Showing papers on "Slug flow published in 1991"

Remobilizing surfactant retarded fluid particle interfaces. I. Stress‐free conditions at the interfaces of micellar solutions of surfactants with fast sorption kinetics

Abstract: Surfactant molecules adsorb onto the interfaces of moving fluid particles and are convected to regions in which the surface flow converges. Accumulation of surfactant in these regions creates interfacial tension gradients that retard the surface flow. In this study it is argued theoretically and demonstrated experimentally that fluid movement on the surface of a drop or bubble can remain unhindered in the presence of a single adsorbed surfactant if, relative to the convective rate of transport of adsorbed surfactant along the surface, desorption is fast, and the bulk concentration is high enough so that diffusion away from the particle is fast. For this circumstance, a uniform surface concentration of surfactant is maintained, and no gradients in surface tension arise to retard the surface velocity. The fluid particle flow behaves as it would in the absence of surfactant save that it has a reduced, uniform surface tension. The remobilization of surfactant‐laden interfaces of fluid particles is demonstrated experimentally in a three‐phase periodic slug flow in a capillary tube in which a train of alternating air and aqueous slugs ride on an annular wetting film of fluorocarbon oil. Surfactant, dissolved in the aqueous slug phase, adsorbs onto and retards the aqueous–oil interface. The hydrodynamics of this flow is such that small changes in the mobility of this interface create large shear rates in the oil layer. This significantly increases the pressure drop required to drive the slug train at constant velocity. Three surface adsorbers are used to demonstrate surface remobilization: The polyethoxy, nonionic surfactants Triton X‐100 and Brij‐35, which have fast desorption kinetics and do not retard the surface flow at high concentrations and, as a counter example, the desorption hindered protein bovine serum albumin, which is shown to be unable to remobilize an interface even at high concentration.

Gas-Rise Velocities During Kicks

Abstract: This paper reports on experiments to examine gas migration rates in drilling muds that were performed in a 15-m-long, 200-mm-ID inclinable flow loop where air injection simulates gas entry during a kick. These tests were conducted using a xanthum gum (a common polymer used in drilling fluids) solution to simulate drilling muds as the liquid phase and air as the gas phase. This work represents a significant extension of existing correlations for gas/liquid flows in large pipe diameters with non- Newtonian fluids. Bubbles rise faster in drilling muds than in water despite the increased viscosity. This surprising result is caused by the change in the flow regime, with large slug-type bubbles forming at lower void fractions. The gas velocity is independent of void fraction, thus simplifying flow modeling. Results show that a gas influx will rise faster in a well than previously believed. This has major implications for kick simulation, with gas arriving at the surface earlier than would be expected and the gas outflow rate being higher than would have been predicted. A model of the two-phase gas flow in drilling mud, including the results of this work, has been incorporated into the joint Schlumberger Cambridge Research (SCR)/BP Intl.more » kick model.« less

Method for monitoring acoustic emissions

Abstract: A non-intrusive method for the determination of characteristics of slug flow in a multiphase flow pipeline comprising the steps of: detecting the acoustic emissions from the pipeline in the ultrasonic frequency range by means of at least one sound transducer, the output from which is an analogue electrical signal, converting the analogue signal to a digital signal, and analyzing the digital signal to determine the characteristics of the slug flow. The characteristics of slug flow which may be determined include distinguishing slug flow from wave flow, the frequency of slugging and the velocity and length of slugs. The method is particularly suitable for studying multiphase flow comprising oil, gas and water.

System for pumping fluids from horizontal wells

Abstract: Apparatus and method for pumping fluids from horizontal wells with a dip tube used without requiring a packer in the well. Gas is separated from the liquid phase ahead of the pump to avoid slug flow of gas into the pump. This increases the amount of oil that can be pumped from the well by avoiding shutdowns resulting from gas-locking of the pump.

