Analysis of the microstructure of high viscosity components in Tahe ultra heavy oil based on the combination of ESI (±) FT-ICR/MS

Abstract

In addressing the challenge of high viscosity in Xinjiang Tahe heavy oil, crucial for optimizing extraction processes, this study focuses on identifying and analyzing the microstructure of key components influencing oil viscosity. The aim is to uncover the underlying reasons for its high viscosity and guide research towards effective viscosity reduction techniques. Electrospray ionization (ESI) combined with fourier transform ion cyclotron resonance mass spectrometry (FT-ICR/MS) characterizes the molecular-level constituents contributing to oil viscosity. The investigation covers the composition and distribution of oxygen-containing, nitrogen-containing, and organometallic compounds, developing a molecular structure model for these critical viscosity-inducing components. Findings reveal Xinjiang Tahe extra heavy oil as a solid mass at room temperature, with significant viscosity reduction observed post-deasphalting, highlighting asphaltenes' pivotal role in viscosity. Analysis indicates a higher content of metal elements (such as V and Ni) in asphaltenes compared to the crude oil itself, with an abundance of porphyrin structures in asphaltenes markedly influencing oil viscosity. Cyclic, aromatic, and unsaturated compound structures are predominantly found in the asphaltenes of heavy oil. Through combined ESI (±) FT-ICR/MS analysis, the crude oil is determined to mainly comprise acidic compounds, non-basic nitrogen compounds, and basic nitrogen compounds, offering significant insight into heavy oil's complex chemical composition. Specifically, non-basic nitrogen compounds in Tahe crude oil, including alkylcarbazoles, alkylbenzocarbazoles, and alkylpolybenzocarbazoles, are identified as key components, with molecular carbon numbers ranging from C12 to C56 and a predominance near C27. Additionally, asphaltenes in Tahe heavy oil exhibit a higher double bond equivalence (DBE) than the crude oil, indicating a greater degree of condensation with an increased number of double bonds and heterocyclic structures. The significant difference in DBE values between asphaltenes and crude oil underscores their impact on viscosity. A detailed molecular structure model of the asphaltenes in Tahe extra heavy oil has been constructed based on FT-ICR/MS analysis, providing a foundational understanding for developing viscosity reduction strategies.