Adsorption and Aggregation Mechanism Study of Heavy Component Resin at Illite Surface in Shale Reservoir:...

The adsorption interaction of heavy components at a mineral surface can reduce the flowability of shale oil and decrease the recovery of shale oil. In this work, the heavy component resin was separated from crude oil, and the adsorption and aggregation interactions at shale Illite surfaces were systematically studied from experimental and theoretical insights. Thermodynamic results indicated the Redlich-Peterson model (R² = 0.990) with the maximum adsorption amount of q_m = 6.19 mg/g, reflecting a composite of monolayer resin adsorption and Illite surface heterogeneity. Kinetic results indicated the pseudo-second-order model with the maximum adsorption rate of 31.48 h^-1, reflecting a chemical domination of resin interaction at the Illite surface. With 170-times increasement for diffusion rate (k_dif) but only 30-times increasement for aggregation rate (k_agg), the 'fast diffusion-slow aggregation' processes were also analyzed for low and high resin concentration stages on the Illite surface. For a theoretical calculation, density functional theory elucidated the 'lying-down' configuration of molecular resin with interaction energy of -1.68 eV. A molecular dynamic simulation obtained the binding energy results of E_bin = -113.31 ∼ -1571.71 kcal/mol for 1-20 resin molecules. As a result, the interaction forces were deduced by combining the experimental and theoretical results, including hydrogen bonding (resin H-Illite O), cation-π interactions (resin aromatic structure-Illite K⁺), electrostatic adsorption (resin S-Illite K⁺), and coordination interaction (resin S-Illite Al, Si). The additional π-π interactions were produced between resin molecules for high resin concentration interaction. This work can clarify the microscopic interactions of heavy components at the surface of shale reservoir, which can effectively reveal the occurrence pattern of shale oil and improve oil recovery.