Shale Asphaltene Nanostructure and Gas Preservation: A Molecular-Level Structure–Function Relationship and Predictive Modeling

The molecular structure of shale asphaltenes plays a crucial role in gas adsorption and preservation. This study integrates multitechnique characterization (SEM, X-ray diffraction (XRD), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), UV, NMR, gel permeation chromatography (GPC)) with molecular simulations to elucidate the structure–function relationship between asphaltene nanostructure and shale gas retention. The constructed molecular models were rigorously validated against experimental density, XRD interlayer spacing, and NMR aromaticity before the simulation. We identified asphaltenes with high aromaticity, moderate aliphatic content, and limited polar functional groups (notably sulfones) that exhibit enhanced methane adsorption. This is primarily governed by optimized van der Waals (vdW) interactions and favorable nanopore connectivity. Key molecular parameters─interaction energy, cohesive energy density (CED), and free volume fraction─were incorporated into a novel quantitative predictive model for shale gas content (Y′ = −0.235Z1 – 0.198Z2 + 0.127Z3 + 0.342Z4 – 0.186Z5). The model demonstrates excellent predictive capability (R2 = 0.96, RMSE = 0.12 m3/t). Furthermore, we introduced a nanostructure complexity index (NCI), integrating aromatic stacking, heteroatom distribution, and pore connectivity, which shows a strong positive correlation with the gas content (r = 0.89). The novelty of this work lies in establishing a microstructure-based predictive framework that moves beyond traditional bulk parameters like TOC, providing a molecular-level tool for assessing shale gas preservation potential based on core-derived asphaltene properties.