Wet Gas Measurement Research Articles

Devices and methods for wet gas flow metering: A comprehensive review

Wet gas is commonly encountered in various industries, including energy, chemical, and electric power sectors. For example, natural gas extracted from production often contains small amounts of liquid, such as water and hydrocarbon condensates, which classifies it as wet gas. The presence of liquid within the gas poses challenges for accurate flow measurement. To improve the performances of wet gas flow metering methods, significant research and development efforts have been invested into the wet gas flow metering technologies due to their vital importance in the production, transfer, and trade benefits.This paper presents a comprehensive overview of the recent development of wet gas flow metering. Firstly, a comprehensive discussion of the Lockhart-Martinelli parameter (Xlm) and its relation to the gas void fraction (αg) is presented, which was mostly overlooked in previous wet gas research work. The occurrence of various flow patterns in wet gas conditions at different orientations (horizontal and vertical) was explored. Following an investigation of pressure impact on the wet gas flow patterns and development of the wet gas regions, a different test matrix for further research work was suggested. After a novel classification of wet gas measurement methods, the paper offers a detailed comparison of differential pressure (DP) meters including Venturi, Cone meter, and orifice meters, by considering both liquid and gas flow rate measurements. Secondly, the paper discusses and compares vortex flow meters, Coriolis and ultrasonic meters in comparison to DP meters. Notable phase fraction meters are also examined and compared to one another. Thirdly, the paper reviewed the concept of existing and potential hybrid wet gas meters, conducting a detailed discussion and comparison with commercial solutions by evaluating their ranges and accuracies. This assessment provides valuable insights into the capabilities of these hybrid meters, highlighting their potential to enhance the measurement of wet gas flow rates.

Experimental investigation on droplet evolutions in co-flow around the bluff body

Annular mist flow widely exists in natural gas and other engineering fields. Vortex flowmeter has gradually become an effective means of wet gas measurement. However, the droplets in the flow field will influence the stability of the vortex. In this paper, the interaction between droplets and vortex was studied by experiments. A novel in-focus criterion was proposed to improve the accuracy of droplet measurement. Simultaneous acquisition of droplet size, velocity, and concentration was achieved. The spatial evolution of droplet parameters was obtained to determine the position where the droplets were evenly distributed. The bidirectional coupling mechanism between droplets and vortex was studied. Firstly, the influence of the vortex flow field on droplets was reflected by the characteristics of droplet distribution around the bluff body. Secondly, the effect of droplets on the vortex signal in the flow field was analyzed based on Stokes number Stp and liquid-phase load φl. When φl < 0.03, the probability distribution of droplet velocity downstream of the bluff body presents double peaks. The exchange momentum between the small droplets and the vortex is stronger, and vice versa for the larger droplets. Finally, the quality factor of vortex signals decreases from -2.09 to -2.18 with the increase in the volume concentration of droplets. It is further demonstrated that the increase in volume concentration of droplets will destroy the vortex structure and degrade the quality of the vortex signal.

Study on double differential pressure measurement method of gas-liquid two-phase flow in high gas content wells

