Study of the liquid‑phase impact on gas flow rate during blowdowns of flowlines and wells at gas-condensate fields

The accurate and reliable measurement of gas flowrate in wet gas conditions continues to be important to the Oil and Gas Industry. The ability to measure wet gas flows is particularly crucial in small, marginal developments that would otherwise be uneconomic to exploit due to the requirement for expensive separation equipment. This paper presents the results of two independent studies conducted on the new NEL high pressure wet gas test facility that uses nitrogen and a kerosene substitute (Exxsol D80) as test fluids to simulate a natural gas/ condensate system. The first study involved the the testing in wet gas of a 6- inch turbine meter in liquid loadings of up to 2% by mass at a pressure of 60 barg and pipe Reynolds numbers from 1 to 9 million. The maximum shift in the turbine meter factor found due to the presence of the kerosene was -0.75% at a Reynolds number of 2.7 million. Mechanisms that could cause the observed shifts are provided. These results presented here differ from published data taken for a similar test arrangement. Possible explanations for the disagreement are given. The second study was performed on a 6-inch (0.55 diameter ratio) Venturi meter manufactured to the ISO 5167 standard. Liquid contents up to 5% by volume, gas velocities from 6-15 m/s and line pressures of 20, 40 and 60 barg were used in the test programme. The calculated overreadings in gas flowrate are consistent with existing data. Introduction The metering of multiphase flows in the field is becoming more common due to requirements for the reduction of costs through removal of expensive separation equipment and the improvement of well management via sufficiently accurate and reliable real-time data. Wet gas flow measurement (as a subset of multiphase flow) is receiving particular attention by the industry due to limitations of existing multiphase flow measurement devices in the required high GVF range. The continued study of the response of current metering technologies using modern experimental test facilities that simulate field conditions is vital to the development of reliable techniques that can be used for determining gas flowrate in high GVF systems. Just such a facility has been available to the Oil and Gas Industry at the National Engineering Laboratory (NEL) since the summer of 1999. The results of two separate wet gas studies using this facility are reported in this paper. Typical examples of a turbine meter and Venturi meter have been exposed to high pressure wet gas flows and the responses obtained compared with their normal dry gas behaviour. The aims of each test programme were slightly different due to the nature of each meter type and their likely applications. For the turbine meter installation in a wet gas line is not advisable due to the likely damage that the meter would sustain. However, there are occasions when liquid can enter a dry gas metering run and therefore it is desirable to know the effect that a small quantity of liquid may have on the calibrated meter factor.

Liquid loading is a major problem in the natural gas industry, in which gas production is limited by the accumulation of liquids in the well tubing. Liquid loading can be prevented by the injection of surfactants at the bottom of the well. The surfactants cause the liquid in the well to foam, thereby changing the gas-liquid flow in the well. The flow is characterized by the TPC (Tubing Performance Curve), which relates the average pressure gradient in the tubing to the gas flow rate. This work has two main goals: (i) To improve the understanding of the effect of surfactants on gas-liquid flow in pipes, which we characterize by a change in the generalised TPC. The generalised TPC relates the average pressure gradient to the gas and liquid flow rates in the pipe. (ii) To provide subsidies for the development of simple physically-based models for the effect of surfactants on gas-liquid flow. We performed experiments in intermediate-scale pipes (lengths of 12 m to 18 m and diameters of 34 mm, 50 mm, and 80 mm) with air and water at atmospheric conditions, without and with surfactants. Multiple parameters, that also vary between different gas wells in the field, were varied: the gas and liquid flow rates, the pipe diameter, the pipe inclination, the surfactant type and the surfactant concentration. We performed a visualisation of the flow without and with surfactants to obtain qualitative results on the effect of surfactants on the flow morphology, and we related these results to quantitative measurements of the generalised TPC and the liquid holdup. The behaviour of the generalised TPC is to a large extent determined by the transition between annular flow and churn flow. In annular flow without surfactants, at large gas flow rates, the water is present in a film along the pipe wall and in entrained droplets in the gas core; the water always moves upwards, which leads to a relatively regular flow morphology. In the churn flow regime, which occurs at low gas flow rates, the liquid film reverses, as the interfacial friction between the gas and the liquid, which drags the liquid upwards, no longer exceeds the gravitational force on the film. This leads to a complex flow morphology, a large liquid holdup and a large pressure gradient. Surfactants cause the formation of foam through the hydrodynamics of the flow. The foam decreases the density and increases the volume of the film at the wall. This changes the balance between the interfacial friction and the gravitational force, which shifts the transition between churn flow and annular flow to lower gas flow rates. As a result, the generalised TPC is changed by the surfactants, leading to a decrease in the pressure gradient at low gas flow rates. An optimum surfactant concentration exists that results in the largest reduction of the pressure gradient. This concentration increases with increasing film thickness; therefore, it increases with decreasing gas flow rate, increasing liquid flow rate, increasing pipe diameter, and decreasing inclination from horizontal. Qualitatively, these results are unaffected by the type of surfactant that is used. From the results obtained in this work, we qualitatively understand the effect of surfactants on the gas-liquid flow, and we understand why surfactants are able to deliquify gas wells. However, a physically-based model is required to translate the results obtained in this work in a quantitative way to the large-scale gas wells. Such a model requires a characterization of the foaming behaviour of the surfactant-liquid mixture using a small-scale setup. We determined that a small-scale sparging setup, often used in the gas industry, is not suitable, because the hydrodynamics in the sparging setup differ too much from the hydrodynamics of annular flow and churn flow. A small-scale shaking test, in which the hydrodynamics more closely resemble churn flow, shows more potential to characterize the foaming behaviour of the surfactants in the context of gas-liquid flows.

