Three-Dimensional Structure of a Huadian Oil Shale Kerogen Model: An Experimental and Theoretical Study

Abstract

The molecular structural information on a kerogen isolated from Huadian oil shale was obtained using solid-state 13 C nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR), and X-ray diffraction (XRD) techniques. Then, a series of Huadian kerogen isomers were constructed on the basis of these structural data. The possible carbon skeleton isomer and the substituted position effects of the aromatic ring, aliphatic ether bond, carboxylic acid, and carboxylic acid derivative as well as the quantity of tertiary and quaternary carbons on Huadian kerogen model stability have been systematically studied on the basis of density functional theory (DFT) calculations. For the carbon skeleton isomer, the calculated total energy decreases with the increasing number of the closed annular space (grid), which is constituted by connecting the aliphatic chain to the aromatic cluster or other aliphatic chain. DFT calculations show an about 16.8 kcal mol −1 decrease in total energy for every grid increase when the number of grids increases from 2 to 11. A significant break in the decrease of the total energy has been obtained for an isomer with 11 grids, which means that a proper number of grids (11 grids is appropriate in this paper) in carbon skeleton should be considered for building the chemical structure of Huadian kerogen. For the substituted position effects, aliphatic ether bonding to quaternary carbon, carboxylic acid attaching to secondary carbon, and carboxylic acid derivative bonding to quaternary carbon seem to give a lower energy structure than other connections. Besides, a high quantity of tertiary and quaternary carbons is conducive to a stable model for Huadian kerogen. The aromatic cluster dispersed distribution also makes a contribution to improve the stability of the model. According to these results, we proposed a relatively stable Huadian kerogen three-dimensional (3D) model. Moreover, this 3D model was testified reasonablely through the match between calculated and experimental 13 C NMR spectra.

Evaluation of the porous structure of Huadian oil shale during pyrolysis using multiple approaches

“…That means the organic carbon content is 31.5%. Guan et al [27] reported that the ratio of hydrogen and carbon of Huadian kerogen is 1.55, which is the type I field and also reported by Sun et al [28]. One would expect a semi-coke yield is about 25% of the kerogen carbon.…”

Study on the Adsorption, Diffusion and Permeation Selectivity of Shale Gas in Organics

“…Falk et al [50] utilized CS1000 and CS1000a as organic structures by using the Configuration-Bias Monte Carlo (CBMC) and MD to simulate the adsorption characteristics of long-chain paraffins on it at the actual temperature of the reservoir and it's the adsorption characteristic curve satisfied with the Langmuir isothermal adsorption model. Guan, et al [51] analyzed the molecular structure information of Huadian oil shale and established the kerogen molecular structure by using NMR, X-ray photoelectron spectroscopy, Fourier transform infrared and a X ray diffraction experiment testing technique combined with DFT. Sui et al [52] established the 3D structure of kerogen II and analyzed the pore size distribution (PSD) of this structure.…”

Molecular Dynamics Study of Transport and Storage of Methane in Kerogen

“…Two approaches have been used to create 3D models from 2D models. First approach considers quantum mechanics calculations, such Gaussian optimization, for finding the most stable conformation (global maxima) (Guan et al, 2015). This approach is not realistic for large systems (more than 500 atoms) (Dupuis et al, 1989;Heller, 2006).…”