IAMG 2001--Cancún Technical Program--Session J

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Using Flash Calculations to determine Phase Compositions and Properties in Petroleum Systems Modeling by Armin Ingo Kauerauf*, and Thomas R. Hantschel, Integrated Exploration Systems, Germany Oil and gas phases are exposed to strongly varying conditions in petroleum systems modeling. Changes in temperature and pressure during migration or subsidence of reservoirs and oil generation or cracking are the main reasons for different compositions and properties of the petroleum phases. The knowledge of compositions and properties is important for the description of reservoirs and migration. Especially overpressure can only be calculated if the amounts and densities of gas and oil are known. The most accurate results of component distribution and phase densities are commonly gained with flash calculations. In petroleum systems modeling they are used in two different ways: Flash calculations are performed to generate data for symmetrical black oil (SBO) models. In SBO models it is assumed that two phase oil and gas systems can be decribed by two components, a light and a heavy one. Both components are contained in the oil and gas phase but it is assumed that the oil phase is mainly made of the heavy component and the gas phase is mainly made of the light component. The light and the heavy components are pseudo components with parameters gained by special averaging methods from sets of pure components. Flash calculations are used to calculate bubble and dew point composition tables. With these data it is possible to perform very fast calculations of oil and gas phase compositions at arbitrary conditions. Easy to handle tools make it possible to create a wide spectrum of these lumped components and the necessary bubble and dew point data for testing and optimization. The other way is the direct usage of flash calculations in every cell of the model at every timestep. Enhanced computer hardware now makes it possible to run models with less than ten components or rapid flash calculation methods e.g. without binary interaction parameters on normal workstations. The results of example calculations are shown. The two methods are compared and it is shown that SBO models should only be used in a limited region of pressure and temperature. Sophisticated petroleum systems simulations should use different SBO models for different temperature and pressure regions. Paper in PDF format Kauerauf and Hantschel, Acrobat PDF, 398k.