Experimental Observations of Fluid Transport Across an Unsaturated Fracture-Intersection

Fluid behavior in unsaturated fracture intersections was experimentally investigated in a glass fracture analog at four different flow rates. Three fractures symmetrically intersected at a single point. One of the fractures (vertical) was used to feed fluid to the intersection area and the subsequent 135 degree branches. Visualization data was collected using digital stills and video. Two flow modes were observed: film flow and capillary droplet accompanied by snapping rivulets. Distribution of film flow across the intersection was not limited to contiguous rock surfaces. The formation of a capillary bridge above the intersection allowed films to be distributed to either branch or both branches. During capillary droplet mode, two types of dynamics were observed at the intersection: (1) saturation of the intersection with continuation of droplet mode into the fracture branches; and (2)transition from droplet to film flow mode that did not saturate the intersection and resulted in film flow along both branches. Data suggests that the contact angle of the invading droplet is responsible for the mode of transport across the intersection. Rivulets where seen to stretch contiguously across the intersection and into both branches while connected to two droplet halves, a distance of ~70 cm.