Macroscopic Experiment Study and Microscopic Molecular Simulation of Adsorption Interaction between Heavy Asphaltene and Shale Illite

Internal adsorption of heavy asphaltene in the shale reservoir can affect shale oil recovery due to the significant impact on oil fluidity. In this work, the adsorption interaction of asphaltene on shale Illite was investigated by both macroscopic experiment and microscopic simulation. Through batch-type and equilibrium adsorption experiments, the results indicated that the interaction process followed the thermodynamic Langmuir-monolayer model with a maximum adsorption amount of qmax = 19.43 mg/g and the kinetic pseudo-second-order (PSO) chemisorption model with an adsorption rate of kPSO = 0.37 g/(mg·h). Through molecular dynamics (MD) simulation, the microscopic adsorption properties were studied for different asphaltene configurations of archipelago, c5pe, and island. The simulation results revealed that archipelago-type asphaltene had the lowest adsorption energy of Eads (archipelago) = -2086.58 kcal/mol and showed the strongest adsorption ability with Illite, which was brought by the steric hindrance reduction through an "upright-insertion" interaction pattern. Furthermore, interaction forces were analyzed to produce between asphaltene and Illite for different asphaltene concentrations. For the lower concentration stage, van der Waals forces, hydrogen bonding interactions, and coordination interactions were revealed for the asphaltene adsorption. For the higher concentration stage, the additional π-π interactions were revealed between asphaltene molecules, which were brought by the polycyclic aromatic hydrocarbon structure and resulted in the agglomeration phenomenon. The multiple interaction forces result in strong and abundant adsorption of asphaltene with Illite. This work provides critical insights into the adsorption study between heavy oil and shale clay, which is of great significance for the recovery enhancement of shale oil.