Gas Void Fraction Research Articles

Research on dynamical overflow characteristics of a vertical H2S‐containing natural gas well

AbstractThis work aims to explore the overflow characteristics of a vertical H2S‐containing natural gas well. A two‐phase flow model for H2S‐containing natural gas well combining with a transient temperature prediction model was established to simulate the overflow process of a vertical H2S‐containing natural gas well. The model was validated by reproducing the field data of Well Longhui #2. The effects of H2S content, mud displacement, drilling fluid density, geothermal gradient, and reservoir permeability on the overflow characteristics of a vertical H2S‐containing natural gas well were studied and analyzed in this work. Results indicate that bubble, slug, and churn flows constitute the main flow patterns in the whole overflow process. The higher the H2S content is, the more obviously the gas void fraction increases. The phase change position of H2S is closer to the wellhead at lower H2S content. An increase in mud displacement indicates the decreases in overflow time. As drilling fluid density increases, the release position of H2S moves up, and the overflow time and shut‐in casing pressure increase. The initial gas void fraction is higher and the gas invasion volume will be larger in gas reservoirs with higher permeability. As the reservoir permeability increases, the shut‐in casing pressure rises while the overflow time declines. With higher geothermal gradient, the wellbore temperature tends to be higher at the same depth, leading to an increase in the H2S solubility. The gasification starting position is further away from the wellhead at higher geothermal gradient. The results of this work could provide important theoretical basis and technical guidance for drilling engineers to reduce a blowout risk during drilling of H2S‐containing natural gas well.

Two-phase flow experiments with Coriolis Mass Flow Metering using complex signal processing

Abstract— Two-phase (gas/liquid) flow is common in many industrial applications but its measurement remains challenging for Coriolis mass flow meters (CMFM), especially for high Gas Void Fraction (GVF). In this paper, we present experimental results applying previously developed complex signal processing techniques for tracking the rapidly changing sensor signals generated by two-phase flow. The techniques are implemented in a new System-on-Chip (SOC) prototype transmitter connected to a commercial Coriolis flow tube. Experiments have been carried out over a range of single phase and two-phase (water/air) flows. The signal tracking as well as mass flow rate and density measurement performance is compared with that of a laboratory version of a commercial Coriolis transmitter with two-phase flow capability. The results show that the complex bandpass algorithms, coupled with flowtube control algorithms, reduce the standard deviation of the mass flow measurement by a factor of 3 or more in 50% of the experiments undertaken. For the density measurement, the corresponding reduction in standard deviation is by a factor of 6.

Gas Void Fraction Measurement of Gas-Liquid Two-Phase CO2 Flow Using Laser Attenuation Technique.

The carbon capture and storage (CCS) system has the potential to reduce CO2 emissions from traditional energy industries. In order to monitor and control the CCS process, it is essential to achieve an accurate measurement of the gas void fraction in a two-phase CO2 flow in transportation pipelines. This paper presents a novel instrumentation system based on the laser attenuation technique for the gas void fraction measurement of the two-phase CO2 flow. The system includes an infrared laser source and a photodiode sensor array. Experiments were conducted on the horizontal and vertical test sections. Two Coriolis mass flowmeters are respectively installed on the single-phase pipelines to obtain the reference gas void fraction. The experimental results obtained show that the proposed method is effective. In the horizontal test section, the relative errors of the stratified flow are within ±8.3%, while those of the bubble flow are within ±10.6%. In the vertical test section, the proposed method performs slightly less well, with relative errors under ±12.2%. The obtained results show that the measurement system is capable of providing an accurate measurement of the gas void fraction of the two-phase CO2 flow and a useful reference for other industrial applications.

