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A three-dimensional ECVT sensing technique is applied to imaging complex slugging phenomena of a gas–solid fluidized bed under ambient and elevated temperature conditions. The study indicates that the time interval between rising slugs decreases with an increase in the gas velocity, reaching a nearly steady time interval value of about 1 s between two slugs when the gas velocity is ∼1.7 m/s above the minimum fluidization velocity. The fluidized bed behaves as a bubbling fluidized bed at low gas velocities. In slugging regime, the slug rise velocity increases with the gas velocity. A mechanistic analysis of forces around the dense phase solid particles suggests that the relationship between the slug rise velocity and the gas velocity for the square-nosed slugging bed is not strictly linear and is highly related to the interparticle forces, internal friction of particles, and gas velocity in addition to the wall stress.

The average bubble diameter and volumetric bubble flux give indications about the overall bed expansion in a fluidized bed. As these properties depend on the particle properties and fluidized bed regime, their accurate predictions have been a challenge. A new set of models for predicting the average bubble properties within the bubbling and slugging regimes in a deep fluidized bed is proposed, where bubble flux is modeled by G = U − c( ) U U U a 0 mf 0 mf, bubble diameter is modeled by db̅ = 0.848G D 0.66 0.34 and transition velocity is modeled by = + φ − − − 1 2.33U ( c 1)( ) U U a h mf D 0.027 0.35 t 0.588 bs mf t 0 . he models are developed using the information obtained from an experimental setup equipped with a ualplane electrical capacitance tomography and a porous distributor plate. Although they are empirical, the proposed models are based on the two-phase theory used in describing the bubble flow in a fluidized bed. These models have been validated, and the results show that they can be used to predict the behavior in different regimes at different gas velocities.

Non-uniform bubble growth occurs in deep fluidized beds, resulting in generation of large bubbles or even slugs. Gas tracer method, in combination with analysis of pressure fluctuations, is employed to quantify the time-averaged and transient characteristics of bubble growth with respect to the bed depth in a 300-mm ID cold flow unit. The bubble distribution, growth and its residence time in the transition from uniform to non-uniform bubble growth and finally to slugging are investigated. In addition, appreciably better conversion and selectivity in a 1200-mm ID industrial fluidized bed reactor with ammoxidation of p -chlorotoluene (PCT) is obtained by eliminating non-uniform bubble growth.

An accurate and predictive modelling of slug flows is required by many industries (e.g., oil and gas, nuclear engineering, chemical engineering) to prevent undesired events potentially leading to serious environmental accidents. For example, the hydrodynamic and terrain-induced slugging leads to unwanted unsteady flow conditions. This demands the development of fast and robust numerical techniques for predicting slug flows. The presented in this paper study proposes a multi-fluid model and its implementation method accounting for phase appearance and disappearance. The numerical modelling of phase appearance and disappearance presents a complex numerical challenge for all multi-component and multi-fluid models. Numerical challenges arise from the singular systems of equations when some phases are absent and from the solution discontinuity when some phases appear or disappear. This paper provides a flexible and robust solution to these issues. A fully implicit formulation described in this work enables to efficiently solve governing fluid flow equations. The proposed numerical method provides a modelling capability of phase appearance and disappearance processes, which is based on switching procedure between various sets of governing equations. These sets of equations are constructed using information about the number of phases present in the computational domain. The proposed scheme does not require an explicit truncation of solutions leading to a conservative scheme for mass and linear momentum. A transient two-fluid model is used to verify and validate the proposed algorithm for conditions of hydrodynamic and terrain-induced slug flow regimes. The developed modelling capabilities allow to predict all the major features of the experimental data, and are in a good quantitative agreement with them.

Typically, fluidized beds are granular systems composed of solid particles through which a fluid flows. They are relevant to a wide variety of disciplines such as physics, chemistry, engineering, among others. Generally, the fluidized beds are characterized by different flow regimes such as particulate, bubbling, slugging, turbulent, fast fluidization, and pneumatic conveying. Here, we report the experimental study of the structural evolution of a granular system due to simultaneous penetration of intruders in the presence of an upward airflow. We found that the granular medium evolves from the static state to the turbulent regime showing the coexistence of three regions in different flow regimes. Interestingly, the cooperative dynamic of intruders correlate with the formation of such regions. As a non-invasive method, we use lacunarity and fractal dimension to quantitatively describe the patterns arising within the system during the different stages of the penetration process. Finally, we found that our results would allow us to relate the evolution of the visual patterns appearing in the process with different physical properties of the system.

International audience; The fluidized particle-in-tube solar receiver concept is promoted as an attractive solution for heating particles at high temperature in the context of the next generation of solar power tower. Similar to most existing central solar receivers, the irradiated part of the system, the absorber, is composed of tubes in which circulate the fluidized particles. In this concept, the bottom tip of the tubes is immersed in a fluidized bed generated in a vessel named the dispenser. A secondary air injection, called aeration, is added at the bottom of the tube to stabilize the flow. Contrary to risers, the particle mass flow rate is controlled by a combination of the overpressure in the dispenser and the aeration air velocity in the tube. This is an originality of the system that justifies a specific study of the fluidization regimes in a wide range of operating parameters. Moreover, due to the high value of the aspect ratio, the particle flow structure varies along the tube. Experiments were conducted with Geldart Group A particles at ambient temperature with a 0.045 m internal diameter and 3 m long tube. Various temporal pressure signal processing methods, applied in the case of classical risers, are applied. Over a short acquisition time, a cross-reference of the results is necessary to identify and characterize the fluidization regimes. Bubbling, slugging, turbulent and fast fluidization regimes are encountered and the two operation modes, without and with particle circulation, are compared.

