Numerical Simulation of Hydraulic Fracture Vertical Propagation in Bedded Shale by Phase-Field Method

ABSTRACT: Volumetric fracturing technology is an effective tool for shale oil exploration. The developed bedding planes and strong inhomogeneity of continental shale make them limited in fracture seam height propagation, which restricts the efficient extraction of shale oil. To better understand the law of hydraulic fracture propagation in the vertical direction, a coupled hydraulic-mechanic-damage model is established based on the phase field method to study the propagation of fractures in bedded shales. Based on this model, the effects of fracturing fluid viscosity and alternative injection methods were simulated. Following research results were obtained. The strong filtration loss of low-viscosity fracturing fluid leads to a shorter fracture height and tends to open the bedding planes. Increasing the viscosity can significantly enhance the penetration capacity of the hydraulic fracture and thus improve the stimulation efficiency. Additionally, the alternative injection method of injecting high-viscosity fracturing fluid before the low-viscosity one can breach the constraints of the laminae in the near-well zone and achieve sufficient reconstruction of the reservoir in the longitudinal direction. Therefore, in practical applications, reasonable fracturing fluid design and injection schemes need to be chosen according to different geological conditions and engineering needs to get better fracturing modification performance. 1. INTRODUCTION Hydraulic fracturing is an important tool for the efficient exploitation of unconventional oil and gas resources (Yu et al., 2023). However, this also increases the risk of water contamination and geological instability. Therefore, numerical simulations are needed to accurately predict hydraulic fractures to guide fracturing scheme optimization while avoiding potential risks (Yang et al., 2022). Current numerical methods for hydraulic fracture propagation investigations are categorized into two main types: discrete and continuous methods. The latter saves the work of dealing with displacement discontinuities of complex crack surfaces when simulating crack extension and is easier to implement numerically. Continuum methods such as the gradient damage model (Sun et al., 2021), screening Poisson method (Areias et al., 2016), peridynamic model (Nadimi et al., 2016, Ni et al., 2020, Qin et al., 2021), and phase field model (PFM) (Zhou & Zhuang, 2020, Liu et al., 2021, Liu et al., 2022, Zhuang et al., 2023) are widely used.