As a crucial factor that influences the hydraulic fracturing effectiveness of coal seams, fracturing fluids have garnered increasing attention. Among them, acid fracturing fluids have demonstrated positive impact on the pore transformation of coal, but high-strength acid fracturing fluids can cause corrosion damage to mechanical equipment. In this study, we employed acetic acid to formulate four types of weak acid fracturing fluids with varying concentrations and conducted soaking experiments. We analyzed the changes in the physical and chemical structure of coal samples before and after treatment using Fourier-transform infrared spectroscopy and X-ray diffraction analysis. The changes in the pore structure of coal samples before and after treatment were characterized by nitrogen adsorption and scanning electron microscopy. Our findings indicate the following: (1) The effects of different concentrations of acetic acid fracturing fluid on functional groups and microcrystalline structure vary. The 5% concentration fracturing fluid had the most significant impact on the organic structure of coal samples, with decreases in the area of hydroxyl structure, aliphatic structure, and oxygen-containing structure of 2.97%, 1.37%, and 0.68%, respectively. The 6% concentration fracturing fluid had the most significant impact on crystal structure, leading to a high degree of recrystallization and a fragile crystal network structure. (2) Fracturing fluids with concentrations below 7% can increase the number of mesopores and simplify the pore structure, while concentrations above 7% can lead to an increase in micropores and a more complex pore structure. (3) After the action of fracturing fluid, carbonate minerals are dissolved, and the pores of coal samples increase. However, excessively high concentrations of acetic acid fracturing fluid can facilitate shedding of mineral particles and block some pore channels, worsening the connectivity between pores. (4) The octadecylamine acetate formed by the combination of octadecylamine and acetic acid develops as a partial film on the surface of a coal body, reducing the roughness of the fracture surface and facilitating the flow of the fracturing fluid. Our findings provide theoretical support for the preparation and selection of weak acid fracturing fluids.

压裂液作为影响煤层水力压裂效果的关键因素，越来越受到人们的关注。其中，酸性压裂液对煤的孔隙改造表现出了积极的影响，但高强度酸性压裂液会对机械设备造成腐蚀损坏。本研究采用乙酸配制4种不同浓度的弱酸性压裂液并进行浸泡实验。利用傅里叶变换红外光谱和X射线衍射分析分析了处理前后煤样物理和化学结构的变化。采用氮气吸附和扫描电镜对处理前后煤样孔隙结构的变化进行表征。研究结果表明：（1）不同浓度的醋酸压裂液对官能团和微晶结构的影响不同。 5%浓度压裂液对煤样有机结构影响最为显着，羟基结构、脂肪族结构、含氧结构面积分别减少2.97%、1.37%、0.68%。 6%浓度压裂液对晶体结构影响最为显着，导致再结晶程度较高，晶体网络结构脆弱。 （2）压裂液浓度低于7%时，中孔数量增多，孔隙结构简单化；浓度高于7%时，微孔增多，孔隙结构更加复杂。 (3)压裂液作用后，碳酸盐矿物溶解，煤样孔隙增大。 但醋酸压裂液浓度过高会促进矿物颗粒脱落，堵塞部分孔隙通道，使孔隙之间的连通性变差。 (4)十八胺与乙酸结合形成的十八胺乙酸盐在煤体表面形成局部膜，降低裂缝表面的粗糙度，有利于压裂液的流动。我们的研究结果为弱酸性压裂液的配制和选择提供了理论支持。