True triaxial hydraulic fracturing test and numerical simulation of limestone

• Published in: Journal of Central South University 2020-10, Vol.27 (10), p.3025-3039
• Main Authors: Yang, Wei-min, Geng, Yang, Zhou, Zong-qing, Li, Lian-chong, Ding, Ruo-song, Wu, Zhong-hu, Zhai, Ming-yang
• Format: Article
• Language: English
• Subjects: Acoustic emission; Crack propagation; Displacement; Engineering; Failure modes; Fracture mechanics; Hydraulic fracturing; Limestone; Metallic Materials; Propagation; Propagation modes; Water injection; Waveforms
• ISSN: 2095-2899; 2227-5223
• DOI: 10.1007/s11771-020-4526-4

Hydraulic fracturing, as a key technology of deep energy exploitation, accelerates the rapid development of the modern petroleum industry. To study the mechanisms of hydraulic fracture propagation and rock failure mode of the vertical well hydraulic fracturing, the true triaxial hydraulic fracturing test and numerical simulation are carried out, and the influence of the principal stress difference, water injection displacement, perforation angle and natural fracture on fracture propagation is analyzed. The results show that the fracture propagation mode of limestone is mainly divided into two types: the single vertical fracture and the transverse-longitudinal crossed complex fracture. Under high displacement, the fracturing pressure is larger, and the secondary fracture is more likely to occur, while variable displacement loading is more likely to induce fracture network. Meanwhile, the amplitude of acoustic emission (AE) waveform of limestone during fracturing is between 0.01 and 0.02 mV, and the main frequency is maintained in the range of 230–300 kHz. When perforation angle θ=45°, it is easy to produce the T-type fracture that connects with the natural fracture, while X-type cracks are generated when 0=30°. The results can be used as a reference for further study on the mechanism of limestone hydraulic fracturing.