Abstract: To investigate the changes of rheology of pulse hydraulic fracturing fluid in response to frequency in shale gas exploitation, we conducted pulse shear tests on guar gum of two different viscosities (30 mPa·s and 10 mPa·s) under five different frequencies (0 Hz, 1 Hz, 3 Hz, 5 Hz and 7 Hz). Test results show that the response of fracturing fluids to pulse frequency varies with the change of viscosity. For fracturing fluid of relatively high viscosity, as frequency rises, the structural viscosity and plastic viscosity both present downward trend in general; whereas apparent viscosity firstly reduces by shear thinning, and then changes slightly when frequency reaches 5 Hz and even more; the flow index of fracturing fluid declines after increasing to a maximum value at frequency 5 Hz. For fracturing fluid of relatively low viscosity, as frequency rises, viscosity changes more slowly than plastic viscosity does, which is favorable for proppant migration during proppant stage, playing a significant role in stabilizing fractures at the later stage of fracturing. In conclusion, the response of rheological properties of highly-viscous fracturing fluid to pulse frequency is less obvious than that of lowly-viscous fluid.

Key words: fracturing fluid, viscosity, pulse frequency, shear thinning behavior, rheology, proppant