Distributed Acoustic Sensing for Monitoring Oil–Water Two-Phase Flow in Horizontal Wells: Experimental Characterization and Flow-Velocity Modeling

Abstract

Distributed acoustic sensing (DAS) enables continuous acquisition of acoustic responses along a wellbore and has considerable potential for production-profile monitoring and flow-state identification in horizontal wells. However, existing studies have focused mainly on correlations between DAS signal characteristics and flow states, while the coupled effects and quantitative relationships among fluid properties, wellbore conditions, and DAS responses remain insufficiently understood. To characterize DAS responses under oil-water two-phase flow, physical simulation experiments were conducted in a horizontal wellbore under different crude-oil viscosities, water cuts, and wellbore inclinations. Spectral characteristics and acoustic-energy variations were analyzed to determine how fluid properties and wellbore conditions affect DAS responses. The results show that the dominant DAS frequency shifts overall toward lower frequencies as crude-oil viscosity increases; DAS acoustic energy generally increases with water cut within the investigated oil–water two-phase conditions; and both spectral and energy responses vary markedly with wellbore inclination. On this basis, an exponential relationship between DAS acoustic energy and average wellbore velocity was established, followed by a multifactor response-surface model incorporating average wellbore velocity, crude-oil viscosity, water cut, and wellbore inclination. The standardized regression results identify average wellbore velocity as the primary factor affecting DAS acoustic energy and indicate coupling between average wellbore velocity and both water cut and crude-oil viscosity. These results provide an experimental basis for DAS-based interpretation of flow parameters and production profiles in horizontal wells.