Reservoir fluid characterisation using gas chromatography-mass spectrometry

The compositional characterisation of naturally occurring hydrocarbon mixtures is an integral part of routine petroleum laboratory analysis. Currently, the measurements of the gas and liquid phase compositions require separate gas chromatographic set-ups with analysis times of up to 1 h. These analyses may lack important information because several critical components are not sufficiently separated. ork uses a GC-MS with a quadrupole mass analyser to routinely provide classification of the eluted peaks into alkanes, iso-alkanes, naphthenes and aromatics as well as to determine their concentration. The selected set-up uses a single injection point and a single analytical column to analyse sequentially both gas and liquid samples. Specific calibration procedures have been developed to allow for the variation of the mz intensities from run to run and for the conversion of peak areas to concentrations. w extended compositional analysis throws light on the distribution of the different types of molecules in the reservoir fluid and provides accurate physical properties for each cut, thus improving the understanding of the thermodynamic and rheological behaviour of the petroleum fluids.