原油-CO_(2)相互作用机理分子动力学模拟研究

Molecular dynamics simulation on interaction mechanisms of crude oil and CO_(2)

CO_(2)的众多驱油机理已经被广泛认同,但受油藏因素影响,不同油藏条件下CO_(2)驱的效果差异较大。因此,需要进一步深化研究CO_(2)与原油的微观相互作用机理,明确不同油藏条件下CO_(2)的驱油方式,最大限度挖潜CO_(2)驱的潜力。利用分子动力学模拟方法研究了组分、温度、压力对油滴-CO_(2)相互作用的影响。求取动力学参数,量化表征油滴-CO_(2)间的相互作用,厘清了不同条件下二者的微观相互作用规律。模拟结果显示,色散力是主导CO_(2)-烷烃分子相互作用的主要作用能,二者相互作用主要包含两方面:一是CO_(2)分子克服烷烃分子间的位阻作用向油滴内部溶解扩散,二是CO_(2)分子对油滴外层分子的萃取吸引作用。随着烷烃分子链长减小、温度降低和压力增加,油滴溶解度参数和CO_(2)配位数增加,油滴外层分子的弯曲度减小,二者的相互作用增强。研究结果认为,在温度较低、压力较高的轻质和中轻质油藏中,应尽可能地实现CO_(2)混相驱和近混相驱,在温度较高、压力较低的中质和重质油藏中,应充分发挥CO_(2)非混相驱的溶解降黏、膨胀原油体积和补充能量的优势。研究结果能够为室内研究和现场实施CO_(2)驱油提供理论指导。

Numerous oil displacing mechanisms of CO_(2) have been widely recognized,but due to reservoir factors,the effectiveness of CO_(2) flooding varies significantly under different reservoir conditions.It is necessary to further deepen the research on the microinteraction mechanisms between CO_(2) and crude oil,clarify the CO_(2) flooding mode under different reservoir conditions,and maximize the potential of CO_(2) flooding.Molecular dynamics simulation methods have been used to study the effects of components,temperature,and pressure on the interaction between oil droplets and CO_(2).The kinetic parameters were obtained to quantitatively characterize the oil droplets-CO_(2) interaction,clarifying the micro-interaction patterns under different conditions.The simulation results show that the dispersion force is the the main driving force of the interaction between CO_(2) and alkane molecules,which mainly includes two aspects:one is the dissolution and diffusion of CO_(2) molecules into the oil droplets by overcoming the steric hindrance between alkane molecules,and the other is the extraction attraction of CO_(2) molecules to the outer layer molecules of the oil droplets.As the chain length of alkane molecules decreases,the temperature decreases and the pressure increases,the solubility parameter of the oil droplets and the coordination number of CO_(2) increase,the curvature of the molecules in the outer layer of the oil droplets decreases,and the interaction between the two is enhanced.It is concluded that CO_(2) miscible and near-miscible flooding should be realised as much as possible in light and medium-light reservoirs with lower temperatures and higher pressures,while in medium and heavy reservoirs with higher temperatures and lower pressures,the advantages of CO_(2) non-miscible flooding in terms of dissolution viscosity reduction,crude oil volume expansion and energy replenishment should be fully exploited.The study results can provide theoretical guidance for laboratorial research and field application of CO_(2) flooding.