页岩储层原油赋存特征及CO_(2)-原油竞争吸附机制分子动力学

Molecular dynamics analysis on occurrence characteristics of shale oil and competitive adsorption mechanism of CO_(2) and oil

针对页岩油赋存状态特殊及CO_(2)提高采收率机制复杂等问题,依据Bakken页岩油藏原油组分及储层岩石成分,采用分子动力学方法建立原油组分及岩石壁面模型,模拟页岩储层原油赋存特征及CO_(2)-原油竞争吸附过程,分析不同原油组分的赋存特征以及原油组分、壁面润湿性、岩石成分对CO_(2)-原油竞争吸附的影响。结果表明:相对分子质量越小、分子结构越简单、分子间作用力越小,油膜浓度越高,分层越明显;分子间作用力对油分子运动能力起主导作用进而影响赋存特征;CO_(2)对油膜组分为n-C_(5)、n-C_(12)、n-C_(20)、吡啶、苯酚、丙硫醇的剥离程度分别为55.29%、23.05%、7.82%、31.36%、20.21%、35.32%;油湿壁面上CO_(2)对原油的剥离程度为30.50%,小于水湿壁面;不同壁面上的竞争吸附效果由好到坏依次为石英(55.29%)、高岭石(34.71%)、干酪根(26.60%);CO_(2)与纳米孔隙内页岩油作用过程分为3个阶段,CO_(2)溶解扩散、萃取原油阶段,CO_(2)与原油竞争吸附阶段,CO_(2)封存、油膜推离阶段。

The occurrence states of shale oil are specific and the mechanisms of CO_(2) injection for enhanced oil recovery(EOR)from shale oil reservoirs are complex.In this study,a crude oil composition model and a rock surface model were established in terms of molecular dynamics simulation based on the crude oil composition and reservoir rock composition of the Bakken shale oil reservoir.Subsequently,the occurrence characteristics of crude oil in shale reservoirs and the competitive adsorption process of CO_(2)-crude oil were simulated using the models,in which the occurrence characteristics of different crude oil components and the effect of crude oil components,rock surface wettability and rock composition on the competitive adsorption of CO_(2)-crude oil were analyzed.The simulation results show that higher oil film concentration and clearer stratification can be promoted by smaller molecular weight,simpler molecular structure and smaller intermolecular force.Intermolecular forces play a dominant role on the motility of oil molecules,thereby affecting the occurrence characteristics of crude oil.The stripping degrees of CO_(2) to the oil film components of n-C_(5),n-C_(12),n-C_(20),pyridine,phenol,and propanethiol are 55.29%,23.05%,7.82%,31.36%,20.21%and 35.32%,respectively.The stripping degree of CO_(2) to crude oil on oil-wet surface is 30.50%,less than that on water-wet surface.The competitive adsorption effects on different rock surfaces are of quartz(55.29%),kaolinite(34.71%)and kerogen(26.60%)in the order from strong to weak.The interaction between CO_(2) and shale oil in nanopores can be divided into three stages of CO_(2) dissolution/diffusion and crude oil extraction,CO_(2) and crude oil competitive adsorption,and CO_(2) storage and oil film pushing and striping.