The dynamic Flory-Huggins-Zuo equation of state

•Asphaltene nanostructures codified in the Yen-Mullins model.•Downhole fluid analysis measures reservoir fluid gradients.•Flory-Huggins-Zuo EoS models asphaltene gradients in reservoir crude oils.•Dynamic FHZ EoS for modeling reservoirs undergoing dynamic processes.

In recent years, the FHZ EoS (Flory-Huggins-Zuo equation of state) has been developed to model asphaltene gradients in reservoir crude oils. Resolution of the nanostructures of asphaltenes in crude as given by the Yen-Mullins model has enabled the explicit form of the gravity (and other) terms in the FHZ EoS. In addition, the recent development of accurate in-situ measurements of crude oil gradients in oil wells has motivated the need for thermodynamic modeling of asphaltene gradients. Many oil reservoirs exhibit thermodynamically equilibrated crude oils which are accurately represented by the FHZ EoS. Nevertheless, there are many reservoirs that are undergoing dynamic processes in geologic time. Consequently, time must be explicitly included in the FHZ EoS. The dynamic FHZ EoS is developed within a generalized formalism herein. Specific application of this formalism to diffusive dynamical processes is derived and corresponding simulations are shown. Extension of the dynamic FHZ EoS to other time-dependent processes of geologic importance is discussed.