One-Dimensional Drift-Flux Modeling of Gas–Liquid Flow in Inclined Gas-Lift Pipelines

Gas-lift performance depends on pipeline inclination and gas injection conditions. This study examines these effects using an unsteady, one-dimensional gas–liquid drift-flux model and a finite-volume solver. The carrier liquid is Newtonian with prescribed density and viscosity; separate solid-particle transport is not modeled. The application cases cover static inclinations of 60–90° from the horizontal, a pipe diameter of 0.1023 m, and an axial length of 197 m. Comparisons with inclined bubble drift and vertical airlift measurements assess different aspects of the formulation. Grid and time step comparisons are reported as sensitivity checks. At a fixed axial injection distance of 185 m below the still-water intersection, the vertical injection depth decreases from 185 m at 90° to 160.21 m at 60°. Thus, the inclination comparison changes both the hydrostatic head and the adopted slip closure. Injection rate comparisons of 0.1–0.4 kg s−1 and axial injection distance comparisons of 160–185 m show changes in gas holdup, phase velocities, and start-up behavior. The results describe comparative gas–liquid hydrodynamics within the stated assumptions; they do not establish compressor energy efficiency or validated deep-sea slurry throughput.