Slug Holdup Research Articles

Unmasking the mystery: The path to accurate liquid slug holdup prediction

Slug flow modeling relies on various correlations for predicting liquid slug holdup (HLS). These correlations, developed from specific experimental ranges, sometimes fail to predict HLS accurately when applied outside their original operational conditions and other times result in strange behavior. The common belief is that these failures are due to limited experimental data ranges, but another significant factor is the inconsistency in HLS values for the same superficial liquid to gas velocity ratio (VSL/VSG). This ratio has not been adequately considered in existing correlations. This study investigates the hypothesis that HLS should remain constant for a given VSL/VSG ratio, assuming the flow regime remains within slug flow. By analyzing different correlations, we identify discrepancies in HLS predictions for identical VSL/VSG values, challenging the assumption that liquid content should be consistent within a stable flow regime. The paper provides evidence supporting this hypothesis and proposes a new approach for more accurate HLS predictions. Our findings highlight the necessity of considering the VSL/VSG ratio to enhance the reliability of liquid slug correlations and models.

Novel correlations for the liquid holdup in a gas-liquid slug flow

This paper introduces novel equations for calculating the slug unit liquid holdup (average liquid holdup) and the slug liquid holdup (slug holdup) in liquid-gas slug flow. The equations were tested across various pipe diameters, incline angles, fluid viscosities and densities, system pressures, and liquid and gas flow rates. The correlation utilizes two dimensionless numbers and displays a self-similar nonlinear symmetrical sigmoidal trend. The two parameters used are the ratio of the no-slip liquid holdup to the in-situ liquid holdup and the ratio of liquid superficial velocity to gas superficial velocity. When the superficial velocities ratio is high, all data converge to a single value of approximatly1 for the no-slip to in-situ liquid holdup ratio. The present unified correlations are simple to implement in any slug flow model. It employs defined parameters, and it has already been tested for varying pipe diameters, inclinations, and fluid viscosities that range from water to 962 cP. The presented correlations are unified and unique and not found in public literature. The suggested correlations exhibit superior performance compared to existing correlations and models.

Slug flow parameters applied to dynamic riser analysis

Slug flow is a typical pattern in the petroleum production system. Its main feature is intermittency. This feature influences the riser dynamic behavior due to the coupling of its geometric configuration and time and space variation of internal fluid parameters. Although the studies that illustrate slug flow intermittency and dynamic riser behaviors have been growing recently, this discussion still needs to be expanded. Most slug models proposed in the literature are simplified and do not adequately capture the intermittency to a proper riser dynamic influence determination. Previous models neglected at least one of the following slug flow mechanisms: random features, bubble shape, liquid slug aeration, wake, and pipeline inclination effects. This paper aims to cover all these phenomena and present a model that provides realistic slug flow data for any riser analysis program. The dynamic riser analysis is not the scope of this paper. This article used a new slug tracking model that captures the intermittency to study the influence of the internal flow over the dynamic riser behavior. The model considers the liquid slug hold-up and its change over the pipe, the oil and gas thermodynamic properties, and the geometrical transition from typically horizontal plane interfaces to vertical concentric bubble shapes. The slug tracking model tests use three gas and liquid ratios (0.55, 0.7, and 0.82) with a 2.05 m/s constant mixture velocity. The maximum relative pressure deviation was 24.1. Time and space analysis of the slug flow parameters demonstrates the slug tracking capacity to reproduce the intermittency of the bubble and liquid slug lengths, void fractions, velocities, and pressures. This intermittence is essential to describe the internal slug flow influence on the structure behavior.

Slug flow characterization in horizontal annulus

AbstractTo characterize slug flows in annuli channels and highlight the effect of the eccentricity on the flow behaviors, experiments were conducted in two horizontal annuli setups (a) concentric and (b) fully eccentric using air and water as the testing fluids. The range of air and water superficial velocities investigated were 0.45–3.49 m/s and 0.15–2.77 m/s, respectively. Slug parameters measured using conductance probes designed for this study include slug length, translational velocity, slug frequency, and slug holdup. It is found that the slug translational velocity is unaffected by the annulus eccentricity; however, parameters including slug frequency, slug holdup, and slug lengths have a higher value in the fully eccentric annulus when compared with the concentric one. We introduced a new definition of hydraulic diameter, which reconciles the correlation between the dimensionless mean slug length and the mixture velocity of the horizontal annuli with different setups.

