Study on the swelling of macromolecular geological organic matter with hydrocarbons and heteroatomic compounds

Abstract

In this study, we conducted swelling experiments on eleven macromolecular geological organic materials using five types of organic solvents. Our primary objective was to investigate the absorption capacity of different solid organic materials in organic fluids and analyze the influence of their chemical structures. The samples utilized in this research included solid bitumen, kerogen, and coal samples from various basins. The chemical structure of the samples was assessed using solid-state ¹³C nuclear magnetic resonance (NMR), while X-ray diffraction (XRD) was employed to monitor any detect the structural changes during the swelling process. Our findings reveal that macromolecular geological organic compounds demonstrate a preferential expulsion of saturated hydrocarbons, followed by polycyclic aromatic hydrocarbons, upon interaction with liquid organic matter. The sulfur-containing compounds in solid organic matter demonstrated higher solubility than hydrocarbon compounds, while the solubility of oxygen-containing compounds varied based on the structure of the aliphatic chain and the proportion of oxygen atoms. This research, introduces LA [= L_ac × A_ac] as a new parameter to assess the combination of aliphatic chain length [L_ac] and [A_ac] abundance in solid organic matter. Furthermore, XRD testing revealed that the chemical structure unit of heteroatom compounds in solid organic matter consists of amorphous carbon, primarily composed of aliphatic chains. In this study, we evaluated the retention capacity of various macromolecular geological organic matter for both hydrocarbons and heteroatomic compounds. Additionally, the extent of swelling was investigated, providing theoretical support to diverse fields including organic petrology, petroleum geology, coal geology, and organic geochemistry.