Two-phase Pipe Flow Research Articles

A fully implicit EOS based compositional two-phase transient flow simulator in wellbores

Transient two-phase flow in pipes and wellbores appears in several processes in petroleum industry. Predicting pressure, temperature and composition behavior during offshore well tests can support investment decisions in exploration. The governing system of equations that model production (or injection) and build-up (or fall off) is composed by the mass conservation of each component, the transport equation for each phase and one overall system energy equation. In this paper we develop a fully implicit equation of state based thermal compositional simulator able to model two-phase multicomponent flow in wellbores and pipes. This simulator is fully compositional and includes thermal effects. The thermodynamics calculations are based on the Peng-Robinson equation of state, and the momentum equations are based on the Single-Pressure Two-Fluid model. The finite volume method is used to discretize the non-linear system of equations, and time is discretized using Euler's implicit technique. The obtained numerical solutions for both co-current as well as countercurrent flow showed excellent agreement when compared to benchmark solutions published in the literature. A well kick-off followed by constant flow rate production and posterior shut-in was also simulated and the numerical results were discussed. It also models surge pressure and gravitational segregation effects in the wellbore. The presented simulator may be applied in numerical pressure transient analysis and pressure behavior in flowlines connecting wellheads and production platforms.

Comparison of well-posedness criteria of two-fluid models for numerical simulation of gas-liquid two-phase flows in vertical pipes

The purpose of the present study is to compare the well-posedness criteria of the free-pressure two-fluid model, single-pressure two-fluid model, and two-pressure two-fluid model in a vertical pipe. Two-fluid models were solved using the conservative shock capturing method. A water faucet case is used to compare two-fluid models. The free pressure two-fluid model can accurately predict discontinuities in the solution field if the problem's initial condition satisfies the Kelvin Helmholtz instability conditions. The single-pressure two-fluid model can accurately predict the behavior of flows in which the two phases are poorly coupled. The two-pressure two-fluid model is an unconditionally well-posed one. If in the free-pressure two-fluid model and single-pressure two-fluid model, the range of velocity difference of two phases exceeds certain limits, the models will be ill-posed. The two-pressure two-fluid model produces more numerical diffusion than the free-pressure two-fluid and single-pressure two-fluid models in the solution field. High numerical diffusion of two-pressure two-fluid models leads to failure to better comply with the problem's analytical solution. Results show that a single-pressure model is a powerful model for numerical modeling of gas-liquid two-fluid-flows in the vertical pipe due to a broader range of well-posed than free-pressure models and less numerical diffusion than the two-pressure mode.

Wall and interfacial shear stresses in laminar two-phase stratified flow in pipes

Exact solutions for separated two-phase flows are useful as a benchmark for numerical codes and for testing closure relations for simplified 1D Two-Fluid models. In particular, the correct representation of the wall and interfacial shear stresses is essential for the modeling of these flows. In this study, a complete set of exact solutions for laminar stratified two-phase flows in inclined pipes is used to explore the wall and interfacial shear stresses. We examine all possible configurations with concave and convex interfaces, which are related to the contact angle of the phases with the pipe surface. A closed-form analytical expression for the average interfacial shear stress was obtained for all cases of stratified two-phase flow. The limiting behavior of the local shear stresses at the triple-point (TP) region, where the interface meets the pipe wall, is determined by residue calculus. It is shown that the shear stresses behavior upon approaching the TP is determined by the fluid's viscosity ratio and the contact angle. The combinations of those parameters that result in convergence or divergence of the shear stresses at the TP are identified. The usefulness of the analytical expressions obtained for correctly predicting the shear stresses variation upon approaching the TP is demonstrated and discussed.

Analysis of interfacial behavior in two-phase flow using image processing

Two-phase flow has a wide range of application from petroleum to space industry. Gas-liquid two-phase flow in horizontal pipe commonly occurs in petro-chemical, nuclear and geothermal industry, where simultaneously gas and liquid are transported through pipelines. During the transportation of gas-liquid flow simultaneously, due to the interaction of two phases, slug forms from the stratified-wavy flow. Slug flow consists of strong aeration at the slug front which is responsible for pipe failure and hazards in industries. Thus, it is required to understand the phenomena of slug formation in industrial pipeline to avoid the catastrophic pipe failure. In the present research, image processing technique is used to accurately analyze the interfacial behavior of two-phase flow. The interfacial behavior plays crucial role, as it is the plane where the two phases interact and interaction of the phases leads to the transition of different two-phase pattern. Experimentally captured images are processed using image processing algorithm, to study the variation of liquid film thickness. With the help of liquid film thickness transition of the interface is analyzed for different superficial Reynolds number of liquid and gas. Further, a PDF analysis is reported to understand the mechanism of the growth of the wavy interface.