Estimating slug liquid holdup in high viscosity oil-gas two-phase flow

Slug flow is one of the most critical and often encountered flow patterns in the oil and gas industry. It is characterised by intermittency which results in large fluctuations in liquid holdup and pressure gradient. A proper understanding of its parameters (such as slug holdup) is essential in the design of transport facilities (e.g. pipelines) and process equipment (slug catchers, separators etc.). In this paper, experimental investigation of slug liquid holdup (defined as the liquid volume fraction in the slug body of a slug unit) is performed. Mineral oil with viscosity, μ=−0.0043T3+0.0389T2−1.4174T+18.141 and air were used as test fluids. A 0.0254 m and 0.0762 m pipe internal diameters facilities with pipe lengths of 5.5 and 17 m respectively were used in the study. Electrical Capacitance Tomography was used for slug holdup measurements. Results obtained in the study shows that slug liquid holdup varied directly as the viscosity and inversely as the gas input fraction. Existing slug holdup correlations and models in literature did not sufficiently predict present experimental results. A new empirical predictive correlation for estimating slug liquid holdup was derived from present experimental databank and from data obtained in literature. The databank's liquid viscosity ranges from 0.189 to 8.0 Pa s. Statistical analysis of the new correlation vis-à-vis existing ones showed that the present correlation gave the best performance with an average percent error, E1; absolute average percent error, E2 and standard deviation, E3 of 0.001, 0.05 and 0.07 respectively, when tested on the high viscosity liquid–gas databank.

On slug frequency in concurrent high viscosity liquid and gas flow

Slug frequency is an important input parameter in most mechanistic and semi-mechanistic models used for estimating slug flow characteristics such as pressure gradient, slug length and slug holdup. It is also essential in the design and sizing of transport and/or production pipelines, process flow control, design and operation of process equipment, etc. This study experimentally investigates slug frequency in two horizontal pipelines with internal diameters (ID) of 0.0254 and 0.0764 m. Test liquids used in the study were mineral oil (with viscosity ranging from 1.0 to 4.0 Poise) and water while compressed air is the gas phase. Effects of liquid viscosity, gas superficial velocity, liquid superficial velocity, pipe internal diameter, pipe length and pressure gradient are discussed. Results indicate that slug frequency increased with increase in oil viscosity; decreased with increase in pipe diameter; and reduces along the length of the pipe. For gas Reynolds number, ReSG≤2500, slug frequency increased with increase in gas superficial velocity, when ReSG>2500, slug frequency decreased with increase in gas superficial velocity. A new slug frequency correlation that accounts for liquid viscosity and gas superficial velocity, hitherto not included in other correlations was proposed. A comparative analysis of the proposed models and existing slug frequency correlation on a high viscosity databank showed that the proposed correlation gave the best prediction with an average absolute percentage error (AAPE) of 19.91%.

Sensitivity Analysis of the Wall Shear Model to the Correlations for Frequency and Slug Holdup in the Gas-Liquid Slug Flow in Pipes

The one-dimensional mixture model efficiently predicts gas-liquid flows dominated by gravity force. The advantages of the mixture model are the absence of interfacial terms and the reduced number of transport equations, but its weakness lies on the constitutive laws to predict the wall shear force of a gas-liquid mixture. The objective of this work is to realize a sensitivity analysis of the wall shear model (based on the intermittent behavior of the gas and liquid structures) to the correlations for frequency and slug holdup in the one-dimensional, steady state mixture model applied to an isothermal gas-liquid mixture flowing in the slug regime. The numerical results for the pressure gradient obtained here are compared against experimental data from previous work.

Pressure Drop Models for Gas/Non‐Newtonian Power‐Law Fluids Flow in Horizontal Pipes

AbstractModels commonly used in literature are evaluated versus 696 data points to predict the pressure drop of gas/non‐Newtonian power‐law fluids flow in horizontal pipes. Suitable models are recommended. A new correlation is developed by ignoring the pressure drop across the gas slug and adopting the liquid slug holdup of gas/non‐Newtonian fluid flow into the homogeneous model. The theoretical curves can capture the test data trends and the overall agreement of predicted values with experimental data is sufficient to be practically applied in industry.

Two-Phase Air–Water Slug Flow Measurement in Horizontal Pipe Using Conductance Probes and Neural Network

This paper presents a method to obtain gas and liquid flow rates of two-phase air-water slug flow in a horizontal pipe through conductance probes and neural network. Contrary to statistical features commonly used in other works, five characteristic parameters of the mechanistic slug flow model are extracted from conductance signals, i.e., translational velocity, slug holdup, film holdup, slug length, and film length, which are used as the neural network inputs. The translational velocity is obtained through cross correlation of signals from the two ring-type conductance probes that are placed apart at a fixed distance. A feedforward neural network is adopted to correlate the characteristic parameters of slug flow and the gas and liquid flow rates and further used as a prediction tool. The experimental results show that the neural network method is able to learn the implicit correlations between the characteristic parameters of slug flow and the corresponding gas and liquid flow rates. It provides a performance for measurement of gas and liquid flow rates in slug flow regime within ±10% of full scale.

