Investigation on the mechanism of multi-directional fracturing with shear thickening fluid by DEM

Conventional hydraulic fracturing, widely used in subsurface resource development, has a fundamental limitation: it creates fractures only in the maximum principal stress direction, restricting permeability enhancement to a single orientation. Recently, using shear thickening fluid (STF) as fracturing fluid was proposed to overcome this limitation. In laboratory experiments of the previous study (Mukuhira et al., 2024, 2025), multiple pressure build-ups and drops were observed, and specimens were fractured in multiple directions. These phenomena have not been observed in conventional fracturing experiments. To investigate the underlying mechanisms, we conducted numerical simulations of STF fracturing. We incorporated a simple model for STF's shear rate-viscosity dependence into the hydrodynamics part of our in-house 2D DEM code (Shimizu et al., 2011). A rock model with a single pre-existing fracture showed local increases in STF viscosity with corresponding flow rate reductions. The results further demonstrated new fracture formation opposite to the pre-existing fracture, which did not occur in the case with Newtonian fluids. The findings indicate that increased viscosity may restrict borehole outflow and flow rate in the pre-existing fracture reduced, leading to higher borehole pressure than with Newtonian fluids. This mechanism partially explains the multiple pressure drops and fracture formations characteristic of STF fracturing.