Experiments and analysis on the influence of multiple closed cemented natural fractures on hydraulic fracture propagation in a tight sandstone reservoir

Abstract

This work designs an experimental model of tight sandstone with a closed cemented pre-existing fracture network (CCPF) to explore the influence of closed cemented natural fractures on the propagation behavior of hydraulic fracture (HF) in tight sandstone formations. The influence of CCPFs with different directions on the initiation, deflection, and propagation of HF is studied based on tri-axial hydraulic fracturing experiments with acoustic emission (AE) monitoring technology. The experimental results show four types of interaction behavior between HFs and CCPFs: deflection I; deflection II; penetration; and composite pattern. When the angle (α) between the HFs and CCPF is 0° ± 15°, their interaction is deflection I. During the process of hydraulic fracturing, the CCPF open with few AE events. When α = 90° ± 15°, the interaction between the HF and CCPFs includes deflection II and penetration patterns. The HF mainly extends in the rock matrix and is accompanied by significant AE events. When α = 45° ± 15°, the interaction is complicated and includes composite and deflection I patterns. The accumulated AE energy of composite interaction pattern shows a ladder-type increase. Under the same in-situ stress conditions, the HF geometry is the most complicated with the largest number of communicated natural fractures when the angle between the maximum principal horizontal stress direction and CCPF is 30°–60°. The experimental model designed in this paper can reproduce the complex propagation patterns of HFs in fractured tight sandstone formations, and the results provide a reliable basis for follow-up theoretical studies and engineering applications.