Abstract
Underwater shock waves generated by pulsed electrical discharges are an effective, economical, and environmentally friendly means of stimulating reservoirs, and this technology has received much attention and intensive research in the past few years. This paper reviews the main results of recent work on underwater electrical wire explosion (UEWE) for reservoir stimulation. A platform is developed for microsecond single-wire explosions in water, and diagnostics based on a voltage probe, current coil, pressure probe, photodiode, and spectrometer are used to characterize the UEWE process and accompanying shock waves. First, the UEWE characteristics under different discharge types are studied and general principles are clarified. Second, the shock-wave generation mechanism is investigated experimentally by interrupting the electrical energy injection into the wire at different stages of the wire-explosion process. It is found that the vaporization process is vital for the formation of shock waves, whereas the energy deposited after voltage collapse has only a limited effect. Furthermore, the relationships between the electrical-circuit and shock-wave parameters are investigated, and an empirical approach is developed for estimating the shock-wave parameters. Third, how the wire material and water state affect the wire-explosion process is studied. To adjust the shock-wave parameters, a promising method concerning energetic material load is proposed and tested. Finally, the fracturing effect of the pulsed-discharge shock waves is discussed, as briefly are some of the difficulties associated with UEWE-based reservoir stimulation.
Highlights
This paper reviews the main results of recent work on underwater electrical wire explosion (UEWE) for reservoir stimulation
A platform is developed for microsecond singlewire explosions in water, and diagnostics based on a voltage probe, current coil, pressure probe, photodiode, and spectrometer are used to characterize the UEWE process and accompanying shock waves
Electrical explosion of a metal wire driven by a pulsed current is a common method for generating (i) a plasma with relatively high temperature and density, (ii) pulsed electromagnetic radiation, and (iii) shock waves (SWs), and this method is used widely in the fields of Z-pinch plasma confinement, warm dense matter, nano-powder preparation, and reservoir stimulation, among others
Summary
Electrical explosion of a metal wire driven by a pulsed current is a common method for generating (i) a plasma with relatively high temperature and density, (ii) pulsed electromagnetic radiation, and (iii) shock waves (SWs), and this method is used widely in the fields of Z-pinch plasma confinement, warm dense matter, nano-powder preparation, and reservoir stimulation, among others. For a wire exploded in a denser medium (e.g., air or water), the pulsed current passes through the metal wire and heats the load in a short period, resulting in fast phase transitions, non-ideal plasmas (coupling parameter Γ ≥ 1), optical emission, and strong SWs, among other outcomes. in the case of underwater electrical wire explosion (UEWE), strong SWs (gigapascal level) can be found in the vicinity of the exploding wire. As the most obvious phenomenon accompanying UEWE, SWs via pulsed discharges are mentioned frequently in connection with shock compression, electrohydraulic forming, non-thermal food processing, and reservoir stimulation, among others.. After the explosion, the load is either a high-resistance aerosol or conducting plasma, and the energy deposition is suppressed, thereby decreasing the DC expansion rate For such circumstances, a third type of SW source was proposed, one in which an energetic material (EM) layer (covering the wire) is used to strengthen the SWs.. We describe the technical details of an experimental setup that we established for researching microsecond wire explosions On this platform, various wire loads have been exploded by different pulsed currents, and we have detected and analyzed the main processes, such as SWs and optical emission. We summarize how the parameters of (i) the pulsed power source, (ii) the wire, and (iii) the medium influence the wireexplosion characteristics, and we present general principles and regulation methods for discharge type, energy deposition, SWs, and optical radiation. By applying frequency-domain analysis, the main SW can be reconstructed and presented more precisely.
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