Performance analysis of a modified black-oil model for a rich gas condensate reservoir
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2005 SPE All rights reserved. The modified black-oil model (MBO) was tested against the fully compositional model and performances of both models were compared using various production and injection scenarios for a rich gas condensate reservoir. We evaluated the performance of MBO model by investigating: The effects of black-oil PVT table generation methods from a tuned equation-of-state, oil-gas ratio (OGR) and saturation pressure versus depth as initialization methods, uniform composition versus compositional gradient with depth, location of the completions, production and injection rates, kv/kh ratios, and vertical wells versus horizontal wells. Contrary to the common belief that OGR versus depth initialization gives better representation of original fluids in place, initializations with saturation pressure versus depth gave closer original fluids in place considering the true initial fluids in place are given by the fully compositional model initialized with compositional gradient. Unrealistic vaporization in the MBO model was encountered in both, production by natural depletion and gas cycling. The changes in oil-gas ratio of the recyled gas showed that, it is not possible to accurately represent the changing PVT properties of the recycled gas with a single PVT table. Unrealistic vaporization also led to different arrival times for the displacement fronts and different saturation profiles for the near wellbore area and for the entire reservoir for the two models even though the production performance of the models was in good agreement. The MBO model representation of compositional phenomena for a gas condensate reservoir proved to be adequate for full pressure maintenance, reduced vertical communication, vertical well with upper completions, and for horizontal well producers.