Slug flow has drawn attention for industrial applications because it is one of the most prevalent and problematic two-phase flows due to severe pressure fluctuations. The effects of rib elements installed at the inner walls of a channel on the flow structure and pressure fluctuations are experimentally investigated with particular focus on how the rib elements alter slugging phenomena as compared with a smooth channel without ribs. Statistical analyses are conducted to elucidate the relation between pressure fluctuations and flow dynamics of slug flow in channels with ribs. For the slug flow in the ribbed channels, pressure fluctuations are alleviated, and the dominant frequency of the peak power magnitude for the pressure disappears. Two distinct mechanisms for air bubble entrainment are suggested depending on the width-to-height ratio of the rib geometry. This accounts for different levels of pressure fluctuation mitigation and the increase in flow randomness as well as pressure loss along the channel.

Severe slugging formation has been investigated experimentally in a two-phase flow-loop composed of a downwardly inclined pipe and a vertical riser. In this study, a bifurcation diagram was made to more clearly identify which flow the current system has at each valve opening. A model was made by inputting the dimensions of the flow loop using OLGA, a multiphase flow simulation program, to compare the experimental results. The model-based control logic was constructed by estimating the transfer function utilizing the OLGA model. The estimated transfer function is used to tune the gain of the PI controller, using the method called the Internal Model Control (IMC). Through this method, PI gain can be easily obtained through only one tuning parameter. When the PI controller gain is obtained through the transfer function of the flow loop system, mitigation of severe slugging was achieved while increasing the flow rate than the case with manual choking.

Refrigerant in the liquid phase and lubricating oil that circulate in refrigeration systems may reach the compression chamber of compressors. This phenomenon of liquid slugging is detrimental to reciprocating compressors because it can damage valves and other components. A three-dimensional Eulerian multiphase model was developed using the software ANSYS CFX to predict the gas-liquid flow in a simplified suction muffler geometry. In addition, an experimental bench was designed to allow the injection of specified volumes of lubricant oil into the suction muffler and measurement of the volume that reaches the muffler outlet. The liquid slugging was observed through glass windows positioned in the test section and recorded with a high-speed camera. Measurements showed that the phenomenon of liquid slugging is random and that the volume of liquid reaching the muffler outlet increases with the oil injection pressure. The numerical model was able to predict the oil volume that reaches the muffler outlet in agreement with measurements in the case of high injection pressures, but it overpredicted the volume when the injection pressure was decreased. The visualization showed changes in the liquid phase morphology that are difficult to predict since closure models for a two-fluid model are typically developed for dispersed morphology.

Severe slugging can occur in a pipeline-riser system at relatively low liquid and gas flow rates during gas-oil transportation, possibly causing unexpected damage to the production facilities. Experiments with air and water are conducted in a horizontal and downward inclined pipeline followed by a catenary riser in order to investigate the mechanism and characteristics of severe slugging. A theoretical model is introduced to compare with the experiments. The results show that the formation mechanism of severe slugging in a catenary riser is different from that in a vertical riser due to the riser geometry and five flow patterns are obtained and analyzed. A gas-liquid mixture slug stage is observed at the beginning of one cycle of severe slugging, which is seldom noticed in previous studies. Based on both experiments and computations, the time period and variation of pressure amplitude of severe slugging are found closely related to the superficial gas velocity, implying that the gas velocity significantly influences the flow patterns in our experiments. Moreover, good agreements between the experimental data and the numerical results are shown in the stability curve and flow regime map, which can be a possible reference for design in an offshore oil-production system.

Experiments on aeration from a bubble diffuser pipe having five aeration holes are carried out to investigate effects of the azimuthal angle of the holes on flows inside and outside the pipe. The azimuthal angle is varied by rotating the pipe. When the hole angle becomes larger than a certain angle, the liquid height inside the pipe is fixed just below the holes, which results in the prevention of slugging inside the pipe. The effects of hole angle on bubble generation mode and bubble size are small except for the large hole angles, at which generated bubbles are to break up due to an interaction between the bubbles and the pipe wall. Hence uniform aeration is easily realized just by rotating the pipe to some extent. Uniform aeration is also realized with a longer diffuser pipe having ten aeration holes by rotating the pipe. The power in aeration is evaluated from the pressure difference and the total gas inflow. Although the decrease in the hole diameter is also effective to realize the uniform aeration, the increase in the azimuthal angle is superior to the former from the point of view of energy saving.

Severe slugging is an undesired multiphase phenomenon in offshore pipeline/riser systems. Previous experimental studies have been limited to relatively short pipelines (no more than 400 m) compared with the subsea fluid transportation system. Here, a much longer pipeline/riser system (46 mm ID) was built to investigate severe slugging. The test loop consists of a 1657 m long horizontal pipeline; 30 m long, 7-degree downward inclined pipeline; and 11.2 m high S-shaped riser. Based on the pressure cycling characteristics, the flow patterns were classified into three broad categories. It was found that the long pipeline resulted in a longer slug production stage during severe slugging flow, eventually leading to longer liquid slugs. The critical gas velocities for the severe slugging region were larger compared with short pipeline/riser systems, while the critical liquid velocities were barely influenced by the long pipeline. The main factors that influenced the flow pattern transitions on the critical gas and liquid velocities for the severe slugging region were different. Based on the existing models, two criteria for severe slugging and unstable flows were developed, and more accurate predictions were obtained when compared with experimental results in the present study and the literature.

