吉木萨尔页岩油注气相态物性变化特征实验研究

Experimental study on the variation characteristics of phase physical properties of Jimsar shale oil gas injection

为探索不同注入气体对页岩油的相态行为及物性变化特征,综合利用高温高压PVT物理模拟实验系统及气相色谱,开展了减氧空气(含氧量10%)、空气、CO_(2)的注气膨胀实验研究,通过实时监测不同油气体系相态行为的变化情况,分析了不同注入气对地层油体系饱和压力、膨胀系数、黏度和密度等物性参数的影响。结果表明,不同注入气体对于地层油的相态行为及物性影响存在显著差异。向页岩储层注入空气,可与原油接触,发生低温氧化反应,空气含氧量越高低温氧化作用越强,越有助于气相溶解至油相中,体系饱和压力越低;注入CO_(2)时,易与原油产生较好的混相作用进而可增强气体的溶解性。受限于较高的溶解饱和压力,高含氧量空气与减氧空气的膨胀系数相差不大,但高含氧量空气的降黏效果较明显,CO_(2)可在压差和扩散作用下进入原油内部,抽提萃取强度更大,膨胀降黏效果最好。高含氧量空气与原油接触时,可产生质量交换,使得轻质组分萃取至气相中,加速重质组分占比升高,原油密度逐渐增大。CO_(2)对于低碳组分的强抽提作用可促使原油轻质组分向重质组分转化,进而导致原油密度上升的幅度更大,注CO_(2)开发有望成为页岩油提高采收率并兼顾埋存的有效途径。该研究成果可为页岩储层注气的高效开发提供借鉴。

To explore the phase behavior and physical property change characteristics of shale oil with different injected gases,the gas injection expansion experiments of oxygen-reducing air(10%oxygen content),air,and CO_(2)were carried out by using high-temperature and high-pressure PVT physical simulation experiment system and gas chromatography.By real-time monitoring of the changes in phase behavior of different oil and gas systems,the effects of different injected gases on the physical parameters such as saturation pressure,expansion coefficient,viscosity,and density of the formation oil system were analyzed.The results show that the effects of different injected gases on the phase behavior and physical properties of formation oil are significantly different.Low-temperature oxidation(LTO)reaction can occur when air is injected into shale reservoirs in contact with crude oil.The higher the oxygen content in the air,the stronger the low-temperature oxidation,the more conducive to the dissolution of the gas phase into the oil phase,and the lower the saturation pressure of the system.When CO_(2)is injected,it is easy to produce a better miscible effect with crude oil,which can enhance the solubility of the gas.Limited by the higher saturation pressure of dissolution,the expansion coefficient of high oxygen-content air is not much different from that of oxygen-reducing air,but the viscosity reduction effect of high oxygen-content air is more obvious.CO_(2)Can enter the crude oil under the action of pressure difference and diffusion,and the extraction strength is greater,and the effect of expansion and viscosity reduction is the best.When high oxygen-content air contacts with crude oil,the mass exchange can be generated to extract light components into the gas phase,which accelerates the increase of heavy component proportion and crude oil density.The strong extraction effect of CO_(2)on low-carbon components can promote the conversion of light components to heavy components,which results in a greater increase in crude oil density.CO_(2)Injection development is expected to be an effective way to improve shale oil recovery and consider storage.This study can provide a reference for the efficient development of gas injection in shale reservoirs.