The production of natural-gas wells contains natural gas and a small amount of liquid, which is a wet gas composed of oil, gas and water. For dynamically monitor the liquid and gas production from a single well, there is an urgent need for a low-cost, small-volume online metering device for wet gas flows through a single well. Aiming at the problem, this paper designs a wet gas flow measurement device for a long-throated Venturi tube based on the double differential pressure method. By combining experiments and numerical simulations, a matching flow calculation model was developed. Based on the experimental data of NEL's 6-inch standard Venturi tube wet gas over-reading, the numerical simulation method is used to carry out the research of high-pressure wet gas measurement under the pressure condition of 2, 4 and 6 MPa. The simulation results of two multiphase flow models, DPM and Euler, are compared with the experimental values of NEL. The results show that the maximum relative error is less than 10%, and the Euler model is more suitable for the numerical simulation of high-pressure wet gas. According to the actual production from the gas well, a long-throated Venturi tube with a throttling ratio of 0.5 and a diameter of DN50 was designed, and a numerical simulation study of wet gas under a pressure of 2, 3 and 4 MPa was carried out. Numerical simulation results show that the change laws of over-reading and liquid-gas mass ratios of high-pressure wet gas are consistent with those of low-pressure wet gas. The numerical simulation results are used to correct the flow calculation model of low-pressure wet gas, and a flow calculation model suitable for high-pressure wet gas in gas wells is obtained. The gas flow prediction accuracy of the flow calculation model was lower than ±3%, and the liquid flow prediction value was lower than ±10%. Compared with other measurement methods without separation of wet gas, the long-throated Venturi tube based on the double differential pressure method has a simple structure and low measurement cost. By further optimizing and expanding the measurement model, after improving the accuracy, it can be installed in the wellhead pipeline to monitor the oil and gas production from a single well in real time. This can provide support for gas reservoir exploitation decisions.

A Detection Method for Vortex Precession Frequency Based on MEMS Three-Axis Acceleration Sensor

Swirlmeters are widely used in the wellhead metering of low permeability gas fields in China. However, the swirlmeter’s piezoelectric sensor has difficult distinguishing the vortex precession signal from fluid pulsation noise, pipeline mechanical vibration, and other interference. In this article, in order to detect the vortex precession frequency signal effectively and accurately from the interference noises, a signal detection method based on micro-electro-mechanical systems (MEMS) three-axis acceleration sensor was proposed. According to the difference between the force direction of vortex signal and interference signals, a dual-differential technique based on three-axis measurement is proposed to eliminate interference noises. The radiated interference of electromagnetic noise was eliminated by adding a notch circuit and radio frequency interference filter to the measuring circuit. Then, the sensitivity characteristics of vortex precession with different swirl angles were investigated by numerical simulation and the performance of the method was evaluated by experiments. The results of experiments show that the method proposed in this article can improve the sensor’s capability of anti-interference and widen the measurement range. Further wet gas experimental results show that the vortex precession frequency signal detected by MEMS-three-axis acceleration sensor (TAAS) does not change its linear output law in spite of the presence of liquid phase. Finally, a correction model of the instrument coefficient of the swirlmeter for wet gas measurement was established. The relative errors of the fitting model are within ±2.0%, the mean percentage error (MPE) is 0.17%, and the mean absolute percentage error (MAPE) is 0.81%. The method proposed in this article can improve the ratio of signal to noise of swirlmeter, overcome the influence of interference noise on the precession frequency, and broaden the gas flow measurement range. It realizes the efficient and accurate measurement of the gas flow rate for wet gas flow.

Study of the factors influencing the over-reading characteristics of the precession Venturi

In the energy industry, such as the gas field, precise measurement of wet gas is becoming increasingly crucial. Many studies have focused on the over-reading (OR) of throttle flowmeter in wet gas measurement. By using the dimensional analysis method, we proposed a precession Venturi and established a new OR correlation based on the gas Froude number, liquid-gas density ratio, and the Lockhart–Martinelli parameter. Experimental tests of air-water flow were conducted, and the relationships between differential pressure and OR with liquid volume fraction were investigated at various pressures and superficial gas velocities. The experimental results show that the uncertainty of gas flow rate measurement is in the range of 0.35%–0.56%, and 90.8% of the points are in the range of 0.35%–0.45%, with a relative error band of ±2.94% calculated by the OR correlation at a confidence probability of 95.5%.