Structure of the near-injector region of nonevaporating pressure-atomized sprays

Abstract: The dense-spray region of pressure-atom ized nonevaporating sprays was studied, emphasizing the properties of the multiphase mixing layer that surrounds the liquid core during atomization breakup. The dispersed-phase properties of a large-scale (9.5-mm injector diameter) water jet injected vertically downward in still air were measured using single- and double-pulse holography for both fully developed and slug flow jet exit conditions. The inner portion of the mixing layer contained large irregularly shaped liquid elements and drops, and the proportion of spherical drops increased and drop sizes decreased with increasing radial distance. For present test conditions, the liquid core and the large liquid elements cause mean liquid volume fractions to be high near the axis; however, the gas-containing region was relatively dilute at each instant. Additionally, the velocities of large drops were generally much larger than small drops and predictions based on the locally homogeneous flow approximation, providing direct evidence of significant separated-flow effects in the flow. Finally, the degree of flow development at the jet exit had a substantial effect on the structure of the mixing layer, with increased turbulence levels increasing the number and size of large irregular liquid elements through distortion of the surface of the liquid core—enhancing rates of removal of liquid from the core.

Separated flow modelling and interfacial transport phenomena

Abstract: A physical explanation of the different types of interfacial waves that appear in stratified and annular gas-liquid flows is presented. The role of waves in affecting process performance is discussed. Particular attention is paid to interfacial drag, gas absorption, the initiation of slug flow and atomization.

A contribution to the mathematical modeling of bubbly/slug flow regime transition

Abstract: A new mathematical modeling approach has been applied to the analysis of bubbly vapor/liquid flows. In particular, an integro-differential equation has been formulated which describes the bubble si...

Solution for Transient Conjugated Forced Convection in the Thermal Entrance Region of a Duct With Periodically Varying Inlet Temperature

Abstract: This work presents an analytical solution of the transient conjugated laminar forced convection problem of a slug flow in the thermal entrance region inside a parallel plate duct. A solution in series form is already known for this kind of problem. This solution leads to a complex eigenvalue problem with transcendental equations. The present solution obtained by using the Laplace transform completely eliminates this problem. The amplitudes and phase lags with respect to the inlet conditions are determined for the complex wall temperature, fluid bulk temperature, and wall heat flux from this solution. The results are plotted for comparison with the results obtained with the series solution.

Heat transfer and solidification of a laminar liquid flow in a cooled parallel plate channel: The stationary case

Abstract: A simple numerical model is presented to predict the steady-state ice layers on the cooled walls inside a parallel plate channel for arbitrary entrance velocity profiles. The effect of two different entrance velocity distributions (a parabolic velocity distribution and a slug flow) on the shape of the ice-layers are examined. The quality of an approximative solution given in literature was checked by comparing with the numerical results. For the case of a fully developed parabolic velocity distribution at the entrance of the cooled channel the results are compared with experimental findings of Kikuchi [8]. A generally good agreement was found.

Measurement and evaluation of two-phase flow parameters

Abstract: The authors' use of fuzzy theory for identification of two-phase flow patterns and flow imaging based on signals from traditional transducers of flow measurement is briefly summarized. The application of the fuzzy identification theory makes it possible to describe the real flow patterns of two-phase flow more accurately and objectively. The flow pattern judgment is based on an original signal (pressure drop or local conductivity) which is only related with the conditions of fluids in the pipe, and the traditional single-phase transducers are used. This method can thus be used to identify flow patterns, in real-time measurement. Experimental results of online measurement of various distributions of two phases were obtained. Three cases of the real distribution, which correspond to the flow pattern of stratified flow, bubble flow, and slug flow, are shown. The experimental results show that the flow pattern image on a CRT agrees fairly well with the picture obtained using a high-speed camera. >

Dispersed bubble and slug flow

Abstract: Void fraction, pressure gradient and flow pattern data are reported for gas-liquid flow near-zero gravity through a 4 cm dia tube about 3 m long. These data were collected during a series of parabolic trajectories flown in a jet airplane which provided 15-20 s of reduced gravity at levels < 0.03g. Flow conditions were such that bubbly or slug flow existed for all runs. High-speed videotapes of the flow were analyzed to obtain the bubble size distribution at two axial locations along the tube. Models for explaining the data are examined.

