a method for re - fracturing of wells having perforated casing that were previously fractured is provided . the method employs degradable ball sealers having a density near that of the injection fluid such that high seating efficiency of balls on perforations is attained . the balls degrade at varying rates , so that some intervals are opened for fracturing while other intervals are still blocked by ball sealers . after fracturing of an interval , the interval may by shut - off by ball sealers that degrade at a much slower rate or that do not degrade . the method may be applied to proppant fracturing or acid fracturing .