Design of ultrasonic flowmeter for wet gas measurement

When an ultrasonic flowmeter (UFM) is applied in the measurement of wet gas, the ultrasonic signal attenuates and fluctuates strongly because of the liquid film and droplets in gas. It is hard to obtain the accurate time of flight (TOF) of ultrasound. Besides, the gas velocity distribution on a pipe cross section changes with different flow patterns, making it difficult to determine the measurement model. In order to solve these problems, a dual-channel UFM is specially designed and a measurement system is built. Then, a dynamic threshold method based on statistical average signal amplitude is proposed to obtain the TOF of ultrasound in wet gas. Combined with the classical void fraction model, the wet gas velocity measurement model for the dual-channel UFM is established based on a neural network. Finally, experiments are carried out on a DN50 wet gas device, where pressure is 0.1 MPa, gas superficial velocity is 5–20 m s−1 and liquid volume fraction is 0.2%–5%. The results show that the average relative error of gas velocity is 0.52% and the maximum relative uncertainty is 0.491%.

Online Measurement of Gas and Liquid Flow Rates in Wet Gas Using Vortex Flowmeter Coupled With Conductance Ring Sensor

Wet gas flow commonly exists in several industries. The online measurement of gas and liquid flow rate is beneficial for economic efficiency. A combination of vortex flowmeter and liquid film sensor was proposed for two-phase flow measurement of wet gas. The specific form is as follows: the dual-modality sensing system was designed and calibrated by an annular mist flow loop. The fluid materials are pure air and water liquid. The ranges of operating pressure, the superficial gas velocity, and superficial liquid velocity are 1.5 bar–3.5 bar, 18.86–37.73 m/s, and 0.0028–0.028 m/s. Then the function relations of liquid film thickness and vortex frequency, with gas and liquid Weber numbers were built, respectively. Finally, a novel model for calculating gas and liquid flow rates in wet gas measurement was established, and solved by the Newton iterative algorithm. It showed that the percentage error (PE) of gas flow rate predicted by the model is within ±1.5%, and the mean absolute percentage error (MAPE) is 0.55%. The full-scale PE of liquid flow rate is within ±5% and the MAPE is 3.48%. The data show that this solution for gas and liquid flow rates measurement of wet gas by combining a vortex flowmeter with a conductance ring sensor is feasible.

Wet gas measurements of long-throat Venturi Tube based on forced annular flow

A wet gas dual-parameter measuring device composed of a cyclone and a long-throated Venturi tube is proposed to overcome the difficulty of measuring the liquid content of wet gases and reduce the error caused by the wet gas flow pattern. The flow pattern is transformed into an annular flow by a cyclone. In this study, the proposed device was compared with a traditional non-cyclone long-throat Venturi tube; furthermore, the pressure difference ratio W between the contraction and expansion sections of the long-throat Venturi tube was introduced as a parameter. Through numerical simulations, the relationship between W, the gas Froude number, over-reading, and liquid-gas mass flow ratio was analyzed, and a new wet gas flow measurement model was established. The reliability of the measurement model was verified through indoor experiments. The experimental results showed that the traditional wet gas measurement device had gas phase and liquid phase errors of ±4.5% and ±10%, respectively; on the other hand, the cyclone-based wet gas measurement device had gas phase and liquid phase errors of ±3% and ±8%, respectively. Thus, the performance of the wet gas measurement device with the cyclone was higher than that of the traditional wet gas measurement device.

Wet gas metering using a vortex cross-correlation meter based on fluctuating pressure measurement

A solution for wet gas metering was developed with a vortex meter by using pressure sensors and correlation technology. For the fluctuating pressure measurement, the micro pressure sensors, especially the probe-transducer systems, were designed to acquire reliable vortex signals. For the experiments, an annular mist flow loop with a film metering system was established, and the tests were conducted on various pressure, gas velocity and liquid flowrate conditions. Then, the dimensionless convection velocity, named convection coefficient, and the peak value of the normalized cross-correlation function, named correlation coefficient were calculated. A piecewise function was developed for the convection coefficient with modified Weber number where the segmentation was determined by the correlation coefficient. Finally, the wet gas measurement model was developed and realized by iterative algorithm. Under the present conditions, the ±5% error bands contain 91% of the relative errors for gas flowrate prediction, the mean absolute percentage error is 2.54%, and the uncertainty of gas flowrate prediction is 2.85%. The primary advantage of the proposed method is that the convection coefficient is almost independent of liquid fraction, no extra systems are necessary for watercut measurement, hence providing a cost-effective solution for wet gas metering.

