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.     

Study on wet gas online flow rate measurement based on dual slotted orifice plate

According to the current technical problems existing in gas and liquid flow measurement for wet gas production, the slotted orifice-couple flow meter was developed and the basic measurement principles for gas and liquid flow was presented. A new wet gas flow meter was developed based on the dual slotted orifice transducer. The flow characteristics of liquid flow through dual slotted orifice plate, the relationship of differential pressure between the dual slotted orifice plate, pressure, temperature, and flow rate of gas/liquid of different aperture ratio were studied. A mathematical measurement model was established to be applied in the flow meter measurement system with dual slotted orifice plate. The model was tested and calibrated by on-site field experiments in the China National Center of Metrology at Daqing Oil field. The results showed that the maximum measurement error of the gas and liquid flow was less than 10% and 15% respectively, when the Gas Volume Fraction (GVF) was greater than 90 vol%. The measurement accuracy of this industrial prototype can meet the requirements of well fluids.     

Multiphase flow measurements using coupled slotted orifice plate and swirl flow meter

Multiphase flow metering is a major focus for oil and gas industries. The performance of a modified version of a close coupled slotted orifice plate and swirl flow meter for multiphase flow was evaluated to provide further development of a new type of multiphase flow meter. The slotted orifice provides well homogenized flow for several pipe diameters downstream of the plate. This characteristic provides a homogeneous mixture at the inlet of the swirl meter for a wide range of gas volume fractions (GVF) and flow rates. In order to evaluate the performance of the designed flow-meter, its response was investigated for varying pressures and water flow rates. The proper correlations were established to provide high accurate two-phase flow measurements. The new proposed approach provides the GVF measurement with less than ±0.63% uncertainty for GVF range from 60% to 95%.     

Pressure drop of wet gas flow with ultra-low liquid loading through DP meters

The most common method to predict the gas and liquid flow rates in a wet gas flow simultaneously is to use dual pressure drops (dual-DPs) from two or even one single DP meter. In this paper, the metering mechanism of applying dual-DPs were overviewed. To fully understand the response of DP meters to wet gas flows, the pressure drops of wet gas flow with ultra-low liquid loading through three typical DP meters were experimentally investigated, including an orifice plate meter, a cone meter and a Venturi meter. The equivalent diameter ratio is 0.45. The experimental fluids are air and tap water. The pressure is in the range of 0.1–0.3 MPa and the Lockhart-Martinelli parameter (X_LM) is less than approximately 0.02. The results show that the upstream-throat pressure drop, the downstream-throat pressure drop and the permanent pressure loss of individual DP meters have unique response to liquid loading. The upstream-throat pressure drop of the orifice plate meter decreases at first and then increases as the liquid loading increases, while that of the cone meter and the Venturi meter increase monotonically. The non-monotonicity of the pressure drop for the orifice plate meter can be attributed to the flow modulation of trace liquid. The downstream-throat pressure drops of all the three test sections decrease at first and then increase. The reason is that the liquid presence in a gas flow increases the downstream friction and vortex dissipation. The permanent pressure loss of the orifice plate meter also shows non-monotonicity. To avoid non-monotonicity, the pressure loss ratio is introduced, which is defined as the ratio of the permanent pressure loss to the upstream-throat pressure drop. Results show that the pressure loss ratio of the Venturi meter has the highest sensitivity to the liquid loading.     

Analysis of high pressure tests on wet gas flow metering with a Venturi meter

This work deals with the flow metering of wet gas issued from high pressure natural reservoirs. Some recent results obtained from tests performed on the CEESI facilities are presented. They are performed at 75 bar with 0.6 beta ratio Venturi meter installed in horizontal pipe configuration. Correction factors obtained are compared to predictions deduced from the flow modelling inside of the meter. These results are analysed in order to explain the agreements or disagreements obtained between the experiments and the flow modelling.     

