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A soft computing method for rapid phase behavior calculations in fluid flow simulations

Gaganis V., Marinakis D., Samnioti A.

To describe the flow of hydrocarbons in the reservoir and in pipelines upstream petroleum engineers utilize compositional simulation models which allow for the accurate description of complex phase behavior phenomena by means of EoS models and detailed compositional characterization. To speed up the conventional time-consuming phase stability and phase split calculations, soft computing has been recently utilized by means of methods such as proxy models and on-the-fly tabulation of phase behavior results.

In this work, a new soft computing pressure-explicit, adaptive interpolation technique is presented which allows for the direct, offline, non-iterative estimation of fluid specific equilibrium coefficients values as functions of the conditions prevailing during the process to be modeled. The so calculated equilibrium coefficients allow for the rapid determination of the number, composition and properties of the phases present in every cell and at every timestep by means of the Rachford-Rice equation, thus greatly reducing the CPU time required for phase equilibrium calculations. Moreover, the proposed method guarantees continuous first and second order phase properties derivatives with respect to p and T. The method is applicable to any type of EoS including the SRK and the PR ones.

The method is fully applicable to depletion projects of all types of oil and gas condensates. Additionally, it can be used for the history matching of the past depletion phase of oil and gas reservoirs before the initiation of EOR projects such as acid or sour gas injection as well as before dry gas reinjection in gas condensate reservoirs.

Journal of Petroleum Science and Engineering. 2021, 205