Experimental Investigation of the Effect of Lateral Trajectory on Flow Stability in Horizontal Gas Wells

Abstract A large-scale experimental investigation was conducted to evaluate the impact of lateral trajectory on flow stability in horizontal wells. The experiment was carried out on a device that featured 50mm inner diameter (ID), 2m long vertical section, and 4m long inclined section, with a 100mm ID and 4m long lateral section, miming a shale horizontal gas well. Three wellbore geometries were modeled by systematically adjusting the deviation angle of the lateral section by ±12° from the horizontal plane. Additionally, the flow patterns, pressure fluctuations, and film reversal gas velocities were measured to evaluate how the wellbore trajectory affects flow stability. Experimental results indicate that lateral trajectory significantly affects slug formation and movement of the lateral section, which increases erratic production in the vertical and inclined sections, mainly manifested by pressure fluctuations and zero liquid flow. The impact of gas and liquid rates in toe-down geometry on flow stability in horizontal gas wells is especially significant during the low-pressure production stage. Meanwhile, the film reversal occurs at the entrance of 45° inclined section and the vertical section when the superficial gas velocity decreases to 12.62 and 6.48 m/s, respectively. The test data showed that pressure drop in the tubing decreases rapidly at first and then slows as the gas rates increases, with a transition point between 2 ~ 3 m/s. It reaches a minimum value at a gas velocity of approximately 19 m/s, after which the pressure drops increase again due to the heightened friction resulting from the high gas velocity. This study identified the optimal regions for wellbore energy optimization and the appropriate occasions for intervention in the artificial lift process. It also clarified the mechanism of liquid slug generation in three different typical lateral trajectories, which is helpful to optimize the wellbore lateral trajectories, ultimately reducing drilling operational costs and time.