Effect of acid fracturing fluid modifying coal microstructure stimulated by ultrasonic

Abstract

The combination of ultrasonic and acid fracturing fluid can strengthen the modification effect on the micropore structure of the coal matrix, thereby enhancing the efficiency of the acid fracturing process. In this research, acetic acid was utilized to formulate acid fracturing fluids with varying concentrations, and the evolutionary traits of both the acid fracturing fluids and ultrasonic waves in relation to coal samples were investigated. The functional group structure, mineral composition, micropore structure and surface morphology of coal samples were characterized by FTIR, XRD, N₂ adsorption at low temperature and SEM-EDS. The results showed that aromatics (I) and branching parameters (CH₂/CH₃) were reduced by 81.58% and 88.67%, respectively, after 9% acetic acid treatment. Acetic acid can dissolve carbonates and clay minerals in coal, create new pores, and increase porosity, pore volume and pore fractal dimension. After modification by 7% acetic acid, the pore volume increased by 5.7 times. SEM observation shows that the diameter of coal surface holes increases, EDS scanning shows that the content of mineral elements in coal decreases, the connectivity of coal holes increases, and the holes expand. The findings of this research offer theoretical direction for optimizing ultrasonic-enhanced acid fracturing fluid modification.

Keywords

Acidic fracturing fluid / Ultrasonic / Coalbed methane / Microstructure

Acknowledgments

This study was financially supported by the National Natural Science Foundation of China (Nos. 52304129 and 52274130), Natural Science Foundation of Sichuan Province (No. 2024NSFSC0971), Guizhou Provincial Basic Research Program (Natural Science) (No. ZK [2023] general 070), and Shandong Key Laboratory of Mining Disaster Prevention and Control, Shandong University of Science and Technology (No. SMDPC202403).

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