Accurate characterization of the CO2-oil mixtures phase behavior will be advantageous for CO2 enhanced oil recovery (EOR) and reservoir production design for CO2 geologic storage projects. Relevant properties which include density, oil swelling factor, solubility and minimum miscibility pressure (MMP) of CO2-oil are typically measured in the laboratory using the conventional time-consuming pressure-volume-temperature (PVT) method. In this study, the phase behavior of CO2-oil mixtures was characterized inside a porous medium at reservoir temperature and pressure using nuclear magnetic resonance imaging (MRI). This research method realizes direct observation and in situ measurement compared with PVT method, effectively reducing the experimental operating pressure and the pressure-loading limit of the measurement equipment. The CO2-oil mixture equilibrium pressures correlated exponentially with the corresponding proton density (M0) and relaxation rates (1/T1, 1/T2); thus, the MRI multiparameter method was first applied to estimate MMP by only measuring several equilibrium pressure points and extrapolating to zero. The CO2 solubility and saturated liquid density linearly decreased as 1/ T1 increased but linearly increased as 1/T2 increased, which indicates that these parameters can be estimated based on the magnetic resonance (MR) relaxation rates. The results demonstrate the remarkable advantage and feasibility of applying MRI techniques for in situ measuring of the physical properties of fluids in porous media within the laboratory.

The gas-liquid diffusion coefficient is of great significance to accurately evaluate the efficiency of CO 2 displacement (CO 2 -EOR) or the long-term geological storage of CO 2 .It is necessary to carry out in-depth theoretical and experimental studies on the gas-liquid diffusion mechanism in porous media.Based on low-field nuclear magnetic resonance technology, the diffusion process of CO 2 in n-hexadecane saturated porous media was dynamically monitored.The one-dimensional proton density curve of the liquid phase changing with time and position during the diffusion process was obtained by using pure phase coded SE-SPI pulse sequence.The concentration distribution of CO 2 in the liquid phase could be obtained according to the relationship between the proton density curve and concentration.Based on Fick's law, a mathematical solution model was established, and the non-iterative finite volume method is used to calculate the CO 2 diffusion coefficient that changes with time and position, compared with the pressure attenuation method, the results were in the same order of magnitude and the error was small, which proved the feasibility and accuracy of monitoring gas-liquid diffusion process by low-field nuclear magnetic resonance technology.This provides an in-situ and rapid method for measuring the gas-liquid diffusion coefficient, which is of great significance for the design and economic evaluation of CO 2 -EOR engineering.

将CO2注入地下油藏,可以实现提高原油采收率与CO2地下永久埋存的"双赢",是最具应用前景和经济效益的"碳中和"有效手段之一.为了有效评价CO2驱油效率,以及准确预测CO2地质埋存量与长期安全性,必须对多孔介质中CO2-油扩散机理进行深入的理论和实验研究.该文利用低场磁共振(NMR)技术实现CO2-油扩散过程的原位动态监测,通过纯相位编码SE-SPI脉冲序列得到溶液随时间和位置变化的一维质子密度曲线,进而得到油相膨胀系数、CO2无量纲浓度等参数;基于菲克第二定律构建了考虑溶液体积膨胀的物理模型,采用非迭代有限体积法计算得到随时间和位置变化的CO2扩散系数,为多孔介质内气-液扩散参数原位测量提供了重要的理论方法与实验数据,对CO2提高石油采收率与地质埋存工程设计、安全性和经济性评价具有重要指导意义.

天然气水合物资源开采过程中涉及多孔介质内固(水合物)-液(水)-气(天然气)复杂相态转变及多相流体流动与热质传递,因此实现多相流体的相分辨是开展研究的关键问题之一.利用Micro-CT技术,以四氢呋喃水合物(THF)作为研究对象,开展了固(水合物)-液(水)两相分辨的造影剂效果评价研究.发现溶液内添加造影剂KI的分辨效果要远好于NaCl,KI的分辨效果随着质量分数的增加先增加后减小,最后处于较低值维持不变,KI质量分数为6％时分辨效果最好,可以实现多孔介质内小密度差的水与水合物相分辨及水合物分解过程相界面变化的动态可视化检测.基于此,利用阈值法可以进一步实现分解过程中水合物饱和度的定量分析,获取多相流动过程的各相流体原位饱和度变化数据.

能源与环境工程专业是伴随我国经济高速增长所面临的能源紧缺和"碳达峰""碳中和"环境压力问题的双重挑战而设立的战略性新兴学科专业.针对专业课程涵盖领域广泛的特点,从自身特色和优势出发,将先进的低场核磁共振仪器以及自主研发的实验装置成果转化到本科基础和创新实验教学中,主要开展"流体弛豫时间与扩散系数测量""多孔介质孔隙度测量""油水相分辨实验""两相流体渗流实验""水合物生成与分解实验"等系列实验项目,培养学生掌握最前沿的科学分析仪器的使用能力,锻炼学生从科研的角度来思考、设计、观察、总结实验项目,并加强独立的分析和解决问题的能力,满足社会对"研究型、创新型"高素质综合人才的需求.

Gas hydrates are widely considered as promising candidates for gas storage, energy transportation and seawater desalination. Critical to such applications is a detailed 3D understanding of hydrate formation. To this end, we employ magnetic resonance imaging (MRI) to non-invasively image the gradual formation of opaque hydrate from CO2 and water in a cylindrical vessel at 1 degrees C and as a function of pressure between 2.0 and 3.5 MPa. A 200 mu m thick dense hydrate layer is consistently observed to form at the gas-water interface accompanied by a similar to 1.4 mm thick porous hydrate layer above it and frequently complex dendritic hydrate formation in the water phase below it. Dissociation is observed to occur preferentially via the thick hydrate layer with the initial hydrate film retained largely intact for an extended period of time. The sequential images of hydrate dissociation inside the water phase are most consistent with a vertical heat and mass transfer controlled hydrate dissociation process. The observed difference between the hydrates formed above and inside the water phase is of mechanistic value in understanding these complex interfacial phase transitions.

CO2 storage in marine hydrates has a high gas storage capacity and long-term storage stability, which has attracted extensive research interest in the field of greenhouse gas (GHG) reduction. The dependence of CO2 hydrate formation properties on the reservoir environment in high-efficiency storage methods should be examined to determine suitable hydrate-based techniques. In this study, the nuclear magnetic resonance (NMR) technique was employed to analyze the hydrate distribution and phase transition process. Hydrates form a solid phase, which results in the T2 relaxation time. The T2 curve in large pores shifts to the left. Several parameters, including the initial water saturation, CO2 formation pressure and temperature, and the application of chemical additives (SiO2 nanoparticles, SDS and their mixtures) were analyzed. A high initial water saturation and suitable temperatures and pressures in marine sediments were found to be conducive to high-efficiency CO2 storage. Regardless of the used additive, the bound water in relatively small pores remained almost unchanged, and the free-water content in large pores linearly decreased with increasing hydrate saturation. Compared to pure seawater, the optimal kinetics additive content was 0.15 wt% SiO2 nanoparticles in 8-hour tests, which improved the water conversion percentage, GHG migration and CO2 storage efficiency by 49.2%, 41.30% and 4.17%, respectively. These results provide greater insights into the hydrate-based CO2 storage in marine sediments and contribute to potential kinetic additive applications.