It has been discovered that fluids viscosified with viscoelastic surfactants (VESs) may have their viscosities reduced (gels broken) by the direct or
indirect action of a biochemical agent, such as
bacteria, fungi, and / or enzymes. The biochemical agent may directly
attack the VES itself, or some other component in the fluid that produces a by-product that then causes
viscosity reduction. The biochemical agent may disaggregate or otherwise
attack the micellar structure of the VES-gelled fluid. The biochemical agent may produce an
enzyme that reduces
viscosity by one of these mechanisms. A single biochemical agent may operate simultaneously by two different mechanisms, such as by degrading the VES directly, as well as another component, such as a glycol, the latter mechanism in turn producing a by-product (e.g. an
alcohol) that causes
viscosity reduction. Alternatively, two or more different biochemical agents may be used simultaneously. In a specific, non-limiting instance, a brine fluid gelled with an
amine oxide surfactant can have its viscosity broken with
bacteria such as
Enterobacter cloacae,
Pseudomonas fluorescens,
Pseudomonas aeruginosa, and the like.