Fluid flow through rough-walled rock fractures with hydrophobic surfaces

The effect of hydrophobic properties of surfaces on fluid flow was investigated through water flow experiments using rough-walled rock fractures. At low Reynolds number (Re < 10), the slip caused by drag reduction at hydrophobic rough-walled surfaces produced larger water flow than for fractures bounded by hydrophilic surfaces. The occurrence of drag reduction was only limited to the linear flow regime. An increased flow velocity due to slip made the flow nonlinearity stronger as the flow became nonlinear, which caused the smaller flow rate through the fracture with hydrophobic surfaces than that with hydrophilic surfaces. Results showed that the drag reduction of 7.92% at Re = 0.64 was changed to apparent drag enhancement of 8.92% at Re = 185 for the creosote-wetted rough-walled fracture. This changeover phenomenon was more pronounced with increasing the roughness of the fracture surfaces. This study implied a dependence of the operation efficiency on surface wettability and flow regime for DNAPL recovery from fractured bedrock and oil recovery or the sequestration of carbon dioxide in fractured petroleum reservoirs.