Comparison of Cubic-Plus-Association and Perturbed-Chain Statistical Associating Fluid Theory Methods for Modeling Asphaltene Phase Behavior and Pressure–Volume–Temperature Properties

Abstract

The tendency of asphaltene, the heaviest and most polarizable component of crude oil, to deposit and block wellbores and pipelines can potentially lead to production loss and significant cost of remediation. Asphaltenes constitute a particular interest in oil production because of the lack of understanding of their molecular structure and the mechanisms by which they precipitate and deposit. Because prevention is far less expensive than removal, a better understanding of asphaltene precipitation and deposition phenomena is of great importance for the oil industry. Precipitation, which is a necessary but not sufficient condition for deposition, requires accurate modeling of asphaltene phase behavior with respect to variations in the temperature, pressure, and composition. Over the past decade, cubic-plus-association (CPA) and perturbed-chain statistical associating fluid theory (PC-SAFT) equations of state (EOSs) have been proposed for modeling complex systems, such as asphaltenic crude oils. In this work, a comparison between CPA and PC-SAFT EOSs is presented to illustrate their potential and limitations on the prediction of asphaltene phase behavior and pressure–volume–temperature (PVT) properties of crude oils over a range of pressures and temperatures. With an optimized characterization, both EOSs are able to give acceptable predictions of the phase behavior and asphaltene precipitation tendency. However, PC-SAFT is superior in the prediction of derivative thermodynamic properties, especially at high pressures.

A theoretically modified PC-SAFT equation of state for predicting asphaltene onset pressures at low temperatures

“…Nonetheless, from the cubic equations, the CPA (Cubic Plus Association) [95], [96], [98] stands out, in which the association term is based on Werthein's TPT; while from the SAFT family, the most used EoS to model the asphaltene phase behavior is undoubtedly the PC-SAFT EoS [50], either with or without the association contribution. Recently, articles have been published in the scientific literature focused on comparing the performance of PC-SAFT versus CPA for the modeling of hydrocarbon mixtures prone to asphaltene precipitation [93], [114], [115]. CPA has a theoretical consistency problem since the physical part-i.e., attractive, and repulsive-is taken from cubic EoS models, such as SRK [67] or Peng-Robinson [68] Naturally, the inclusion of an association term makes PC-SAFT a "heavier" model, computationally speaking.…”

“…Following Szewczyk and Béhar [83], calorimetric measurements of asphaltene flocculation enthalpies and compositional analysis support the idea that the asphaltene flocculation process, at reservoir conditions, is a thermodynamic transition from one liquid phase (crude oil) to another liquid phase (asphaltene rich phase). Knowledge of the physicochemical characteristics of phases present during the asphaltene precipitation process has promoted the development, use, and modification of many thermodynamic models (e.g., equations of state) for predicting asphaltene onset pressures (AOPs) [95], [96], [98], [111], [114], [116], [119], [120], [142], [143], [144]. For example, Chapman…”

The Phase Behavior of Heavy Oil and Propane Mixtures

“…These models are capable of predicting the full range of phase behavior but, until recently, have had limited success in predicting the amount of heavy phase in the LL region, as will be discussed in more detail later. Chapman and coworkers (Chapman et al, 1989;Ting et al, 2003;Gonzalez et al, 2005Gonzalez et al, , 2007Panuganti et al, 2012, Alhammadi et al, 2015 have modeled a range of petroleum phase behavior, including VL and LL boundaries, using the Perturbed Chain form of Statistical Association Fluid Theory (PC-SAFT). Kontogeorgis,…”

Modeling of asphaltene and water associations in petroleum reservoir fluids using cubic‐plus‐association EOS

“…Zhang et al also compared the CPA EOS with the EOS based on perturbed‐chain statistical association fluid theory (PC‐SAFT). AlHammadi et al stated that the CPA and PC‐SAFT EOSs gave reasonable predictions on the asphaltene onset pressures and precipitation. Arya et al presented that the CPA EOS was able to correlate the onset pressures of asphaltene, and asphaltene P‐T phase envelopes for different amounts of gas injection.…”