Transient gas–liquid–solid flow model with heat and mass transfer for hydrate reservoir drilling

The three–phase gas–liquid–solid flow, caused by hydrate decomposition in cuttings is a main concern during drilling through gas–hydrate reservoir. In this study, a transient gas–liquid–solid flow model is developed considering the coupling interactions between hydrate dynamic decomposition, cuttings transport and heat transfer in multiphase flow. Using this model, the transient gas–liquid–solid flow behaviors are investigated. Numerical simulations show that the decomposition rate of hydrate in formation is only 1/140 of that in annular cuttings for a unit depth, therefore, the influences of hydrate decomposition in hydrate layers can be neglected. Hydrate particles undergo three processes from bottom hole to wellhead in annulus: non–decomposition, slow decomposition and rapid decomposition. In annulus where the depth is more than 400 m, hydrates decompose slowly and the decomposed gas hardly expands due to the high pressure. While, if the hydrates and decomposed gas return upwards to the position where the depth less than 400 m, the gas void fraction increases significantly, not only due to the faster decomposition rate of hydrates but also due to the more intense expansion of decomposed gas. After the hydrate particles return upwards to the wellhead, the behaviors of gas–liquid–solid flow tend to be a quasi–stable state. If there is no backpressure device at the wellhead, that is, the wellhead backpressure is 0 MPa, the gas void fraction at the wellhead can reach 0.68, which is enough to cause blowout accident. Increasing wellhead backpressure to 2 MPa through managed pressure devices and lowering the inlet temperature of drilling fluid to 17.5 °C except adjusting drilling fluid density can manage the gas void fraction within 10%.

Application of Artificial Neural Network Model to a Voltage–Current System in the Estimation of Void-Fraction in a Gas–Liquid Flow

Void fraction in gas–liquid flow has been estimated using the artificial neural network (ANN) with electrical current response (ECR) from a voltage–current (VC) system, which measures electrical currents through the combination with eight electrodes attached around a pipe for gas–liquid flow. The ANN model for ECR with the number of neurons ${N} =3136$ has the lowest relative error and absolute error, respectively, in estimating void fraction of gas–liquid flow, among five different numbers of neurons ( ${N} =392, 784, 1568, 3136$ , and 6272) on a hidden layer of the ANN model for ECR. With regard to the change in total loss during the training process, the ANN model for ECR with ${N=3136}$ shows good convergence as $28\times 10^{-4}$ for void fraction estimation in gas–liquid flow compared to other ANN models with different numbers of neurons ${N}$ . In this paper, electrical currents measured by the VC system in the static experiment with eight void fraction conditions are used to optimize the ANN model for ECR in order to estimate void fraction of gas–liquid flow. In the gas–liquid flow with seven void fraction conditions, the optimized ANN model for ECR is applied for void fraction estimation in order that the estimation performance according to the number of neurons on the hidden layer is evaluated.

110th Anniversary: Numerical Simulations of Gas–Liquid Two-Phase Flow in Vertical Pipe Implementing Population Balance Modeling

Population balance modeling in a gas–liquid two-phase bubbly flow allows us to predict the bubble size distribution. The prediction of bubble size distribution is of utmost importance as it prevails the heat, mass, and momentum transport mechanisms. In the present work, numerical simulations of gas–liquid two-phase flow in a vertical pipe have been performed using population balance modeling. The effects of different coalescence and breakage models have been studied. The wall peak and core peak case in the bubbly flow regime is considered for the prediction of the radial distribution of the gas void fraction, interfacial area concentration, bubble size distribution, Sauter mean diameter, and gas and liquid velocities. Numerical simulations were performed with the Euler–Euler two-fluid model and the k–ω SST turbulence model. The population balance equation is solved using the traditional class method. The combination of Brownian coalescence and Ghadiri breakage model is recommended for the prediction of th...

The Impact of Journal Bearing Wear on an Electric Submersible Pump in Two-Phase and Three-Phase Flow

