Abstract

Hydraulic fracturing enhances productivity in low-permeability reservoirs. The introduction of nanomodified gels for hydraulic fracturing has raised the need to revise traditional approaches to their breakdown, as nanoparticles significantly change the kinetics and mechanisms of degradation. In this paper, for the first time, a systematic experimental study of the effects of chemical breakers on the rheological properties of nanomodified guar gels has been conducted. Two commercial oxidative breakers were used, which generate free radicals and cleave the guar polymer backbone, reducing viscosity. The effect of breaker concentration (0–1.82 wt%), as well as the concentration, size, and morphology of nanoparticles on gel breaking, has been studied. Guar gum was used as a gelling agent, and spherical SiO2 and Al2O3 nanoparticles, as well as aluminum oxide nanofibers (ANFs), were used as additives. An increase in breaker concentration accelerates gel breaking. For instance, at 0.68 wt% breaker, complete degradation occurs in about 3 h, whereas at 1.82 wt% it takes only about half an hour, with the viscosity dropping to 30 mPa·s. While nano-additives can either slow down or accelerate degradation depending on their type, size, and concentration, the addition of 0.4 wt% ANFs prolong the degradation time to more than two hours even at the highest breaker concentration. These effects are attributed to the competition between polymer chain scission by free radicals and the formation of physical crosslinks mediated by nanoparticles. The results demonstrate the possibility of purposefully controlling the kinetics of breaking of nanomodified gels for hydraulic fracturing by optimally selecting the breaker composition and nano-additive parameters.

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