Premium
Liquid CO 2 high‐pressure fracturing of coal seams and gas extraction engineering tests using crossing holes: A case study of Panji Coal Mine No. 3, Huainan, China
Author(s) -
Cheng Xiaojiao,
Wen Hu,
Fan Shixing,
Chen Jian,
Zhai Xiaowei,
Yu Zhijin,
Tong Xiaozhang,
Lei Chengxiang,
Xu Yanhui,
Cheng Bangkai,
Li Ruikang
Publication year - 2020
Publication title -
international journal of energy research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.808
H-Index - 95
eISSN - 1099-114X
pISSN - 0363-907X
DOI - 10.1002/er.6124
Subject(s) - coal mining , borehole , coal , extraction (chemistry) , petroleum engineering , permeability (electromagnetism) , volumetric flow rate , geology , mining engineering , geotechnical engineering , chemistry , engineering , waste management , mechanics , chromatography , biochemistry , membrane , physics
Summary Owing to the low coal permeability coefficients and poor gas extraction efficiencies associated with the extraction of coal in the Huainan coal mining area, the aim of this study was to design, for the first time, a high‐pressure low‐temperature liquid CO 2 (LCO 2 ) pump for engineering tests with respect to the fracturing of coal seams and the improvement of CH 4 recovery in China. To reasonably calculate the initiation pressure for the coal seam fracturing as well as the gas flow parameters, theoretical analysis with field testing were integrated in the design. In addition, considering the interim gas extraction standard, the gas extraction equivalent radius based on this standard was calculated. The test results revealed a maximum LCO 2 pressure of 20.6 MPa, which surpasses the theoretical maximum pressure (19.5 MPa) required for the fracturing of coal seams. During the entire gas extraction process, the CO 2 concentrations in boreholes K 1 and K 3 decrease exponentially with time, showing attenuation coefficients of 0.0205 and 0.0231, respectively. The attenuation coefficients of the three attenuation stages of the original coal seam gas flow rate were 0.0314, 0.2142, and 0.1198, which were higher than those corresponding to the test area. The CH 4 concentration in boreholes K 1 and K 3 in the test area were both higher than that in the original coal seam, and the maximum CH 4 flow rates in these boreholes were 1.31‐ and 1.72‐fold higher than that in the original coal seam, respectively. The comparative analysis of CH 4 concentrations and flow rates indirectly showed an improvement in the permeability of the coal seam. Further, a quantitative equivalent gas extraction evaluation method based on LCO 2 fracturing of coal seam and gas displacement was proposed. Furthermore, based on a comprehensive evaluation, the effective displacement radius caused by the LCO 2 fracturing test was 9 m, with a displacement efficiency of 23.95%, and a displacement volume ratio of 0.21. This method offered the possibility of realizing the quantitative evaluation of the LCO 2 injection amount and the gas extraction effect, and provides a basis for optimizing the LCO 2 fracturing of coal seams as well as the gas extraction process.