Electric submersible pumps (ESPs) provide artificial lift within oil wells. ESPs commonly fail from mechanical vibrations that increase as bearing clearances increase from debris, gas, and liquid pumped through the ESP. In order to understand journal bearing wear within an ESP, three stages of a mixed flow electric submersible pump were subjected to hydraulic fracture sand slurry in water. One hundred seventeen hours were conducted with sand and water, followed by 68 h with air added at 15% inlet gas volume fraction. The journal bearings were severely worn by the end of testing, and pump vibrations increased with increased bearing clearances. Bearing vibrations and clearances became significantly larger than the impeller labyrinth seal vibrations and clearances, indicating that the labyrinth seals became the dominant rotor support once the bearings were worn. Adding air increased the wear and rotor vibration orbit variability. Rotor vibration orbits were entirely independent of gas void fraction by the end of testing, indicating that the lubricant composition no longer directly impacted vibrations. Fine axial cracks from heat checking were observed on the journal of the bearings. Results indicate that controlling journal bearing wear is a critical factor for increasing operating lifetimes. Alternative bearing geometry and materials should be investigated to prevent the occurrence of three-body abrasion, limit the resultant wear rate from three-body abrasion, and limit the damage from heat checking.

Design and simulation of a multienergy gamma ray absorptiometry system for multiphase flow metering with accurate void fraction and water-liquid ratio approximation

Abstract Multiphase flow meters are used to measure the water-liquid ratio (WLR) and void fraction in a multiphase fluid stream pipeline. In the present study, a system of multiphase flow measurement has been designed by application of three thallium-doped sodium iodide scintillators and a radioactive source of 133Ba simulated by Monte Carlo N-particle (MCNP) transport code. In order to capture radiations passing across the pipe, two direct detectors have been installed on opposite sides of the radioactive source. Another detector has been placed perpendicular to the transmission beam emitted from the 133Ba source to receive radiations scattered from the fluid flow. Simulation was done by the MCNP code for different volumetric fractions of water, oil, and gas phases for two types of flow regimes, namely, homogeneous and annular; training and validation data have been provided for the artificial neural network (ANN) to develop a computation model for pattern recognition. Depending on applications of the neural system, several structures of ANNs are used in the current paper to model the flow measurement relations, while the detector outputs are considered as the input parameters of the neural networks. The first, second, and third structures benefit from two, three, and five multilayer perceptron neural networks, respectively. Increasing the number of ANNs makes the system more complicated and decreases the available data; however, it increases the accuracy of estimation of WLR and gas void fraction. According to the results, the maximum relative difference was observed in the scattering detector. It was clear that transmission detectors would demonstrate the difference between the flow regimes as well. It is necessary to note that the error calculated by the MCNP simulator is <0.5% for the direct detectors (TR1 and TR2). Due to the difference between the data of the two flow regimes and the errors of data in the simulation codes of the MCNP, it was possible to separate these flow regimes. The effect of changing WLR on the efficiency for a constant void fraction confirms a considerable variance in the results of annular and homogeneous flows occurring in the scattering detector. There is a similar trend for the void fraction; hence, one can easily distinguish changes in efficiency due to the WLR. Analysis of the simulation results revealed that in the proposed structure of the multiphase flow meter and the computation model used for simulation, the two flow regimes are simply distinguishable.

Interphase forces analysis in the whole flow passage of a multiphase rotodynamic pump

To understand the internal flow and interphase forces characteristics in the multiphase rotodynamic pump, simulations were performed using ANSYS_CFX for the whole flow passage with medium combination of air-water. The reliability of simulation was verified by comparing with the experimental data of external characteristics. The results showed that the drag is dominant for the interphase forces in the impeller and guide vane passages, followed by the lift and added mass forces, then the turbulent dispersion force, and it can be neglected relative to drag. With the increased IGVF (inlet gas void fraction), all interphase forces in the impeller and guide vane passages will increase, also, the variation range of interphase forces in the impeller was greater than that in the guide vane.

Investigation on gas-liquid two-phase flow centrifugal pump performances for different rotational speeds

Performance characteristics of a centrifugal pump under gas-liquid mixture are presented, using a direct coupled single-stage, single-suction centrifugal pump. Both experimental and numerical simulations comparison are carried out, for three different rotational speeds and different inlet gas volume fractions, the results of which are presented, based on dimensionless coefficients from similarity laws. The numerical results show that good agreement is obtained with experimental data at nominal rotational speed for several flow coefficients. It is found that the running of the pump is near the sudden break down of the present pump when the inlet void fraction is below 7%. However, numerical results are less sensitive to rotational speed effects compared with experiment ones; the influence of decreasing rotational speed on pump performances is more and more pronounced when inlet gas void fraction increases and flow coefficient decreases. Froude number effects are taken into account in order to explain part of these differences.

