The effects of fluid viscosity on the propagation of hydraulic fractures at the intersection of pre-existing fracture

Abstract

Hydraulic fracturing is a technique used in the development of shale oil reservoirs, enhanced geothermal system in hot dry rock, etc. The behavior of hydraulically induced fractures is of great interest in such applications. Although hydraulic fractures tend to propagate in the direction of maximum principle stress in theory, the direction of hydraulic fractures does not always correspond with that expected from regional stress due to pre-existing fractures. Furthermore, it has been indicated that the behavior of hydraulic fracture is influenced by the viscosity of injection fluid. Although the effects of pre-existing fractures and the viscosity of injection fluid on the effectiveness of the hydraulic fracturing are individually investigated, the prediction of the combination effect of them still remains as a big challenge. In order to examine the degree of the effectiveness of using high viscous fluid in hydraulic fracturing in naturally fractured rock, we developed a 2D numerical simulation code using discrete element method (DEM) that includes the coupling of solid-fluid interaction, and performed a series of numerical tests. The results show that hydraulic fracture is trapped by the pre-existing fracture in the low viscous fluid case, while it propagates beyond the pre-existing fracture in the high viscous case. The results also show that hydraulic fracture propagation could easily be retarded when the interaction angle of hydraulic fracture and pre-existing fracture is high. We conclude that high intersection angle between the hydraulic fracture and pre-existing fracture requires high viscous fluid for effective hydraulic fracturing.