Fracture aperture is the perpendicular width of an open fracture. However, this definition does not capture the reality of fracture wall roughness, gouge, degree of mineral infill and lateral continuity. For these reasons it is difficult to truly determine a fracture aperture within a rock body. In quantifying flow through fractures, apertures can be detailed in terms of the flow character of equivalent parallel plates, leading to a hydraulic aperture term.
As flow through open fractures is a function of the cube of the aperture width, large open fractures are very important within a reservoir. Resistivity imaging tools can allow estimates to be made of fracture aperture. Resistivity imaging devices emit a current that is distorted and concentrated around a fracture filled by conductive drilling mud. This excess current is a function of the fracture width, so knowing this for a given fracture and the tool response it is possible to calculate a fracture aperture. Even when these calculations are influenced by mineral fills, wall spalling and other factors it is still possible to obtain a ranking of fracture widths.
LUTHI, S. M. 2000. Geological Well Logs, Springer, Berlin, p373.