An Investigation of PVT Effects on Geochemical Fingerprinting of Condensates From Gas Reservoirs

摘要

One of the tools used for the characterization of gas reservoirs is the geochemistry of gas condensates. The fingerprinting of liquid gas condensates by gas chromatography in particular, may provide information regarding reservoir compartmentalization, which can be a major uncertainty at the early field appraisal stage. An important concern is the capture of suitable liquid samples. When the flowing bottom-hole pressure falls below the dew point pressure, for example, condensate will drop out near the well bore and the captured sample may not be representative of the formation fluid. We conducted three sets of tests simulating the effect(s) of gas-liquid phase fractionation on fingerprinting analyses: (1) at different pressures (all below the dew point) at reservoir temperature in order to simulate dropout of liquids in the near well bore area; (2) to investigate the effect of variations in separator temperature and pressure; (3) to evaluate fingerprint variations during a field deliverability test from a well that was previously shut in. Geochemical fingerprints obtained on our laboratory fractionated samples show that condensates obtained from gas wells with flowing bottom-hole pressures below dew point may not be suitable for compartmentalization studies. Differences in separator pressure and temperature affect the fingerprints of gas condensates but the effects are small and unlikely to alter conclusions regarding potential fluid flow barriers. We suggest a number of best practices for the collection and analysis of gas condensates for fingerprinting studies.