Numerical Study of Fracture Network Evolution during Nitrogen Fracturing Processes in Shale Reservoirs

Xiangxiang Zhang, Jianguo Wang, Feng Gao and Xiaolin Wang
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Xiangxiang Zhang: School of Mechanics and Civil Engineering, China University of Mining and Technology, Xuzhou 221116, China
Jianguo Wang: School of Mechanics and Civil Engineering, China University of Mining and Technology, Xuzhou 221116, China
Feng Gao: School of Mechanics and Civil Engineering, China University of Mining and Technology, Xuzhou 221116, China
Xiaolin Wang: School of Engineering, University of Tasmania, Hobart, TAS 7005, Australia

Energies, 2018, vol. 11, issue 10, 1-22

Abstract: This paper develops a numerical model to study fracture network evolution during the nitrogen fracturing process in shale reservoirs. This model considers the differences of incompressible and compressible fluids, shear and tensile failure modes, shale heterogeneity, and the strength and permeability of both shale matrix and bedding planes through the coupling of mechanical-seepage-damage during fracturing fluid injection. The results show that nitrogen fracturing has a lower breakdown pressure and larger seepage zone than hydraulic fracturing under the same injection pressure. Tensile failure was identified as the major reason for the initiation and propagation of fractures. Ignoring the effect of bedding planes, the fracture initiation pressure, breakdown pressure, and fracturing effectiveness reached their maxima when the stress ratio is 1. Under the same strength ratio, the propagation path of the fractures was controlled by the stronger effect that was casused by the bedding angle and stress ratio. With increasing the strength ratio, the fracture number and shearing of the bedding plane increased significantly and the failure pattern changed from tensile-only mode to tensile-shear mode. These analyses indicated that the fracture network of bedding shale was typically induced by the combined impacts of stress ratio, bedding angle and strength ratio.

Keywords: bedding shale; fracture network; nitrogen fracturing; combined impact; failure number (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2018
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (3)

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