Streamer Dynamics Simulation of Water Vapor and CH₄/CO₂ Gas Mixtures in Unconventional Oil and Gas Development Scenarios

Underwater high-voltage electric pulse reservoir reconstruction technology is an environmentally friendly and lowcost fracturing method with great potential in unconventional oil and gas development. However, the production of associated gas during operation inevitably affects the breakdown characteristics and efficiency of the water medium. In this study, the electron transport parameters of $\mathrm{H}_{2} \mathrm{O} / \mathrm{CH}_{4} / \mathrm{CO}_{2}$ gas mixtures were calculated based on the Boltzmann equation, and a twodimensional streamer dynamics model in a non-uniform electric field was established. The results indicate that the streamer morphology of gas mixture with high water vapor content and $\mathrm{CH}_{4} / \mathrm{CO}_{2}$ appears as coarse columnar with suppressed branching. Furthermore, increasing the CH<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> and CO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> content reduces the ionization and attachment coefficients while increasing electron mobility, directly leading to an increase in streamer propagation velocity and electron density at the streamer head.