Chemical transformation of asphaltenes during thermal upgrading of heavy and extra-heavy oils

Abstract

Steam based-thermal methods for improving oil recovery mainly includes steam injection, steam-assisted gravity drainage (SAGD) and cyclic steam injection (CSS). One of main goal of these methods is to achieve in-situ upgrading of heavy and extra-heavy oil. The high content of high-molecular compounds like asphaltenes is the one of main problems that is need to be solved during the process of the upgrading of heavy oils. Therefore, studying changes in the structure and properties of asphaltenes induced by thermal treatment is currently an important task aimed at searching for optimum technologies of upgrading of heavy and extra-heavy oils. In this study, upgrading experiments were carried out in a stainless-steel 500-ml batch Parr reactor (4575/76 HP/HT Reactor) equipped with a heating mantle and a temperature controller. In a typical experiment, the reactor was loaded with crude oil and water at a weight ratio of 1:3, respectively. The reactor was heated at 5°C/min to 250°C, generating a final pressure of approximately 450 psi for 10 h (29 psi initial N2 pressure). Four different heavy and extra-heavy oil obtained from different countries were investigated. The asphaltenes were precipitated using n-heptane from these oils before and after reaction. Then the properties of these obtained asphaltenes were analyzed. Generally with the help of Fourier Transform InfraRed FTIR spectroscopy,13 С NMR, EPR spectroscopy and SARA analysis before and after thermal treatment, we can concluded that, the amount of asphaltenes and resin is reduced after upgrading, whereas saturated and aromatic hydrocarbons increased, due to the destruction of its high molecular weight components. The results of this work indicate that using of 13C NMR spectroscopy to analyze asphaltenes can broaden the understanding of changing of its structure. And by FTIR spectroscopy we can evaluate that the aromaticity of asphaltenes decreases due to the destruction reactions of С=Сar bond and decomposition of aromatic rings.