Dedicated wet-gas flowmeters are now commercially available for the measurement of gas and liquid flow rates. They offer a more compact measurement solution than the traditional separator approach. The interpretation models of traditional multiphase flowmeters emphasize the liquid rate measurements; they have been used to well test and meter mostly liquid-rich flow streams. These models were not developed for the measurement of gas flow rates, particularly those of wet gas. A new interpretation is described that allows a traditional multiphase flowmeter to operate in a dual mode either as a multiphase meter or as a wet-gas meter in 90% to 100% gas. The new interpretation model was developed for a commercially available multiphase flowmeter consisting of a venturi and a dual-energy composition meter. This combination results in excellent predictions of the gas flow rate, and in addition, liquid rate and water-cut predictions are made with an acceptable accuracy with no additional measurements. The wet-gas and low-liquid-volume-fraction interpretation model is described together with the multiphase flow meter. Examples are presented of applying this model to data collected on flow loops, with comparison to reference flow rates. The data from the Sintef and NEL flow loops show an error, better than ± 2% reading for the gas flow rate, at line conditions; the absolute error in the measured total liquid flow rate at line conditions of was better than ± 2 m3/h (< ± 300 bpd). This new interpretation model offers a significant advance in the metering of wet-gas multiphase flows and yields the possibility of high accuracies to meet the needs of gas-well testing and production allocation applications without the use of separators. Introduction There has been considerable focus in recent years on the development of new flow measurement techniques for application to surface well testing and flow measurement allocation in multiphase conditions without separating the phases. This has resulted in new technology from the industry for both gas and oil production. Today, there are wet-gas flow meters, dedicated to the metering of wet-gas flows, and multiphase meters, for the metering of multiphase liquid flows. The common approach to wet-gas measurement relates gas and liquid flows to a "pseudo-gas flow rate" calculated from the standard equations. This approach addresses the need for gas measurement in the presence of liquids and can be applied to a limit of liquid flow (or gas volume fraction, GVF), though the accuracy of this approach decreases with decreasing GVF. The accurate determination of liquid rates by wet-gas meters, however, is restricted in range. The application and performance of multiphase meters has been well documented through technical papers and industry forums, and after several years of development is maturing.1 Some multiphase measurement techniques can perform better, and the meters provide a more compact solution, than the traditional separation approach. It is not surprising that the use of multiphase flowmeters has grown significantly, the worldwide population doubling in little over a 2-year period.2 Multiphase flowmeter interpretation emphasizes the liquid rate measurement. The application of multiphase flowmeters has been predominantly for liquid-rich flow stream allocation and well testing. Of these two approaches, neither has been optimized for the measurement of gas and liquid flow rates across the range of GVF typical for wet-gas production, prompting the need for further development in wet-gas flow measurement. Furthermore, the benefits of multiphase flow measurement are now being sought for gas wells. To address the need for a broad solution to wet-gas flow measurement, a new interpretation model has been developed using the hardware platform of a commercially available dual-energy-venturi multiphase flowmeter. This model has been used for excellent predictions of the gas flow rate across the full range of GVF, from 90% to 100%. In addition, liquid rate and water-cut predictions are achieved to an acceptable accuracy with no additional measurements.
Summary Dedicated wet-gas flowmeters are now commercially available for the measurement of gas and liquid flow rates and offer a more compact measurement solution than does the traditional separator approach. The interpretation models of traditional multiphase flowmeters emphasize the liquid rate measurements and have been used to well test and meter mostly liquid-rich flow streams. These models were not developed for the measurement of gas flow rates, particularly those of wet gas. A new interpretation is described that allows a traditional multiphase flowmeter to operate in a dual mode either as a multiphase meter or as a wet-gas meter in 90 to 100% gas. The new interpretation model was developed for a commercially available multiphase flowmeter consisting of a venturi and a dual-energy composition meter. This combination results in excellent predictions of the gas flow rate; the liquid rate prediction is made with acceptable accuracy and no additional measurements. The wet gas and low-liquid-volume-fraction interpretation model is described together with the multiphase flowmeter. Examples of applying this model to data collected on flow loops are presented, with comparison to reference flow rates. The data from the Sintef and NEL flow loops show an error (including the reference meter error) in the gas flow rate, better than ± 2% reading (95% confidence interval), at line conditions; the absolute error (including the reference meter error) in the measured total liquid flow rate at line conditions was better than ± 2 m3/h (< ± 300 B/D: 95% confidence interval). This new interpretation model offers a significant advance in the metering of wet-gas multiphase flows and yields the possibility of high accuracies to meet the needs of gas-well testing and production allocation applications without the use of separators. Introduction There has been considerable focus in recent years on the development of new flow-measurement techniques for application to surface well testing and flow-measurement allocation in multiphase conditions without separating the phases. This has resulted in new technology from the industry for both gas and oil production. Today, there are wet-gas flowmeters, dedicated to the metering of wet-gas flows, and multiphase meters, for the metering of multiphase liquid flows. The common approach to wet-gas measurement relates gas and liquid flows to a "pseudo-gas flow rate" calculated from the standard single-phase equations. This addresses the need for gas measurement in the presence of liquids and can be applied to a limit of liquid flow [or gas volume fraction, (GVF)], though the accuracy of this approach decreases with decreasing GVF. The accurate determination of liquid rates by wet-gas meters is restricted in range. The application and performance of multiphase meters has been well documented through technical papers and industry forums, and after several years of development is maturing (Scheers 2004). Some multiphase measurement techniques can perform better, and the meters provide a more compact solution, than the traditional separation approach. It is not surprising that the use of multiphase flowmeters has grown significantly, the worldwide number doubling in little over a 2-year period (Mehdizadeh et al. 2002). Multiphase-flowmeter interpretation emphasizes the liquid rate measurement, and the application of multiphase flowmeters has been predominantly for liquid-rich flow stream allocation and well testing.
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