Molecular Dynamics Study on Mechanism of Preformed Particle Gel Transporting Through Nanopores: Deformation and Dehydration

摘要

Understanding the translocation mechanism of preformed particle gel (PPG) through the nanoporous medium is crucial for gel treatment during enhanced oil recovery. On the basis of nonequilibrium molecular dynamics simulation, the translocation process of PPG in silica nanopores consisting of two different diameters was investigated. During the simulation, an external pulling force was applied to PPG representing the injection pressure. The simulation results suggest that a synergetic deformation and dehydration of PPG occurs during the translocation from the wide side into the narrow side. The energy barrier of the translocation process mainly result from the conformational energy change of PPG (mainly from the angle bend and dihedral torsion) and the dissociation energy barrier between PPG's hydrophilic groups and water. Furthermore, the nanopore size has a crucial impact on the translocation mechanism of PPG, not only the degree of the deformation and dehydration near the entrance, but also the translocation mechanism after they entered the nanopore. For a nanopore with a large diameter, PPG can reabsorb water to induce a complete hydration layer around it after entry. However, for the nanopore with a small size, the compression from the pore restricts PPG's rehydration ability. Without the screen and lubrication of the hydration layer, the pulling force needed to drive PPG increased rapidly, which means a larger injection pressure in the macroscopic view. The findings are helpfid for understanding the translocation process of PPG in points media on molecular level and, also, will facilitate technology developments for enhancement of recovery efficiency of petroleum.