Experimental Study on Mechanical Behavior of Hydraulic Fractures in Shale Reservoirs with I-shaped, X-shaped and T-shaped Natural Fractures

ABSTRACT: Natural fractures in shale reservoirs are diverse in type and complex in morphology, posing a challenge to understanding the effect of different types of natural fractures on the mechanical behavior of hydraulic fractures in parallel and vertical direction of horizontal well planes. To address this issue, physical simulation experiments on large sized shale samples with prefabricated I-shaped, X-shaped, and T-shaped natural fractures were conducted by a true triaxial hydraulic fracturing system. And the initiation and propagation laws of hydraulic fracture under the effect of different types of natural fractures were investigated. Results show that the hydraulic fractures in shale reservoirs with I-shaped natural fractures exhibit symmetrical initiation, while the shale reservoirs with X-shaped and T-shaped natural fractures exhibit asymmetric initiation. Among these natural fractures, X-shaped natural fractures displayed the strongest inducing ability, and the secondary natural fracture in X-shaped natural fractures is significantly contributing to this effect. The induction ability of T-shaped natural fractures is followed by the X-shaped natural fractures, particularly concerning the induction ability of the main natural fracture in T-shaped natural fractures. And I-shaped natural fractures have the weakest induction ability. Additionally, the bedding played a crucial role in inhibiting hydraulic fracture propagation along the direction of vertical principal stress. The bedding in shale reservoirs with straight natural fractures has the strongest inhibitory effect on the hydraulic fractures propagation, followed by shale reservoirs with T-shaped natural fractures, and shale reservoirs with X-shaped natural fractures have the weakest inhibitory effect. The research results provide guidance for analyzing the fracturing effect of shale reservoirs with different types of natural fractures.