Investigation of the Evolution of Stratum Fracture during the Cavity Expansion of Underground Coal Gasification

Zhen Dong, Haiyang Yi (), Yufeng Zhao, Xinggang Wang, Tingxiang Chu, Junjie Xue, Hanqi Wu, Shanshan Chen, Mengyuan Zhang and Hao Chen
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Zhen Dong: Research Institute of Petroleum Exploration & Development, PetroChina, Beijing 100083, China
Haiyang Yi: North China Institute of Science and Technology, Langfang 065201, China
Yufeng Zhao: Research Institute of Petroleum Exploration & Development, PetroChina, Beijing 100083, China
Xinggang Wang: Research Institute of Petroleum Exploration & Development, PetroChina Tuha Oilfield Company, Hami 839009, China
Tingxiang Chu: North China Institute of Science and Technology, Langfang 065201, China
Junjie Xue: Research Institute of Petroleum Exploration & Development, PetroChina, Beijing 100083, China
Hanqi Wu: PetroChina Gas Storage Company, Beijing 100101, China
Shanshan Chen: Research Institute of Petroleum Exploration & Development, PetroChina, Beijing 100083, China
Mengyuan Zhang: Research Institute of Petroleum Exploration & Development, PetroChina, Beijing 100083, China
Hao Chen: Research Institute of Petroleum Exploration & Development, PetroChina, Beijing 100083, China

Energies, 2022, vol. 15, issue 19, 1-15

Abstract: The evolution of fracture zone controls the safety of underground coal gasification (UCG) in terms of gas emission and water leakage. In order to understand the fracture propagation in the confining rock of a UCG cavity with various influence factors, this paper implemented a set of numerical models based on different geological and operating conditions. Analysis was implemented on the mechanism of fracture propagation and its evolution characteristics, suggesting that (a) continuum expansion of the cavity leads a near-field fracture circle in confining rock initially, followed by the roof caving and successive propagation of shear band. (b) The key observed influence factors of fracture propagation are the grade of confining rock, overburden pressure, dimension of the cavity and gasifying pressure, the linear relationships between them, and the fracture height. Additionally, the fracture depth in the base board was mainly caused by tensile fracture. (c) A model was proposed based on the evolution of fracture height and depth in roof and base board, respectively. Validation of this model associated with orthogonal tests suggests a good capacity for predicting fracture distribution. This paper has significance in guiding the design of the gasifying operation and safety assessment of UCG cavities.

Keywords: underground coal gasification; fracture evolution; cavity expansion; safety assessment; gas emission; water leakage (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: 2022
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