Underwater shock wave generated by exploding wire ignited energetic materials and its application in reservoir stimulation

Electrical wire explosion (EWE) has been extensively studied as an efficient source of underwater shock waves (SWs), with potential applications in electrohydraulic forming, reservoir stimulation, etc. The amplitude, impulse and energy of EWE shock waves are, however, limited by the energy storage of the power source, which is sometimes technically difficult or very expensive to increase, for example in a deep and narrow wellbore. In these situations, it is possible to further enhance the SWs by additional energetic materials that can be ignited by the EWE plasmas. The concept is quite alike the bridge wire detonator, but in this case the EWE operates with much higher current, and the energetic materials of much lower sensitivity, such as ammonium perchlorate /aluminum mixture (AP /Al), AP /Al /nitromethane mixture, CuO /Al /nitromethane mixture, can be directly ignited. The SW of this hybrid load contains a high amplitude, short-pulse EWE component generated by EWE and detonation of energetic materials, and a relatively low amplitude, long-pulse component generated by the combustion of energetic materials (mainly Al) behind the detonation wave front. This approach provides a practical compromise among limited energy storage, strong shock waves, and safe usage of explosives. In this talk, we present experimental results and engineering applications of this hybrid SW load, including the EWE characteristics in a powdered and muddy Al-based energetic material, physical process of the ignition, combustion and SW formation, the SW characteristics, the SW generator with automatic load feeding, and finally applications in enhanced recovery of coal bed methane. The promises and challenges in this SW-based dynamic reservoir stimulation technique will also be discussed.