Abstract
Numerical models widely used for hydrocarbon phase behavior and compositional flow simulations are based on assumption of thermodynamic equilibrium. However, it is not uncommon for oil and gas-condensate reservoirs to exhibit essentially non-equilibrium phase behavior, e.g., in the processes of secondary recovery after pressure depletion below saturation pressure, or during gas injection, or for condensate evaporation at low pressures. In many cases, the ability to match field data with equilibrium model depends on simulation scale. The only method to account for non-equilibrium phase behavior adopted by the majority of flow simulators is the option of limited rate of gas dissolution (condensate evaporation) in black oil models. For compositional simulations, no practical yet thermodynamically consistent method has been presented so far except for some upscaling techniques in gas injection problems. Previously reported academic non-equilibrium formulations have a common drawback of doubling the number of flow equations and unknowns compared with the equilibrium formulation. In the paper, a unified thermodynamically consistent formulation for compositional flow simulations with non-equilibrium phase behavior model is presented. Same formulation and a special scale-up technique can be used for upscaling of an equilibrium or non-equilibrium model to a coarse-scale non-equilibrium model. A number of test cases for real oil and gas-condensate mixtures are given. Model implementation specifics in a flow simulator are discussed and illustrated with test simulations. A non-equilibrium constant volume depletion algorithm is presented to simulate condensate recovery at low pressures in gas-condensate reservoirs. Results of satisfactory model matching to field data are reported and discussed.
Highlights
Compositional equation-of-state (EOS) flow simulations are essential for oil and gascondensate reservoirs with intensive interphase mass transfer
We present formulation for the non-equilibrium phase behavior model suitable both for compositional flow simulations, upscaling and stand-alone phase behavior simulations
The unified formulation is first derived in terms of the non-equilibrium phase behavior model for compositional simulations suitable to be incorporated in existing generalpurpose EOS-based implementations without principal modifications to flow simulation algorithms
Summary
Compositional equation-of-state (EOS) flow simulations are essential for oil and gascondensate reservoirs with intensive interphase mass transfer. Limited number of studies introduce non-equilibrium phase transitions in compositional flow simulation models [26, 32] Those models are not straightforward to implement as an extension over existing numerical codes for the equilibrium case. The most significant factor not necessarily associated with the influence of porous media is the limited area of interphase contact which hinders components' mass transfer between phases In this case, scale factor is of great importance in phase behavior and compositional flow simulations. The unified formulation is first derived in terms of the non-equilibrium phase behavior model for compositional simulations suitable to be incorporated in existing generalpurpose EOS-based implementations without principal modifications to flow simulation algorithms. We show how the unified non-equilibrium formulation can be used for simulation of condensate revaporization at low pressures using a non-equilibrium constant volume depletion (NCVD) algorithm verified with a real gas-condensate field case
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.