Direct steam generation in parabolic-trough solar collector requires reliable and efficient two-phase flow modelling tools. One-dimensional models based on 6 equations are a suitable approach. The present article aims to show that RELAP5 is able to simulate a single-loop system including transients caused by sudden events like solar collector defocusing or fast changes in direct solar irradiance. The numerical results have been validated with experimental data from the DISS facility located at Plataforma Solar de Almeria. Six operation days have been compared using a new heat loss correlation, which has been measured on the same facility. The implemented model considers connection pipes, elbows, change of height, thermal insulation in the passive sections, collectors slope and absorbers. The numerical results are in good agreement with the experiments and it proves that RELAP5 can reproduce the underlying thermo-hydraulic phenomena. An additional numerical study of severe slugging in the connection pipes has been done, where two adjacent collectors linked by a connection pipe have been simulated at a pressure of 5 bar. Based on 374 tests, slugging phenomenon has been reported for low values of inlet mass flow rate and low quality in the entering two-phase mixture.

The algorithm and implementation details of a new parallel CFD-DEM solver that uses both CPU and GPU resources for computations are presented in this study. The new solver supports complex geometries, various shapes of mesh, converges at very high fluid velocities and executes with available computational resources of a simple desktop computer. At first, verification studies were performed for the solver. Among three parts of the solver, the DEM solver and coupling solver results were verified by simple problems for which analytical solutions exist. Then, the solver results were evaluated in three cases of gas-solid flows with various geometries (from simple to complex) and various numbers of particles. For a large system that contains 870 k particles, it took around 6 h (with two CPU cores) to complete each second of simulation while in a smaller system with 47 k particles, it took only 30 min (with one CPU core). Results obtained by the new solver were compared with experimental data. The solver can properly predict the frequency of bubble passage and intensity/share of macrostructures in the bubbling regime, while underestimates intensity/share of meso-structures. The hydrodynamics of a spouted bed with draft tube was well-captured in terms of the fountain shape and its maximum height, particle concentration profile in different parts and time-averaged upward velocity of particles. The solver was also used to investigate the particle dynamics in a Wurster bed. Two velocity profiles were tested. In the first velocity profile, an unstable fountain with slugging conveying in the draft tube was observed while in the second velocity profile, a stable fountain with dispersed conveying in the draft tube. This was found to be attributed to the formation of the bubbles in the annulus region.

Summary The drift-flux model is applied to simulate numerically highly transient slug flows in complex configurations. The study is focused on the terrain-induced slugging phenomenon. Previously published transient experimental data on multiphase flows in complex configurations with near-horizontal segments are closely investigated. The numerical implementation of the drift-flux model is briefly described. By varying the specific tuning parameters of the drift velocity, a close match with the transient experimental data for air/water flows is obtained. To verify the quality of the numerical solution and agreement with experimental data, the problem-specific criteria are introduced. These criteria are the time of the first slug arrival, average amplitude of slugs, average period between the slugs, average cumulative liquid production per slug, and total produced mass over the observation period. The model developed was used to predict severe slugging for the synthetic case involving the flow of hydrocarbon oil and gas and is representative of the realistic field-scale problem. The possible ways of further improving the drift-flux model and its potential practical applications are outlined.

The hydrodynamic velocity and effect of the reaction temperature on the cracking performance were investigated for the production of light oil through the rapid pyrolysis of heavy oil in a circulating fluidized bed reactor. From this study, the gas velocity in the loop seal to prevent slugging, the transport gas velocity to form a dense phase of solids on the bottom of the riser, and the minimum bubbling fluidization velocity for stable solid circulation in the reheater were determined. Under the steady supply of feed through the internal mixing with steam inside the feed nozzle, the reactivity for a temperature change from 527 to 574 °C was investigated. As a result, the residue (>535 °C) conversion and liquid yield of up to 71.1 and 78.2%, respectively, were found. The maximum impurity removal rates for sulfur, Conradson carbon residue, and metals (nickel and vanadium) were found to be 18.7, 50.4, and 83.6%, respectively.

In chemical and energy industries, fluidization concerning rod-like particles is often encountered, but little effort has been made in this respect. Understanding fluidization of rod-like particles is crucial for the guidance of relevant industrial process. To investigate the fluidization of the rod-like particles with different aspect ratios, CFD-DEM coupling algorithm is employed in this article to simulate a bubbling fluidized bed, in which the rod-like particles are modeled by super-ellipsoids. The simulations results show that, in the case of same particle volume, the rod-like particles with smaller aspect ratio obtain larger force from the gas and the particles can absorb more energy from fluid flow, and the fluidization phenomenon, like slugging and bubbles, is easier to form. The local voidage fraction and particle's projected face area perpendicular to fluid flow direction are directly related to particle orientations, which have great influence on drag force and fluidization. Due to the significance of particle orientation, a further investigation is made for the factors that influence the distribution of particle orientation. The results show that particle orientation is greatly affected by fluidization time, fluidization velocity, and the structure of the fluidized bed.

A slowly-moving bed slagging coal gasifier (SMB gasifier) is developed for utilizing those largely-reserved coals with high ash fusion temperature (> 1500 °C). Mathematical modelling is regarded more effective than experimental studies to understand and optimize the performance of the gasifier at industry scale. In this paper, a three-dimensional (3D) computational fluid dynamics (CFD)-based mathematical model has been developed to study the shape and size of the so-called high-turbulence zone in the SMB slagging coal gasifier. Reynolds number and volume fraction of solid phase are used to define the boundary of high-turbulence zone, with their critical values 250 and 0.6, respectively. The influences of gasifying agent velocity and coal particle size on the shape and size of the high-turbulence zone are also investigated. The simulation results indicate that with the increase of coal particle size and gasifying agent velocity, the shape of high-turbulence zone is changed from boot-shape to arch-shape, and the slugging in the upper part of the gasifier is confirmed.

