fluid under pressure through conduit 14 into the fracture by way of perforation 16 the foamed treating fluid which is selected can have a specific gravity less than or substantially the same as the specific gravity of the foamed preflush fluid the foamed treating fluid enters fracture 10 and flows through channel 18 to fill the upper portion of fracture 10 in order to achieve separation and segregation of the foamed fluids in the fracture the specific gravity of the treatment fluid preferably is at least 0 03 less than the specific gravity of the foamed preflush fluid at the conditions existing within the formation most preferably foamed treatment fluids are utilized having a specific gravity at least about 0 1 less than the foamed preflush fluid at the conditions in the formation when the present method is utilized to effect fracture acidizing the treating fluid can comprise aqueous acid solutions having specific gravities in the range of from about 1 02 to about 1 34 at room temperature particularly preferred aqueous acid solutions comprise hydrochloric acid or hydrochloric acid organic acid mixtures such as for example hydrochloric acid acetic acid mixtures the aqueous acid solution is foamed prior to introduction into fracture 10 in the same manner as the preflush fluid as is well understood by those skilled in the art the foamed acid treating fluid is moved through channel 18 while fracture 10 is maintained in an open position by fluid pressure exerted thereon so that the fracture can be extended and high capacity flow channels can be etched in the upper faces of the open fracture the acid can be moved through channel 10 by pumping a foamed overflush fluid into the formation that is approximately the same specific gravity as the foamed acid treating.