Abstract:
Large-scale hydraulic fracturing technique was commonly used in the development of shale oil and gas reservoirs. The natural fracture and lamination have significant influences on the propagation of hydraulic fracture. Four shale outcrops with the dimension of 400×400×400 mm were selected to investigate the interactions between natural and hydraulic fracture by utilizing tri-axial fracturing test system and acoustic emission (AE) monitoring system. Experimental results indicated that hydraulic fracture will form a non-planar fracture network in space when it encounters the natural fractures (crossing or deflecting along the natural fractures). Natural fractures with big aperture or low bonding strength often cause a deflection of hydraulic fracture so that it is difficult to form a new principal hydraulic fracture. Fracture fluid flowing into the lamination distributed elliptically when hydraulic fracture penetrates the bedding plane. AE signal concentrates on the direction of crack initiation along the rock mass, while it is weaker as hydraulic fracture propagates along natural fracture. Therefore, whether hydraulic fracture could penetrate natural fracture is predominated by the fracture aperture and bonding strength of natural fracture. It is easy to form a spatial non-planar fracture network when hydraulic fracturing is conducted in fractured shale reservoirs. The volume of fracturing fluid penetrating into the lamination is less than that in principal hydraulic fracture. It is believed that the investigation on the interactions between hydraulic and natural fracture would be useful for prediction of the hydraulic fracture propagation and network hydraulic fracturing.
