Static Evolution and Flow Characteristics of Foam in Fractures

Foam has been widely used in enhanced oil recovery (EOR) in recent years. Its flow and propagation within fractures play a pivotal role in mitigating the channelling issues arising from reservoir heterogeneity. In this work, two visual fracture models were designed to simulate the in situ generation, static evolution, and propagation of foam in fractures. The effects of the gas holdup and fracture surface roughness on the number and shape of bubbles were investigated. The influences of foam quality, fracture surface roughness, and fracture aperture on foam propagation and volume changes during the flow process were systematically analysed. The results indicated that increasing the fracture surface roughness promoted the in situ generation of bubbles. With increasing gas holdup, the average diameter and relative volume of the bubbles gradually increased and then decreased. In particular, when the gas holdup was greater than 80 %, the bubble changed more obviously. Within fractures, bubbles underwent continuous drainage, coarsening, and coalescence, leading to a transition in foam shape from regular spherical to irregular polyhedral, accompanied by the gradual thinning of the liquid film until rupture. However, the foam occupied a larger volume within the fracture than before. From top to bottom along the fracture vertical direction, due to significant gravity, the foam quality increased and the foam mobility increased gradually, exhibiting low-flow velocity foam, high-flow velocity foam, and a liquid phase. The liquid drainage rates of foam were low and the area occupied by foam in the fracture expanded as the foam quality increased, surface roughness increased and the fracture aperture narrowed. This phenomenon was significant for expanding the foam propagation in fractures.