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

Yuwei Li, Dan Jia, Wei Li and Kunpeng Zhang
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Yuwei Li: Department of Petroleum Engineering, Northeast Petroleum University, Daqing 163318, China
Dan Jia: Department of Petroleum Engineering, Northeast Petroleum University, Daqing 163318, China
Wei Li: Department of Petroleum Engineering, Northeast Petroleum University, Daqing 163318, China
Kunpeng Zhang: State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing 102200, China

Energies, 2018, vol. 11, issue 5, 1-13

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.

Keywords: coal; T-type fracture; stress intensity factor; vertical fracture; horizontal fracture (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
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