Fluid Topology in Pore Scale Two-Phase Flow Imaged by Synchrotron X-ray Microtomography

A flow experiment including drainage and imbibition by water and surfactant was performed on a water-wet Berea sandstone. The three-dimensional (3-D) pore scale changes of the fluid configuration were captured under flow using synchrotron X-ray computed microtomography. Euler characteristic of ganglia and connected pathway was calculated to study topology of these entities. In addition, Betti numbers and volumes of the ganglia and connected pathway were calculated to study their contribution in the flow. Results showed that Euler characteristic of the ganglia and the whole phase (ganglia plus connected pathway) versus saturation exhibited hysteresis in imbibition and drainage. However, the Euler characteristic of the connected pathway versus saturation had insignificant hysteresis in imbibition and drainage. Results of the Betti numbers and volume changes in nonwetting ganglia and connected pathway showed that the ganglia contributed to the flow by creating internal redundant connections, volume exchange with the connected pathway and saturation change. Further, the number of redundant connections in nonwetting connected pathway increased in drainage and decreased in imbibition, smoothly in both cases, with insignificant sensitivity to the changes in rate and interfacial tension.