DEVELOPMENT OF EQUATIONS STATE FOR GAS CONDENSATES FOR COMPOSITIONAL PETROLEUM RESERVOIR SIMULATION

摘要

In this paper, we describe our experience in the development of an equation-of-state (EOS) model for compositional reservoir simulation studies of gas condensates, especially those near the critical point. We focused on the following tasks: (1) heavy-end pseudoization; (2) selection of the measured data to match and the EOS parameters to adjust; and (3) evaluation of model predictive capability.We compared several methods for each of the above tasks for a number of gas condensates, one of which is a near-critical gas condensate showing experimentally significant compositional change with depth. The combination of the different methods offers up to 44 different heavy-end descriptions. The Peng-Robinson (PR) EOS was then used with these fluid descriptions to predict the phase behavior of gas condensates. We observed that none of these 44 heavy-end descriptions is significantly better than the others, although they give very different properties of pseudocomponents. Tuning EOS-parameters to match experimental data is necessary' in order to well describe the phase behavior of gas condensates. The matched experimental data should include both phase amount and volume information. The initial guesses significantly affect the quality of the matches; those initial guesses using the Gaussian quadrature method for lumping lead in general to satisfactory matches. Tuning molecular weights of pseudocomponents (critical properties and acentric factor vary with them through correlations) in combination with independently tuning pseudocomponent critical properties is found to be a better procedure than other available tuning procedures. The model developed using this procedure can well capture the compositional variation and other associated property changes with depth for near-critical gas condensates tested in this work. The volume-shift parameters need to be used after the model matches phase-amount data.