A numerical study of fracture initiation under different loads during hydraulic fracturing
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A numerical study of fracture initiation under different loads during hydraulic fracturing TANG Shi-bin(唐世斌)1, DONG Zhuo(董卓)1, WANG Jia-xu(王嘉旭)1, MAHMOOD Ahmad 2 1. State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian 116024, China; 2. Department of Civil Engineering, University of Engineering and Technology Peshawar (Bannu Campus), Bannu 28100, Pakistan © Central South University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Abstract: The fracture initiation behavior for hydraulic fracturing treatments highlighted the necessity of proposing fracture criteria that precisely predict the fracture initiation type and location during the hydraulic fracturing process. In the present study, a Mohr-Coulomb criterion with a tensile cut-off is incorporated into the finite element code to determine the fracture initiation type and location during the hydraulic fracturing process. This fracture criterion considers the effect of fracture inclination angle, the internal friction angle and the loading conditions on the distribution of stress field around the fracture tip. The results indicate that the internal friction angle resists the shear fracture initiation. Moreover, as the internal friction angle increases, greater external loads are required to maintain the hydraulic fracture extension. Due to the increased pressure of the injected water, the tensile fracture ultimately determines the fracture initiation type. However, the shear fracture preferentially occurs as the stress anisotropy coefficient increases. Both the maximum tensile stress and equivalent maximum shear stress decrease as the stress anisotropy coefficient increases, which indicates that the greater the stress anisotropy coefficient, the higher the external loading required to propagate a new fracture. The numerical results obtained in this paper provide theoretical supports for establishing basis on investigating of the hydraulic fracturing characteristics under different conditions. Key words: hydraulic fracturing; internal friction angle; stress anisotropy coefficient; finite element method Cite this article as: TANG Shi-bin, DONG Zhuo, WANG Jia-xu, AHMAD Mahmood. A numerical study of fracture initiation under different loads during hydraulic fracturing [J]. Journal of Central South University, 2020, 27. DOI: https://doi.org/10.1007/s11771-020-4470-3.
1 Introduction Hydraulic fracturing is an effective technology which has been widely used in unconventional development of energy resource including tight gas and oil reservoirs, coal bed methane and enhanced geothermal systems. During the hydraulic fracturing process, high-pressure water is injected into the reservoirs to create a large amount of
fractures. The hydraulic fracturing technology has been highly developed during the last decades in North America and recent years in China. However, there are still several other limitations that require further studies. Understanding of how the injected water pressure extends the pre-existing fr
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