Transient Multiphase Flow Analysis of Toe-Down, Toe-Up, and Horizontal Shale Gas Wells

Abstract This study focuses on the transient gas-liquid flow behavior in three distinct well trajectories—toe-down, toe-up, and horizontal—within a shale gas reservoir. The objective is to elucidate how varying production rates affect liquid holdup, pressure distribution, and slug formation, thereby guiding more effective wellbore design and operational strategies. A transient multiphase flow model was constructed using OLGA, incorporating actual field data from a representative Luzhou-block shale gas well (Well X). Two additional trajectory scenarios—toe-up and horizontal—were generated by systematically adjusting maximum true vertical depth, wellhead-to-bottom-hole elevation difference, and measured depth at the target point. The simulations captured real-world wellbore geometry, fluid properties, and operational conditions. Comparative analyses then quantified variations in flow regimes and evaluated overall stability under different gas production rates (10,000–100,000 m 3 /d). Simulation outcomes show that toe-down wells often accumulate liquid in horizontal segments, while toe-up wells face significant slugging in inclined sections at lower production rates. Horizontal wells typically exhibit more uniform fluid distribution, although localized liquid retention can emerge in deviated zones. Increasing the gas production rate reduces liquid holdup initially, but frictional losses dominate when rates exceed a certain threshold, leading to diminishing returns in liquid removal. Toe-down wells maintain relatively stable bottom-hole pressures across varying operational conditions, indicating a balance between liquid buildup and gas flow. In contrast, toe-up wells are prone to severe slug formation at reduced rates, highlighting the importance of selecting optimal production rates. Collectively, these findings underscore the critical role of well trajectory design in enhancing flow stability and mitigating liquid accumulation, providing valuable insights for completion practices and operational decision-making.