Wet Gas Venturi Metering

Abstract

Abstract Introduction Multiphase metering is becoming increasingly important in the development of marginal oil and gas fields. Many of these fields are only economically viable if they can be tied back to existing platform infrastructure, reducing the capital expenditure required by significant margins. In such cases, several fields are often tied back to common facilities requiring each unprocessed stream to be metered before co-mingling. Multiphase metering is also a valuable technology in well management, providing on-line information on the production flow; and in well testing, reducing the capital expenditure required to investigate potential new wells. Wet gas metering is at the high gas fraction end of multiphase metering, typically with a gas volume fraction (GVF) above 90%, and mostly above 95%. Standard multiphase meters cannot operate satisfactorily in such conditions. The development of Wet Gas Meters is therefore a key requirement of the oil and gas industry. There are two principal approaches to wet gas metering. The first is to use a dedicated wet gas meter which has been designed to measure the flow rates of both the liquid and gas phases. The second is to use some standard dry gas meter and applying corrections to the measurements based on knowledge of how the meter in question is affected by the presence of a liquid phase in the gas stream. The second method requires prior knowledge of the liquid flow to correct for the gas flow. Obviously the first method is desirable from the point of view of continuous measurement and well management, however if the liquid flow is known to remain reasonably constant, or change slowly then the second method can be used subject to a suitable means of determining the liquid flow being available. The work presented in this paper is relevant to both methods. Using the second method with a Venturi meter requires a detailed knowledge of the performance of Venturi meters in wet gas flows. The data contained in this paper offers a significant contribution to this knowledge. The data may also prove useful in the development of commercial Wet Gas Meters based on Venturis. Wet Gas Flow Measurement at NEL NEL currently have two large projects running in the area of wet gas measurement. The two projects cover the two approaches described above. Flow Programme Project. Under the 1999–2002 Flow Programme, supported by the UK's Department of Trade and Industry (DTI), this project is looking at the performance of standard dry gas meters in wet gas applications. The meters that have been tested in this project comprise three Venturis, two V-Cones, one Vortex, one Turbine, and one Coriolis. The meters were tested at pressures from 15 to 60 bar, at superficial gas velocities (SGVs) in the range 2 to 20 m/s, and with liquid loadings up to 5% liquid volume fraction (LVF). The test results from the Venturi tests are presented in this paper. NEL Wet Gas JIP. This project, which started in June 2002, is a joint industry project supported by a large number of major oil and gas companies. The project aims to investigate the performance of commercially available Wet Gas Meters. These will be meters designed specifically for the measurement of both the gas and liquid phases of wet gas flows. These meters will be of an in-line design as far as possible, but meters or flow systems based on partial or full separation will also be considered. At present there are only a few meters on the market, most of which are based on differential pressure technology. One of these meters has now been tested. Throughout the life of the project, new meters will likely become available, and the advantages and disadvantages of alternative technologies will become clearer. Flow Programme Project. Under the 1999–2002 Flow Programme, supported by the UK's Department of Trade and Industry (DTI), this project is looking at the performance of standard dry gas meters in wet gas applications. The meters that have been tested in this project comprise three Venturis, two V-Cones, one Vortex, one Turbine, and one Coriolis. The meters were tested at pressures from 15 to 60 bar, at superficial gas velocities (SGVs) in the range 2 to 20 m/s, and with liquid loadings up to 5% liquid volume fraction (LVF). The test results from the Venturi tests are presented in this paper. NEL Wet Gas JIP. This project, which started in June 2002, is a joint industry project supported by a large number of major oil and gas companies. The project aims to investigate the performance of commercially available Wet Gas Meters. These will be meters designed specifically for the measurement of both the gas and liquid phases of wet gas flows. These meters will be of an in-line design as far as possible, but meters or flow systems based on partial or full separation will also be considered. At present there are only a few meters on the market, most of which are based on differential pressure technology. One of these meters has now been tested. Throughout the life of the project, new meters will likely become available, and the advantages and disadvantages of alternative technologies will become clearer.