Molecular Dynamics Study Of Fluid Migration Behavior Under Shale Reservoir Conditions

Shale oil,as an important unconventional energy source,has become the focus of global energy exploration and development.Traditional research methods are limited by experimental instruments and sample processing techniques,making it difficult to explore the displacement mechanism of shale oil in reservoirs at the nanoscale.Therefore,researchers have begun to use simulation-based research methods to study microscopic-scale flow.In this work,molecular dynamics(MD)simulation method was used to investigate the initiation and migration of shale oil in nanochannels,and to explore the influencing factors and microscopic mechanisms of dynamic oil displacement processes.This not only provides theoretical guidance for the exploration and development of shale oil,but also promotes the application of basic theoretical issues such as microscopic flow.The research content of this thesis is divided into three parts:1.Study on the mechanism of oil displacement in different shale nano-pores of shale oil reservoirs:In this part,mainly explore the occurrence and migration behavior of shale oil in three types of shale nanopores:kaolinite,calcite,and silica.The results show that shale oil is distributed symmetrically along the central axis in the pores,but its distribution along the pore direction is non-uniform.The influence of different shale surfaces on the displacement of shale oil is significant.Shale oil migrates faster in kaolinite and calcite pores,while in silica pores,it is displaced in an up-and-down alternating manner.Further research has shown that van der Waals interaction is the primary interaction between fluids and solid surfaces,and the wettability of shale surface is an important factor affecting the displacement behavior of shale oil.2.Analysis of factors affecting the enhanced oil recovery of water-flooded shale oil reservoirs:This study used molecular dynamics simulation to investigate the impact of reservoir physical conditions on shale oil displacement,and provided a theoretical explanation for the behavior of shale oil displacement at the molecular level.The study also explored the law of starting pressure gradient in shale oil reservoirs.The results showed that pore size and temperature had a small impact on shale oil displacement in the high-alumina clay and calcite system,but had a significant impact on the silica system.Combining the calculation results of interfacial tension and starting pressure gradient,it was proved that wettability and pore size were important factors affecting the starting pressure gradient of shale systems.3.Study on the displacement law of surfactant shale oil by tail chain branching degree:Molecular dynamics simulations were conducted to investigate the adsorption behavior of tailbranched molecules at the oil/water interface and their impact on the non-equilibrium oil displacement process.The results indicate that tail branching favors the reduction of interfacial tension at the oil/water interface,leading to an increase in interfacial thickness and more uniform coverage.Additionally,the addition of surfactants facilitates the displacement of shale oil,and tail branching improves the oil displacement rate and utilization efficiency of surfactants.