Reconstruction of realistic kerogen molecular models in shale oil and gas reservoirs: the physicochemical inversion method

Abstract

In recent years, unconventional energy resources such as shale oil and gas reservoirs have attracted lots of attention. Kerogen serves as both the parent material and a critical reservoir medium for shale oil and gas. Its microstructure determines mechano-chemical properties, which significantly influence hydrocarbon generation and transport within shale. However, traditional methods for reconstructing kerogen molecules might contain some unreasonable bonds and focus predominantly on monomeric structures, neglecting the heterogeneous distribution of molecular masses in realistic kerogen groups. To address the limitations, we propose the physicochemical inversion method (PIM). Through pyrolysis experiments, we clarified the rules of kerogen pyrolysis and obtained structural information on pyrolysis products. PIM incorporates pyrolysis mechanisms into the reconstruction workflow of the molecular group model. Thereby, the new method can establish more reasonable bonding between the small molecule products and the residues combining multiple spectral information and bond dissociation energy data. Guided by PIM, a kerogen molecular group of 16 macromolecules has been reconstructed. Its carbon skeleton aligns closely with the experimental ¹³C nuclear magnetic resonance spectrum, and the products yielded from pyrolysis simulations correspond with experiments. The reconstructed model captures features of mining area kerogen, and its molecular mass distribution follows an approximately unimodal distribution. PIM can be extended to the reconstruction of kerogen, coal, and asphaltene molecular models, offering a theoretical foundation for studying the pyrolysis and transport mechanisms of organic matter within shale.