Parameter Studies on Hydraulic Fracturing in Brittle Rocks Based on a Modified Hydromechanical Coupling Model

Abstract

In this paper, we present a numerical study of hydraulic fracturing in brittle rock by using particle flow simulation. The emphasis is put on the influence of in situ stress, differential stress, fluid injection rate, fluid viscosity and borehole size on hydraulic fracturing behavior. To this end, an improved hydromechanical coupling model is first introduced to better describe fluid flow and local deformation of particle-based rocks. A series of parameter sensitivity studies are then conducted under the framework of particle flow simulation. Modelling results suggest that the breakdown pressure and time to fracture both linearly increase with confining stress, and hydraulic fracturing patterns present a distinct transition from brittle to ductile. Fluid injection rate and fluid viscosity have similar influences on hydraulic fracturing propagation, their value decrease leads to borehole pressure decrement and time to fracture prolongation. However, the former mainly controls the time to initial cracking, while the latter largely decides the duration of fracturing propagation. As for borehole radius, its increases can directly enhance the fluid diffusion zone, which further intensifies the nonlinear property of borehole pressure, leads to breakdown pressure decrease, prolongs time to fracture and forms more complex hydraulic fractures.