Ultrasonic method for measuring water holdup of low velocity and high-water-cut oil-water two-phasefl ow

摘要

Oil reservoirs with low permeability and porosity that are in the middle and late exploitation periods in China’s onshore oilfi elds are mostly in the high-water-cut production stage. This stage is associated with severely non-uniform local-velocity flow profiles and dispersed-phase concentration (of oil droplets) in oil-water two-phase flow, which makes it diffi cult to measure water holdup in oil wells. In this study, we use an ultrasonic method based on a transmission-type sensor in oil-water two-phase flow to measure water holdup in low-velocity and high water-cut conditions. First, we optimize the excitation frequency of the ultrasonic sensor by calculating the sensitivity of the ultrasonicfi eld using thefi nite element method for multiphysics coupling. Then we calculate the change trend of sound pressure level attenuation ratio with the increase in oil holdup to verify the feasibility of the employed diameter for the ultrasonic sensor. Based on the results, we then investigate the effects of oil-droplet diameter and distribution on the ultrasonicfi eld. To further understand the measurement characteristics of the ultrasonic sensor, we perform a flow loop test on vertical upward oil-water two-phasefl ow and measure the responses of the optimized ultrasonic sensor. The results show that the ultrasonic sensor yields poor resolution for a dispersed oil slug in waterfl ow (D OS/Wfl ow), but the resolution is favorable for dispersed oil in waterfl ow (D O/Wfl ow) and veryfi ne dispersed oil in waterfl ow (VFD O/Wfl ow). This research demonstrates the potential application of a pulsed-transmission ultrasonic method for measuring the fraction of individual components in oil-water two-phasefl ow with a low mixture velocity and high water cut.