Effect of different types of fracturing fluid on the microstructure of anthracite: an experimental study

ABSTRACT

A systematic understanding of the effects of different fracturing fluids on the chemical and pore structure of coal is of great significance for the exploitation of coalbed methane (CBM). In this study, Fourier-transform infrared spectroscopy and mercury intrusion porosimetry were used to analyze the chemical and pore structure of coal samples treated by different fracturing fluids. The results show that fracturing fluid treatment has little effect on the coal aromatic structure. The oxygen-containing and hydroxyl structures of the coal samples treated by acidic and viscoelastic surfactant (VES) fracturing fluids increased by >17%, which is beneficial for gas desorption and thereby increases CBM yield, whereas those of the coal sample treated with deionized water decreased by 3.8%. The acidic and VES fracturing fluid treatments are also beneficial for coal pore connectivity, which promotes gas migration. The three types of fracturing fluids increased the macropore volume by >350%. The deionized water treatment reduced mesopores and micropores by 20% and 5%, respectively, while the transition pores increased by 2.3%, resulting in a 2.6% increase of the specific surface area, which is not conducive to gas desorption and migration. The acidic fracturing fluid treatment increased the mesopore volume by 53.3%, reduced the transition pore and micropore volumes by 5.3% and 32.5%, respectively, and reduced the surface area by 13.2%, which reduces the amount of adsorption sites and facilitates gas migration. However, the adsorption pores and mesopores after VES fracturing fluid treatment decreased by 17.6% and 26.7%, respectively, which indicates that this treatment does not transform most adsorption pores into migration pores.

KEYWORDS:

• Fracturing fluid
• chemical structure
• pore structure
• coal
• coalbed methane

Acknowledgments

This study was Funded by National Natural Science Foundation of China (No. 51804050, 51774055), the Natural Science Foundation of Chongqing, China (No. cstc2019jcyj-bshX0041) and the Postdoctoral Science Foundation Project Funded by State Key Laboratory of Coal Mine Disaster Dynamics and Control (No. 2011DA105287-BH201908).

Disclosure statement

No pontential conflict of interest was reported by the author(s).

Credit author statement

Ge Zhaolong: Conceptualization, Investigation, Formal analysis, Visualization, Writing-original draft, Wang Zepeng: Validation, Methodology, Hu Jinhong: Resources, Data Curation, Wang Yingwei: Reviewing and Editing, Zhou Zhe: Investigation, Li Ruihui: Investigation.

Additional information

Notes on contributors

Ge Zhaolong

Ge Zhaolong, Professor, Doctoral supervisor, Young Changjiang Scholar, Vice president of School of resources and security, Chongqing University.

Wang Zepeng

Wang Zepeng, Doctoral candidate, Majoring in unconventional natural gas exploitation.

Hu Jinhong

Hu Jinhong, Associate researcher.

Wang Yingwei

Wang Yingwei, Researcher, Office director of State key laboratory of coking coal exploitation and comprehensive utilization.

Zhou Zhe

Zhou Zhe, Associate Professor, Master Supervisor.

Li Ruihui

Li Ruihui, Postgraduate, Majoring in unconventional natural gas exploitation.