This document is an expanded abstract.

Summary

A new approach based on the statistical associating fluid theory (SAFT) is presented here to model eight light crudes, with the SARA analysis as the only input for the model. Within the characterization procedure of Punnapala and Vargas (2013), the aromaticity parameter and the asphaltene molecular weight were fixed to all crude oil samples, while the asphaltene aromaticity is the only fitted parameter of the model. A correlation for this parameter with the flashed gas molecular weight allows full predictions of the phase behavior without the need of any asphaltene onset data. The predictive molecular model was used to study asphaltene instability as a function of injected CO2 and natural gas concentration. The model can also accurately reproduce routine PVT experiments such as constant composition expansion, differential vaporization and multi-stage separation tests performed on the crude oils, thereby providing a unified framework for phase behavior studies.

Introduction

Asphaltenes are defined as fossil fuel derived constituents that are insoluble at ambient conditions in large excess of light hydrocarbons such as n-pentane and n-heptane and soluble in toluene. Their exact chemical structure vary from one crude oil to another, but in general, they are known to be the heaviest and the most polar fraction of crude oil consisting of polyaromatic molecules surrounded by aliphatic and heteroatomic chains.

Asphaltene deposition can occur during different stages of production and processing due to changes in pressure, temperature and composition. Oilfield reports indicate that asphaltene deposition in a well can lead to complete cease of fluid flow and production. Moreover, the cost of a typical asphaltene remediation job can get as high as $500,000 onshore or $3,000,000 offshore. Downstream wise, asphaltene deposition can cause fouling in rotating equipment and plug tubing and flow lines.

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