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

Abstract

Summary One of the tools used for the characterization of gas reservoirs is the geochemistry of gas condensates. The fingerprinting of 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 bottomhole pressure falls below the dewpoint pressure, for example, condensate will drop out near the wellbore and the captured sample may not be representative of the formation fluid. We conducted two sets of tests simulating the effect(s) of gas-/ liquid-phase fractionation on fingerprinting analyses: (1) at different pressures (all below the dewpoint) at reservoir temperature (RT) region in order to simulate dropout of liquids in the near-wellbore area and (2) to investigate the effect of variations in separator temperature and pressure. Geochemical fingerprints obtained on our laboratory-fractionated samples show that condensates obtained from gas wells with flowing bottomhole pressures below dewpoint 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.