Online measurement of gas and liquid flow rate in wet gas through one V-Cone throttle device

A water model study was undertaken to investigate bubble dispersion and inclusions removal by bubble adhesion in continuous casting mold. The water flow rate was varied in the range of 37-74 L/min, which is equivalent to 1.0-2.0 m/min of the casting speed in continuous casting process. The gas flow rate was varied in the range of 0-2.5 L/min. Silver coated hollow glass beads (SCHG) and plastic particles were used to imitate the inclusions and to investigate the effect of wettability, i.e., contact angle of the inclusions with liquid, on inclusion removal by bubble adhesion. Effect of gas and water flow rates on bubble dispersion in the mold was systematically determined. Inclusion removal at different gas and water flow rates was quantitatively determined. It was identified that the wettability of inclusions with liquid was a decisive factor in inclusion removal: with low wettability, i.e., high contact angle, removal efficiency increased with increasing gas and liquid flow rates, whereas removal efficiency was hardly affected by gas flow rate with high wettability, i.e., low contact angle. To interpret the results of the water model experiments, various computational fluid dynamics (CFD) models which had been reported were applied. None of them was able to represent the experimental results within an acceptable discrepancy. Two new CFD models, which employed a modified Reynolds number and force field theory around the bubble, were developed to simulate bubble dispersion and inclusion removal, respectively. The results indicated that these models could simulate bubbles dispersion and inclusion removal and showed reasonable agreement with results of water model in continuous casting mold.

The mechanism of flow of air and water through packed glass fibres has been studied. Pressure drops and liquid hold ups were measured as a function of gas and liquid flow rates and the packing characteristics. It has been found that the pressure difference measured is dependent upon the history of previous gas and liquid flow rates in the bed. The liquid hold up is defined entirely by the gas and liquid flow rates. An analysis of the flow mechanism shows that the capillary forces interact with the fluid pressures in the bed. For example an increase in gas flow rate followed by a reduction to the same flow rate has been shown to reduce the resistance of the bed to gas flow even though the liquid flow rate is unchanged. A measure of the irreversibility of the flow operation is suggested.

