PD ISO/TR 12748:2015 - Page 4

Natural Gas. Wet gas flow measurement in natural gas operations. | Status: Current

1 Scope This Technical Report describes production flow measurement of wet natural gas streams with WGFMs in surface and subsea facilities. Wet natural gas streams are gas-dominated flows with liquids like water and/or hydrocarbon liquids3) (see 2.67 for a detailed definition). This Technical Report defines terms/symbols, explains the various concepts, and describes best practices of wet gas flow meter design and operation. It addresses metering techniques, testing, installation, commissioning, and operation practices such as maintenance, calibration, and verification. It also provides a theoretical background of this comprehensive, challenging and still evolving measurement technology. There are four general methods in measuring wet natural gas flow. Each approach is detailed below.

• — Single-phasegas flow meter with correction factor: Uses a single-phasegas flow meter (often a conventional gas flow metering device) with a correction factor for the effect of liquid on the metering system. In these cases, the liquid flow rate required to determine the correction factor, should be estimated from an external source.
• — Two-phaseWGFM: The gas and liquid (both water and hydrocarbon liquid combined) flow rates are predicted with no additional external information regarding the liquid flow rate required. This is generally known as a two-phaseWGFM and will be referred to in this Technical Report simply as WGFM.
• — WGFM: A flow meter that measures the gas and liquid flow rates, and also the gas, water and hydrocarbon liquid ratios (or “phase fractions”) with no external information required regarding the liquid flow rate.
• — Phase separation/Measurement after phase separation: This traditional and conventional method of wet gas flow metering uses a two-or three-phase separator with single-phase flow meters measuring the outgoing single-phase flows.

The first three of these methods, which emerged in the last two decades, may be described as in-line wet gas flow metering, i.e. wet gas flow measurement is executed with WGFMs without separating the gas and liquid phases. This Technical Report discusses in detail these first three methods. Several best practice documents have already been issued to describe, among other topics, wet gas flow measurement[9][10][11][12]. The last method is more conventional and describes wet gas flow measurement after the gas and liquid phases have been separated. Wet gas meters can be used in multiphase flow metering systems that utilize partial separation technologies. This method is only briefly discussed in this Technical Report.