Dominant factors affecting breakdown voltage in the repetitive spark gap switch for unconventional reservoir exploitation

Abstract Spark gap switch (SGS) is widely used in pulsed power supplies, whose frequency and amplitude of output voltage are highly dependent on its repetitive breakdown performance. However, the breakdown characteristics of SGS used in unconventional reservoir exploitation under high-temperature and high-pressure downhole conditions remain poorly understood. In this paper, a plasma fluid model is employed to investigate factors affecting the breakdown voltage of the repetitive SGS in dry air, and the simulation model is validated experimentally. The simulation results indicate that the cumulative temperature and the discharge products, specifically nitrogen oxides, are the dominant factors affecting the breakdown voltage of SGS in a sealed environment. When the electrode gap is set to 4 mm, the breakdown voltage amplitude decreases from 11 722 V to 9023 V as the temperature increases from 443 K to 723 K. The breakdown voltage decreases approximately linearly with increasing NO x concentration, primarily due to the fact that NO x is more easily ionized compared to air. Furthermore, a higher NO content in NO x leads to a lower breakdown voltage. In contrast, sputtered metal particles that adhere to the electrode and the conductivity of the downhole liquid have relatively minor effects on the breakdown voltage. These results are helpful in designing a pulsed power supply that can output stable frequencies and shock waves, which can be used to enhance the efficiency of unconventional reservoir exploitation.