Severe slugging is a well-known instability in multiphase flow through a pipeline-riser system that is characterized by sharp pressure changes and violent flow fluctuations. This can cause safety and operational problems in the production of oil and gas. Particularly for deepwater risers, which can be up to 3000 m long, the operating pressure in the pipeline and riser can be high (that is a few hundreds of bar). Most lab experiments carried out so far for severe slugging were conducted at atmospheric pressure. The present study contains new experiments at elevated pressure. Thereto a new large-scale pipeline-riser system was established with 300 bar maximum pressure. To study the effect of the pressure at the riser top on severe slugging, experiments for the stability boundaries and for the amplitude and frequency of the slugging were carried out for pressures in the range of 0–50 barg. The results show that an increased backpressure gives a reduced region of severe slugging in the flow pattern map, whereas it also mitigates pressure fluctuations and decreases the slug frequency. Based on these experimental results, the existing prediction model for the stability of steady state operation and the transition to severe slugging was modified to incorporate the effect of the backpressure.

The number of slug units that traverses a particular point at a given time within a defined pipe cross-section is known as slug frequency. The behaviour of this critical parameter for two-phase flow in high viscosity oils is significantly different from those of conventional oils (of less than 1 Pa s). In this experimental investigation, new data on slugging frequency in high viscosity oil-gas flow are reported. Scaled experiments were carried out using a mixture of air and mineral oil in a 17 m long horizontal pipe of 0.0762 m ID. A high-speed Gamma Densitometer of frequency of 250 Hz was used for data acquisition over a time interval of 30 s. For the range of flow conditions investigated, increase in oil viscosity was observed to strongly influence the slug frequency. Comparison of the present data with prediction models available in the literature revealed discrepancies. A new correlation incorporating the effect of viscosity on slug frequency has been proposed for horizontal flow. The proposed correlation will improve the prediction of slug frequency in high viscosity oils.

Operating forces and magnitude of loads from gas-liquid slug flows exerted on a horizontally orientated 90 o bend are investigated. The distributed forces are either Newtonian, associated with the fluids motion or Configurational, inherent to the internal distributions of the phases. The forces are derived through the conventional balances of mass and linear momentum arising from the volume of fluid (VOF) description of gas-liquid flows. The study uses the integral form of the momentum balance to estimate the operating forces budget. Invoking dynamical time scales separation discloses the connection of the Lamb vector (vortex-force) to the local time rate of momentum. An interesting outcome being an explicit expression for Favre-Reynolds stress that reveals the contribution of void fraction fluctuations in the redistribution of the stress across the interface. Numerical simulations are performed to determine the magnitude of Newtonian loads on bend using a segmented domain technique to represent the fully established slug flow regime. The time-dependent traces of the relevant flow variables such as liquid hold-up, flow rates and resultant forces on the bend are recorded and analysed. Compared to the isotropic component, the deviatoric stresses are shown to have a marginal contribution to the total forces. It is also shown that loading cycles on bends are much higher than slugging cycles; this is an important feature for the structural integrity assessment of pipelines with bends.

The dynamics of gas fluidization is investigated by means of multiresolution analysis. Empirical mode decomposition (EMD) and the Hilbert-Huang transform approach applied to the signals of pressure fluctuation of the bed have been used for this purpose, operating in bubbling and slugging regimes. To elucidate the different components of the different scales, recurrence plots (RP) and recurrence quantification analysis (RQA) have been used. These techniques can distinguish the three different scales of gas fluidization: micro-scale, meso-scale and macro-scale, and classify every mode on its scale. Three modes from the EMD have been related to each dynamic component: particle interaction, local bubble dynamics and bed oscillation, showing evidence of this relationship. To show that the complexity of the modes matches with their characteristics, two measures have been computed: the apparent entropy and Lemped–Ziv complexity.

A gas-lift well sometimes suffers from slugging. As slugs reduce production volumes and cause other issues on the surface, we would like to mitigate or avoid them. The production choke and gas injection choke are two points at which the operator may influence the slug. For this to work, the operator must know that a slug is going to occur in advance so that avoidance actions can be implemented. The operator also needs to know by how much to change each choke. We find that a slug can be forecast successfully five hours in advance given typical field instrumentation of the well. This is based on an LSTM machine learning approach given historical data only.

Summary A gas-lift well sometimes suffers from slugging. As slugs reduce production volumes and cause other issues on the surface, we would like to mitigate or avoid them. The production choke and gas injection choke are two points at which the operator may influence the slug. For this to work, the operator must know that a slug is going to occur in advance so that avoidance actions can be im-plemented. We find that a slug can be forecast successfully five hours in advance given typical field instrumentation of the well. This is based on an LSTM machine learning approach given historical data only.