An Overview of Wellhead Burning: Fundamental Science to Burn Performance Prediction

ABSTRACTWhile wellhead burning has been an oil field hazard for generations, the development of capping response technologies and practices by industry experts has enabled the oil exploration community to shift its views of wellhead burning from a hazard to an oil spill response tool. This review covers some of the fundamental scientific aspects and technical issues of wellhead burning that engineers and policy makers will need to consider as this mitigation strategy is examined as a standard oil spill response tactic. For context, we examine a potential wellhead blowout scenario over a range of oil flows and examine the regimes of two-phase pipe flows, their dependence on wellbore velocities and gas-liquid ratios, and how those regimes will influence the burn efficiency with some insight from our experimental observations from two-phase spray burn testing. Among the critical findings that we present is that the worst-case discharge flow rate cannot be assumed to be the worst-case wellhead burning scenario.

Effects of density, viscosity and surface tension on flow regimes and pressure drop of two-phase flow in horizontal pipes

Two-phase gas/liquid flow in pipes is a common occurrence in the petroleum, chemical, nuclear and geothermal industry. In the petroleum industry, it is encountered in the production, transportation, and processing of hydrocarbons from the oil and gas fields. In designing these systems, accurate prediction of pressure drop is imperative, which is determined from the flow pattern and flow regime map. Unfortunately, most of the flow regime maps were developed for the air-water system and widely used for the oil/gas system. Despite the practical importance, the general applicability of these maps is not addressed. In order to improve the generality of flow regime maps, it is necessary to evaluate the effect of density, viscosity, and surface tension, which differ by great magnitude on flow regime maps. Thus, this study evaluates the effect of density, viscosity, and surface tension on the flow regime map. To evaluate the effect of fluid properties, experiments were conducted using a horizontal flow loop of 9.15 m (30 ft) pipe length and 0.0254 m (1-inch) pipe diameter with a two-phase air/liquid system. The surface tension was varied using the surfactant solution, viscosity was varied with the aid of glycerin, and density was varied with the aid of calcium bromide. The superficial velocity of the liquid ranges from 0 to 3.048 m/s (0–10 ft/s) and superficial gas velocity ranges from 0 to 18.288 m/s (0–60 ft/s) respectively. The experimental data were used to generate a flow pattern map and to predict the effect of these properties on the variation in the boundaries of different flow patterns and pressure drop. The results show that the flow patterns and transition boundaries were affected by fluid properties. The boundary between the annular and slug-annular flow at high velocity, the slug flow and pseudo-slug flow at medium velocity, and inertial wave and ripple wave flow at low velocities are affected by the variation in surface tension, viscosity, and density. The decrease in surface tension shifted the boundary between annular and slug flow toward the left-bottom corner of the flow regime map, while, similar effects were observed due to an increase in viscosity, which is opposite to the effect of surface tension. The increase in density shifts the boundary toward the top-right corner of the flow regime map. The effect of density on the flow pattern transition is significant compared to the viscosity, while the viscosity effect is higher than the surfactant. The effect of fluid properties on pressure drop is noticeable at high velocities, however, the pressure drop is not evident to reveal the flow pattern and boundary transition quantitatively.

