Introduction

Wet gas refers to the term for well flow where the gas volume fraction (GVF) is greater than 90% and usually greater than 95% under metering conditions.Wet gas flow meterIt is a typical low liquid phase gas-liquid two-phase flow. At present, wet gas flow meters are mainly based on differential pressure devices. At the 90% confidence level, the measurement uncertainty of existing WGMs for gas and liquid flow rates is about 5% to 10%, which can meet the accuracy requirements of reservoir management, but it cannot be used for production distribution and formation measurement. The measurement errors are 2% to 5% and 0.25% to 1% respectively. Over the years,high accuracy WGMThe development of WGM has always been a key demand in the natural gas industry. Since the measurement uncertainty of DP meters is affected by factors such as fluid temperature, density, fluid velocity distribution, and fluid viscosity, the accuracy of existing WGMs is difficult to improve [1]. Based onCoriolis Mass Flow Meter(CMF) inMeasuring single phase flowIt has unprecedented accuracy and reliability, and the accuracy of CMF is not affected by the above variables. This article aims to explore the feasibility of using CMF mass flow meter as a WGM to respond to the needs of the natural gas industry.

CMF issues in gas-liquid two-phase flow measurement

Early micro-motion experimental results showed that CMFGas-liquid two-phase flowPoor performance. The main evidence is a dramatic increase in flow tube damping, rapid changes due to the chaotic nature of the interaction between the liquid, compressible gas and flow tube walls. This phenomenon directly leads to the saturation of the flow tube drive circuit, which is used to overcome the damping effect and keep the flow tube vibrating at a constant amplitude. Rapid changes in damping will lead to rapid changes in flow tube vibration parameters such as frequency, amplitude, and phase from the CMF sensor. Changes in sensor signals increase the difficulty of information extraction, ultimately leading to poor frequency and phase tracking. The result is that appropriate driving current cannot be generated in time. there will beSensorA phase shift occurs between the input and drive output, and the flow tube may vibrate in forced mode. Therefore, inGas-liquid two-phase flow measurement, the accuracy and repeatability of CMF will be greatly reduced.

In recent years, CMF technology has undergone many improvements, including CMF tube geometry design based on numerical simulation, tube balancing systems, and signal processing technology. The possibility and feasibility of multiphase flow metering based on CMF technology should now be reconsidered. Ideal CMF operation is for the flow tube to vibrate with constant amplitude at its natural frequency. The vibration frequency of the flow tube is a function of fluid density, and the phase difference between the two CMF sensors is a function of mass flow rate. Before applying CMF to moisture metering, there are two issues that need to be resolved. One is to keep the flow tube vibration as stable as possible, and the other is to obtain accurate readings of mass flow and density from the sensor signal.

Theoretical analysis

In order to apply CMF to wet gas flow measurement, it needs to withstand the complex forces of two-phase fluids under different flow patterns. Therefore, the simpler the tube, the less additional force the tube will experience. Assuming that the diameter of the Coriolis tube is the same as the size of the connecting pipe, the Coriolis tube has no effect on the flow pattern and therefore no additional force is exerted on the Coriolis tube by the two-phase fluid. If so, a straight tube Coriolis flow meter would be a good choice for wet gas flow measurement. Since the force of the two-phase fluid is superimposed with the Coriolis force, it is almost impossible to distinguish or separate them. This superimposed force is also the main source of high noise in the CMF sensor signal. On the other hand, there are also some disadvantages.

AsSingle phase flow meter Straight tube CMF. The sensor signal produced by a straight tube has a high frequency, low amplitude, and low phase difference range compared to a typical curved flow tube. In other words, their signal-to-noise ratio is very low, and it is much more difficult to extract a good quality measurement signal and ensure continuous flow tube oscillation than for bent tubes. Our experiments using CMF as WGM show that the signal-to-noise ratio is not as high as the curved pipe CMF reported by Henry [3]. In our experimental study, we selected and tested two micro-bend tube CMFs, and they showed good performance in all test ranges. Details are given in the next section. Furthermore, a major problem with existing WGMs is that their turndown ratio is less than 10:1. Unfortunately, due to the natural characteristics of gas-liquid two-phase flow, the total mass flow rate of wet gas in the production pipeline always varies by a factor of more than 100, which results in random saturation of DP readings. The straight tube CMF has a turndown ratio of 1000:1 and can easily handle natural changes in gas and liquid flow rates. Therefore,Straight tube mass flow meterYesWet gas metering comparisonSuitable choice.