Severe slugging is a cyclic flow regime which causes intermittent delivery of oil and gas which usually leads to flow separator flooding, production reduction, platform trips and plant shutdown. This paper presents a novel method for severe slugging mitigation. It describes the use of a Venturi for the improvement of system stability, increase in production and recovery. A Venturi is coupled to the pipeline-riser system upstream of the choke valve before the topside test separator for severe slug mitigation. Experiments were carried out in a 2″ pipeline-riser system which comprises of a 40 m long horizontal pipe connected to a 10.23 m high S-shape riser followed by a 5.2 m horizontal topside section. The effects of Venturi on severe slugging were investigated, gas perturbation method was used to analyse the effects of Venturi on the stability of the system, and the traditional choking technique and Hopf bifurcation technique were combined and used to investigate the stability and production increase performance of the pipeline-riser with Venturi applied. Experimental results show that with the Venturi applied, the system achieves stability quicker than without the Venturi in the pipeline-riser and reduced the pressure fluctuation range by 57 %. In addition, combining the Venturi with the choke valve to choke the pipeline-riser (bifurcation study) stabilised the system at higher valve opening and lower pressure compared to choking the pipeline-riser with the choke valve only. For the case studied (Vsl = 0.25 m/s and Vsg = 0.37 m/s) bifurcation (critical valve opening) occurred at 18 % valve opening and average riser base pressure value of 2.8 barg for the plain riser. However, with Venturi applied bifurcation occurred at a larger valve opening of 21% and a lower average riser base pressure value of 2.5 barg. The low loss of energy due to the gradual change in geometry of the Venturi may account for its ability to achieve stability at a lower riser base pressure. Thus, Venturi increased the valve opening by 17% and reduced the riser base pressure by 11%. These in practice translate to an increase in oil and gas production. This is a cost-effective severe slug mitigation method, its deployment at the topside is an additional advantage when compared with other methods that require subsea deployment. The increase in brown fields due to diminishing reserves of oil from reservoirs have made oil recovery very vital. This technique will help to extend the operational life of a reservoir, thus enhancing oil recovery and flow assurance.

The well discussed in this paper has a history of sand production and has exhibit long cyclic slugging behavior with a frequency of several days and reduced average production. The lower completion has a 2000-ft gap between the mule shoe and the packer that is exposed to the larger diameter of 7-in. liner. It is not fully understood whether the slugging is caused by the gap at the lower completion or by sand transportation or both. Dynamic wellbore modelling with sand particle transport is essential to model the abovementioned complex slugging behavior. A stepwise approach was adopted to allow systematic evaluation of this complex slugging phenomenon. Initially, a lumped inflow with no sand transportation was assumed. In the next stage, sand transportation was included with zonal inflow details added. Several sensitivities on sand particle sizes, particle density, zonal productivity index, etc. were carried out, all of which were aimed at reproducing the long cyclic slugging behavior observed in the field. Transient simulations successfully produced the slugging behavior observed in the field. Cyclic slugging was seen to be caused by the flow dynamics generated by particles of small to medium size. Some of the key findings were complete blockage by porous sand stationary bed at the lower completion gap (with subsequent pressure buildup), transition from stationary bed to moving bed, rate-dependent velocity of a slow-moving particle bed (eventually producing to surface), and fresh sand particle production from the reservoir at increased drawdown. Measured data from the sand detector confirmed the production of sand, particularly around the same period as predicted by simulation. Potential slug mitigation solutions were established that should help to achieve higher and stable production. One solution was to achieve higher flow velocity and therefore enable sand transportation as a continuous moving bed (i.e., no blockage), such as reducing the gap size at the lower completion section together with either tubing size reduction or electric submersible pump (ESP) installation. The other solution was to implement an appropriate sand control/sand consolidation method. Sand production is a common flow assurance issue and sometimes can result in unstable flow behavior causing reduced production. This work is the first attempt to implement particle transport modelling in transient multiphase flow simulation to successfully address a slugging issue in a real well. The analysis helped in understanding the mechanism causing the slugging and arriving at a potential mitigation solution. Further, it provides a step-by-step workflow and a template to address such problems.

The use of accelerometer signals for early recognition of severe slugging is investigated in a pipeline-riser system conveying an air&ndash, water two-phase flow, where six accelerometers are installed from the bottom to the top of the riser. Twelve different environmental conditions are produced by changing water and gas superficial velocities, of which three conditions are stable states and the other conditions are related to severe slugging. For online recognition, simple parameters using statistics and linear prediction coefficients are employed to extract useful features. Binary classification to recognize stable flow and severe slugging is performed using a support vector machine and a neural network. In multiclass classification, the neural network is adopted to identify four flow patterns of stable state, two types of severe slugging, and an irregular transition state between severe slugging and dual-frequency severe slugging. The performance is compared and analyzed according to the signal length for three cases of sensor location: six accelerometers, one accelerometer at the riser base, and one accelerometer at the top of the riser.

Riser slug flow poses a significant challenge to offshore oil production systems, most especially for oil fields in their later life. Active control of slugging through choking has been proven a practical approach in eliminating riser slug flow in oil production pipeline-riser systems. However, existing conventional active slug control systems may reduce oil production significantly due to excessive over choking. Again, some of the existing active slug flow control systems rely on seabed measurements, which are difficult to maintain, costly to install, unreliable, and seldom readily available. This study is an experimental investigation of the feasibility of active riser slug control by taking topside differential pressure measurement from the inlet of the venturi flow meter to the throat. Experimental results indicate that under active slug flow control, the system was able to eliminate slug flow at a higher valve opening when compared to manual choking. A valve opening of 24% with riser base pressure at 2.85 bar from open loop unstable of 23% was recorded, which is superior to manual choking which maintained flow stability up to 21% valve opening with riser base pressure of 3.8 bar.

