Chemical breakers are used in hydraulic fracturing fluids to reduce the molecular weight of guar polymers which reduces fluid viscosity and facilitates the flowback of residual polymer providing rapid recovery of polymer from the proppant pack. Ineffective breakers or misapplication of breakers can result in screenouts or flowback of viscous fluids both of which can significantly decrease the well productivity.Breaker activity of low to medium temperature range oxidative and enzymatic breaker systems was evaluated, including ammonium persulfate, sodium persulfate, calcium and magnesium peroxides, and galactomannanase enzyme in linear gel fluids at temperatures from 75 o F-300 °F. Low temperature and high temperature viscometers were used to generate linear gelbreak curves with time at desired temperature. The amount of unbroken gel and residue, generated at different temperatures and breaker concentrations, was also determined using a "residue-after-break test (RAB)," for two oxidizers and one enzyme breaker, all used for similar temperature applications in the field.Viscosity measurement showed that reduction in the gel viscosity depends on both the breaker concentration and temperature. Also, increasing breaker concentration does not necessarily mean more reduction in viscosity. This paper provides a guideline of oxidative and enzyme breaker optimum use concentrations for specific temperatures in the form of breaker activity "S" curves. Enzyme breakers were found to provide a more homogeneous break and generate less residue compared to the oxidztive breakers in the resdiue-after-break (RAB) tests.
IntroductionGuar is a naturally occuring polymer used as a gellant in hydraulic fracturing fluids to increase fluid viscosity. This viscosity is required to carry the porppant into the fractue after the frature has been created in order to keep it open when the pumping is stopped. Once the poppant is delivered into the fracture, the fluid viscosity needs to be reduced so that it is easy to flow back and clean-up the formation.
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