Recovery of Waterflood Residual Oil Using Alkali, Surfactant and Polymer Slugs in Radial Cores

Abstract: An experimental study has been conducted to examine mobilization and recovery of waterflood residual oil in radial cores. Alkali, surfactant, and polymer slugs of various compositions, sizes and sequences were tested. Core flood experiments were conducted with unfired radial Berea sandstone disks at a flow rate of 8 cm3/h. David Lloydminster crude oil (total acid number of 0. 45 mg KOH/g oil) was used. The results of the present work showed that the composition and sequence of the injected chemical slug play an important role in mobilization and recovery of residual oil. For slugs lacking either mobility control, or low interfacial tension, no oil bank was formed and tertiary oil recovery was less than 20% Sor. A significant oil bank and tertiary oil recovery up to 70 % Sor were obtained with slugs having mobility control and low interfacial tension. However, maximum oil cut, incre-mental oil recovery and surfactant propagation were found to be functions of the alkali content in the slug. The incremental oil recovery, oil cut and slug injectivity greatly improved as the alkali concentration (sodium carbonate) in the combined slug was increased. A slight delay in surfactant breakthrough and a significantly slower rate of surfactant propagation were observed at higher sodium carbonate concentrations.

Experimental Study of Gas Rise Velocity and Its Effect on Bottomhole Pressure in a Vertical Well

Abstract: A 500 ft vertical well was used to study slip velocity of air in mud and pressure gradients through a 2.93" annulus (5.43 ­ 2.50") during continuous two phase flow in flowing liquids and in stagnant liquid columns. The well was instrumented to measure liquid- and air flow rate, surface back pressure and annular pressure gradients. Tests were undertaken with a broad range of air and liquid rates, different liquid properties, and with the injection of air slugs at different rate combinations. It was possible to detect these slugs as they passed the pressure transducers in the annulus. Results were applied to determine gas rise velocity. Correlation has been developed for gas rise velocity, which was used to estimate gas and liquid hold up. The in situ gas velocity and terminal settling velocity were determined for both dispersed bubbly flow and slug flow. The resulting pressure gradients have been compared to estimates from 8 different empirical correlations. The best results were obtained by using the Zuber & Findley correlation for holdup estimation with a gas holdup of 0.6 to distinguish the boundary between bubble and slug flow. This high transition value was mainly caused by the geometry of the well (tool joints) and partly by the rheology of the mud. A very good agreement between recorded and estimated downhole pressure was achieved, with a mean error of approximately 1% and a standard derivation of 2.9%.

Instability in Simulated Granular Chute Flows

Abstract: Numerical simulations show that two‐dimensional granular solids in an inclined chute can flow as a steady, uniform stream or as intermittent groups, or slugs. Slugs, or groupings of the flowing solids, were found to be enhanced with decreases in the coefficient of restitution of the granular particles and with decreases in the bulk number density or concentration of solids. A statistical parameter was developed to describe the degree of uniformity of the distribution of the granular particles along the chute. This parameter was found to have a predictable value at a well‐defined transition point when the flow changed from a uniform to a sluglike behavior. An explanation is presented describing the significance of this parameter in terms of the mechanics of the flow process.

Two-phase flow interfacial drag for once-through steam generators

Abstract: This paper reports on the current version of the RELAP5/MOD2 computer code which underpredicts the degree of superheat in the secondary side of the steam generator bundles. Many studies have concluded that this is due to overprediction of the interphase drag force. New interphase drag correlations have been developed for the bubbly and slug regimes. These correlations were implemented in the current version of the RELAP5/MOD2 computer code. Steady-state conditions for 65, 75, and 100% power loads of 30-tube once-through steam generator tests are simulated. The calculated primary- and secondary-side temperature profiles show that the new interphase drag correlations achieve closer agreement with experimental data than the temperature profiles of the original code.

