An experimental investigation into surface roughness of a hydraulic fracture

The fracture surface roughness is an essential characteristic of the hydraulic fracturing process and has not been fully explored. The surface asperities play a significant role in proppant flow and settlement, fluid leak-off and fracture tip movement. In this study, we performed an experimental investigation to evaluate the fracture surface roughness of a hydraulic fracture generated in the lab tests. The experiments were conducted using a polyaxial cell and a cuboid siltstone block with dimensions of 20 cm × 20 cm × 16.5 cm. The fracturing fluid was injected into a drilled hole in the specimen to initiate and propagate the hydraulic fracture in nearly homogeneous siltstone material. Low injection rates were applied to all lab tests to maintain slow and stable fracture propagation as in the field. The fracture surfaces were digitised by surface mapping techniques utilising high-resolution laser scanning method and analysed using a standard statistical way. Our results showed that the surface topography and roughness parameters are different in various selected segments. However, they follow an increasing trend in radial directions from the initiation point at the wellbore wall toward the specimen borders.