The extraction of a representative sample of wet gas is often required for reservoir management, compensation monitoring, allocation or taxation. The sample can be used as a more accurate alternative to tracer techniques to correct the over-measurement caused by the presence of liquid in the gas. The liquid and gas samples can also be analysed for composition to determine the hydrocarbon/methanol/water ratio of the liquid and the energy value of the gas making the system a high accuracy alternative to multiphase flow meters in high GVF well test and allocation measurement applications.
The patented Jiskoot wet gas sampling system comprises a take-off probe and a bypass loop in an enclosure containing a mass flow meter, two molecular sieves and two sample collection receivers. The take-off probe is mounted in the line at a suitable position and has multiple inlet points to profile the pipeline. The number and size of the inlets are designed for each application dependant on the flow regimes present. The flow loop is designed to maintain sample representivity through the bypass loop and to have minimal dead volume.
The wet gas flows through a molecular sieve, which removes and traps all the liquids from the gas stream. The liquid is retained in the sieve and the mass flow of dry gas is measured by the flow meter. A sample of dry gas is also taken for analysis. The molecular sieves will have been weighed using a mass balance before placing in the system. At the end of the sampling process the molecular sieves are removed and weighed and the increase in mass noted.
The liquid mass ratio to dry gas is established by comparing the mass of liquids collected with dry mass of gas from which it was extracted. This ratio can be used in a variety of equations to directly compensate the wet gas measurement totals.
Once removed from the system the sample of dry gas can be analysed in the laboratory. The liquid trapped in the molecular sieve can be removed using a laboratory sample extractor and the liquid samples analysed for content.
The patented Jiskoot wet gas sampling system offers a very high accuracy alternative to tracer techniques and multiphase meters in high GVF measurement applications.
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