Wet gas

A wet gas is any gas with a small amount of liquid present. The term "wet gas" has been used to describe a range of conditions ranging from a humid gas which is gas saturated with liquid vapour to a multiphase flow with a 90% volume of gas. There has been some debate as to its actual definition but there is currently no fully defined quantitative definition of a wet gas flow that is universally accepted.

Wet gas is a particularly important concept in the field of flow measurement, as the varying densities of the constituent material present a significant problem.

A typical example of wet gas flows are in the production of natural gas in the oil and gas industry. Natural gas is a mixture of hydrocarbon compounds with quantities of various non hydrocarbons. This exists in either a gaseous or liquid phase or in solution with crude oil in porous rock formations. The amount of hydrocarbons present in the liquid phase of the wet gas extracted depends on the reservoir temperature and pressure conditions, which change over time as the gas and liquid are removed. Changes in the liquid and gas content also occur when a wet gas is transported from a reservoir at high temperature and pressure to the surface where it experiences a lower temperature and pressure. The presence and changeability of this wet gas can cause problems and errors in the ability to accurately measure the gas phase flowrate.

It is important to be able to measure these wet gas flows accurately to quantify production from individual wells and to maximise the use of equipment and resources which will assist with the reduction of costs.

There are a number of specific terms used to describe the characteristics of wet gas flow:

Superficial gas velocity is the gas velocity if there were no liquid present in the wet gas flow. In wet gas flows the gas velocity is higher due to a reduction in the pipe area caused by the presence of the liquid.

Superficial liquid velocity is the liquid velocity if there were no gas present in the wet gas flow.

Liquid load is the ratio of the liquid mass flow rate to the gas mass flow rate and is normally expressed as a percentage.

GVF – Gas volume fraction is the ratio of the gas volumetric flow rate to the total volumetric flow rate.

LVF – Liquid volume fraction is the ratio of the liquid volumetric flow rate to the total volumetric flow rate.

Hold up is the cross sectional area occupied by the liquid in the pipe carrying the wet gas flow.

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Wikipedia