Measurement of Gas Holdup in Slug Region of Horizontal Oil–Gas–Water Three-Phase Flow by a Distributed Ultrasonic Sensor

Oil–gas–water slug flow is the most common flow pattern in the horizontal pipe, which presents complex pseudoperiodic motion alternating between the film region and the slug region. The water in the slug region is a continuous phase, which is filled with nonuniformly distributed gas bubbles and oil droplets. Aim at measuring the gas holdup in the slug region, a distributed ultrasonic sensor (DUS) is developed which consists of one transmitter and three receivers A–C fixed at the pipe circumference. The measurement responses of the DUS and a wire-mesh sensor (WMS) are obtained in the experiment of horizontal oil–gas–water three-phase flow. Based on the flow visualizations of the WMS, bubble radii are extracted on 2D planes, and the relationship between average bubble size and the instantaneous gas holdup is derived. Thus, ultrasonic attenuation MCBL model is modified by considering the bubble size, absorption, and scattering attenuation at the gas–liquid interface. According to the responses of receiver A, the modified MCBL model is used to measure the gas holdup at the pipe center. Besides, side receivers B and C provide complementary information about scattering off the gas bubbles in the ultrasonic path. Statistic models are constructed based on the responses of receivers B and C to measure the gas holdup at the side of the pipe cross section. Generally, the DUS enables us to successfully measure the gas holdup in the slug region of the oil–gas–water slug flow.