Key Takeaways & Executive Findings
- •• Ultrasonic-assisted acid fracturing fluid significantly enhances coal microstructure modification, improving acid fracturing efficiency. • Acetic acid treatment reduces aromatic and branching parameters in coal, indicating chemical alteration of organic matter. • Acid dissolution of carbonates and clay minerals creates new pores, increasing porosity, pore volume, and fractal dimension. • Optimal concentration of 7% acetic acid increases pore volume by 5.7 times, improving pore connectivity and surface morphology.
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.
1. Introduction
The combined effect of ultrasonic waves and acid fracturing fluids intensifies the effect of microstructure modifications. This augmentation is instrumental in boosting the efficiency of acid fracturing operations, making them more effective in real-world, on-site applications. The gas explosion accidents caused by it account for about 40% of the total accidents of coal mine disasters, [1] seriously threatening the safe production of coal mines. Hence, the efficient exploitation of coalbed methane significantly reins in the likelihood of gas-related incidents, playing a pivotal role in the nation's energy strategy and development.
Coal represents a type of porous medium rock that contains a great many pores and fractures. At the microscopic level, coal harbors extensive microscopic pore architectures. Owing to intricate geological procedures, medium- to high-rank coalbed methane reservoirs across China typically exhibit traits such as low porosity, low permeability, a robust adsorption capacity, and elevated in-situ stress. As a result, the effect of directly drilling to extract coalbed methane in the traditional way is rather poor. Consequently, hydraulic fracturing technology has been progressively implemented in the realm of coalbed methane extraction starting from the 1970s. The fundamental principle underlying hydraulic fracturing technology lies in injecting fracturing fluid into the coal seam under high pressure. When the fluid pressure exceeds the breakdown pressure of the coal rock, fractures will be generated in the coal seam. These fractures will provide flow channels for coalbed methane [2,3].
Fracturing fluid serves as a medium for pressure transmission, which exerts a direct influence on the fracturing efficacy of coalbed methane reservoirs and constitutes a crucial element of hydraulic fracturing technology. As hydraulic fracturing technology progresses, a wide variety of fracturing fluids have emerged, such as water-based ones, oil-based ones, foam ones, and acidic ones.
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ZUO Shaojie, GAN Rui, WEN Zhijie, ZHANG Liang, JIANG Zhizhong, ZHAO Fuping, LIU Chengwei, LI Kun, XU Zhiyuan (2025). Effect of acid fracturing fluid modifying coal microstructure stimulated by ultrasonic. SinoTechIntel Verified Research. https://doi.org/10.1016/j.ijmst.2025.01.005
Research & Educational Purpose Only:The translations, structured abstracts, analytical annotations, and data reports provided by SinoTechIntel are intended exclusively for academic research, internal corporate R&D, and educational benchmarking. They do not constitute formal engineering, chemical safety, legal, or professional advice.
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Frequently Asked Questions
What is the effect of ultrasonic-enhanced acid fracturing fluid on coal microstructure?
The combination of ultrasonic and acid fracturing fluid strengthens the modification effect on the micropore structure of coal, enhancing acid fracturing efficiency. Acetic acid dissolves carbonates and clay minerals, creating new pores and increasing porosity, pore volume, and fractal dimension.
How does acetic acid concentration affect coal pore volume?
The study found that after modification by 7% acetic acid, the pore volume increased by 5.7 times, indicating an optimal concentration for enhancing pore structure.
What analytical techniques were used in this study?
The researchers used FTIR, XRD, N2 adsorption at low temperature, and SEM-EDS to characterize functional groups, mineral composition, micropore structure, and surface morphology of coal samples.
What are the key findings regarding functional groups in coal?
After 9% acetic acid treatment, aromatics (I) and branching parameters (CH2/CH3) were reduced by 81.58% and 88.67%, respectively, indicating significant chemical alteration of coal's organic structure.
How does this research contribute to coalbed methane extraction?
The findings offer theoretical direction for optimizing ultrasonic-enhanced acid fracturing fluid modification, which can improve the efficiency of coalbed methane extraction by enhancing coal permeability and gas flow.
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