Wet gas flow measurement is becoming increasingly important in today's oil and gas industry. Many high producing gas fields are exploited and some are facing the end of the production lifetime. For gas fields approaching the final stages and marginal fields have one thing in common: the natural gas is wet.
The term "wet" means that the natural gas line also carries a relatively small amount of free liquid by volume. The definition of wet gas is when the flow of gas and liquids has a Lockhart-Martinelli parameter X in the range of 0 < X ‰¤ 0,3. The fluid of interest to be measured is the natural gas and not so much the hydrocarbon liquids.
Wet gas metering is a difficult application and therefore a standard (dry) flowmeter cannot be used.
The term "wet gas” is a 2 phase flow measurement with a maximum liquid volume of 10% and therefore a minimum of 90% gas volume (90% GVF — Gas Volume Fraction)
Well testing, hydrocarbon allocation metering, hydrocarbon sales metering and monitoring critical factors such as water breakthrough.
EMCO wet gas metering is based on the classical venturi tube according to ISO 5167-4 with single pressure tappings. A third tapping may be applied for better check on liquid flow rate changes using the pressure loss ratio method.
Calculating the differential pressure for the wet gas meter using the international recognized ISO standard 5167-1 is resulting in a higher differential pressure than a similar calculation for a dry gas.
This overreading has to be corrected for in computers using a number of algoritms.
The size of overreading depends on the liquid volume fraction, the static pressure, the gas and liquid densities and the velocity.
The mechanical design of the wet gas metering section is influenced by the choice of algorithm for overreading correction.