Advances in the Flory–Huggins–Zuo Equation of State for Asphaltene Gradients and Formation Evaluation

Abstract

Recent advances in the understanding of the molecular and colloidal structure of asphaltenes in crude oils are codified in the Yen–Mullins model of asphaltenes. The Yen–Mullins model has enabled the development of the industry’s first asphaltene equation of state for predicting asphaltene concentration gradients in oil reservoirs, the Flory–Huggins–Zuo equation of state (FHZ EOS). The FHZ EOS is built by adding gravitational forces onto the existing Flory–Huggins regular solution model that has been used widely to model the phase behavior of asphaltene precipitation in the oil and gas industry. For reservoir crude oils with a low gas/oil ratio (GOR), the FHZ EOS reduces predominantly to a simple form, the gravity term only, and for mobile heavy oil, the gravity term simply uses asphaltene clusters. The FHZ EOS has successfully been employed to estimate the concentration gradients of asphaltenes and/or heavy ends in different crude oil columns around the world, thus evaluating the reservoir connectivity, w...