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Energies 2018, 11(5), 1196; https://doi.org/10.3390/en11051196

Model of T-Type Fracture in Coal Fracturing and Analysis of Influence Factors of Fracture Morphology

1,2,*
,
1
,
1
and
3
1
Department of Petroleum Engineering, Northeast Petroleum University, Daqing 163318, China
2
Harold Vance Department of Petroleum Engineering, Texas A&M University, College Station, TX 77843, USA
3
State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing 102200, China
*
Author to whom correspondence should be addressed.
Received: 5 April 2018 / Revised: 24 April 2018 / Accepted: 2 May 2018 / Published: 9 May 2018
(This article belongs to the Section Energy Sources)
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Abstract

Special T-type fractures can be formed when coal is hydraulically fractured and there is currently no relevant theoretical model to calculate and describe them. This paper first establishes the height calculation model of vertical fractures in multi-layered formations and deduces the stress intensity factor (SIF) at the upper and lower sides of the fracture in the process of vertical fracture extension. Combined with the fracture tip stress analysis method of fracture mechanics theory, the horizontal bedding is taken into account for tensile and shear failure, and the critical mechanical conditions for the formation of horizontal fracture in coal are obtained. Finally, the model of T-type fracture in coal fracturing is established, and it is verified by fracturing simulation experiments. The model calculation result shows that the increase of vertical fracture height facilitates the increase of horizontal fracture length. The fracture toughness of coal has a significant influence on the length of horizontal fracture and there is a threshold. When the fracture toughness is less than the threshold, the length of horizontal fracture remains unchanged, otherwise, the length of horizontal fracture increases rapidly with the increase of fracture toughness. When the shear strength of the interface between the coalbed and the interlayer increases, the length of the horizontal fracture of the T-type fracture rapidly decreases. View Full-Text
Keywords: coal; T-type fracture; stress intensity factor; vertical fracture; horizontal fracture coal; T-type fracture; stress intensity factor; vertical fracture; horizontal fracture
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Li, Y.; Jia, D.; Li, W.; Zhang, K. Model of T-Type Fracture in Coal Fracturing and Analysis of Influence Factors of Fracture Morphology. Energies 2018, 11, 1196.

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