Wet gas over-reading correction for ultrasonic flow meters

Oil and gas operators rely on accurate flow rate measurements to optimize production and generate more from their reservoirs, particularly in wet gas fields. A cost-effective solution for these flow measurements is the use of single-phase measurement technologies with an over-reading correction that corrects the gas flow rate for the presence of the liquid phase. Traditional flow measurement technologies in wet gas fields are Venturi meters and orifice plate meters that involve differential pressure measurements. Over the years, a higher installed base of ultrasonic flow meters is observed in wet gas fields. Ultrasonic flow meters have advantages over conventional wet gas technologies; however, an over-reading correction method for this measurement technology has not yet been derived. The current work is a first attempt to devise a correction method based on a large data set of ultrasonic measurements in horizontal configuration at conditions comparable to field applications. The correction method is a physical model for the gas void fraction and is based on the dominant dimensionless numbers in wet gas flows that originate from the fundamental equations of multiphase flow dynamics. This approach leads to the definition of the over-reading correction in different flow regimes in terms of these dimensionless numbers and is supported by an extensive set of measurement data and evidence from visual observation of the flow patterns. The correction method is capable of correcting the ultrasonic over-reading with a resulting uncertainty of about 4% for a 95% confidence interval for a range of conditions relevant to the oil and gas industry.

Combined releases of oil and gas under pressure; the influence of live oil and natural gas on initial oil droplet formation

Both oil droplets and gas bubbles have simultaneously been quantified in laboratory experiments that simulate deep-water subsea releases of both live oil (saturated with gas) and additional natural gas under high pressure. These data have been used to calculate particle size distributions (50–5000 μm) for both oil and gas. The experiments showed no significant difference in oil droplet sizes versus pressure (from 5 m to 1750 m) for experiments with live oil. For combined releases of live oil and natural gas, oil droplet sizes showed a clear reduction as a function of increased gas void fraction (increased release velocity) and a weak reduction with increased depth (increased gas density/momentum). Oil droplets were reduced by a factor of 3 to 4 during simulated subsea dispersant injection (SSDI) and no significant effect of pressure was observed. This indicates that SSDI effectiveness is not dependent on water depth or pressure.

Numerical simulation of gas–liquid flow behavior in the nozzle exit region of an effervescent atomizer

The pressure drop and particular geometric structure of the nozzle exit region of an effervescent atomizer cause complex changes in the flow pattern, which could affect the spray performance. In this study, the gas–liquid two-phase flow behavior in the nozzle exit region of the effervescent atomizer was investigated numerically. The results show that the flow behaviors in the nozzle exit region have disparate characteristics with different upstream flow regimes. For upstream churn flow, the liquid film morphology is closely related to fluctuation in the gas–liquid velocity, and the flow parameters (fluids’ velocities and gas void fraction) at the exit section vary regularly with time. For upstream bubbly flow, the instantaneous gas void fraction is determined by the bubble distribution inside the mixing chamber. The bubble will form a tadpole-like shape as a result of the complex flow field and the surface tension. The flow parameters at the exit section are in an oscillatory decay, and the fluctuation amplitude is larger than for churn flow. For upstream slug flow, the gas void fraction varies significantly with time. The discrete characteristic of the gas–liquid flow parameters at exit section is very obvious.

Analysis and interpretation of radiometric signals in a liquid-gas bubble flow

The article presents the analysis of signals from a radiometric system consisting of two scintillation probes and two gamma radiation sealed sources. Calculations and interpretation were carried out for the bubble flow of the water-air mixture in the horizontal pipeline. The analysis of the obtained signals was done in time and frequency domain. In the frequency domain, a range of usable frequencies was identified, which were associated with changes in gamma-ray intensity recorded in the time domain. The gas phase velocity, void fraction and statistical parameters of the signal were also calculated.

