PRCI

Recent Results

Gas Sampling at Hydrocarbon Dew Point Conditions

This project evaluated the ability of four natural gas spot sampling methods, including two zero emissions sampling methods, to capture accurate, representative samples of gas streams at or near their hydrocarbon dew point (HDP).  Two of the sampling methods tested were variations on the GPA fill-and-empty method, with additional steps intended to heat the sampling equipment above the HDP or clear condensed hydrocarbon liquids from the sample line. The other two sampling methods, which use the A+ Q2 sample cylinder and a constant-pressure floating-piston sample cylinder, were developed to prevent condensation of heavy hydrocarbons
during the sampling process.

The methods were tested using the API Sampling Protocol, on production gas streams with nominal heating values ranging from 1,025 Btu/scf to 1,140 Btu/scf, and in ambient temperatures 10°F to 30°F below the stream HDP.  The test sites were chosen with the intent that the gas stream would be above its HDP and free of entrained liquids, while the ambient temperature and sample equipment would be below the HDP.

Key Results

Tests of the sampling methods continued so that data could be collected on the sampling methods’ performance in two-phase streams.  Results were analyzed to assess (1) the repeatability of samples from each cylinder, and (2) the ability of the sampling methods to reproduce (obtain a representative sample of) the pipeline gas composition. All samples collected on gas streams free of liquids satisfied the API repeatability and reproducibility criteria. However, because the protocol and its acceptance criteria were intended for use in single-phase gas streams, the sampling methods could not be evaluated using the API Sampling Protocol and data from the two-phase streams. Additional repeatability and reproducibility statistics were developed, using two statistical methods developed as possible alternatives to the API Sampling Protocol. All three methods appeared to capture the performance of the sampling methods through their reproducibility statistics. The Final Report is available for members on PRIME.

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