Nonequilibrium Phase Behavior of Condensate Gas Flow in Porous Media.

The description and quantification of condensate gas flow in porous media are often inadequate when considering nonequilibrium phase behavior. This study presents a systematic approach that integrates experimental research with advanced mathematical techniques. A pressure depletion test conducted on a long core demonstrates that a higher condensate recovery can be achieved with faster pressure drop rates. A novel mathematical nonequilibrium compositional model, which is based on kinetic interphase mass transfer between gas and oil phases, was developed. This model accurately captures dynamic changes in the interface area between phases and corrects nonequilibrium thermodynamic equations. It can seamlessly transition between equilibrium and nonequilibrium phase behavior during two-phase flow in porous media. The model exhibits deviations of less than 5% from experimental results for condensate recovery and gas-oil ratio predictions when comparing pressure drop rates of 2.5 and 5 MPa/h. Its predictions closely match experimental data, showing a superior accuracy over the standard equilibrium model. The characteristic phase behavior parameters, such as condensate saturation and pseudocomponent composition, are highly sensitive to pressure drop rate, highlighting the nonequilibrium model's ability to address condensate hysteresis. This study provides a solid theoretical foundation for reservoir simulations of the pressure depletion process in condensate gas reservoirs and other scenarios involving nonequilibrium subsurface fluid flow and recovery.