Liquid Holdup Measurement in Crude Oil Transportation Using Capacitance Sensors and Electrical Capacitance Tomography: Concept Review

Abstract Liquid holdup is one of the most significant parameters in multiphase flow. Accurate measurement of liquid holdup is required to calculate pressure drops in oil and gas wells which is essential in analyzing the well production, performance, well designing and optimization. This study reviewed different methods used in measuring liquid holdup and highlighted the most effective methods currently used in multiphase combinations. More importantly, liquid holdup measurements using capacitance sensors in slug flow, bubble flow, churn flow, annular flow and coaxial flow are discussed. The features considered during the review include, electrode material, angle of rotation, curvature and guard electrodes. The operational issues observed when using capacitance based sensors were highlighted. In single capacitance sensors like the helical arrangement which has high sensitivity, error in symmetry and inability to measure fluids with lower dielectric constants were however observed. Concave sensors are more accurate for phase shift detection but lower sensitivity compared to the helical type. From the knowledge and technical gaps identified from literature, this study proposed Electrical Capacitance Tomography tool with dual capacitance sensor for effective liquid holdup measurement in oil and gas transportation pipelines because of its ability to determine the dielectric permittivity distribution inside the pipeline from external capacitance measurements with real-time imaging of the multiphase flow.