Water-cut measurement using a planar microwave resonant sensor under flowing operating conditions

Accurate monitoring of water content in flowing oil/bitumen pipelines remains a critical challenge in the petroleum industry, as it directly affects production optimization, custody transfer, and reservoir management. In this study, we present a new microwave sensor approach for real-time, noncontact quantification of water content in flowing oil-water mixtures under operating conditions. The sensing approach exploits the strong dielectric contrast between water and oil/bitumen by monitoring the flowing stream over a defined microwave frequency range and tracking resonance frequency shifts associated with changes in effective permittivity. The sensing system consists of a planar battery-less sensing tag electromagnetically coupled to a reader at a specific distance, enabling contactless monitoring. The sensor shows high sensitivity within the 600–850 MHz frequency band and a total resonance frequency shift of about 18 MHz across the full water-cut range. To replicate oilfield-relevant operating conditions, we constructed a laboratory-scale flow loop to circulate two-phase oil-water emulsions. The experiments were conducted at water cuts from 0 to 100 wt% and temperatures from 24 to 110 °C at 150 psig. The sensor shows a continuous, monotonic response across the entire emulsion spectrum ( i.e ., water-in-oil, oil-in-water, and phase-inversion regimes). The proposed technique offers fast, instantaneous response, high sensitivity, and robust performance under elevated temperature and pressure, while remaining low-cost, passive, and easy to integrate with existing pipeline infrastructure.