In many unprocessed natural gas measurement locations between wellheads and process plants, water and condensate are entrained with the gas flow. How measurement at these locations is used for reservoir management, monitoring, control, production allocation, and custody transfer. The accuracy of wet gas metering is of great importance, especially allocation and custody meters, because of the monetary value of the large volume of unprocessed natural gas being transferred daily.

This paper presents the effect of orifice meter orientation, installed in horizontal, upflow, and downflow positions, on the accuracy of flow measurement. Tests were conducted at the Chevron Petroleum Technology Company's Air How Facility in La Habra, California. Two-inch orifice meters with three different orifice/pipe diameter ratios (beta ratios) were selected for testing. Air and water were used as flowing fluid, and they were controlled and measured by sonic nozzles and turbine meter, respectively.

The effects of liquid entrainment on metering error are characterized at each operating position. The results of this study indicated liquid entrainment in orifice meters always contributes lower gas flow rate measurement, up to −2% at vertical upflow position. In order to minimize metering errors in wet gas flow measurement, an orifice meter should be installed in a horizontal position with a mid-range beta ratio.

Currently, there is no acceptable correlation to adjust low liquid entrainment in orifice metering flow. To maintain metering accuracy, the author recommends improving system design to avoid liquid entrainment in orifice meters. In addition, unaccountable liquid condensate accumulation in the meters is a potential loss of revenue.

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