Understanding the agglomeration process of nanoparticles (NPs) can help to decrease their adhesion during fluidization. Herein, the mutual effects between the mechanical properties and interparticle cohesive forces of the TiO2 NPs as well as the fluidization regimes were studied in a conical fluidized bed. Young’s modulus and hardness of the agglomerates were determined by nanoindentation test. The size range of NPs, porous simple-agglomerates, and dense complex-agglomerates were 23 ± 3 nm, ~ 40–80 μm, and ~ 170–270 μm, respectively. Pressure fluctuation analysis exhibited a transition flow regime from a particulate phase to bubbling, slugging, turbulent fluidization, and spouting regime. The ratio of hydrodynamic to interparticle force was applied to describe the bed characteristics, while the granular Bond number obtained from settling experiments was used to find the agglomerates fractal dimension. The laser images showed the size, structure, and number of agglomerates depends on the type of fluidizing gas and fluidization regime. The dependency of the hardness on the fluidization regime showed the interparticle force diminishes with decreasing the asperity radius of agglomerates. The results showed full fluidization takes place, where the primary complex-agglomerates breakdown into simple-agglomerates and re-agglomerate into secondary complex-agglomerates with the fragile structures and irregular shape that simply fluidized at the spouting regime.

S-shaped riser may be used for connecting a subsea well and floating platform for the multiphase oil-gas flow transportation. A buoyancy module is installed in the longitudinal direction of the riser section enabling a hog and sag bend arrangement. This design offers a solution to decouple motion from the boundaries and lower the riser stresses. There is an increasing tendency to implement S-shaped risers for offshore platforms operating in deep waters or harsh environments. However, a generic S shape may cause a terrain-induced, severe slugging under certain practical operational/geometrical conditions and flow rates. This phenomenon leads to unstable and intermittent slug flows creating fluctuations of pressure, fluid fraction and velocity components. In this paper, the flow pattern characteristics and formation process of a severe slugging in an S-shaped rigid riser transporting the liquid-gas flows are studied using 3-D computational fluid dynamics simulations based on a finite volume method. Numerical results are validated by comparing with experimental results in the literature. Severe slugging behaviors are presented and discussed.

The application of real - time monitoring technologies presents a means to harnessing proactive or reactive controls in minimizing severity effects of slugging in the production system. This paper presents the development of a non-intrusive optical infrared sensing (NIOIRS) setup, for slug monitoring in pipes. The flow characteristics monitored were the development of slug flows and average phase fractions of gas and liquid in a vertical test section (0.018m by 1m) for superficial velocities of 0-0.131 m/s for water and 0 – 0.216 m/s for air. The measurement principle was based on the disparities in refractive indices of each phase in the sensing area. The sensing component of the sensor consisted of two pairs of IR emitters and photodiodes operated at wavelengths of 880 nm specifications. A circuit, for signal conditioning, amplification and data acquisition was set up to convert infrared light detected into voltage signals. Development of slug flow regimes was monitored from signal distributions binned under reference voltages. The transitions from bubble to slug flow, were observed at 10 percent count of the signal distributions around typical sensor response for air. Validation from photos showed good agreements with the sensor response. A single peaked distribution around the response for water indicated bubble flow regimes, with the development of two peaks indicated increasing gas slugs for increasing superficial gas velocities compared to liquid slug in the pipe. Phase fraction results were interpreted from a derived calibration models, which were based on the average observed response and reference responses of water and air over time. This model was compared with swell level changes, photographs and homogenous and drift flux correlation with agreement within maximum error bands +/− 0.5 % based on the swell level method and +/− 0.3% based on photographs. The Real-time application was carried out via the execution of an algorithm which incorporated the calibration information from the NIOIRS. The derived signals were processed and analyzed onto a display to identify slug flow development and phase fractions in real-time. A cheap and accurate sensing setup has been developed with the potential of real time monitoring of flow regimes and phase fraction determination.

Deepwater Gulf of Mexico wells that exhibit liquid loading and subsea flowlines that suffer fluid slugging are both common issues that have historically been difficult to mitigate without expensive hardware changes or deferral of production. A novel black oil foamer (BOF) chemical technology has shown to be able to mitigate liquid loading, increase production, and reduce fluid slugging in both dry tree wells, subsea wells, and subsea flowlines. This presentation will detail three example cases where the black oil foamer technology was utilized successfully. For the first example case, liquid loading was the primary issue leading to shortened production time between shut-ins, causing slugging, and reduced overall production rates. For the second example, significant slugging was experienced in an 18-mile subsea tieback to the point that the field would be shut in for topside vessel level controller issues. The final case trialed different well lineups that would historically cause severe slugging in an 11 mile subsea tieback. In the first example, the benefits of using the black oil foamer included increased oil production and greatly improved well uptime, as well as significantly reducing slugging. The benefits demonstrated in the second and third examples were a significant reduction in slugging, allowing the field to operate with minimal shut-in risk and reducing equipment damage. Novel & Additive Information All three examples have proven the concept of using the black oil foamer chemistry to manage liquid loading and slugging risks in deepwater applications in an economically advantageous way.