基于槽式孔板的凝析天然气计量技术

介绍了一种新型气液两相流量传感器——槽式孔板的结构特点和工作原理，并将其应用于凝析天然气计量技术研究。结合实验数据和理论模型详细分析了影响槽式孔板两相压降倍率的各种因素，利用曲面拟合技术给出了传感器两相压降倍率与压力、气体富劳德准数、Lockhart-Martinelli参数之间的相关式，该相关式计算精度可以满足生产计量的精度要求，为低含液率的凝析天然气流量计研制奠定了基础。     

Experimental research of single-hole and multi-hole orifice gas flow meters

As energy efficiency is becoming more important today due to limited energy resources as well as their rising prices and environment issues, it is crucial to have reliable measurement data of different fluids in production processes. Because of its simplicity, affordability and reliability, orifice flow meters are again becoming subject of numerous researches. Conventional single-hole orifice (SHO) flow meter has many advantages but also some disadvantages like higher pressure drop, slower pressure recovery, lower discharge coefficient etc. Some of these disadvantages can be overcame by multi-hole orifice (MHO) flow meter while still maintaining advantages of conventional SHO meter. Both SHO and MHO flow meters with same β ratios were experimentally tested and compared. Results showed better (lower) singular pressure loss coefficient and lower pressure drop in favour of the MHO flow meter. Experimental data indicates that MHO flow meter is superior to the conventional orifice flow meter, but further research is necessary to make the MHO a drop-in replacement for a SHO flow meter.     

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.     

Study on the metering characteristics of a slotted orifice for wet gas flow

Wet gas metering is a subset of multiphase flow metering. A slotted orifice is selected for the development of a wet gas meter (WGM). With the help of Computational Fluid Dynamics (CFD) technology, the static pressure, velocity and density contours across the slotted and the standard orifice flow meter have been analyzed. Based on the experimental data the two-phase multipliers of the slotted orifice have been investigated. Two new differential pressure correlations of the slotted orifice are put forward for the first time and appropriate conclusions are discussed.     

Study on application of wet gas metering technology in shale gas measurement

The application of wet gas flow meter at shale gas wellhead is of great significance to reduce the investment and operation cost of shale gas extraction. In this paper, the flow conditions at the wellhead of shale gas and the principles of the current wet gas flow meters are briefly analyzed. A wet gas flow meter was tested on the wet gas flow test facility, and its performance of flow rates evaluation is studied, which is helpful to optimize the wet gas metering process design of shale gas wellhead and to improve the wet gas metering technology. This study shows that the measurement principles of the current wet gas flow meters are feasible, however, the calibration by using the wet natural gas at working conditions can help to enhance the meter's measure performance.     

Wet gas overreading characteristics of a long-throat Venturi at high pressure based on CFD

Based on the operational conditions of the PetroChina Southwest Oil & Gas well field, this study aims to explore the wet gas flow overreading (OR) characteristics of a nonstandard long-throat Venturi by the means of computational fluid dynamics (CFD) technique. The studied prototype structure size is an inner diameter of 50 mm, a diameter ratio of 0.4 and a throat length of 50 mm. According to the field experiment, the simulation pressure is 3 MPa gauge. Through a comparative study of the multiphase flow models and turbulence models, combined with the analysis of the Baker׳s flow regime and interparticle space under the field conditions, this paper eventually employed DPM model and Eulerian model for wet gas simulation, respectively, and RSM for turbulence model. An equivalent droplet diameter adjustment method was implemented to improve the precision of prediction. During post-processing, the liquid phase distributions and the wall pressure profiles were investigated. The numerical results indicate that the differential pressure in convergent section of long-throat Venturi by using DPM model is less than that by using Eulerian model, and the differential pressures in the divergent section by using the two models are analogous. Afterwards, the OR prediction correlations based on the differential pressure ratio method were proposed, and then compared and validated by the industrial field tests. The root mean square errors (RMSE) and the average relative errors predicted by Eulerian model were 4.24% and 3.78%, 5.69% and 5.01% by using DPM model, respectively. In conclusion, Eulerian model is more suitable for wet gas flow prediction. And some advice on the improvement of the multiphase flow simulation is provided to get a more preferable performance in wet gas flow prediction.     

