The paper presents efficient implementation of the non-equilibrium phase transitions model in compositional simulator. Reservoir non-equilibrium phase behavior effects are examined and simulated with the new approach.
Compositional simulators are widely used for modeling light oil reservoirs, gas injection projects, and gas-condensate reservoirs. Some features for modeling phase transition hysteresis are implemented in black oil simulators, but not in compositional simulators. Though some non-equilibrium phase transition models for compositional simulators were reported in the literature, they were not implemented in industrial simulators because of their complexity. A new physical-based approach is presented in this paper. Modifications for this model are required only to the thermodynamic block of a simulator. All equations and matrix structures for the hydrodynamic (flow) block are not modified.
The new approach is implemented as an extension block in a general purpose reservoir simulator. Implementation of the feature allows to model effects of phase transition hysteresis in compositional simulations. Criterion for determining phase transition type (equilibrium or non-equilibrium) is justified and also implemented.
The application of the new option requires minimum additional input data, which is good for history matching problems. The new approach is tested with numerical cases based on real reservoir data.
The paper argues in favor of the need to adjust pVT properties of the hydrocarbon system and apply non-equilibrium models of phase transitions for purposes of upscaling and history-matching flow simulation models (FSMs) to actual production data. Since most of FSMs are based on the Black Oil model, it features prominently in the paper.
The paper considers certain information from laboratory experiments and production data that points to non-equilibrium phase transitions in the in-situ hydrocarbon mix. Provided are also the results of numerical experiments demonstrating the need for upscaling the fluids' pVT properties, and evidence of non-equilibrium effects from the enlarged size of cells in the FSM computational grid. In conclusion, the paper considers capabilities of various commercial flow simulators and new approaches to simulation of non-equilibrium phase behavior effects in the Black Oil model.
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