Pore-scale dynamics and the multiphase Darcy law

A pore-scale experimental investigation of microscopic steady-state flow during co-injection from very low to high flow rates in the pore space of a sandstone is applied using 4D synchrotron X-ray micro-tomography to advance our understanding of flow regimes. We report the results of micro-CT imaging experiments directly visualizing the simultaneous flow of both a wetting and a non-wetting fluid through a Bentheimer sandstone, at pore-scale resolution. For small flow rates, both fluids flow through unchanging, distinct, bicontinuous 3D pathways. At higher flow rates, however, the non-wetting fluid continually breaks up into discrete ganglia; these are then advected through the medium. We propose that the non-wetting fluid breaks up when the sum of the viscous forces exerted by the wetting and the non-wetting fluids exceed the capillary forces at the pore scale.本研究采用4D同步辐射X射线显微断层扫描（4D synchrotron X-ray micro-tomography）技术，针对砂岩孔隙空间内共注入过程中从极低到极高流速下的微观稳态流动开展孔隙尺度实验，以深化对流动模态的理解。本研究报道了显微CT成像实验的结果：该实验以孔隙尺度分辨率直接可视化了润湿相流体与非润湿相流体同时流经本泰默砂岩（Bentheimer sandstone）的流动过程。当流速较小时，两种流体均沿稳定不变、界限分明的双连续三维通道流动；然而当流速升高时，非润湿相流体会持续破碎为离散的流体团簇，随后这些团簇会在多孔介质中被对流输运。我们提出：当润湿相与非润湿相流体所施加的粘性力之和超过孔隙尺度下的毛细作用力时，非润湿相流体会发生破碎。