Datensatz

Zusammenfassung

To understand the hydraulic fracturing behavior for low permeable crystalline rock which is distinguished from other rock formation, many experimental and numerical studies have been carried out specially focusing on fracturing regime and poroelastic response. The most revolutionary work is fracture mechanics based approach to account for the fracture initiation and propagation in hydraulic fracturing process. According to this concept, hydraulic fracture initiates when the stress intensity factor exceeds the fracture toughness at the tip of the fracture at the wellbore wall and it continues to grow until the stress intensity factor is less than the fracture toughness. This fracturing process can be divided into two different regimes depending on how the injected fluid pressure acts on the fracture surface. When the pressurization rate is low or low viscosity injection fluid is injected, the fracturing process is under toughness-dominated regime resulting in unstable fracture propagation. On the contrary, with high pressurization rate or high viscosity injection fluid, it gets close to viscosity-dominated regime leading to stable fracture propagation. Though previous works have contributed to understand the two different behaviors, in terms of fracturing regime, how these different processes evolve and affect the fracturing result has not been well investigated. In most cases, simplified approaches have been used for numerical model and analysis of experimental results. In this study, we investigated varying fracturing process especially focusing on the evolution of fracture propagation depending on fracturing-regime influence parameters. Different pressurization rate and injection fluid viscosities are employed to realize different fracturing regimes in the granite. Acoustic emission and a couple of visual inspection techniques such as thin section analysis and X-ray imaging technique were utilized to observe the fracture pattern.