致密油压后渗吸分子动力学模拟

在渗吸采油过程里,致密油储层微纳米孔隙中流体的吸附散和运移行为难以通过常规实验手段来描述。采用分子动力学模拟研究在不同温度、不同时间下渗吸过程中原油从孔道置换的现象和致密油自身的赋存状态,并分析分子间的作用机制。模拟结果表明,原油的自身扩散能力和压裂液剥离能力是导致原油被置换出孔道的两种现象“析出”和“剥离”的原因。烷烃自扩散能力导致“析出”少量的游离态原油会在升温的影响下产生微弱增加,而由于压裂液对原油的配位数接近于1说明油水两相混相,大量的原油成油带状被“剥离”出孔道,剩下孔道内吸附态的原油随着温度的提升逐渐减少,并且从范德华力的角度解释原油对岩石表面的吸附是从远离压裂液一端率先发生。此外也揭示了压裂液中内部组分和岩石表面的羟基结合生成氢键和隔绝分子层使原油剥离的机理。此研究结果全面深刻的从分子尺度探究了压裂液/致密烷/纳米级孔道体系下渗吸驱油机理,对致密油开发具有指导意义。

Molecular Dynamics Simulation of Spontaneous Percolation of Tight Oil after Pressure

In the process of imbibition recovery, the adsorption and migration behavior of fluid in micro and nano pores of tight oil reservoir is difficult to be described by conventional experimental methods.Molecular dynamics simulations were used to study the displacement of crude oil from the pore channel and the state of crude oil itself during the percolation process at different temperatures and times, and to analyze the intermolecular mechanism of action. The simulation results show that the self-diffusion ability of crude oil and the stripping ability of fracturing fluid are the causes of two phenomena, "precipitation" and "stripping", which lead to the replacement of crude oil out of the pore channel. The alkane self-diffusion ability leads to the "precipitation" of a small amount of free crude oil that increases slightly under the influence of warming, while a large amount of crude oil is "stripped" out of the pore in the form of oil strips due to the fact that the coordination number of fracturing fluid to crude oil is close to 1, indicating that the oil and water phases are mixed, leaving The adsorbed crude oil in the pore channel gradually decreases with the increase of temperature, and the adsorption of crude oil on the rock surface is explained from the van der Waals force point of view as occurring first from the end away from the fracturing fluid. In addition, the mechanism of hydrogen bonding between the internal components of the fracturing fluid and the hydroxyl groups on the rock surface and the isolation of the molecular layer to strip the crude oil is also revealed.The results of this study comprehensively and profoundly explored the imbibition displacement mechanism of fracturing fluid/densified alkane/nanoscale pore system from the molecular scale, which has guiding significance for tight oil development.