Instability in Granular Chute Flows

Abstract: Numerical simulations showed that granular flows in a vertical chute can flow as a steady, uniform stream or as an intermittent slug flow. In numerical experiments slugs or grouping of the flowing solids was found to be enhanced with decreases in the coefficient of restitution of the granular particles and with decreases in the bulk number density or concentration of the solids. A statistical parameter was developed to describe the degree of uniformity of the flow along the chute. When tested over a wide range of solid concentrations this parameter was found to have an approximately constant value at a well defined transition point when the flow changed from a uniform to a slug-like flow.

Finite Element Analysis of Steady Periodic Convection-Diffusion Transport

Abstract: To analyze steady periodic convection-diffusion transport problems, a numerical procedure is presented that combines the method of complex temperature and a Galerkin-type finite element approach. Numerical results are obtained for unsteady heat transfer in parallel-plate channels with time-varying inlet temperature and participating walls. Slug flow is considered first, to validate the algorithm developed, by comparing its predictions with an analytical exact solution. The analysis is then enlarged to consideration of laminar flow, also accounting for axial conduction in the duct walls.

An Analysis of Miscible Flooding Chase-Fluid Strategies

Abstract: This paper presents a fractional-flow-theory analysis of miscible flooding chase-fluid strategies. Graphical solution methods to analyze flood performance for arbitrary solvent/water ratios, chase gas/water ratios (GWR's), and solvent slug sizes are presented. The graphical solution techniques include methods to predict the effects of wave interference, an important precursor to oil-bank destruction or loss in mobility control. An examination of interference leads to a deeper understanding of the miscible slug process. The advantages and disadvantages of chase-water, chase-gas, and simultaneous chase-gas/water injection are summarized. The analysis provides the theoretical basis for many chase-fluid design practices, including the idea of a minimum solvent slug size to ensure displacement integrity and the concept of an optimal chase GWR to minimize solvent requirements.

Forces on a pipe bend resulting from clearing a pool of liquid upstream

Abstract: The forces experienced by a bend in a pipe when a pool of water upstream is cleared by a rush of air have been measured. These forces are found to be negligible as long as a transition to slug flow does not occur. This transition does not occur as long as the maximum liquid fraction in the pool is less than 20%. The forces experienced at the bend are greatly reduced if the slug has traveled more than 6 L/D`s, a distance which is more than sufficient to insure that the slug has entrained air. The effect of an upstream expansion on the force experienced by the bend as a cleared air-water plug passes through it has also been measured. A conservative estimate of the maximum force can be made by assuming that the plug is composed entirely of liquid and moves at the mixture velocity characteristic of the small pipe. The measured maximum force decreases rapidly with increasing distance. These measurements will help in designing piping supports for lines which cannot be properly sloped or are downstream of a pressure relief valve. 2 refs.

Stability analysis of fluid-fluid interfaces

Abstract: Two problems in pipe flow are discussed in which the stability of fluid–fluid interfaces plays an important role. A stability analysis for a simplified 2-D geometry is presented. In gas–liquid pipe flow different flow regimes occur. This is known to be related to the stability properties of the flow. We shall present a linear stability analysis of plane two-phase Poiseuille flow. Two different unstable modes can occur, corresponding to experimental findings for pipe flow. The first is a finite wavelength mode related to the transition to wavy flow via a Hopf bifurcation. The second unstable mode is an infinite wavelength mode, which may be related to the transition to slug flow. Core-annular flow can be used to transport very viscous crude oils. The crude oil is surrounded by a thin water film, which prevents the core from touching the wall. In the hydrodynamic force balance, waves on the interface play an important role. A linear stability analysis of plane Poiseuille-Couette flow can predict the wavelength in agreement with experimental results even far beyond the critical point. No non-linear analysis is available as yet.