Study of interaction mechanisms between hydraulic fracture and weak plane with different strengths and widths using the bonded-particle model based on moment tensors

Abstract

Tight reservoirs contain a large number of weak planes, commonly seated with minerals. The weak plane may facilitate or impede hydraulic fracture propagation that depends on several factors, e.g. bond strength/stiffness of weak plane, size of weak plane, approaching angle, in situ stress, etc. To study the effects of weak plane strength and width on hydraulic fracture propagation and interaction mechanism, a bonded-particle model (BPM) in 2D coupling hydro-mechanical is used in the present study. The results show that the hydraulic fracture is more prone to be arrested by the weak plane in the condition of a low weak plane strength or low approaching angle. Under low differential stress, a thin weak plane has a significant effect on the offsetting distance of the hydraulic fracture within the weak plane. Under high differential stress, a thick weak plane is more prone to arrest the hydraulic fracture. As the hydraulic fracture approaches to the weak plane, the hydraulic fracture near-tip stress is influenced by the weak plane strength and width. The arrested mode can be caused by the shear slippage of weak plane or opening and dilation of weak plane. The macro-failure nature of weak plane changes from ‘Shear’ to ‘Compaction’ as the weak plane strength decreases. While the weak plane width does not affect the macro-failure nature obviously.