【作者】 朱宁军；

【导师】 宋永臣；

【作者基本信息】 大连理工大学 ， 能源与环境工程， 2013， 博士

【摘要】 二氧化碳提高原油采收率(CO2-EOR)是改善全球环境和增加国内石油能源供给的重要技术。在CO2-EOR技术中,CO2与油的最小混相压力和在多孔介质中的渗流特性是影响油采收率的关键问题。传统的测试方法难以得到多孔介质内流体在相互作用区域的速度和过渡带面积,限制了数值模拟中这些参数的确定。本文开发了多孔介质中C02与油相态和渗流的核磁共振成像(MRI)和X射线CT可视化测量方法,开展了测量C02与油的最小混相压力、观测多孔介质内C02与油的相态变化和探明近混相驱替中C02与油的渗流特性等方面的实验研究。首先,根据MRI理论和油气混相原理,提出了测量油气最小混相压力(MMP)的MRI方法,建立了MRI实验系统,探索了MRI法测CO2与油MMP的可行性。定量测量了CO2/正烷烃体系MMP,建立了C02/正烷烃体系MMP的预测关系式,获得了CO2/正烷烃体系MMP与平均含碳量的关系。同时观测了C02/正烷烃体系在PVT筒中的相态变化,结果显示：压力升高,CO2/正癸烷体系气液界面按半球形、碟形、平面到消失依次变化；两相接触角增大,同时液相体积增大,在接近MMP时膨胀剧烈。建立了多孔介质内X射线CT相态变化测试系统,直接观测了填砂多孔介质内CO2/正癸烷体系相态随压力的变化。研究发现：孔隙越小,气液灰度差减小的趋势越缓慢,多孔介质减小了油气相互扩散的速度,实验证明了多孔介质对C02/正癸烷体系的最小混相压力的影响,多孔介质的粒径越小,体系最小混相压力越高。系统地研究了CO2与正癸烷在单管、并联管以及填砂和砂岩岩心等多孔介质中的近混相渗流特性。阐明了多孔介质内C02与正癸烷两相过渡区域速度和面积随压力的变化规律,为油气藏开采的数值模拟研究中参数的确定提供了有力的实验基础。在单管和并联管中,发现了只有当注气速度大于临界注气速度时,C02与油的界面才能向驱替方向推进。在填砂模型中,CO2与油的过渡区域面积随着压力的升高逐减小,并在压力大于等于MMP时减小为一薄层；过渡区域的速度与体积速度的比值随着压力的增大而趋向于一定值。在人造岩心中,正癸烷驱替效率的拐点对应压力略大于体系在PVT筒中的MMP,进一步证明了多孔介质对CO2/正癸烷体系的最小混相压力的影响；驱替前沿速度与体积速度比值随压力变化趋于一定值,该定值与渗透率正相关；油气混相后流动性增大、同时在岩心渗透率各向异性等多种因素的作用下,流体产生明显的指进现象,实验值与指进长度的估算值相符。更多还原

【Abstract】 Carbon dioxide enhanced oil recovery (CO2-EOR) is the important technique for the global environment improvement and domestic oil energy supply increasement. It is the key for CO2-EOR to study on the phase state change and seepage characteristics of CO2/oil system in porous media. Nevertheness, for the fluids invisibility in porous media, the phase state and seepage parameters can not be measured precisely. Therefore, Magnetic Resonance Imaging (MRI) and X-ray CT were applied for visualization measurement of the phase state change and seepage characteristics of CO2/oil system, based on the traditional minimum miscibility pressure (MMP) measuring methods.According to MRI theory and gas/oil miscible principle, MRI technique was proposed in this study for determination of the MMP. MRI technique was verified by comparing the MMP values with those obtained by traditional methods. The MMP of CO2/n-decane system was modeling. The correlation between MMPs of CO2/n-alkane and the average carbon number was obtained. The results presented that the interface pattern was hemispherical at normal pressure and then changed from dish like to flat as pressure increased, and at last disappeared. The contact angle of the two phases and the volume of liquid phase enlarged as pressure increased.The phase state of CO2/n-decane system in glass bead packed column was visualized by using X-ray CT. In bulk fluid, the gray values of the images are proportional to the fluid densities. Mutual solubilities of CO2/n-decane system were calculated by modified PR EOS. In the porous media, the the gray values difference between the gas and liquid phases reduces as the pore scale decreases, which indicates a delay diffusion process and larger MMP of CO2/n-decane system.Near miscible displacement of CO2/n-decane in the single and parallel narrow channels, glass bead packed column and synthetic sandstone cores were conducted. In the single and parallel narrow channel, the injection rate should be concrolled more than a critical value to ensure the migration velocity of the interface of CO2and oil more than the oil expansion velocity. In the glass bead packed column, the transition zone area of the two phases decreases with the growing pressure. The ratio of the velocities of the transition zone and the "volumetric front" grows with the increaseing pressure to a certain value. In the synthetic sandstone cores, the recovery efficiency increases with the larger injection rate in the same permeablity cores. The cross pressure of the fit line of the recovery efficiency is larger than the MMP. Also, the ratio between the velocities of the transition zone and the " volumetric front" grows with the increaseing pressure to a certain value which increases with the permeability. Fingering performs during the miscible displacement because of the fluids properties, small permeability, large ratio between the diameter and the length of the core, along with the small ratio between the diameter of inlet/outlet and the core. The wavelength values estimated are just in good agreement with the experimentally observation values.更多还原