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Experimental Study on the Damage and Cracking Characteristics of Bedded Coal Subjected to Liquid Nitrogen Cooling
Abstract Liquid nitrogen ($ LN_{2} $) cooling can induce significant cracking damage in coalbed methane (CBM) reservoirs. To investigate the combined effects of $ LN_{2} $ cooling and bedding angles on the mechanical behaviors of bedded coal, coal specimens with different bedding angles (0°, 30°, 60° and 90°) were cooled. The variations in the surface features and P-wave velocity of the specimens were analyzed. The mechanical properties (tensile strength, peak strain and absorbed energy) were measured under Brazilian test conditions and compared. Furthermore, the crack propagation processes and the failure mechanisms were observed and compared. The results showed that $ LN_{2} $ cooling can induce considerable thermal damage inside the coal, resulting in the deterioration of the coal’s mechanical properties. This deterioration led to easier cracking and a higher fragmentation degree under splitting load. In addition, the reductions in tensile strength, peak strain and absorbed energy exhibited obvious anisotropic characteristics. The thermal cracks induced by $ LN_{2} $ cooling participated in the formation of macrocracks. After $ LN_{2} $ cooling, the failure mode remained unchanged from that before cooling at bedding angles of 0°, 30° and 90°. Notably, a transition from mixed-mode failure (primarily caused by tensile failure) to tensile failure occurred at the 60° bedding angle. This transition caused the specimen to fail at a relatively lower load, resulting in maximum reductions in tensile strength (34.8%), peak strain (27.6%) and absorbed energy (55.0%) at the 60° bedding angle. This paper provides new insights into the $ LN_{2} $ fracturing of bedded coal seams.
Experimental Study on the Damage and Cracking Characteristics of Bedded Coal Subjected to Liquid Nitrogen Cooling
Abstract Liquid nitrogen ($ LN_{2} $) cooling can induce significant cracking damage in coalbed methane (CBM) reservoirs. To investigate the combined effects of $ LN_{2} $ cooling and bedding angles on the mechanical behaviors of bedded coal, coal specimens with different bedding angles (0°, 30°, 60° and 90°) were cooled. The variations in the surface features and P-wave velocity of the specimens were analyzed. The mechanical properties (tensile strength, peak strain and absorbed energy) were measured under Brazilian test conditions and compared. Furthermore, the crack propagation processes and the failure mechanisms were observed and compared. The results showed that $ LN_{2} $ cooling can induce considerable thermal damage inside the coal, resulting in the deterioration of the coal’s mechanical properties. This deterioration led to easier cracking and a higher fragmentation degree under splitting load. In addition, the reductions in tensile strength, peak strain and absorbed energy exhibited obvious anisotropic characteristics. The thermal cracks induced by $ LN_{2} $ cooling participated in the formation of macrocracks. After $ LN_{2} $ cooling, the failure mode remained unchanged from that before cooling at bedding angles of 0°, 30° and 90°. Notably, a transition from mixed-mode failure (primarily caused by tensile failure) to tensile failure occurred at the 60° bedding angle. This transition caused the specimen to fail at a relatively lower load, resulting in maximum reductions in tensile strength (34.8%), peak strain (27.6%) and absorbed energy (55.0%) at the 60° bedding angle. This paper provides new insights into the $ LN_{2} $ fracturing of bedded coal seams.
Experimental Study on the Damage and Cracking Characteristics of Bedded Coal Subjected to Liquid Nitrogen Cooling
Du, Menglin (author) / Gao, Feng (author) / Cai, Chengzheng (author) / Su, Shanjie (author) / Wang, Zekai (author)
2021
Article (Journal)
Electronic Resource
English
BKL:
38.58
Geomechanik
/
56.20
Ingenieurgeologie, Bodenmechanik
/
38.58$jGeomechanik
/
56.20$jIngenieurgeologie$jBodenmechanik
RVK:
ELIB41
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