When running sector models, it is often impractical to include every hydraulic fracture stage within the simulation grid. External fractures provide a way to approximate the stress shadow from previous stages located outside the model domain.
Each external fracture is defined by its geometry — either as height, length, and net pressure, or as a fracture volume and net pressure (in which case the simulator assumes a radial shape and calculates the equivalent radius). The Sneddon solution is used to compute the stress field around each external fracture, and these stresses are added to the simulation.
External fractures should be placed at locations outside the simulation grid. They do not participate in fluid flow; their sole purpose is to capture the mechanical stress shadow that would otherwise be absent from the model.