Analysis of pressure fluctuations for oil-gas two-phase flow in a horizontal pipe using the bubble number density equation

Visualization experiments and numerical simulations of two-phase flow are conducted to study the pressure fluctuation characteristics of oil-gas flow in horizontal pipes. The two-fluid model based on the Eulerian–Eulerian method is adopted, and the bubble number density equation (BNDE) is introduced to the simulation to predict the bubble size and distribution within the pipe. The bubble size and pressure variations in the pipe obtained from the simulations agree well with the recorded values from the experiments. The fast Fourier transform (FFT) algorithm is used to analyze the characteristics of pressure fluctuations, and the results show that the sudden pressure increase in the pipe sections is related to gas injection. The bubble number density increases with liquid flow rate (Ql ), which causes the oil-gas flow to be more turbulent while increasing the amplitude of high-frequency fluctuations. The maximum amplitude for the dominant frequency is observed near the pump inlet for low liquid flow rates. At high liquid flow rates, more liquid vortices are found near the gas orifice, and there is a maximum amplitude for the dominant frequency in this section. Due to the high swirling strength at larger inlet gas volume fraction (IGVF), there is an obvious increase in the amplitude of low-frequency fluctuations, while the amplitude of high-frequency fluctuations is nearly the same under all IGVF.

Investigations on the slug two-phase flow in horizontal pipes: Past, presents, and future directives

Precise prediction of the gas–liquid slug flow is crucial for proper design and operation at various industrial processes. This paper provides a comprehensive review of published experimental and numerical works in horizontal pipes, including a critical analysis of state-of-the-art parameters used to characterize the slug flow regime. The discussed slug characteristics are slug length, slug frequency, and slug velocity. Throughout the paper, an endeavor does devote to discerning the areas where modern development work is needed. Accordingly, some observed gaps in the literature, comprising hydrodynamic behavior at the transition zone and the interaction between slug flow and structural pipe. The lack of comprehensive laboratory experimental information for high liquid viscosity and the viscosity impact on the slug characteristic is also observed. On the contrary, robust and less empirically independent CFD models are required for accurately predicting the slug characteristics with a minimal computational cost.

Flow status identification based on multiple slow feature analysis of gas–liquid two-phase flow in horizontal pipes

A gas–liquid two-phase flow is a highly complex and random process with complicated and variable flow statuses. The status identification of two-phase flows focuses on the situation of flow processes over specific time periods, as reflected by flow regimes, phase holdup, flow velocity, and other parameters. Aiming to discover how to obtain flow status information and identify the flow statuses of gas–liquid two-phase flows in horizontal pipes, a meticulous identification method based on multiple slow feature analysis combined with Bayesian inference is proposed, with concurrent monitoring of steady states and process dynamics. In this method, representational models for different typical flow regimes are established to describe both the steady states and temporal distributions. On this basis, by monitoring statistics and developing a Bayesian inference-based index, the current flow status can be identified online. Besides status identification, process dynamics are monitored to detect the dynamic characteristics of the current process with meaningful physical interpretation and deep process understanding. The application of this method to typical flow regimes and the status of transitions from bubble flow to slug flow demonstrates the feasibility and efficacy of the proposed method.

Experimental and theoretical investigation of the spreading behaviors of oil droplets on the surfaces with different wettabilities

Due to the oil field development enters the period of high water cut, the flow drag of oil-water two-phase flow in nonmetallic pipes requires further research. Moreover the dynamic spreading behavior of oil droplet on a pipe’s wall is of great significance to investigate the flow drag. However, the spreading behaviors of oil droplets on surfaces with different wettabilities in water system are still not clear. In this study, firstly, considering the effect of surface wettability and oil droplet diameter, the spreading behaviors of oil droplets on non-metallic and metallic substrates were observed using a high-speed imaging system. Then, according to the spreading behaviors of oil droplets on the substrates and based upon the energy balance theory, a theoretical model of the spreading behavior of oil droplets was developed for predicting the dimensionless maximum spreading diameter. The quantitative relationships among the dimensionless maximum spreading diameter, the diameter of oil droplets, the properties of oil and water, and the wettabilities of surfaces were obtained. Finally, the theoretical model was verified using experimental data with deviations generally ranging within ± 10%.

Flow and heat transfer for a two-phase slug flow in horizontal pipes: A mechanistic model