The effects of horizontal well geometry remain debatable in most production modeling works. Most of recent reports fail to mention the effects of well geometries, especially in severe slugging cases. This study presents a qualitative comparison between different well geometries and their impacts in production performance of horizontal wells. The study utilizes a transient multiphase simulator to mimic the production from a horizontal well over a 12-hour period. The well has a 2-7/8″ ID tubing with TVD of approximately 5000 ft and MD of 10000 ft and maximum inclination angle of 10º within the horizontal section. The trajectories of horizontal section in the well include 5 cases, 5 undulations, hump (one undulation upward), sump (one undulation downward), toe-up and toe-down. These configurations are the representative examples of horizontal wells. A reservoir with a given deliverability equation and several perforation stages is used to provide well inflow. The impacts of reservoir deliverability, GOR, pressure and temperature are studied for all well geometries. The simulation results offer some valuable insights into the effects of well trajectory on production performance, including borehole pressure profile, liquid holdup, gas and liquid rate variations with time, and cumulative gas and liquid production. At high production rates, severe slugging is not observed, and thus, the well geometry effects are minimized with a consistent production at the surface. However, toe-up configuration exhibits a slightly better performance than the others. As the productivity and pressure reduces throughout the life of a well, the impacts of well trajectories become clearer. The presence of severe slugs and blockage of perforations near the toes causes a noticeable drop in production. During severe slugging, the pressure profile reveals longer fluctuation cycles, resulting in extreme separator flooding issues. The slugging frequencies are compared among different well geometries. Toe-down case exhibits lower slugging severity. As a result, toe-down well produces the highest cumulative liquid and gas rates. The presence of liquid blockage is observed in lateral and curvature sections. The toe-up and hump configurations exhibit the most severe slugs with minimum cumulative gas and liquid productions. The differences in productions among well trajectories exceed 30% under different well configurations. With the augmented growth of production from unconventional reservoirs, horizontal well technology has grown in oil and gas industry, yet study of well geometry in production system remains to be limited. This study is a unique effort to optimize well configuration and perforation placement in order to alleviate multiphase flow problems in the wellbore. Providing the practical potential on simulation works, this study provides a predictive guidline to connect well geometry selection and production optimization.

To identify conveniently multiphase flow regimes in subsea pipeline-risers, we study in this paper experimentally two-phase flows in a 1657 m long pipeline with an S-shaped riser to simulate field experiment, within a wide range of gas and liquid velocities. Three flow regimes, namely severe slugging, transitional flows, and stable flows, are analyzed based on three differential pressure and one pressure signals at the top of the riser; comparatively speaking, the positions of these signals in the experimental system are similar to those of the sea level signals in industrial fields, which are easy and less expensive to obtain. The obtained signals are decomposed into six scales via a multi-scale wavelet analysis, and further four statistical parameters on each scale are extracted, including mean values, standard deviations, ranges, and mean values of absolute. We compared the effects of six SVM classifiers with different kernel functions on the recognition rate of flow regimes, and it is found the recognition rates of SVM classifier with quadratic and cubic kernel functions are the highest. Further, the principal component analysis is employed to reduce the dimension of statistical parameters and it indicates that the recognition rate tends to increase with the rising number of principal components from 1 to 6, and it remains constant if the principal component number is further increased. Moreover, The results suggest that the recognition rate obtained from the pressure difference between the top of the riser and the separator peaks, and then it comes that from the pressure signal at the top of the riser, and that for the pressure difference signal at the top of the riser is the least satisfying one. As for the optimal differential pressure signals between the top of the riser and the separator, the results show that the recognition rate increases rapidly from 70.2% to 90.4% when the sample duration rising from 2.3 s to 18.6 s, and when the sample duration exceeds 74.4 s, the recognition rate exceeds 92.9% and remains unchanged.

Slug multiphase flow is known to be the most prevalent regime because of its extensive encounters associated with chaotic behaviour, complexity and instability that cause significant fluctuations in operating conditions and thus lead to undesirable effects. In this study, the effect of varying crude oil grades on slug characteristics is numerically investigated. A partitioned one-way coupling framework of fluid–structure interaction (FSI) one-way coupling framework is adopted to investigate the influence of changing oil grades and slug characteristics on the maximum induced stresses in horizontal carbon steel pipe. It was found that increasing crude oil density causes frequent slugging and promotes the formation of liquid slugs further upstream near the inlet with high translational velocity and short wavelength. Therefore, the maximum induced stresses resulting from the interaction between slugs and the inner surface of pipes are strongly dependent on crude oil grade. In modelling extra heavy crude oil, a 40% increase in maximum induced stresses is recorded when the liquid superficial velocity decreases from 1 to 0.86 m/s at a constant natural gas superficial velocity.

Pressurised fluidised beds have been widely used in industry, e.g., for coal gasification. However, gas-solids flow dynamics at high pressure, closely relevant to fluidised beds performance, is not yet well understood. For this purpose, electrical capacitance tomography (ECT) and pressure fluctuation measurements were carried out in a pilot-scale pressurised circulating fluidised bed (PCFB), operated at pressures ranging from 0.2 MPa to 1.3 MPa and gas velocities from 0.5 m/s to 2.65 m/s, to investigate the effects of pressure on gas-solids flow characteristics. The critical flow regimes transition velocities and bubble properties were examined by ECT images along with time and frequency domain analysis. The results indicate that a wide range of flow regimes including bubbling, slugging, turbulent and fast fluidisation, can be identified with distinct transition velocities in the pressurised fluidised bed. With an increase in pressure, the minimum fluidisation velocity and transition velocities between different flow regimes decrease for particles under investigation, i.e., quartz sand with mean diameter of 352 µm. With an increase in pressure, a more homogeneous flow structure with smaller bubbles and lower bubble rise velocities takes place compared with that at ambient pressure condition. The novelty of this research lies in first time demonstration of ECT measurements for high-pressure hydrodynamics over a wide range of flow regimes. The minimum fluidisation velocity can be derived without de-fluidising a PCFB, and bubble rise velocity can be obtained by cross-correlation of dual-plane ECT signals.

