two spaced apart zones of a formation are simultaneously hydraulically fractured . a lower density fracturing fluid is injected into an upper zone of the formation via an annulus of a perforated wellbore communicating with the upper zone thereby causing a fracture to propagate . simultaneously therewith , a higher density fracturing fluid is injected into a lower spaced apart zone via a tube within the wellbore which fluidly communicates with the lower zone thereby causing simultaneously the propagation of a second fracture . neither fracture contacts the other although complete fracture growth is obtained .