In view of the practical importance of gas–liquid two-phase flow in many applications, such as chemical engineering, petroleum engineering, nuclear engineering, etc., a reliable model of flow and heat transfer for two-phase flow is of practical importance in the two-phase flow analysis. Among various two-phase flow regimes, slug flow is most complicated due to the intrinsic randomness and intermittency. This paper aims at developing a novel mechanistic model of flow and heat transfer for two-phase slug flow in horizontal pipes. First, a hydrodynamic model of two-phase slug flow is developed using the concept of slug unit cell. Then, a heat transfer model is deduced based on the hydrodynamic model. The overall heat transfer coefficient is integrated by the local heat transfer coefficients of liquid slug, liquid film, and elongated bubble. The newly developed mechanistic model is well validated by the experimental results. Finally, the dependence of the heat transfer performance on the overall flow parameters, such as superficial liquid velocity and superficial gas velocity, and the local flow parameters, such as slug frequency, pressure drop, void fraction, and ratio of slug length to unit cell length, is comprehensively investigated. The heat transfer enhancement of two-phase slug flow compared with single-phase flow is mainly attributed to the turbulence increase in liquid by the injection of air and the decrease in thermal boundary layer by the frequent alternation between the liquid slug and the elongated bubble.

Heat Transfer Coefficient, Pressure Gradient, and Flow Patterns of R1234yf Evaporating in Microchannel Tube

Abstract This paper presents the heat transfer coefficient, pressure gradient, and flow pattern of R1234yf in a microchannel tube. Both heat transfer coefficient and pressure gradient are presented against real saturation pressure, while flow pattern captures at the exit of data points are presented in the same plot. The experiment was conducted on a 24-port microchannel tube with an average hydraulic diameter of 0.643 mm. The experiment covers mass flux from 100 to 200 kg m−2s−1, heat flux from 0 to 6 kW m−2, vapor quality from 0 to 1, and inlet saturation temperature from 10 to 30 °C. Comparing the correlations to the HTC measurements at very low quality (about 0.1), Gorenflo, D., and Kenning, D. (2010, Pool Boiling, in: VDI Heat Atlas, 2nd ed, Springer, pp. 757–788) agree with the results. As vapor quality increases, pressure gradient increases. The adiabatic pressure gradient is a strong function of mass flux and saturation pressure (temperature). Flow patterns of R1234yf are also affected by mass flux and saturation pressure. The heat transfer coefficient is a strong function of mass flux and heat flux. The saturation temperature has a smaller effect on HTC in the condition range (10 – 30 °C). Under the test range, the accelerating pressure drop is insignificant compared to friction. Comparing to the results, Mishima, K., and Hibiki, T. (1996, “Some Characteristics of Air-Water Two-Phase Flow in Small Diameter Vertical Tubes,” Int. J. Multiph. Flow, 22(4), pp. 703–712) and Muller-Steinhagen, H., and Heck, K. (1986, “A Simple Friction Pressure Drop Correlation for Two-Phase Flow in Pipes,” Accessed March 1, 2018)., 20, pp. 297–308.) have small mean absolute error (MAE) to predict local pressure gradient. For the heat transfer coefficient, Sun, L., and Mishima, K. (2009, “An Evaluation of Prediction Methods for Saturated Flow Boiling Heat Transfer in Mini-Channels,” Int. J. Heat Mass Transf, 52(23–24), pp. 5323–5329) and Gungor, K. E., and Winterton, R. H. S. (1986, “A General Correlation for Flow Boiling in Tubes and Annuli,” Int. J. Heat Mass Transf, 29(3), pp. 351–358) have an MAE less than 30%.

Frictional Pressure Drop and Liquid Holdup of Churn Flow in Vertical Pipes with Different Viscosities

Churn flow commonly exists in the pipe of heavy oil, and the characteristics of churn flow should be widely understood. In this paper, we carried out air and viscous oil two-phase flow experiments, and the diameter of the test section is 60 mm. The viscosity range of the oil was 100~480 mPa·s. Based on the measured liquid holdup and pressure drop data of churn flow, it can be concluded that, due to the existence of liquid film backflow, positive and negative frictional pressure drop can be found and the change of frictional pressure drop with the superficial gas velocity is related to superficial liquid velocity. With the increase of viscosity, the change rate of frictional pressure drop increases with the increase of the superficial gas velocity. Combining our previous work and the Taitel model, we proposed a new pressure drop model for viscous oil-air two-phase churn flow in vertical pipes. By comparing the predicted values of existing models with the measured pressure drop data, the proposed model has better performance in predicting the pressure drop.

