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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.

Item Type:	Refereed Article
Keywords:	Bedding shale, fracture network, nitrogen fracturing, combined impact, failure number
Research Division:	Engineering
Research Group:	Mechanical engineering
Research Field:	Solid mechanics
Objective Division:	Energy
Objective Group:	Mining and extraction of energy resources
Objective Field:	Oil and gas extraction
UTAS Author:	Zhang, XX (Mr Xiangxiang Zhang)
UTAS Author:	Wang, X (Professor Xiaolin Wang)
ID Code:	128423
Year Published:	2018
Web of Science® Times Cited:	6
Deposited By:	Engineering
Deposited On:	2018-09-20
Last Modified:	2018-11-08
Downloads:	127 View Download Statistics