For further understanding of hydraulic fracture initiation and propagation mechanisms of coalbeds, hydraulic fracturing experiments under triaxial stress were carried out on the raw coal specimens from a coalmine with a large-size true triaxial hydraulic fracturing test system. The initiation and propagation characteristics of coalbed hydraulic fracture were studied under different triaxial stress states. The experimental results indicate that the stress state and coal cleat had a direct effect on hydraulic fracture initiation and propagation. The existence of small-scale cleat caused the hydraulic fracture propagation pressure to fluctuate frequently within a narrow range. The swerve of many fracture propagation paths was observed, and the filtration of fracturing fluid led to loss of propagation pressure. These problems are not conducive to the formation of high conductivity hydraulic fracture. The coalbed hydraulic fracture will be more complex with lesser degree of principle stress difference, and horizontal and vertical fractures may be both generated. This experiment may provide references for further exploration of coalbed fracturing mechanisms.
DONG Guang
. Hydraulic fracturing experiment of coalbed methane well under triaxial stress[J]. Science & Technology Review, 2015
, 33(1)
: 43
-46
.
DOI: 10.3981/j.issn.1000-7857.2015.01.007
[1] Wei H, Li L, Wu X, et al. The analysis and theory research on the factor of multiple fractures during hydraulic fracturing of CBM wells[J]. Procedia Earth and Planetary Science, 2011, 3: 231-237.
[2] Jing X. An experimental method on hydraulic fracturing of coal-bed reservoir[J]. Procedia Earth and Planetary Science, 2011, 3: 422-428.
[3] Zhai C, Li M, Sun C, et al. Guiding-controlling technology of coal seam hydraulic fracturing fractures extension[J]. International Journal of Mining Science and Technology, 2012, 22(6): 831-836.
[4] 董光, 邓金根, 朱海燕, 等. 煤层水力压裂裂缝导流能力实验评价[J]. 科学技术与工程, 2013, 13(8): 2049-2052. Dong Guang, Deng Jingen, Zhu Haiyan, et al. Experimental evaluation on conductivity of hydraulic fracture in CBM wells[J]. Science Technology and Engineering, 2013, 13(8): 2049-2052.
[5] Settari A, Cleary M P. Three dimensional simulation of hydraulic fracturing[J]. Journal of Petroleum Technology, 1984, 36: 1170-1190.
[6] Aghighi M A, Rahman S S. Initiation of a secondary hydraulic fracture and its interaction with the primary fracture[J]. International Journal of Rock Mechanics and Mining Sciences, 2010, 47(5): 714-722.
[7] Dawson G K W, Esterle J S. Controls on coal cleat spacing[J]. International Journal of Coal Geology, 2010, 82: 213-218.
[8] Medhurst T P, Brown E T. A study of the mechanical behavior of coal for pillar design[J]. International Journal of Rock Mechanics and Mining Sciences, 1998, 35(8): 1087-1104.
[9] Huang B, Liu J. The effect of loading rate on the behavior of samples composed of coal and rock[J]. International Journal of Rock Mechanics and Mining Sciences, 2013, 61: 23-30.
[10] 单学军, 张士诚, 李安启, 等. 煤层气井压裂裂缝扩展规律分析[J]. 天然气工业, 2005, 25(1): 130-132. Shan Xuejun, Zhang Shicheng, Li Anqi, et al. Analyzing the fracture extended law of hydraulic fracturing in coal-bed gas wells[J]. Natural Gas Industry, 2005, 25(1): 130-132．
[11] 吴晓东, 席长丰, 王国强. 煤层气井复杂水力压裂裂缝模型研究[J]. 天然气工业, 2006, 26(12): 124-126. Wu Xiaodong, Xi Changfeng, Wang Guoqiang. The mathematic model research of complicated fractures system in coalbed methane well[J]. Natural Gas Industry, 2006, 26(12): 124-126.
[12] 杜春志, 茅献彪, 卜万奎. 水力压裂时煤层裂缝的扩展分析[J]. 采矿 与安全工程学报, 2008, 25(2): 231-234. Du Chunzhi, Mao Xianbiao, Bu Wankui. Analysis of fracture propagation in coal seams during hydraulic fracturing[J]. Journal of Mining & Safety Engineering, 2008, 25(2): 231-234.
[13] 唐书恒, 朱宝存, 颜志丰. 地应力对煤层气井水力压裂裂缝发育的影 响[J]. 煤炭学报, 2011, 36(1): 65-69. Tang Shuheng, Zhu Baocun, Yan Zhifeng. Effect of crustal stress on hydraulic fracturing in coalbed methane wells[J]. Journal of China Coal Society, 2011, 36(1): 65-69.
