a composition including a wellbore work fluid and a polymer having mechanically labile chemical bonds is injected downhole , and combines with fluid present downhole to yield a composite fluid . mechanical energy is provided to the composite fluid downhole to cleave the mechanically labile chemical bonds in the polymer . the polymer may be used as a viscosifier , friction reducer , or fluid loss additive . cleaving the mechanically labile chemical bonds with mechanical energy allows precise degradation downhole .