A simple correlation for prediction of the liquid slug holdup in gas/non-Newtonian fluids: Horizontal to upward inclined flow

This paper studies the liquid slug holdup of gas/non-Newtonian fluids in horizontal and inclined pipes. The results of the study show that the liquid slug holdup significantly increases for a given mixture velocity as the liquid phase becomes more shear-thinning. A new empirical correlation for estimating the liquid slug holdup is developed as a function of the Reynolds of liquid phase and inclination angle. The proposed equation is based on measured data consists of 271 data points with inclination angles ranging from 0° to 75° from horizontal. A good agreement is obtained between theory and experimental data. These results substantiate the general validity of the correlation presented for prediction of the liquid slug holdup in gas/non-Newtonian two-phase slug flow.

Analyses of liquid film models applied to horizontal and near horizontal gas–liquid slug flows

An analysis of liquid film models for horizontal and near horizontal gas–liquid slug flows is developed. The models’ formulations employ the one dimensional separated phase momentum equations. The formulations differ among themselves, by neglecting some terms on the momentum balance and also on the closure relations. A comparative analysis discloses the differences amongst the formulations. The sensitivity of the liquid film models to the changes on the bubble velocity, liquid slug holdup and liquid viscosity is accessed through a series of parametric runs. Finally, the model is tested against experimental data taken for continuous horizontal slug flow. The tests were designed to check if the models are able to capture the stochastic film properties provided the properly closure relations.

Liquid slug holdup in horizontal and slightly inclined two-phase slug flow

A new empirical equation for estimating liquid slug holdup in horizontal and slightly inclined two-phase flow is developed as a function of mixture velocity, liquid viscosity and inclination angle. The proposed equation is based on measured data consists of 316 data points for horizontal flow and 107 data points for inclined flow, with inclination angles ranging from −10° to 9° from horizontal. Based on the present measured data and data from other sources, the new equation is shown to be a significant improvement over the published models for both the horizontal and inclined slug flow.

Void fraction measurements in vertical slug flow: applications to slug characteristics and transition

A conductance probe is used to detect the instantaneous void fraction at the centerline of a vertical tube in upward gas-liquid flow for a wide range of gas flow rates, so that various flow patterns and the transitions between them could be studied. The information was digitized and recorded for further processing, which included short-time-averaging and histograms. The results obtained were used for flow pattern recognition and for the estimation of the liquid slug holdup and its length. Certain conclusions regarding the existing two-phase flow models were drawn.

An Analysis Of Two-Phase Flow In Inclined Pipes With Zero Net Liquid Production

Abstract A two-phase gas-liquid flow in upward inclined pipes with zero net liquid production is considered. The models of slug and stratified flow regimes are proposed for predicting the pressure drop. Estimated values of pressure loss compare well with the experimental results obtained with 26 mm and 51 mm pipes at angles of inclination of + 1 degree, + 5 degrees and + 9.2 degrees. Introduction Transportation of hydrocarbon mixtures by pipelines has been recently gaining in importance as Canada begins an era of increasing dependence on production from offshore fields. Although the commercial pipelines follow the terrain variations, most of the research endeavor has been focused on horizontal and vertical flow. The subject of this study is to investigate a special case of the gas-liquid flow in upward inclined pipes: a case of zero net liquid production. Such a situation may occur under any of the following conditions:pipeline is shutdown and a hydrocarbon mixture is cooled below its bubble point;liquid to gas ratio is very low; andliquid slug is introduced into the pipeline as a "kick " from a gas well. In all these cases fluid accumulates at the low sections of a pipeline. After the start-up some of the liquid is sheared off by the flowing gas and the remaining liquid circulates in the uphill pipeline section resulting in a zero net liquid flow rate. The liquid presence significantly affects the pressure drop in a pipeline initially designed for gas flow only. The main goal of this investigation is to describe the physics of the problem to the extent [hat the pressure drop could be correctly determined in design calculation. Model Development Gregory et al. (1981) conducted an experimental study on systems featured with zero net liquid production. The intermittent flow pattern was observed at superficial gas velocities up to 2 m/s. At higher rates fluid stratification occurred. Due to the zero liquid flow rate no comparison with existing flow maps is possible. Any step increase in gas velocity was accompanied by a corresponding decrease in liquid holdup. Intermittent Flow Over the past two decades a considerable amount of research has been done on intermittent flow in horizontal pipes. A major contribution was made by Dukler and Hubbard (1975) who proposed a semi-empirical model for slug flow. A major drawback of the model is the fact that quantities such as slug frequency and gas holdup in liquid slugs cannot be predicted from the first principles. Later on, Nicholson et al. (1978) modified this model. Recently attempts have been made to close the model: Barnea et al. (1983) suggested a method of predicting the slug holdup, and Maron et al. (1982) described the slug characteristics in terms of the boundary layer theory. Difficulties of the gas liquid slug flow modelling may be appreciated by inspecting Figure 1 which show the schematics of this flow pattern together with the symbols used in the mathematical description.