Layered Threshold Pressure of Tight Oil in Nanopores: A Molecular Dynamics Simulation Study

S Wang and J Wang and HQ Zhang and S Chen and SY Yin and HQ Liu and ZS Wang, ENERGY & FUELS, 37, 10235-10247 (2023).

DOI: 10.1021/acs.energyfuels.3c01255

Nanoscale pores are widely developed in tight oil, andthe scaleeffect significantly affects the dynamic behavior of crude oil moleculesat different positions in the nanopores. The molecular dynamics simulationmethod was used to study the mechanism of threshold pressure of tightoil molecules at different positions in quartz and calcite nanoporesand the influence of pore radius on threshold pressure. The resultsshow that the mobilizing of crude oil molecules at different positionsin nanopores is mainly affected by liquid-solid interactionsand intermolecular friction. The interactions between naphthenic acidsand pore walls are the main contributing factor to the threshold pressureof boundary crude oil molecules. Van der Waals interaction and weakhydrogen bonds mainly contribute to the bonding of naphthenic acidswith quartz walls, and strong electrostatic interaction and stronghydrogen mainly contribute to that with calcite walls. Except forthe boundary layer, the threshold pressure of other layers relatesto the interactions between saturated hydrocarbon, aromatic hydrocarbon,and adjacent layers as well as the molecular friction, among whichfriction between the saturated hydrocarbon and the adjacent moleculesis dominant. It is challenging for crude oil to mobilize in quartzpores smaller than 3 nm. However, when the quartz pore width exceeds7 nm, the mobilizing law of crude oil is scarcely affected by thepore width. The mobilizing laws of crude oil differ in calcite poressmaller than 11 nm, while that stays nearly the same in pores largerthan 11 nm. Finally, a prediction model for the threshold pressureof tight oil molecules at different positions in quartz and calcitenanopores is proposed, which provides theoretical guidance for precisecontrol of working fluid properties to improve tight oil recovery.

Return to Publications page