Ying-Yu Ren

Multi-Scale Long-Range Magnitude and Sign Correlations in Vertical Upward Oil–Gas–Water Three-Phase Flow

Abstract In this article we apply an approach to identify the oil–gas–water three-phase flow patterns in vertical upwards 20 mm inner-diameter pipe based on the conductance fluctuating signals. We use the approach to analyse the signals with long-range correlations by decomposing the signal increment series into magnitude and sign series and extracting their scaling properties. We find that the magnitude series relates to nonlinear properties of the original time series, whereas the sign series relates to the linear properties. The research shows that the oil–gas–water three-phase flows (slug flow, churn flow, bubble flow) can be classified by a combination of scaling exponents of magnitude and sign series. This study provides a new way of characterising linear and nonlinear properties embedded in oil–gas–water three-phase flows.

Ultrasonic method for measuring water holdup of low velocity and high-water-cut oil-water two-phase flow

Oil reservoirs with low permeability and porosity that are in the middle and late exploitation periods in China’s onshore oil fields 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 difficult 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 ultrasonic field using the finite 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 ultrasonic field. To further understand the measurement characteristics of the ultrasonic sensor, we perform a flow loop test on vertical upward oil-water two-phase flow 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 water flow (D OS/W flow), but the resolution is favorable for dispersed oil in water flow (D O/W flow) and very fine dispersed oil in water flow (VFD O/W flow). This research demonstrates the potential application of a pulsed-transmission ultrasonic method for measuring the fraction of individual components in oil-water two-phase flow with a low mixture velocity and high water cut.

Nonlinear Dynamic Characteristics of Oil-in-Water Emulsions

Abstract In this article, the nonlinear dynamic characteristics of oil-in-water emulsions under the addition of surfactant were experimentally investigated. Firstly, based on the vertical upward oil–water two-phase flow experiment in 20 mm inner diameter (ID) testing pipe, dynamic response signals of oil-in-water emulsions were recorded using vertical multiple electrode array (VMEA) sensor. Afterwards, the recurrence plot (RP) algorithm and multi-scale weighted complexity entropy causality plane (MS-WCECP) were employed to analyse the nonlinear characteristics of the signals. The results show that the certainty is decreasing and the randomness is increasing with the increment of surfactant concentration. This article provides a novel method for revealing the nonlinear dynamic characteristics, complexity, and randomness of oil-in-water emulsions with experimental measurement signals.

Multi-Scale Morphological Analysis of Conductance Signals in Vertical Upward Gas–Liquid Two-Phase Flow

Abstract The multi-scale analysis is an important method for detecting nonlinear systems. In this study, we carry out experiments and measure the fluctuation signals from a rotating electric field conductance sensor with eight electrodes. We first use a recurrence plot to recognise flow patterns in vertical upward gas–liquid two-phase pipe flow from measured signals. Then we apply a multi-scale morphological analysis based on the first-order difference scatter plot to investigate the signals captured from the vertical upward gas–liquid two-phase flow loop test. We find that the invariant scaling exponent extracted from the multi-scale first-order difference scatter plot with the bisector of the second-fourth quadrant as the reference line is sensitive to the inhomogeneous distribution characteristics of the flow structure, and the variation trend of the exponent is helpful to understand the process of breakup and coalescence of the gas phase. In addition, we explore the dynamic mechanism influencing the inhomogeneous distribution of the gas phase in terms of adaptive optimal kernel time–frequency representation. The research indicates that the system energy is a factor influencing the distribution of the gas phase and the multi-scale morphological analysis based on the first-order difference scatter plot is an effective method for indicating the inhomogeneous distribution of the gas phase in gas–liquid two-phase flow.

Measurement of Pressure Drop and Water Holdup in Vertical Upward Oil-in-Water Emulsions

This paper aims to experimentally investigate pressure drop and water holdup in vertical upward oil-in-water emulsions. As a key factor to extract water holdup with differential pressure method, friction factor is complicatedly associated with the Reynolds number of mixed fluid. However, due to the fact that oil and water phase cannot be easily separated in emulsions, the traditional quick-closing valve (QCV) method is incapable of determining water holdup, which is imperative to determine the Reynolds number of mixed fluid. In this paper, regarded as an auxiliary measurement method, an arc type conductivity probe (ATCP) is utilized to derive water holdup parameter. Combining water holdup and differential pressure information, we extract friction factor and analyze its relationship with the Reynolds number of mixed fluid. Besides, drag reduction phenomena in surfactant aqueous solution and oil-in-water emulsions are discussed as well. Finally, water holdup is predicted using differential pressure information and experimental expression of friction factor, the result of which proves the effectiveness of differential pressure method for the measurement of water holdup in oil-in-water emulsions.

Ultrasonic method for measuring the gas holdup of gas-liquid bubbly flow in a small-diameter pipe

Based on ultrasonic sound pressure attenuation, the ultrasonic pulse transmission method is proposed for measuring gas holdup in gas-liquid two-phase bubbly flows. Two ultrasonic transducers are positioned on opposite sides of a vertical upward pipe with an inner diameter of 20 mm. To obtain the relationship between ultrasonic attenuation and gas holdup, the mean value of the first pulse sequence of ultrasonic signals is first extracted as the measured signal. We used the quick closing valve method to obtain the gas holdup as the set value. Second, the relationship between the gas holdup and measured ultrasonic signals was established. The experiment result shows that the ultrasonic attenuation rate is significantly different at low and high gas holdups, as indicated by the bubble size images with a high-speed camera. We also investigated the ultrasonic field distribution using numerical simulation. The bubble size has an important effect on the ultrasonic attenuation coefficient, which provides a further physical explanation and reference for the experimental phenomena.