Ball sealers

A method is described for using ball sealers as a diverting agent when treating a subterranean formation penetrated by a well provided with casing having perforations at a plurality of levels. Ball sealers sized to plug a perforation, a first fluid having a density greater than the ball sealers and a second fluid less dense than the ball sealers are introduced into the casing concurrently or in any order. The amount of the first fluid introduced should be sufficient to fill the lower portion of the casing to a level between the lower perforations to be plugged and the upper perforations to be left open to fluid flow. Once the ball sealers are disposed below the upper perforations, treating fluid is injected into the casing to cause a flow of the second fluid through the lower perforations to carry the ball sealers down the casing to plug the lower perforations and to cause fluid flow through the upper perforation which the ball sealers did not plug.