【作者】 赵越超；

【导师】 宋永臣；

【作者基本信息】 大连理工大学 ， 能源与环境工程， 2011， 博士

【摘要】 温室气体减排和能源的稳定供给是当今世界经济发展所面临的两个重大问题。开展CO2地质埋存与提高石油采收率的基础研究具有重要的理论和现实意义。本研究应用MRI技术分别得到了填砂、人造岩心和天然岩心等多孔介质试样的孔隙结构分布图像,并实现了量化分析,测量的岩心平均孔隙度结果与常规方法基本吻合,在“孔群级”尺度上清楚地观察到岩心内部的孔隙变化和非均质性特征,应用统计学方法,对不同截面上测量的孔隙度分布进行分析与表征。当多孔介质中油峰和水峰的谱线可以明显分开时,利用化学位移选择自旋回波成像法来实现多孔介质中油、水两相流体饱和度的定量分析是可行的。亲水天然储层砂岩岩心自发逆向渗析过程中,靠毛细管力作用的不平衡性,小孔隙吸水,大孔隙排油。渗析过程达到平衡后,剩余油主要被圈闭在大孔隙中,低孔隙区采收率比高孔隙区高。对地质埋存过程的C02在含水多孔介质内的两次运移过程研究发现,CO2从填砂底部注入后,由于浮力作用,窜流现象非常明显,CO2沿渗透性较高的某些孔隙通道迅速向上突破窜流,一旦窜流通道形成后,后续C02将一直沿着该通道窜流,波及范围很小。从填砂顶部注入C02,窜流现象减弱,驱替前缘分布不规律,波及范围较大。驱替前缘在整个填充管内基本保持匀速推进。利用MRI技术实现了对多孔介质内CO2驱油过程中的各相流体赋存位置变化、粘性指进、重力超覆和窜流现象,以及C02前缘及混相区的形成、发展及运移过程的动态可视化监测；并可通过MRI信号对驱替过程中各相流体的饱和度进行量化分析；可以确定驱替过程中各相流体的饱和度分布和采收率,与常规方法结果误差在10%以内。经过分析含油饱和度曲线的规律,可以确定驱替前缘的推进速度,应用岩心分析方法对MRI获得的多孔介质内“原位”饱和度数据进行分析,得到了多孔介质内各相流体的局部达西相速度,并对驱替过程中毛细管力、粘度及重力的影响进行了评估。超临界CO2混相驱的最终采收率比气态CO2非混相驱显著提高。束缚水的存在对驱替过程中饱和度变化规律影响不大。采收率除了受润湿性和孔隙度影响,还受到填充模型的孔隙结构及孔隙分布的均匀性的影响。对于中等偏亲油岩心的宏观均质人造岩心,水驱后注入超临界CO2混相驱,可进一步提高采收率。储层宏观平面非均质性和垂直裂缝的存在会导致CO2混相驱采收率下降较大,但驱替结束后,除裂缝外,残余油分布较均匀,说明CO2扫油波及范围较均匀,受岩心结构非均质性影响不大。更多还原

【Abstract】 Greenhouse gases emission reduction and energy demand are the two significant issues for the world economy development. Thus, research on the CO2 geological sequestration and enhancing oil recovery is of great theoretical and realistic significance.In this study, quantitative analysis had been realized using MRI technique to obtain the pore structure distribution images of sand pack, artificial core and natural core, respectively. The measurement results of average core porosity based on MRI method agreed well with The measurement results based on the conventional material balance method. The porosity distributions and heterogeneity of those cores were observed clearly in the level of "pore group". The observed porosities at different section were analyzed and characterized quantitatively with the statistics method.It can quantitatively analyze the saturation of oil and water using chemical shift selective spin echo imaging sequence if the peaks of oil and water in porous media can be obviously distinguished.The water was imbibed through small pores and low permeability layer, at the same time, the oil was expelled through large pores and high permeability layer due to the effect of capillary forces during the spontaneous counter-current imbibition process in the water-wet natural reservoir sandstone core. When the imbibition process approaches the equilibrium, the residual oil is mainly trapped in large pores, while the recovery is higher in the small pores area than in the large pore area.Two CO2 migration processes in porous media saturated with water were visualized using the MRI technique. CO2 injection from the bottom caused obvious CO2 channeling along some high permeability parts of the core caused by buoyancy. Once the channeling formed, the CO2 followed along the channels and have no impact on the residual water. When the CO2 was injected from the upper side, the phenomenon of CO2 channeling weakened, but the CO2 front profile was irregular. The velocity of the CO2 front was uniform and the distribution curve of the water saturation in the FOV was regular.During CO2 flooding process, the phenomenon, such as onset of viscous fingering, gravity override, CO2 channelling, and the formation, progress and migration of the piston-like miscible regions and CO2 front can be visually detected using MRI technique.In addition, The measurement results of oil saturation based on MRI method were agreed well with the results based on conventional material balance method, the error rate for the MRI method was less than 10%, Through the analysis of the oil saturation profile, the velocity of the CO2 front has been evaluated. A special core analysis method was applied to in situ oil saturation data to directly evaluate the local Darcy phase velocity of the fluids, and the effect of viscosity, buoyancy, and capillary pressure on CO2 miscible displacement.CO2 miscible displacement enhance oil recovery evidently more than CO2 immiscible displacement. The irreducible water can scarcely change the oil saturation curves. Recovery rate can be determined by wettability, porosity, structure of the sand pack and the homogeneousness of the pore distribution. For the slightly oil-wet homogeneous artificial core plug, CO2 miscible displacement can enhance oil recovery after the water flooding. The heterogeneous of the reservoir and the vertically oriented fracture have a great influence on the oil recovery seriously in three stacked core plugs. Lower permeability causes lower recovery rate. When the displacement finishes, the residual oil spatial distribution is homogeneous in every piece of core.更多还原