Electric Fracturing Using Flying Capacitor Multi-Level Converters

Abstract

The authors propose a new structure using multilevel converters to generate high pulsing voltage discharges in water for electric fracturing process of shale gas. This solution is a new alternative to hydraulic fracturing process able to minimize environmental impacts related to exploration and exploitation of shale gas. This new structure is able to generate shock waves under subsonic and supersonic modes by combining serial connection between two Flying Capacitor Multi-level Converters (FCMC) and capacitor bank controlled by two Thyristors connected in inverse parallel. The two different discharge modes leading to dielectric breakdown in water gap will be studied. The development of supersonic discharge will be investigated electrically using FCMC supplied with 50 kV. The pulse widths of IGBTs are calculated to obtain a bi-exponential waveform characterized by a rise time less than 100 ns and a duration of wave tail around 800 ns. The simulation results are carried out by taking into account the breakdown of dielectric water around inter-electrodes space. Whatever the water breakdown mode, the peak pressure linearly depends from the peak current. Moreover, the electro-acoustic efficiency is better using a supersonic discharge.