54 / 2021-09-03 15:20:59

Study on Damage of Coal Pore Structure by Clean Fracturing Fluid

clean fracturing fluid；pore structure；coalbed methane；nitrogen adsorption; adsorption and desorption

In the process of hydraulic fracturing, the contact between fracturing fluid and coal rock will occur physical and chemical reactions, which will inevitably cause damage to the pore structure of coal rock. Fracturing fluid is an important part of hydraulic fracturing stimulation. With years of development, fracturing fluid system has experienced the development process of water-based fracturing fluid, active water fracturing fluid, clean fracturing fluid and foam fracturing fluid. Clean fracturing fluid is widely promoted in coalbed methane wells because of its good fracturing effect and less damage to coal reservoirs. Domestic and foreign scholars have carried out a lot of research on the pore structure of coal and rock, but there are few studies on the pore structure of coal and rock treated with clean fracturing fluid.



In this paper, two sets of experiments were carried out. Firstly, coal samples with high, medium and low rank were selected and soaked with clean fracturing fluid. The effect of clean fracturing fluid on pore structure of coal samples with different rank was observed through low-temperature N₂ adsorption experiment and scanning electron microscopy ( SEM ). Then methane adsorption and desorption experiments were used to further verify the change of pore structure of coal samples after clean fracturing fluid treatment.



The experimental results show that the pore structure, specific surface area and surface fractal dimension of coal samples after clean fracturing fluid treatment have changed. The influence degree of clean fracturing fluid on pore structure of different coal samples is : Gengcun low rank coal > Pingba middle rank coal > Jiulishan high rank coal.  The specific surface area and fractal dimension of coal samples treated by clean fracturing fluid are increased compared with raw coal. The results further reveal the influence of clean fracturing fluid on methane adsorption and desorption capacity of different rank coal rock, and provide theoretical basis and guidance for the application of clean fracturing fluid in different coalbed methane wells.



Acknowledgement

This project is financially supported by China Postdoctoral Fund ( 2018M642749 ). Henan Provincial Key Scientific Research Program for Colleges and Universities ( 19B620001 ). Outstanding Youth Fund of Henan University of Technology ( T2021 - 5 ). The authors are grateful for their support.



References

1. SUN Maoyuan, FANG Zhiqiang. Present status of the exploitaion & utilization of Chinese coalbed methane and the strategic option for its industrialization [J]. Natural Gas Industry, 2007, 27(03): 1-5．


2. YUAN Liang, XUAN Junhua, ZHANG nong, et al. Development orientation and status of key technology for mine undergroud coal bed methane drainage as well as coal and gas simultaneous mining [J]. Coal Science and Technology, 2013, 41(9): 6-11．


3. LI Xiangchun， LI Zhongbei， ZHANG Liang, et al. Pore structure characterization of various rank coals and its effect on gas desorption and diffusion [J]. Journal of China Coal Society, 2019, 44(SI): 142-156．


4. Duber S, Rouz JN. Calculation ofreflectance values for two models of texture of carbon materials [J]. Internation Joural of coal geology, 1999, 38: 333-348.


5. JIAN Bo, HOU Quanlin, WANG Guilian, et al. Structural evolution of Nano-scale Pores of tectonic coals in southern north China and its mechanism [J]. ActaGeologica Sinica, 2005, 79（2）: 269-285.


6. ZHAI Cheng, SUN Yong. Experimental study on evolution of pore structure in coal after cyclic cryogenic fracturing [J]. Coal science and technology, 2017, 45(6): 24-29.


7. LU Yiyu, YANG Feng, GE Zhaolong，et al. Comparative experiment on influence of clear fracturing fluid and water on coal seam permeability [J]. Journal of China Coal Society, 2015, 40(1): 93-97.


8. KANG Yili, CHEN Defei, LI Xiangchen. Effect of fracturing fluid treatmenton pore structure of coal [J].Journal ofChina University of Petroleum(Editionof Natural Science), 2014(5): 102-108.


9. DE.B J H. The structure and properties of porous materials [M]. London：Academic Press, 1958.

 

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