Measurement of Width and Pressure in a Propagating Hydraulic Fracture

Measurements of width and pressure in a propagating hydraulic fracture have been made in tests conducted at the U.S. DOE's Nevada test site. This was accomplished by creating an "instrumented fracture" at a tunnel complex (at a depth of 1,400 ft [425 m]) where realistic in-situ conditions prevail, particularly with respect to stress and geologic features such as natural fractures and material anisotropy. Analyses of these data show that the pressure drop along the fracture length is much larger than predicted by viscous theory, which currently is used in models. This apparently is caused by the tortuosity of the fracture path, multiple fracture strands, roughness, and sharp turns (corners) in the flow path resulting from natural fractures and rock property variations. It suggests that fracture design models need to be updated to include a more realistic friction factor so that fracture lengths are not overestimated.