Flow-Loop Investigation and DAS-Based Flow-Rate Prediction for Gas–Water Two-Phase Flow Under Near-Horizontal High-Rate Gas-Well Conditions

Gas–water two-phase flow at high gas rates and low water cuts generates complex acoustic responses, necessitating experimental calibration for distributed acoustic sensing (DAS)-based flow-rate estimation. Near-horizontal air–water flow-loop experiments were conducted at well inclinations of 85°, 88°, and 90°, covering different flow-rate and water-cut combinations. Spectral analysis showed that DAS signal energy was concentrated below 500 Hz. Four flow regimes were identified: bubbly, slug, stratified, and wavy flow. Flow-regime-dependent characteristic Reynolds numbers (Re) were correlated with frequency-band energy (FBE), and the fitted coefficients were compiled into a database. For each inclination, Gaussian process regression was used for coefficient interpolation within the calibration range, while Bayesian ridge regression enabled limited extrapolation near the calibration boundaries. Measured FBE and reconstructed Re–FBE relationships were used to estimate characteristic Reynolds numbers and calculate total flow rates. Across 26 independent validation conditions, absolute relative errors ranged from 0.05% to 8.98%, with a mean absolute percentage error of 3.01%, compared with 18.28% for cross-correlation. These results support quantitative DAS-based flow-rate estimation under the tested laboratory conditions. Application to actual gas wells requires further calibration and validation under representative high-temperature and high-pressure conditions.