Numerical analysis of pressure fluctuation in a multiphase rotodynamic pump with air–water two-phase flow

Pressure fluctuation in single-phase pumps has been studied widely, while less attention has been paid to research on multiphase pumps that are commonly used in the petroleum chemical industry. Therefore, this study investigates the pressure fluctuation for a multiphase rotodynamic pump handling air–water two-phase flow. Simulations based on the Euler two-fluid model were carried out using ANSYS_CFX16.0 at different Inlet Gas Void Fractions (IGVFs) and various flow rate values. Under conditions of IGVF = 0% (pure water) and IGVF = 15%, the accuracy of the numerical method was tested by comparing the experimental data. The results showed that the rotor–stator interaction was still the main generation driver of pressure fluctuation in gas–liquid two-phase pumps. However, the fluctuation near the impeller outlet ascribe to the rotor–stator interaction was weakened by the complex gas–liquid flow. For the different IGVF, the variation trend of fluctuation was similar along the streamwise direction. That is, the fluctuation in the impeller increased before decreasing, while in the guide vane it decreased gradually. Also, the fluctuation in the guide vane was generally greater than for the impeller and the maximum amplitude appeared in the vicinity of guide vane inlet.

Debottlenecking Through Produced-Water Partial Processing Unlocks Production

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 187109, “Partial Processing: Produced-Water Debottlenecking Unlocks Production on Offshore Thailand MOPU Platform,” by C.H. Rawlins, SPE, eProcess Technologies, prepared for the 2017 SPE Annual Technical Conference and Exhibition, San Antonio, Texas, USA, 9–11 October. The paper has not been peer reviewed. An operator in the western Gulf of Thailand installed two water-management partial-processing systems on its mobile offshore production units (MOPUs) to increase oil production. Water removed at the production manifold is treated and transferred directly to the injection system, thus bypassing primary separation, transfer piping, fluid heating, and floating storage facilities. Water debottlenecking increased oil production by 80% and reduced the in-field transfer volume by 62%. Introduction In mature oil basins, the ability to sustain oil production depends on managing an increasing volume of produced water. The partial-processing method seeks bulk (not complete) removal of a throughput-constraining phase from oil and gas production using compact processing equipment. Partial-processing technology normally is installed on facilities that have space or weight constraints, where traditional separation technologies will not fit. Fitting within or around existing process equipment, partial-processing equipment maximizes the capability of an existing facility footprint. The constraining phase may be gas or water, and specific technologies are available to address each. The application detailed in this paper addresses produced-water debottlenecking. Removal of the water constraint unlocks production potential from mature or marginal fields and has been shown to increase hydrocarbon production. Design Stages and Setup For water-constrained systems, the most significant benefit comes from the removal of bulk water as far upstream as possible. High-water-cut wells are combined into a discrete manifold that may handle part or all of the field production. The partial-processing system is on this manifold, upstream from the existing process equipment. Debottlenecking at this point opens capacity in the flow lines, transfer piping, and processing facilities. The partial-processing skid can be installed on unmanned platforms with limited utilities and space and weight constraints. Bulk water removal and treatment may have two or three stages. The first stage, preseparation, involves bulk water removal from the multiphase-flow stream. A specially designed liquid/liquid hydrocyclone (preseparator) removes a bulk portion (60–95%) of the water from the flow stream. Next, the removed bulk water passes to the deoiler hydrocyclone, which operates in a standard produced-water-treating mode. For example, the preseparator will reduce oil content from 10 to 0.2%. The deoiler will take the 2,000-ppm oil down to or near discharge quality (20–50 ppm), depending on oil properties, pressure drop, and temperature. A tertiary treatment stage is optional and is used for difficult separation (e.g., cold fluids with heavy oil) or very stringent disposal requirements (e.g., low oil-in-water levels for enhanced-oil- recovery injection). This stage uses a compact flotation unit (CFU) for both degassing and oil polishing. The CFU removes gas effervescing from solution after the deoiler (which can be 5–10% of the gas void fraction) and uses that gas to float the fine oil droplets.