A new correlation of wet gas flow for low pressure with a vertically mounted Venturi meter

Wet gas metering has become an increasingly important technique for many industries. However, the over-reading phenomenon reduces the accuracy of Differential Pressure meters. This research fills the vacancy of correlations and presents a new correlation for low pressure between 0.82 and 1.52 MPa with a vertically mounted Venturi meter to calculate the over-reading coefficient accurately. Based on the correlational analysis, the over-reading coefficient is a function of the Lockhart-Martinelli parameter, density ratio, and gas Froude number. The constant coefficients in this correlation are obtained by nonlinear regression. Effect of low gas velocity with gas Froude number under 1.5 is taken into consideration as well. The average relative error is 1.9% and the root mean square error is 3.0%. Furthermore, a new method to calculate the over-reading coefficient for industrial applications is put forward due to the difficulties of online measurements of the Lockhart-Martinelli parameter which is substituted with the void fraction. The void fraction is calculated by an empirical correlation using quality and an approximate algorithm is utilized to obtain gas Froude number. For this new method, the average relative error is 2.3% and the root mean square error is 3.7%. This quality-based method will be helpful to resolve the limited applicability of gamma-ray attenuation for wet gas flow metering in industry regarding vertical low pressure conditions.     

Investigation on the swirlmeter performance in low pressure wet gas flow

Wet gas flow is a subset of gas-liquid two-phase flow, and the swirlmeter has been used in wet gas flow metering more and more recently. The swirlmeter performance in low pressure wet gas flow was investigated. It is found that the entrained liquid present in a gas stream tends to induce a negative bias in the gas flow rate reading of swirlmeter comparing with equal gas flow rate. When the Lockhart-Martinelli parameter X, which is closely related to the liquid fraction, is bigger than a threshold value, the swirlmeter will not properly work due to the disappearing of vortex precession. It is also found that the liquid-induced gas flow rate reading errors of swirlmeter are dependent on X and the gas densiometric Froude number Fr_g. A correlation for swirlmeter in low pressure wet gas flow is proposed, and it corrects the liquid-induced gas flow rate errors to an accepted accuracy under the tested conditions. It implies that the swirlmeter with the proposed correlation and the known liquid fraction may be used to meter the gas flow rate in wet gas applications with a relatively low liquid fraction.     

Horizontally installed cone differential pressure meter wet gas flow performance

Differential pressure (DP) meters which utilise a cone as the system’s primary element are increasingly being used to measure wet natural gas flows (i.e. mixtures of natural gas, light hydrocarbon liquids and water). It is therefore important to understand this meter’s response to wet natural gas flows. Research into the wet gas response of the horizontally installed cone DP meter is discussed in this paper. Consideration is given to the significant influence of the liquid properties on wet gas flow patterns and the corresponding influence of the flow pattern on the cone DP meter’s liquid phase induced gas flow rate prediction error. A wet natural gas flow correlation for 4 in. 0.75 beta ratio cone DP meters with natural gas, hydrocarbon liquid and water flow has been developed from multiple data sets from three different wet gas flow test facilities. This corrects the liquid induced gas flow rate prediction error of a wet gas flow up to a Lockhart–Martinelli parameter of 0.3, for a known liquid flow rate of any hydrocarbon liquid/water ratio, to ±4% at a 95% confidence level.     