Flow Regimes Identification-based Multidomain Features for Gas–Liquid Two-Phase Flow in Horizontal Pipe

Accurate flow regimes identification is of great significance for the deep understanding of the flow structure and ensuring the safe and economic operation of actual production in the multiphase flow process. For the flow regimes identification of the gas-liquid two-phase flow in the horizontal pipe, a multidomain features processing scheme is proposed. The water holdup data are acquired by conductance rings sensor, and processed by the improved empirical wavelet transform (EWT) to obtain the Fourier spectrum in the frequency domain and decomposition components in the multiscale domain. The obtained multidomain feature information is quantified to get the high-dimensional feature vectors of different flow regimes. To make the features more representative and realize the visualization of the structural relationship between the flow regime samples, the isometric feature mapping (Isomap) method in manifold learning is used to synthesize the feature structure relationships and map them to low-dimensional space. The obtained low-dimensional feature vectors of training samples are input into the support vector machine (SVM) to acquire the flow regimes identification model. Compared with other flow regimes identification schemes that feature reduction uses different manifold learning methods, or feature extraction is not in multidomain, or data preprocessing uses traditional wavelet transform, the proposed scheme can better retain the global structural relationship of the flow regimes, has the characteristics of strong stability, and the identification rate of the gas-liquid two-phase flow regimes in the horizontal pipe is over 95%.

Evaluation of Velocity Impact on Sand Particles in Two-Phase Annular Flow in Horizontal Pipes

Experimental investigations on sand particles in annular flow in horizontal pipes were presented. The aim is to enhance the knowledge related to sand transportation in the oil and gas industry. More so, to add values in facilitating the optimum design of oil and gas production systems where annular flow is often encountered. The experimental investigations were conducted using a closed-loop consisting of a horizontal pipe with an internal diameter of 2-inch (0.0504m). The experimental investigations covered both: water/sand flow and water/air/sand annular flow. The water/sand flow experiments were carried out to establish sand transport regime in liquid such as sand saltation, sand streak, and sand suspension. While, water/air/sand annular flow experiments revealed that the only the only sand transport regime in annular flow are saltation and suspension. Sand concentration profile in the annular flows were also estimated by using the sampling method. It was found that the bigger the sand particle size (500microns) leads to higher concentration of sand being transported at the bottom of the pipe because of gravity effect, while the smaller the sand particle size (212microns), leads to the higher sand concentration. Also, the sand concentration increased at the gas core as the superficial gas velocity increases.

Pneumatic transport of heavy minerals in a horizontal pipe: An Eulerian-Eulerian approach

Abstract This article presents a computational study based on the Eulerian-Eulerian model for computing the pressure drop and hydrodynamics of the gas-solid two-phase flow in a horizontal pipe. The solid particles considered in the analysis are the heavy minerals with a density of 7860 and 11,350 kg/m3. The flow situation corresponds to the upper limit of the dilute phase flow, where the inter-particle and the wall-particle collisions play a significant role. The numerical procedure agrees well with the experimental data and ensures good accuracy of the computed results. The analysis outcomes show that the gas-solid two-phase flow pressure drop increases with an increase in the inlet concentration and the density of the solid-phase. The radial distribution of the velocity and volume fraction profiles of both phases are asymmetric. The gas-phase possesses a relatively high velocity than the solid-phase. The gas-phase velocity reduces with an increase in the inlet concentration and the density of the solid-phase. The heavier particles have a slightly greater tendency to settle. With an increase in the inlet solid-phase volume fraction, the solid-phase concentration increases both at the top and the bottom portion of the pipe.

LASER-BASED DIAGNOSTICS OF SLUG FLOW BOILING IN A HORIZONTAL PIPE

We present results from an experimental investigation on flow boiling, in the slug flow regime, of refrigerant R245fa through a 12.6-mm inner diameter horizontal plain pipe using particle image velocimetry (PIV) and an interface detection method. The study is supplemented by an overview of the state-of-the-art in experimental research of two-phase dispersed pipe flows and the development of modern optical and laser-based full-field nonintrusive measurement techniques as applied to these flows. We consider different flow conditions, with heat fluxes over the range 5.3 to 7.9 kW/m2 and mass fluxes from 300 to 460 kg/m2 s. Significant disturbances in the instantaneous velocity fields are revealed in both the noses and tails of slugs, with their values being two times higher behind vapor bubbles. The slug passage frequency is determined based on the results of the interface detection method. The vapor bubble velocity is found to increase linearly with the interfacial velocity of the two-phase mixture, while its gradient grows with the heat flux. Moreover, at increased heat fluxes the bubbles may move even faster than the mixture itself, which implies that they must significantly enhance local turbulence, thereby additionally intensifying heat transfer. This research demonstrates the applicability of laser-based diagnostic techniques to boiling slug flows, to which such experimental methods have not been widely applied in macroscale geometries. In addition to the conclusions, we provide practical recommendations for possible future research in this particular field of fluid mechanics and the further development of sophisticated laser-based measurement techniques for boiling, and similar, flows.

