Laboratory to provide a concise review and recommendations which can then be promulgated through the API, as a major step in enhancing safety and ultimately well performance.

Prediction of perforating gunshock loads and the associated risk of tool damage is very important because of the high cost of nonproductive time associated with fishing jobs, particularly for deep-water wells. We have examined real examples of gunshock damage to determine how these incidents could have been prevented by using the most current (2014) capabilities in simulation software to predict gunshock loads. Our goal was to evaluate the latest software advances for predicting perforating wellbore dynamics and the associated gunshock loads and gauge the usefulness of the simulations in common perforating operations. Both low- and high-pressure wells are susceptible to gunshock damage when they are perforated with inappropriate gun systems and/or under adverse conditions. Examples of tool damage due to gunshock include bent tubing and unset or otherwise damaged packers and wireline weak-point pull-offs. Using gunshock simulation software, we can identify perforating jobs with significant risk of gunshock damage, and then we can make changes to the perforating equipment or job execution parameters to reduce gunshock loads to safe levels, thus reducing the risk of equipment damage and nonproductive time. Using the latest gunshock software, engineers can also evaluate the sensitivity of gunshock loads to changes in perforating equipment, such as gun type, charge type, shot density, tubing size and length, cable size, rathole length, and placement/setting of packers and shock absorbers. We analyzed two examples of gunshock damage: a tubing-conveyed perforation (TCP) job with 7-in. guns that produced a bent firing head fill-sub and tubing joints and a deep-water wireline job that broke the cable weak point. For both cases, we first simulated and analyzed the jobs as run to understand the observed damage and then we developed solutions to reduce the gunshock loads to a safe level. Introduction The objective of well perforating is to connect the reservoir rock to the wellbore for hydrocarbons to be easily produced or for fluids to be easily injected. Perforating with hollow carrier guns begins with the detonation of shaped charges contained inside thick-walled tubes called gun carriers. Shaped charges create high-velocity jets (~ 25,000 ft/sec) that produce tunnels in the reservoir rock. Shaped charges are selected based on the target completion type, either to penetrate deeply into the reservoir or, sacrificing penetration, open up an enlarged area for flow. When the shaped charges detonate, the hollow carriers deform due to internal gas pressure and debris impacting the inner side of the carrier. At the same time, the perforating jets puncture the hollow carrier wall, and the detonation gas inside the gun interacts with the wellbore fluid. All of these events combined lead to the onset of wellbore hydrodynamics, which includes large-amplitude pressure waves that produce very large loads on the equipment. The origin of gunshock loads generated by wellbore pressure waves will be explained in the gunshock studies presented in the following sections.

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