Characterization of Two-phase Slug Flow using Distributed Acoustic Sensing in Horizontal Pipes

Abstract

Abstract This article discusses the use of Distributed Acoustic Sensing (DAS) to monitor and characterize two-phase slug flow in horizontal pipes. This technology utilizes a regular telecommunication fiber connected to a DAS interrogator to detect flow signals and provide substantial insights into flow characterization and quantification. The capabilities of the DAS are highlighted through a series of experimental tests using various rates of two-phase liquid and gas fluids. The experiments were conducted in a multiphase flow loop consisting of a transparent polyvinyl chloride (PVC) horizontal test section measuring 14 m. long and 5 cm. inner diameter. A fiber cable was wrapped helically on two 35 cm. long sections, around 61 cm apart, with 11 loops per cm on each section. Mineral oil, tap water, and compressed air were used as the testing fluids. The oil phase velocity varied from 0.2 to 0.8 m/s, while the gas phase varied from 19 to 95 LPM. The facility was also equipped with a high-speed camera and an Electrical Capacitance Volumetric Tomograph (ECVT) system for cross-validating purposes. New low-frequency strain-rate analysis of the DAS signal demonstrates its capabilities of quantifying two-phase slug flow characteristic parameters, including the slug frequency, slug body length, slug translational velocity, the slug unit, and the liquid film region lengths. The results were compared with the data obtained from the high-speed camera, located right next to the wrapped fiber section, and ECVT, located after the second wrapped section. The three measurements show good matches for all tested flowing conditions. The results will shed light on the production prediction and profiling for slug flow in wellbores or surface pipeline systems. Compared to other sensors that can also characterize slug flow, such as optical or conductivity/capacitance sensors, DAS technology has the advantages of real-time and continuous measurement over long distances. It can also be applied in harsh environments such as in downhole wellbore conditions where other sensors may not withstand. It opens the doors of production profiling in wellbore/pipeline over long distances which cannot be realized by other point sensors. The cost is relatively low in the field application compared to other point sensors, especially in conditions where measurements are required at multiple locations, with the fact that fiber cable is much cheaper compared to other sensors. For the first time, this study shows in detail the capability of DAS in characterizing two-phase slug flow in horizontal pipes, and its potential for production profiling in horizontal wells and surface pipeline systems. New insights on the low-frequency DAS signal are discussed along with the physical interpretation of the slug flow dynamics. The new analysis will be beneficial to the petroleum industry in advancing production profiling technologies, production process optimization, and operation safety management.