An adaptive CEEMD-ANN algorithm and its application in pneumatic conveying flow pattern identification

The accurate measurement of dust concentration using electrostatic sensor is serious affected by two-phase flow patterns in practice. In this paper, the electrostatic sensor signals of flow in a pneumatic conveying pipeline were collected, and the electrostatic fluctuation signals of three typical flow patterns of gas–solid two-phase flow in the horizontal pipe were obtained. By combining complementary ensemble empirical mode decomposition (CEEMD) and a back propagation (BP) neural network, an algorithm for flow pattern identification is proposed. This algorithm can adaptively determine the number of layers of the intrinsic mode function (IMF) decomposition and the number of input vectors for the neural network, ensuring the minimum size vector is used. The selected IMF energy feature as the input of the BP neural network can effectively ensure that an accurate flow pattern discrimination rate is obtained. The experimental results show that the algorithm proposed in the paper can guarantee the recognition rate of the flow pattern to reach more than 99%, yet through adaptive adjustment ensure that the size of trained BP neural network input is as small as possible, and the guaranteed algorithm calculation is kept at a minimum.

Mathematical Modelling of Sewage Overflow Through Pipe-Manhole Drainage Sewer Systems Using CFD: A Case of Mbale City, Eastern Uganda

The major objective of this study was to design a model to optimize sewage flow through pipe-manhole drainage systems using Computational Fluid Dynamics (CFD). Multi-phase flows like two-phase flow in transport pipes is a common occurrence in many industrial applications such as sewage, water, oil, gas transportation and power generation. Accurate prediction of fluid velocity and pressure drop is of utmost importance to ensure effective design and operation of fluid transport systems. Numerical simulations were performed at different pipe inclinations and fluid flow velocities. A two-dimensional pipe of 0.5 m in diameter and 20 m long was used with a Standard k−ε turbulence and the volume of fraction (VOF) free surface model to solve the turbulent mixture flow of air and water. The CFD approach is based on the Navier-Stokes equations. Results show that the flow pattern behaviour and numerical values of liquid velocities and pressure drop compare reasonably well. It is concluded that the most effective way to optimize a sewer network system in order to minimize the overflows through Pipe-manhole drainage system for Mbale Municipality conditions is by considering minimum and maximum sewer velocities in the range 0.67 ms−1 to 5.5 ms−1 respectively, sewer diameters, slope gradients for optimal sewer design and expanding the number of sewer network connections of household, municipal and industries.

Calculation of mass transfer coefficients for corrosion prediction in two-phase gas-liquid pipe flow

Internal corrosion in industrial environments involving gas-liquid flow can be a serious concern. For example, in the oil and gas industry, corrosive water phase is usually transported in pipes along with liquid and/or gas hydrocarbon phases. These gas-liquid flows develop complex flow patterns where the liquid phase can distribute in quite different ways (as stratified layers, intermittent slugs, annular film, etc.) depending on the gas and liquid flow rates and pipe inclination. In these circumstances, the water phase can flow at very high velocities leading to high turbulence and mass transfer rates that can accelerate corrosion of the metallic pipe surface. In general, proper prediction of corrosion rates via mechanistic electrochemical models requires the knowledge of the mass transfer rate of corrosive species in the aqueous phase. There are very few studies in the open literature that show specific experimental data or propose ways to compute mass transfer rates in gas-liquid flow; particularly, for large pipe diameters. The present study introduces a methodology for the estimation of mass transfer rates in gas-liquid flow via the Chilton-Colburn analogy and near-wall eddy diffusivity distribution based on the mechanistic gas-liquid flow modeling. The proposed mechanistic models cover a wide range of fluid's properties and flow rates, different flow patterns and pipe inclinations, and show good agreement with mass transfer experimental data from large-scale gas-liquid flow.