With 20 years of operations, multiphase flowmeters (MPFMs) using a combination of venturi and multi-energy gamma-ray absorption have gained acceptance in the oil and gas industry by demonstrating reliable measurement and operational robustness. Nonetheless, some challenging operating scenarios are encountered such as significant water salinity changes in multiphase and wet-gas flows and rapid detection of small water quantities during production.
Although MPFMs are not affected by small water salinity changes, inaccurate flow rates can be calculated when water salinity significantly departs from the initial properties. To maintain measurement metrology as per specifications, the water-point should be manually modified to track variations; however, this operation is time consuming and may incur nonproductive time. The salinity change measured by a newly developed sensor can be provided seamlessly to MPFMs to automatically update the water point calibration, thus ensuring good flow rate measurement performance over a wider water salinity range. Extensive validations at several flow loop facilities and field tests, including frac flowback operations, demonstrate the robustness of the method in terms of hardware reliability and the delivery of high-quality data when used with MPFMs with digital connectivity, which opens the way to unmanned production monitoring operations. Interpreting multiphase mixture's dielectric constant and electrical conductivity simultaneously measured by the new microwave water salinity sensor at a high data acquisition rate shows that water salinity can be tracked online in the presence of oil, gas, and sand, and small water quantities down to 50 ppm (part-per-million) water volume fraction (WVF), from the typical ~1000-ppm WVF for the MPFM, can be detected rapidly in multiphase and wet-gas flows.
This paper describes the working principles of the new sensor that enable additional capabilities to maintain accurate water-liquid ratio (WLR) measurement in situations where significant water salinity changes occur and to provide a rapid, much lower WVF detection level. Successful cases demonstrating an accurate real-time salinity monitoring in flow loop tests and in field operations are also presented.