Characterization of flow homogeneity downstream of a slotted orifice plate in a two-phase flow using electrical resistance tomography

Two-phase flows are complex and unpredictable in nature, commonly encountered in a majority of fluid transport systems. The accurate measurement of two-phase flow is critical for a wide range of applications from wet stream to multiphase flows. There are different methods to meter two-phase flow in various industries. One approach is to produce a flow meter that does not require the individual flow components to be separated and measured separately. This goal can be met if a homogenized mixture is produced which can be measured by a standard single phase flow meter. The slotted orifice plate was invented as a flow meter for single phase flows, it is independent upon upstream flow conditions. Slotted orifice plate flow meter's utilization in two-phase flow revealed that it is highly capable of working as a flow conditioner transforming most of the multiphase flow regimes into a fairly uniform mixture. This study measures how the relative homogeneity of an air/water mixture varies downstream of the slotted plate in a horizontal pipe for various upstream conditions including elongated bubble and slug flow regimes using electrical resistance tomography (ERT). According to this study, the optimal location with a maximum homogeneity was determined to be between 1.5 and 2.5 pipe diameters downstream of the slotted orifice plate. This indicates that placing a slotted orifice plate at the obtained distance upstream of another flow meter such as a venturi coupled with a density measuring device like a radiation based densitometer or an electrical impedance device will help in obtaining accurate multiphase flow rate measurement.     

Wet gas metering with a horizontally mounted Venturi meter

Wet gas metering is becoming an increasingly important problem to the Oil and Gas Industry. The Venturi meter is a favoured device for the metering of the unprocessed wet natural gas production flows. Wet gas is defined here as a two-phase flow with up to 50% of the mass flowing being in the liquid phase. Metering the gas flowrate in a wet gas flow with use of a Venturi meter requires a correction of the meter reading to account for the liquids effect. Currently, most correlations in existence were created for Orifice Plate Meters and are for general two-phase flow. However, due to no Venturi meter correlation being published before 1997 industry was traditionally forced to use these Orifice Plate Meter correlations when faced with a Venturi metering wet gas flows. This paper lists seven correlations, two recent wet gas Venturi correlations and five older Orifice Plate general two-phase flow correlations and compares their performance with new independent data from the NEL Wet Gas Loop with an ISA Controls Ltd. Standard specification six inch Venturi meter of 0.55 beta ratio installed. Finally, a new correlation is offered.     

CFD study of pressure loss characteristics of multi-holed orifice plates using central composite design

The study on the use of multi-holed orifice plate for measuring flow rate is a growing area of research. As compared to standard orifice plate, multi-holed orifice plates (MO) have number of advantages, such as, these plates require minimum straight piping at the upstream without compromising the pressure losses and provide better accuracy in the measurement of flow rates. In this study, a systematic methodology is adopted for investigating the effect of different geometrical parameters on pressure loss coefficient and values of parameters under investigation varied using central composite design. The geometrical parameters chosen for the study are: (a) Number of holes; (b) Multi-hole Diameter ratio and (c) Compactness of holes. Commercial computational fluid dynamics code (ANSYS Fluent) is employed to perform simulations for 15 different settings of these parameters to analyze their effect on pressure loss coefficient and flow development length at downstream of multi-holed orifice plates. It is found that values of pressure loss coefficient is a strong function of multi-hole diameter ratio, whereas, the flow conditioning properties are strongly affected by the number of holes.     

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.     

基于三轴加速度探头的涡街湿气分相流量测量

针对涡街湿气测量过读问题,提出了基于加速度检测的涡街过读校正和分相流量测量方法。设计了高频响三轴加速度探头,分别对敏感元件、探头尺寸和封装进行了优化设计。干气标定结果表明,在4.43×10⁴～1.81×10⁵雷诺数范围内,测量精度为±1.0%,线性度为1.06%。然后,在不同湿气工况(载气压力和流量、液相流量)下测试了输出频率和加速度幅值特性,以气、液相韦伯数为参数,分别建立了涡街过读和两相加速度幅值模型。最后,联立两方程建立了湿气测量模型,并利用牛顿迭代算法进行求解。预测结果表明,气相测量误差在±1.0%以内,不确定度0.46%,液相全量程误差在±15%以内,不确定度10.04%。与未过读校正时最大8%的测量误差相比,气相测量精度大大提升,同时实现了湿气中分相流的在线测量。