The induction of pulses in trickle-bed reactors by cycling the liquid feed

In 2021, estimation shows that the worldwide annual hydrogen production is around 94 Mt. Exploitation of native hydrogen being not mature, it is obtained by its separation from other elements by different methods such as steam methane reforming, and electrolysis of water. The latter supplied by a renewable power source will take part in the development of a green hydrogen economy [1]. In this context, Proton Exchange Membrane (PEM) Electrolyzer is a promising technology due to its flexibility and very quick adaptation to load variations. However, its current development still confronts some limitations at a large industrial scale. For instance, efficiency and durability are directly impacted by the mass transport and electrical transfer within the porous materials at the anode side. Limitation of the water supply to the catalyst layer happens once there is a poor oxygen evacuation which decreases the performance of the device by inducing high overpotential. Furthermore, the PTL has an important role as an electrical conductor for charge transfer from the catalyst layer [1]. The efficiency of all the transport phenomena through the PTL and porous electrode assembly depends on their transport properties which are related to their microstructure and operating conditions. For instance, PTL with a large pore size allows good water and gas transport, while produced electrons choose a long-distance path generating an electrical resistance higher than that in the case of PTL with a small pore size [1]. So, controlled and optimum porosity and pore size could contribute to efficient water, gas, and electron transport. To define the best porous layers morphologies, a deep and accurate understanding of the phenomena is developed in this work by combining modeling and experiments.The magnetic resonance imaging (MRI) technique was used to quantify the water content within the porous layer during the two-phase flow. Instead of the real PTL made of titanium which is paramagnetic and cannot be used in the MRI, borosilicate filters with thickness, porosity, and pore size similar to the PTL were used. After positioning the sample in the 600 MHz vertical imager (Figure 1-A), a constant water flow rate is introduced while the gas flow rate is varied. The saturation profiles measured through the porous material depend on the gas flow rate and a semi-dryness of the sample occurs (Figure 1-B) with a residual quantity trapped between pores (minimum stable water content). The water flow rate variation in the channel does not affect saturation, but a higher gas flow rate is needed to reach a minimum stable water content for higher water flow rate.The gas pressure drop through the porous medium was measured and bubble formation in the channel was also analyzed. The results show that the pressure drops and types of flow (slug, annular, and bubble flow) depend on orientation of the water channel (horizontally and vertically) and flow direction (up or downward), and on the water and gas flow rates.To reach a better understanding of the dynamic characteristics of water and oxygen transport over the PTL, the phase-field model based on the Cahn-Hilliard theory was used to simulate the two-phase flow through a porous medium [2]. In this model, the modified Navier-Stokes equations for two phases are coupled with a phase-field equation for describing the diffuse interface. Numerical simulations performed in the COMSOL® multiphysics software were carried on 2D geometries composed of spherical solid grains of different sizes, having properties similar to the PTL used in the MRI experiments. Gas is injected on one side of the sample and flows through the porous medium initially saturated and evacuated on another side in contact with the water channel (Figure 1-C). Gas flow in the porous medium and bubble formation in the water channel are studied while varying the gas and water flow rates. The simulation results give information about the gas pathways within the porous medium and the saturation profiles over time, depending on the gas/water flow rates, which will be compared with experimental results.[1] J. Parra-Restrepo, “Caractérisation des hétérogénéités de fonctionnement et de dégradation au sein d’un électrolyseur à membrane échangeuse de protons (PEM),” Université de Lorraine, 2020.[2] J. W. Cahn and J. E. Hilliard, “Free Energy of a Nonuniform System. I. Interfacial Free Energy,” The Journal of Chemical Physics, vol. 28, no. 2, pp. 258–267, Feb. 1958. Figure 1

Gas flow rate distributions in parallel minichannels for polymer electrolyte membrane fuel cells: Experiments and theoretical analysis

In-service welding is a kind of important method to ensure the integrality of oil gas pipeline and the thermal cycle of which is significant for repairing. Used SYSWELD to establish model and simulate thermal cycle of in-service welding on X70 steel gas pipeline, compared thermal cycles of in-service welding and air-cooling welding, studied the influence of gas pressure and flow rate on thermal cycle. The result shows that peak temperature of the coarse grain in heat affected zone (CGHAZ) of in-service welding is similar to air cooling welding, but the cooling time of t8/5, t8/3 and t8/1 decreases at certain degree. Peak temperature of CGHAZ of in-service welding doesn’t vary match with gas pressure and flow rate either. t8/5, t8/3 and t8/1 decrease when gas pressure increases. t8/5 varies with the gas pressure linearly. When the pressure is less than 4MPa, t8/3 and t8/1 decrease rapidly while gas pressure increases. When the pressure is more than 4MPa, t8/3 and t8/1 decrease slowly while gas pressure increases. t8/5, t8/3 and t8/1 decrease when the flow rate increases. When gas flow rate is less than 10m/s, t8/5, t8/3 and t8/1 decrease rapidly while flow rate increases. When gas flow rate is more than 10m/s, t8/5, t8/3 and t8/1 decrease slowly while flow rate increases.

Since 2016, Oil and Gas Institute – National Research Institute (INiG – PIB) has been conducting new research to determine the relationship between ambient temperature and gas temperature in industrial diaphragm gas meters during the measurement, and to develop new recommendations for billing systems using industrial diaphragm gas meters with a throughput of until 25 m3/h. In the first stage, work was carried out, in which the obtained test results confirmed that the heat exchange process in an industrial diaphragm gas meter depends on the ambient temperature, the gas temperature at the inlet to the gas meter, the flow rate of the gas flowing, as well as the casing surface and the gas volume of the gas meter. In the next stage, work was carried out to determine the relationship between ambient temperature and gas temperature at the industrial diaphragm gas meter connection during the measurement. The obtained results undermined the thesis, which indicated that the gas inlet temperature is equal to the gas temperature at the depth of the gas network. In the last stage, work was carried out to determine the course of changes in gas temperature in industrial diaphragm gas meters as a function of ambient temperature and cyclical changes of the gas flow rate, which were to reflect the work of gas meters installed at customers’ premises. The analysis of the obtained test results once again showed a strong dependence of the gas temperature inside industrial diaphragm gas meters on the ambient temperature, but also on the flow rate of gas. The obtained results of laboratory tests will be used to carry out a thermodynamic description of the heat exchange process in an industrial diaphragm gas meter, which would allow the determination of the gas billing temperature as a function of the ambient temperature, the temperature of the inflowing gas and the gas flow rate. The calculated gas temperature values could be used to determine the temperature correction factors applicable when settling gas consumers billed on the basis of measurement with the use of industrial diaphragm gas meters.

