Residual CO2 trapping in oil-wet sandstone

CO2 geo‐sequestration in oil reservoirs is an economically attractive solution as it can be combined with enhanced oil recovery (CO2‐EOR). However, the effectiveness of the associated three‐phase displacement processes has not been tested at the micrometer pore‐scale, which determines the overall reservoir‐scale fluid dynamics and thus CO2‐EOR project success. We thus imaged such displacement processes in‐situ in 3D with x‐ray micro‐computed tomography at high resolution at reservoir conditions, and found that oil extraction was enhanced substantially, while a significant residual CO2 saturation (13.5 %) could be achieved in oil‐wet rock. Statistics of the residual CO2 and oil clusters are also provided, they are similar to what is found in analogue two‐phase systems although some details are different, and displacement processes are significantly more complex.

油藏中的二氧化碳地质封存（CO2 geo-sequestration）是一项具备经济吸引力的解决方案，因其可与CO₂强化采油（CO2-EOR）技术相结合。然而，相关三相驱替过程的有效性尚未在微米级孔隙尺度下得到验证——而孔隙尺度的流动特性决定了油藏尺度的整体流体动力学行为，进而直接影响CO2-EOR项目的成败。为此，本研究在油藏条件下，采用高分辨率X射线显微计算机断层扫描（X-ray micro-computed tomography）对该三维原位驱替过程进行了成像观测，结果发现原油采收率得到显著提升，同时在亲油岩石中可实现13.5%的可观二氧化碳残余饱和度。本研究同时提供了残余二氧化碳与油簇的统计特征数据：尽管部分细节存在差异，但这些统计结果与类似两相系统中观测到的特征相近，且驱替过程的复杂程度显著更高。