A new class of shaped charge was introduced to the industry in late 2007 that generates a secondary reaction in the perforation tunnel immediately after it has been formed. The reaction is highly energetic and drives the break up and expulsion of crushed zone material and compacted debris. This profoundly alters the geometry and quality of the resulting tunnels when compared to conventional perforators and underbalanced perforating techniques. This leads to significant improvements in the percentage of open, effective tunnels, the productivity of the perforated interval, and the ease and reliability with which the perforated formation can be stimulated.
Since their launch, reactive perforating systems have been applied to a variety of well and formation types - both conventional and unconventional - under a wide range of pressure and effective stress conditions. As a result, the applicability of the reactive perforating concept is being demonstrated and accepted for an increasing number of situations. Nevertheless, the industry is only just beginning to understand how reactive perforating can be applied and how well and completion designs should be optimized to take full advantage of the benefits this new technology affords.
This paper describes the application of reactive perforators to a number of geographically and lithologically different situations, for the purpose of transferring generic learnings and identifying opportunities for further study. Several clear opportunity areas are already emerging, such as perforating prior to hydraulic fracturing - notably in unconventional gas plays - and re-perforation of depleted or damaged intervals. Other areas are still to be properly explored, such as perforation prior to acidization - especially in carbonates, perforation of unconsolidated sandstones, and perforation of injection wells.
In conclusion the paper identifies those areas where the technology has shown greatest success and summarizes the key learnings that will assist operators in shortening their own learning curve when applying reactive perforator technology.
For more than thirty years, the military ballistics industry has been investigating - and investing in - reactive materials as a means to extract greater effectiveness from its devices (Hambling, 2008). By replacing metal casings with inert materials that combine to release explosive amounts of energy on impact, weapons can be more effectively tailored to particular targets and greater effect can be achieved with a smaller munition. British defense contractor QinetiQ has concentrated on applying this technology to shaped charges, replacing the metal charge liner with reactive materials to dramatically increase the amount of energy released. The transfer of this technology into oilfield shaped charges was a logical outstep, although it took more than eight years to achieve breakthrough performance under the tight constraints imposed by the borehole.
Reactive perforators are an entirely new class of shaped charge. The introduction of new materials, and a multitude of ways to configure them within the charge, has opened up a whole new playground for oilfield ballistic specialists, allowing them to create previously unthinkable geometries and post-penetration effects. Reactive liner perforators incorporate a proprietary combination of metals into the powdered metal mixture used to form the shaped charge liner. Under the tremendous heat and pressure of detonation, these metals react to form an intermetallic. This reaction is highly exothermic and the reaction rate is such that the majority of the heat release occurs within the newly formed perforation tunnel. Heating of the tunnel, and of the fluid in the surrounding rock, results in a significant pressure spike of very short duration. Following the path of least resistance, the pressure relieves towards the wellbore, breaking up and expelling compacted fill from within the tunnel and damaged, low-permeability rock from the so-called "crushed zone" along the tunnel walls. The result is a clean tunnel with minimal residual impairment to flow. In sufficiently low permeability targets, the over-pressure is sustained long enough for rock failure to occur, forming small fractures at the perforation tunnel tip (where the majority of the reactive material is concentrated). These fractures are highly beneficial to production, injection, and fracture stimulation activities.