An experimental study was conducted in a sieve tray column. This study used a simulated flue gas consisting of 30% CO2 and 70%. A 10% mass fraction of methyl diethanolamine (MDEA) aqueous solution was used as a solvent. Three ramp-up tests were performed to investigate the effect of different load changes in inlet gas and solvent flow rate on CO2 absorption. The rate of change in gas flow rate was 0.1 Nm3/h/s, and the rate of change in MDEA aqueous solution was about 0.7 NL/h/s. It was found that different load changes in inlet gas and solvent flow rate significantly affect the CO2 volume fraction at the outlet during the transient state. The CO2 volume fraction reaches a peak value during the transient state. The effect of different load changes in inlet gas and solvent flow rate on the hydrodynamic properties of the sieve tray were also investigated. The authors studied the correlation between the performance of the absorber column for CO2 capture during the transient state and the hydrodynamic properties of the sieve tray. In addition, this paper presents an experimental investigation of the bubble-liquid interaction as a contributor to entropy generation on a sieve tray in the absorption column used for CO2 absorption during the transient state of different load changes.

Experimental study and CFD modelling of a two-phase slug flow for an airlift tubular membrane

Flow metering of multiphase pipeline is an urgently problem needed to be solved in oilfield producing in China. Based on the principle of multiphase oil and gas flow in the open channel, four liquid metering models(Falling Model I, Falling Model II, Open Channel Model and Element Resistance Model) and one gas model were obtained to calculate the gas and liquid flow rate, in which the water cut was measured by the differential pressure. And then a new type of multiphase meter system was developed based on these models and neural networks were developed to improve the estimating results of gas and liquid flow rate with the new metering system. At last a lot of experiments of multiphase metering were finished in lab and field. According to the experiments, the results of the metering system show that the liquid flow rate error was no more than 10%, and gas flow rate error was no more than 15%, which can meet the demand of the field flow rate measurement. Furthermore the relationship between liquid and gas flow rate and characteristic signals was found out through the experiments so as to deepening the study on multiphase flow metering technology.

Design and off-design performance analysis of supercritical carbon dioxide Brayton cycles for gas turbine waste heat recovery

Analytical aspects of different adjustment of parameters of an inductively coupled plasma atomic emission spectrometer (ICP‐AES) were investigated. The ICP‐AES was a LABTAM 8440M (now called GBC) spectrometer. Since at many times, the elemental concentration of the analyte is near to the detection limit, the lowest possible detection limit has to be reached. When the signal‐to‐background ratio (SBR) is maximized, the detection limit is the smallest. This is the reason why the effects of each adjustable parameters on the signal‐to‐background ratios were investigated. Seven adjustable parameters can be analyzed in this equipment: (i) viewing height, (ii) forward power, (iii) sample gas, (iv) coolant gas, (v) auxiliary gas, (vi) flushing gas, and (vii) sample uptake flow rates. Furthermore aerosol distribution by droplet size and nebulization efficiency were also examined applying three different sample gas flow rates and four elements [iron (Fe), magnesium (Mg), manganese (Mn), and nickel (Ni)]. The alkali metals with low excitation energy [potassium (K), lithium (Li), and sodium (Na)] were detectable in higher regions of the plasma, some alkali‐earth and transition metals with medium excitation energy [calcium (Ca), srontium (Sr), and copper (Cu)] were well detectable in medium height, whereas the maximum signal‐to‐background ratios of the other elements with relatively high excitation energy [e.g. cadmium (Cd), Ni, and phosphorus (P)] reached in lower regions of the plasma. On the basis of results the compromised viewing height for all the elements is found 5 mm, the optimum sample gas flow rate 1.14 dm3 min‐1 and the forward power 1200 W. Change of coolant and auxiliary gas flow rates has not changed the signal‐to‐background ratios significantly. Consequently the optimum argon flow rates in aspect of consumption of argon are the possible lowest flow rates, where plasma remains stable. For coolant and auxiliary gas flow rates these values are 10 dm3 min‐1 and 0.1 dm3 min‐1, respectively. Changing the rate of peristaltic pump (i.e. sample uptake rate) the signal‐to‐background ratios increase to 4‐ or 5‐fold of the original values, therefore the optimum sample uptake rate is considered 4 cm3min‐1. Increase of flushing gas flow rate has not changed the signal‐to‐background ratios significantly, except in case of sulfur (S) and P, because of oxygen (O2) absorption from the air. When analysis of S and P content is necessary, 0.13 dm3min‐1 and 0.2 dm3 min‐1, respectively, of flushing gas flow rate is recommended to use.