Variations in surface fractal characteristics of coal subjected to liquid CO2 phase change fracturing
Corresponding Author
Xianfeng Liu
State Key Laboratory of Coal Mine Disaster Dynamics and Control, School of Resources and Safety Engineering, Chongqing University, Chongqing, China
State Key Laboratory Cultivation Base for Gas Geology and Gas Control, Henan Polytechnic University, Jiaozuo, China
Correspondence
Xianfeng Liu and Zepeng Wang, State Key Laboratory of Coal Mine Disaster Dynamics and Control, School of Resources and Safety Engineering, Chongqing University, Chongqing 400044, China.
Email: [email protected] (X. L.) and [email protected] (Z. W.)
Search for more papers by this authorCorresponding Author
Zepeng Wang
State Key Laboratory of Coal Mine Disaster Dynamics and Control, School of Resources and Safety Engineering, Chongqing University, Chongqing, China
Correspondence
Xianfeng Liu and Zepeng Wang, State Key Laboratory of Coal Mine Disaster Dynamics and Control, School of Resources and Safety Engineering, Chongqing University, Chongqing 400044, China.
Email: [email protected] (X. L.) and [email protected] (Z. W.)
Search for more papers by this authorDazhao Song
School of Civil and Resource Engineering, University of Science and Technology Beijing, Beijing, China
Search for more papers by this authorXueqiu He
School of Civil and Resource Engineering, University of Science and Technology Beijing, Beijing, China
Search for more papers by this authorTao Yang
School of Safety Engineering, North China Institute of Science and Technology, Beijing, China
Search for more papers by this authorCorresponding Author
Xianfeng Liu
State Key Laboratory of Coal Mine Disaster Dynamics and Control, School of Resources and Safety Engineering, Chongqing University, Chongqing, China
State Key Laboratory Cultivation Base for Gas Geology and Gas Control, Henan Polytechnic University, Jiaozuo, China
Correspondence
Xianfeng Liu and Zepeng Wang, State Key Laboratory of Coal Mine Disaster Dynamics and Control, School of Resources and Safety Engineering, Chongqing University, Chongqing 400044, China.
Email: [email protected] (X. L.) and [email protected] (Z. W.)
Search for more papers by this authorCorresponding Author
Zepeng Wang
State Key Laboratory of Coal Mine Disaster Dynamics and Control, School of Resources and Safety Engineering, Chongqing University, Chongqing, China
Correspondence
Xianfeng Liu and Zepeng Wang, State Key Laboratory of Coal Mine Disaster Dynamics and Control, School of Resources and Safety Engineering, Chongqing University, Chongqing 400044, China.
Email: [email protected] (X. L.) and [email protected] (Z. W.)
Search for more papers by this authorDazhao Song
School of Civil and Resource Engineering, University of Science and Technology Beijing, Beijing, China
Search for more papers by this authorXueqiu He
School of Civil and Resource Engineering, University of Science and Technology Beijing, Beijing, China
Search for more papers by this authorTao Yang
School of Safety Engineering, North China Institute of Science and Technology, Beijing, China
Search for more papers by this authorFunding information: Program for Changjiang Scholars and Innovative Research Team in University, Grant/Award Number: IRT_17R112; the State Key Laboratory Cultivation Base for Gas Geology and Gas Control (Henan Polytechnic University), Grant/Award Number: WS2019B08; National Natural Science Foundation of China, Grant/Award Numbers: U19B2009, 51974127, 51634001
Summary
Enhancement of coal permeability plays the key role in methane extraction underground coalmine. As the physical blasting method, liquid CO2 phase change fracturing (LCPCF) technique can effectively stimulate the coal reservoirs, further enhance the coal permeability. In this work, the combination of scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) was adopted to quantitatively evaluate the variations in the pore/fracture structure and fractal characteristics of coal subjected to LCPCF. Fracture fractal dimension (DF) and pore fractal dimensions (DP1, DP2) are calculated based on the SEM images and MIP data, respectively. After conducting LCPCF, a large number of microfracture and macropore clusters are generated and observed in SEM images. The maximum fracture ratio in treated coal is enhanced by approximately 200% compared with that in raw coal. MIP results show that pore distribution within coal exhibits a nonlinear alteration with four stages and the pore connectivity of coal is improved after LCPCF. The impact of LCPCF on pore/microfracture characteristics of coal is closely correlated with the distance from the fracturing borehole. The maximum values of DF and DP1 are found at the distance of around 2.0 m, indicating the best fracturing effect at such distance. It has been found that the effective influence scope of LCPCF on coal is within 7.0 m. The evolution of coal pore/fracture structure during LCPCF is attributed to the new pore/fracture generation and the conversion of original micropores into larger ones. Knowledge of these properties is essential for the application LCPCF in methane drainage.
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