A new overreading model for wet gas vortex metering based on vorticity transport mechanism

Abstract Vortex flowmeters are widely used in wet gas metering, however, the output gas flowrate is over-predicted, leading to large measurement error. To improve the wet gas measurement accuracy by vortex flowmeters, the meter overreading was modelled based on the particle-laden vorticity dynamic equation and vorticity transport mechanism. The scaling parameters were revealed and different droplet entrainment conditions were considered. For the experiments, an annular mist flow loop with film metering device was developed to study the vortex metering characteristics. Then, a new overreading equation was developed by using the scaling group of droplet mass loading and macroscopic Stokes number. Finally, performances of the existing overreading correlations were evaluated and analyzed in detail. The results indicate that the proposed equation provides a uniform prediction for the meter overreading, the relative deviations are within ±1.0% error band, and the predicted accuracy is greatly improved compared with other overreading correlations.

Invariant system for measuring the flow rate of wet gas on Coriolis flowmeters

One of the important tasks of modern flow measurement is to measure the flow rate and the amount of wet gas. This task becomes especially important when there is a need to obtain information about the amount of dry gas at the production facilities. The paper presents the principle of operation and structure of the invariant wet gas measurement system. The work of the invariant flow measurement system is based on the application of the principle of multichanneling and the method of partial flow measurement. Coriolis flowmeters are used as the main elements of the system. The proposed measurement system does not imply the use for gases with abundant droplet moisture. The authors propose a method of verification of the measurement system, which is currently limited by the measurement error of moisture in the gas equal to 5%. The article also provides information on the results of the test of the system.

Online Measurement of Wet Gas by Modeling Frequency and Amplitude Characteristics of a Vortex Flowmeter

In this article, an accurate online measurement of gas flowrate in wet gas was developed by modeling the frequency and amplitude characteristics of a vortex flowmeter in annular mist flow. The low-frequency modulation behaviors of the vortex signals were analyzed by the ridge method based on continuous wavelet transform (CWT). It indicates that the instability of frequency and amplitude of the signals both enhance with the increase of liquid loading; and therefore, a feature extraction method based on ridge-averaged was proposed and validated by the tests. A film extraction device was developed to measure the flowrate of the liquid film and further obtain the droplet mass loading. Then, a uniform linear equation for the overreading was obtained experimentally on the basis of the scaling parameter analysis in particle-laden flow. A uniform exponential equation for the dimensionless signal amplitude of the sensor output was developed with droplet mass loading. Finally, a wet gas measurement model with the simultaneous equations from these two correlations was established and the iterative solution algorithm was given. In the present cases, the percentage errors (PEs) of the gas flowrate predicted by the modeling are within ±1.5% and the mean absolute PE is 0.37%. The method proposed in this article can achieve accurate measurement of gas flowrate by using only one vortex flowmeter and, hence, creates a simple inexpensive metering system for wet gas flow.

A CFD study of wet gas metering over-reading model under high pressure

The venturi flow meter is increasingly being preferred in multiphase flow measurement because of its shorter upstream and downstream straight sections, less influenced by the flow pattern and relatively small pressure loss. However, when the venturi is used for wet gas measurement, the over-reading phenomenon occurs due to the presence of a small amount of liquid. Many scholars have established over-reading models to correct the measured values of wet gas. Regrettably, the applicability of these over-reading models under actual high pressure operating conditions has not been verified. Therefore, this review focuses on numerical simulation of the flow of wet gas in the venturi tube under high pressure conditions (11MPa/13MPa/15 MPa). The discrete phase model (DPM) and the standard k-ε model was employed in this review. The simulations results reveals the flow characteristics of wet gas in venturi tube, which includes the flow field distributions, droplet concentration distributions and wall pressure profile distributions, and indicates that the over-reading values increases with the increase of Lockhart-Martinelli parameters and gas volume flow rate, but decreases with the increase of pressure. Moreover, the ISO model has the best performance under high pressure conditions.

