岩心微流动的核磁共振可视化研究

摘要

岩心微流动可视化是研究化学驱油微观机理的一项重要流体实验新方法，重点介绍采用低场核磁共振成像技术研究天然岩心中流体分布可视化的新进展。提出和分析了国产低场核磁共振成像岩心驱替装置面临的图像不清、材料干扰等问题，通过合理选材、优化参数，从硬件和软件2方面进行了改进与优化，消除了干扰因素。开展了天然岩心的驱替实验，采集了油水的实时 NMR信号与 MRI 成像信号，以及不同驱替阶段油水的 NMR-T2谱，得到分辨率较高的油水分布图像。结果显示残余油随着驱替PV数的增加而减少，具有初期减少明显而后趋缓的特点，并发现岩心中存在端部油残滞现象，其范围距端部4mm左右。研究了通过获得的油水分布图像计算含油饱和度的方法，其结果与传统方法一致，误差在10%以内，这也说明了油水分布图像的可靠性。这不仅为计算饱和度提供了一种新方法，而且该方法的另一个优势是可以分析任意局部位置的油水饱和度。研究结果表明，在研究岩心微流动过程中流体分布的可视化方面，核磁共振成像技术是值得深入研究的新方法。%Core micro flow visualization is an important method to study the microcosmic mechanism of the chemical flooding.The latest results of core micro flow visualization by MRI technology in our research group was introduced in detail.Some questions on low field MRI core displacement system (MRICDS)were put forward,and improvement and optimization were made from the two aspects of hardware and software to eliminate interference factors.The exper-iments of fluid image test during water-flooding process were successfully carried out using the improved MRICDS.The real-time signals of NMR and MRI of the oil-water distribution during the flow test were collected,and NMR-T2 spectrums and oil or water distribution images were obtained in different stages.The images with high resolution can meet the request of visually an-alyzing the fluid distribution in the core.Experimental results show that residual oil decreases with PV increasing.The trendline of oil distribution drops rapidly first and then slowly.Images also show the phenomenon of residual oil gathering in the end area in core flow tests and its influ-ence range is about 4mm from the end.A new method of oil saturation by the oil-water distribu-tion map of MRI was introduced,and its results are consistent with that of the traditional method and the error is within 10%.This also shows that the reliability of the oil-water distribution map.This provides a new method for the study of oil saturation.Especially the other advantage of the method is that it can analyze the oil-water saturation at any local position.The results also indicate that the new method of MRI is worthy of further development for fluid distribution visu-alization during core micro flow.