A Laser-Based Calibration-Free Water-Cut Meter

Accurate inline measurement of water-cut (WC) in crude-oil production is essential for effective well and reservoir management. Existing water-cut meters typically require well-specific calibration which can be time-consuming and challenging, especially when servicing multiple wells or commingled lines. For example, water-cut meters based on near-infrared (NIR) absorption spectroscopy require a priori knowledge of oil absorbance spectra for each crude-oil type or well site. To address this issue, this article describes the development of a NIR laser-based device with a novel algorithm that removes the dependence on oil calibration. The developed sensor probes water absorption lines near 5000 cm−1 (for water cut in the range 0%–10%) and 7000 cm−1 (for water cut in the range 10%–100%). To validate the sensor performance, a benchtop flow-loop was built to circulate known mixtures of water and oil. The sensor was demonstrated to work accurately (±5% absolute, 95th percentile) in oil-water (OW) flows with light oils and oil-substitutes (glycol, gasoline, and diesel) over the full range (0%–100%) water-cut. The sensor was also found to be quite immune to the presence of salt and sand in the flow, and to process-temperature variations.