A V-Cone meter measurement correlation in low pressure wet gas based on Chisholm model

To gain a deeper understanding of the performance of V-Cone meter in low pressure wet gas measurement, the over-reading of the V-Cone meter was experimentally investigated in the present study. The equivalent diameter ratio of the V-Cone meter is 0.55. The experimental fluids were air and tap water. The operating pressure and the gas volume fraction ranged from 0.1 MPa to 0.4 MPa and 97.52%–100%, respectively. The results showed that the existing V-Cone wet gas correlation, which was developed for the medium and high pressure wet gas cannot be well extended to the low pressure conditions. The Chisholm exponent monotonically decreased with the ratio of liquid-to-gas mass flow rate increasing, and was almost not affected by the gas to liquid density ratio and the gas densiometric Froude number in the present test ranges. A measurement correlation dedicated for the low pressure wet gas was developed. In the present cases, the relative deviation of the gas mass flow rate predicted by the new correlation was within ±4.0% and ±3.0% under the 95% and 90% confidence level, respectively; the average relative deviation was 0.046%. Our results provide insights into the measurement performance of V-Cone meter in low pressure wet gas and may help to develop a more comprehensive wet gas correlation.

Experiment and Numerical Simulation on Gas-Liquid Annular Flow through a Cone Sensor.

The cone meter has been paid increasing attention in wet gas measurement, due to its distinct advantages. However, the cone sensor, which is an essential primary element of the cone meter, plays a role in the measurement of wet gas flow that is important, but not fully understood. In this article, we investigate the gas-liquid annular flow through a cone sensor by experiment and numerical simulation. Emphasis is put on the influences of pressure recovery characteristics and flow structure, and how they are affected by the cone sensor. The results show that the vortex length is shortened in gas-liquid annular flow, compared with that in single-phase gas flow. The pressure recovery length is closely related with the vortex length, and shorter vortex length leads to shorter pressure recovery length. The gas-liquid distribution suggests that flow around the apex of back-cone is very stable, little liquid is entrained into the vortex, and no liquid appears around the low pressure tapping, which makes a more stable pressure at the apex of cone sensor feasible. This finding highlights the importance of obtaining the low pressure from the back-cone apex, which should be recommended in the multiphase flow measurement. Our results may help to guide the optimization of the cone sensor structure in the wet gas measurement.

Over-reading modeling of the ultrasonic flow meter in wet gas measurement

In this paper, the basic mechanism of two-path ultrasonic flow meter is studied, investigating the propagation characteristics of the ultrasonic wave in stratified and annular two-phase flow. The experimental results suggest that void fraction and liquid film thickness at the reflected point of the ultrasonic wave are the primary factors that lead to the over-reading of the ultrasonic flow meter. Based on the film thickness estimation correlation a USM over-reading model for determining the gas phase flow rate is developed under the certain circumstances, in which the liquid flow rate is assumed known. The experiments at the line pressure range of 0.2–1.1 MPa in two-phase flow were conducted to validate this developed model. A DN80 V-turn one-time reflected two-path ultrasonic meter was used. By comparing the experimental data with the master meters’ data, all the relative deviations of the predicted points by the model were within ±15% and in addition, 88% points drop within the error band of ±5%. As this work depends on the propagation characteristics of the ultrasonic wave in two-phase flow, it provides the basis for further establishing a flow measurement model of wet gas by the use of ultrasonic technology.

Experimental investigation of the phase fraction of wet gas based on convective heat transfer

In the present stage, wet gas measurement is playing an increasingly significant role in the oil and gas industry. Phase fraction is an important parameter for the determination of pressure drop and heat transfer coefficient in wet gas flow. In this paper, experimental investigations of the wet gas phase fraction based on convective heat transfer (CHT) is conducted. In order to describe the “over reading” of CHT coefficient due to the existence of the liquid phase, it is innovative to define ω as the ratio of the CHT coefficients of wet gas and gas alone. An easy-to-use correlation is proposed by using the gas flow rate and the temperature measured before and after the electrical heating belt. The experiment was carried out in the wet gas flow loop in Tianjin University. System pressure ranges from 0.6MPa to 1.2MPa, and gas mass fraction (GMF) is from 23.8% to 100%. Final results show that the relative deviation of all data points are less than ±15%. There is no doubt that this correlation provides new data on the phase fraction in wet gas annular flow and benefits other researchers in wet gas measurement.