Gas-solid micro fluidized beds have unique characteristics such as bed pressure drop overshoot, delayed minimum and bubbling/slugging but advanced turbulent fluidization, as well as negligible gas back-mixing. The data covering a wide range of operating conditions reported by various researchers are summarized, and analyzed in an effort to gain in-depth understanding about these characteristics. Based on the analysis, an approximate quantitative criterion to distinguish micro and macro fluidized beds is proposed, and the boundaries between non-fluidizable and fluidizable zones are defined. In micro fluidized beds, gas-solid flow can be situated in particulate, bubbling, slugging and turbulent fluidization regimes based on superficial gas velocity, ratios of D t / d p and H s / D t . Hydrodynamic characteristics of these flow regimes are discussed, and the correlations for U mf , U mb , U ms , and U c are developed based on analysis of experimental data. Finally, generalized fluidization maps applicable to micro fluidized beds are proposed based on the developed correlations. Through the analysis, some uncertainties and even contradictories among the reported data are identified, which would guild future studies to bring the micro fluidized bed technology forward.

In the two-phase flow field, a traditional mathematical model for simulating the transition of severe slugging flow presents a challenge when liquid slugs completely block pipelines. Accordingly, an advanced and practical slug model that is derived from a mixture model associated with a slip closure is essential to solving the problem in cooperation with the two-fluid model. The model can offset numerical instability that arises from the discontinuous function of the friction factor across the transition from one flow pattern to the other. Two numerical schemes, the non-iterative and the iterative, are developed, and the proposed schemes can stably predict the transient problems under the Courant–Friedrichs–Lewy (CFL) condition for semi-implicit/implicit schemes. In the present work, pressure transients produced by a complex phenomenon, named water hammer effect, are captured using the single-phase flow model in one-dimension to verify the applicability of the numerical schemes and the friction factor model. At last, the analysis of the two-phase transient flow in a pipeline-riser system indicates that the significant advantage of the present schemes is the robustness that the numerical prediction of the severe slugging behaviour is accurate and stable.

The upstream offshore multi-phase well-pipeline-riser installations are facing huge challenges related to slugging flow: An unstable flow regime where the flow rates, pressures and temperatures oscillate in the multi-phase pipelines. One typical severe slug is induced by vertical wells or risers causing the pressure to build up and hence originates the oscillating pressure and flow. There exist many negative consequences related to the severe slugging flow and thus lots of investments and effort have been put into reducing or completely eliminating the severe slug. This paper reviews in details the state-of-the-art related to analysis, detection, dynamical modeling and elimination of the slug within the offshore oil & gas Exploration and Production (E&P) processes. Modeling of slugging flow has been used to investigate the slug characteristics and for design of anti-slug control as well, however most models require specific facility and operating data which, unfortunately, often is not available from most offshore installations. Anti-slug control have been investigated for several decades in oil & gas industry, but many of these existing methods suffer the consequent risk of simultaneously reducing the oil & gas production. This paper concludes that slug is a well defined phenomenon, but even though it has been investigated for several decades the current anti-slug control methods still have problems related to robustness. It is predicted that slug-induced challenges will be even more severe as a consequence of the longer vertical risers caused by deep-water E&P in the future.

The hydrodynamics of a slugging fluidized bed is investigated numerically by using a two-fluid model suggested by Brandani and Zhang [22]. Numerical simulations are carried out in the platform of a commercial software package, CFX 4.4, by adding user-defined subroutines. The bed expansion ratio, the pressure drop fluctuation and its power spectrum density at the equipment scale and the solids volume fraction distributions at the grid scale are predicted to explore the slugging fluidization characteristics for Geldart group D particles. By comparing with the experimental data in the literature, the numerical model is found to have better predictive ability when the viscous force term is considered in the gas phase momentum equation.

The fluidization behavior of a binary mixture of Geldart D type particles in a shallow vibrated gas-fluidized bed (VFB) was systematically studied by using a high-speed dynamic camera. This study drew a comparison between the fluidization of a VFB and a conventional gas-fluidized bed (CFB). The results show that the characteristic air velocities in a VFB, such as the minimum fluidization velocity, the minimum bubbling velocity and the minimum slugging velocity, have considerable reductions in comparison with that in a CFB. It is indicated that the vibration significantly changes the gas-solid two-phase flow structure and improves the dispersion uniformity of air flow in the bed. The air pressure waves, as the main transmission mode of vibration energy, can improve the air-solid contact efficiency and organize the excess fluidizing air to form periodic slugs. In a VFB of Geldart D type particles, there are four distinct fluidization regimes: static bed, bubbling fluidization, slugging fluidization and turbulent fluidization. The results show that a good performance of density segregation in a VFB of Geldart D type particles happens in the stage of gentle slugging.

We report results from a computational study of the transition from bubbling to slugging in a laboratory-scale fluidized-bed reactor with Geldart Group B glass particles. For simulating the three-dimensional fluidized-bed hydrodynamics, we employ MFiX, a widely studied multi-phase flow simulation tool, that uses a two-fluid Eulerian-Eulerian approximation of the particle and gas dynamics over a range of gas flows. We also utilize a previously published algorithm to generate bubble statistics that can be correlated with pressure fluctuations to reveal previously unreported details about the stages through which the hydrodynamics progress during the bubbling-to-slugging transition. We expect this new information will lead to improved approaches for on-line reactor diagnostics, as well as new approaches for validating the results of computational fluidized-bed simulations with experimental measurements.