Pressure-fluctuation feature characterization and flow-pattern identification in gas–water two-phase flow

Abstract

Wellbore inclination redistributes the gravitational components acting on gas–water two-phase flow, thereby altering phase distribution and the wall-pressure fluctuation response. Understanding this mechanism is essential for interpreting production-logging responses in gas–water flow. In this study, three-dimensional transient numerical models were developed for horizontal, 45° deviated, and vertical wells using the volume-of-fluid interface-capturing method coupled with the large-eddy simulation wall-adapting local eddy-viscosity turbulence model. Fourteen gas–water flow conditions were simulated, covering gas superficial velocities of 0.2–8.0 m/s and liquid superficial velocities of 0.1–3.8 m/s, and wall-pressure signals were collected using an 18-channel monitoring array distributed along the upper and lower wall surfaces. The results show that stratified flow in horizontal wells exhibits clear phase separation, whereas slug and bubbly flows in vertical wells remain approximately axisymmetric. In the 45° deviated wellbore, slug flow is marked by upward displacement of gas slugs and an inclined, asymmetric gas–liquid interface. Under identical inlet velocities, the peak pressure fluctuation in the 45° deviated wellbore reaches approximately 7500 Pa, about 1.53 times that observed in the vertical wellbore. The gas-slug propagation velocity captures the axial coherent motion, while the fluctuation intensity is additionally controlled by gas-slug offset, asymmetric liquid-film distribution, and liquid-slug momentum sweeping. Based on a seven-dimensional multiphysics feature set, the linear discriminant analysis classifier achieved a flow-pattern identification accuracy of 97.62%. These findings provide a physical basis for flow-pattern identification in complex wellbores and for the interpretation of distributed acoustic sensing monitoring data.