二甲醚作为一种重要的溶剂,在溶剂与蒸汽共注提高稠油采收率技术中具有良好前景。针对二甲醚在稠油中扩散行为和分布特性不明确的问题,建立了C6—C30不同碳数的油相与二甲醚的体系模型,并通过分子动力学模拟计算了二甲醚在油相中的配位数、扩散系数以及两相的密度分布、相互作用能等关键参数,研究二甲醚在原油组分中的扩散规律。研究表明:随着碳数的增加,烷烃和二甲醚分子的密度呈不均匀分布,二甲醚分子周围的烷烃分子数量减少;在温度为120 ℃、压力为5 MPa条件下,二甲醚-C6和二甲醚-C30体系中二甲醚的扩散系数分别为2.19×10-8 m2/s和1.10×10-8 m2/s,随着碳数的增加,烷烃和二甲醚的扩散系数逐渐降低,这是烷烃分子尺寸增大和形状复杂化所致。在范德华力主导的影响下,烷烃与二甲醚相互作用能的绝对值先增加后降低;随着碳数的降低,油与二甲醚界面的质量传递速率提高,更多的二甲醚溶于油中,原油体积膨胀且黏度降低,油田开发效果显著提升。该研究可为优化二甲醚在油田现场中的应用提供理论支持。
Dimethyl ether,an important solvent,shows promising potential in the technology of co-injection of solvent and steam to enhance heavy oil recovery.In order to address the issue of unclear diffusion behavior and distribution characteristics of dimethyl ether in heavy oil,a system model is established for C6-C30 oil phase and dimethyl ether with varying carbon num-bers.Molecular dynamics simulation is used to calculate the coordination number,diffusion co-efficient,density distribution,and interaction energy of dimethyl ether in the oil phase.The study aims to investigate the diffusion law of dimethyl ether in crude oil components.The results indicate that as the carbon number increases,the density distribution of alkanes and dimethyl ether molecules becomes uneven,resulting in a decrease in the number of alkanes surrounding dimethyl ether molecules.At 120 ℃ and 5 MPa,the diffusion coefficients of dimethyl ether in dimethyl ether-C6 and dimethyl ether-C30 systems are 2.19×10-8 m2/s and 1.10×10-8 m2/s,respectively.The diffusion coefficients of alkanes and dimethyl ether gradually decreased with an increase in carbon number,which can be attributed to the increase in molecular size and complexity of shape of alkanes.Under the influence of Van der Waals force,the interaction energy between alkanes and dimethyl ether initially increases and then decreases.As the carbon number decreases,the mass transfer rate at the oil-dimethyl ether contact increases,resulting in greater dissolution of dimethyl ether in the oil.This leads to an expansion in the volume of crude oil and a decrease in viscosity,resulting in a significant improvement in oilfield development.This study provides theoretical support for optimizing the application of dimethyl ether in the oilfield,and has important implications for future research in this area.
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