Computational study of bubbly jets in stagnant water

The air-water bubbly jets in a stagnant water are numerically investigated by using a CFD software package with the realizable k–e turbulence model. The focus is on the jet evolutionary behaviors in terms of the gas void fraction, the axial water velocity, the turbulent kinetic energy (TKE), the entrainment coefficient, and the momentum and buoyancy fluxes in a wide range of the bubbly jets (with the initial gas volume fractions ranging from 0 to 0.83). The computational results are found generally in good agreement with the experimental results reported in the literature. Both the gas void fraction and the axial water velocity follow the Gaussian distribution in the radial direction as expected, however a double-peak distribution is found for the TKE at some distance away from the nozzle. With the increase of the longitudinal distance, their peak values generally are decreased until reaching approximately their terminal values. The non-dimensional relations are revealed in both the radial and longitudinal directions. The potential core and the spreading rates of the bubbly jets are then investigated. The liquid volume flux of the bubbly jets is found to increase almost linearly along the centerline with an entrainment coefficient of 0.037-0.065. The momentum flux of the bubbly jets increases due to the buoyancy force, and the relative importance of the momentum and buoyancy fluxes is also discussed.

Experimental investigation of the oil based Aphron drilling fluid for determining the most stable fluid formulation

Colloidal gas Aphrons, as a type of low weighted drilling fluid, have been recently used and their positive effect on formation damage has been proven. The stability of Aphron fluids is an important issue that can affect fluid loss. The purpose of this study is to provide the most stable oil-based Aphron drilling fluids. In this study, the continuous phase of the created fluids are made using oil based fluids and bubbles covered with Dodecyl benzene sulfonate and dispersed in the continuous phase which was viscositfied with the vegetable oil based polyurethane polymer. The stability of Aphron fluid is analyzed taking the drained liquid volume, Aphron half-life, and gas void fraction into account. It is observed that the oil based Aphron fluid including 13.4 kg/m3 concentration of the surfactant and 15 kg/m3 polymer was the most stable fluid, in which the sizes of bubbles have minimum variation with time.

Study on effervescent spray morphology based on internal gas-liquid two-phase flow patterns

Abstract The study on the spray morphology of effervescent atomization based on the internal gas–liquid flow patterns were conducted by the combination of experiment and numerical simulation methods. Both time-average and fluctuation characteristics of the spray morphology under various internal flow patterns were given out. The analysis on the corresponding relationship between internal flow and spray morphology was further present out. Results showed that the internal flow pattern has little influence on the time-average characteristic of the spray morphology, but takes great effect on the fluctuation characteristics of spray morphology. In churn flow, the spray half cone angle varies in a narrow range. In bubbly flow, the instantaneous spray cone angle pulsates in a wide range. In slug flow, the spray morphological pulsating phenomenon is of polarization, the spray half cone angle distributes mainly in the low or high value ranges decided by whether gas’s contributing to the jet breakup. The instantaneous gas–liquid phase distribution in the exit orifice region and the variation law of gas void fraction at the nozzle exit is the direct cause of the spray morphology.

Quantification of Gas Distribution and Void Fraction in Packed Bubble Column Using Electrical Resistance Tomography

Random or structured packing is typically used in the chemical reactors to increase the contact area between the gas and liquid phases, and thus improve reaction efficiency. Knowledge of how packing types and sizes affect the gas distribution and the overall gas void fraction is critical for the optimal design and operation of industrial processes. In this paper, a method of in situ quantifying the gas distribution and void fraction in a packed bubble column using electrical resistance tomo-graphy (ERT) is proposed. A 3-D simulation validation shows that the ERT is able to quantitatively determine the gas void fraction within 4% relative error against the theoretical value. The experiment was conducted in a bubble column, packed with 6-mm glass beads and 16-mm plastic pall rings. The results demonstrate that the gas distribution and the void fraction are considerably changed by different packing materials. All of these facts suggest that ERT is a reliable imaging tool for the real-time measurement of complex two-phase flows in the packed bubble column reactors.