Experimental investigation of wet gas over reading in Venturi

In the present age, wet gas measurement is playing an increasingly significant role in the oil and gas industry. Venturi, a classic single-phase flow meter, proved to be a reliable and accurate wet gas flow meter, but it requires correction. Finding a simple wet gas model of Venturi for all possible applications is a common target of researchers and engineers. In this paper, a double differential pressure Venturi is used to reveal the flow characteristics of wet gas and establish a more accurate correlation that performs well in laboratory and on-site tests. Based on a dimensionless analysis and the experimental data, the essential dimensionless groups in wet gas including the differential pressure ratio, gas liquid density ratio, gas Froude number and Lockhart–Martinelli parameter are studied. By using these crucial parameters, the wet gas correlation is established. The results of the laboratory experiment in the Tianjin University wet gas test loop indicate that the relative deviations of this correlation are better than ±1% and that the standard deviation is 0.34%. Despite the different working conditions of a laboratory and the Tarim oilfield, the usage of the wet gas correlation exhibits a system deviation of 18% and a small dispersion. Thus, after the modification, the relative deviations of cumulative flow are all less than ±1%. There is no denying that this wet gas correlation promotes the development of a widely used correlation to a certain extent and benefits other researchers in wet gas measurement.

Experimental Study on the Influence of Longer Throat Venturi Tube Pressure Tappings Position to Wet Gas Measurement Model

Venturi tubes are widely used for wet gas metering. To explore the influence of longer throat Venturi tube pressure tappings position to wet gas measurement model, a theoretical analysis of Venturi pressure drop at various parts is presented at first. A Venturi prototype with longer throat is designed, which inner diameter is 50 mm and beta ratio is 0.4. The distances between pressure tappings and the entrance of throat are 0.5, 3.75 and 7 times the throat diameter, respectively. The experiment verifications are carried out at the wet gas test double closed loop in Tianjin University. The range of operational pressure is from 0.2 MPa to 0.8 MPa and the dryness ranging from 0.5 to 1. Based on the test data, the relationship between over-reading gradient and Lockhart-Martinelli parameter is acquired, as well as the regularity between the K value sensibility and liquid-gas mass ratio. The length of throat has a significant impact on over-reading and K value. Over-reading model and liquid-gas mass ratio model are built based on K value, Froude number and the gas-liquid density ratio, and gas and liquid flow rates are calculated by using iteration method. Through analyzing the influence of different pressure tappings position to the relative error and uncertainty of the gas and liquid flow rates, it is advised that 3.75 times the throat diameter away from the entrance of the throat is the optimum pressure tappings position, where the uncertainty of the gas and liquid flow rates are 5.06% and 2.15%, respectively.

Using CFD to Understand Multiphase and Wet Gas Measurement

Computational fluid dynamics (CFD) flow modelling has proved to be a useful tool in single-phase flow metering. More recently, the increase in computer power has made multiphase models viable. However, there is a range of modelling approaches, which makes practical simulation of the behaviour of multiphase and wet gas flows in metering and/or sampling devices as much an art as a science. This paper introduces alternative modelling approaches to show what can be achieved using CFD modelling and to highlight the limitations of the technique. A series of case studies are presented in which CFD analysis has been used to study the following issues in multiphase and wet gas measurement or sampling: Effects of heavy oil multiphase flow in a Venturi Behaviour of multiphase swirl flow in a Venturi Modelling of wet gas flows in Venturis, cone meters, and orifice plates Effective sampling methods