Effects of ultrasonic-alkaline fracturing fluid on the microstructure and wettability of coal

Abstract

Enhancing coalbed methane (CBM) extraction efficiency is critical for safe coal mining and clean CBM utilization. Combined ultrasound and alkaline fracturing fluid treatment improves coal matrix micropore modification, thereby increasing the effectiveness of alkaline fracturing. In this study, the improvement effect of ultrasound-alkaline fracturing fluid on coal permeability was investigated using FTIR, XRD, BET, SEM-EDS, contact angle measurements, and other methods. The results indicate that ultrasound and alkaline solution interact synergistically. Ultrasound provides physical impact, while the alkaline solution drives chemical dissolution. Together, these effects increase hydrophilic groups, reduce oxygen-containing groups, break the compact internal structure of coal, and dissolve as well as fragment certain minerals, markedly increasing internal pore abundance and widening pore pathways. An alkaline solution containing 2% NaOH demonstrates the most significant improvement in coal pore development. Additionally, ultrasound-alkali treatment enhances the hydrophilicity of the coal surface, which facilitates gas release. This study provides a theoretical foundation for the efficient extraction of coal seam gas.