Quantitative Analysis of the Effect of NaClO Stimulation in Anthracite and Bituminous Coal with FTIR and LF-NMR

Oxidant stimulation is increasingly used to enhance gas and oil production. Unlike acid stimulation, which dissolves minerals, oxidant stimulation modifies coal microstructures through reactions with the coal matrix. However, the stimulating effect of oxidation on coal lacks quantitative characterization. This study investigates the effects of NaClO stimulation on anthracite and bituminous coal microstructures. Various measurements, including LF-NMR, FTIR, SEM, and 3D-XRM, assess the physical and chemical changes in coal. Results indicate that NaClO stimulation significantly alters coal’s molecular and porous structures. FTIR reveals notable changes in coal’s chemical composition, such as increased hydroxyl groups, aromatic hydrocarbons, and oxygen functional groups with rising NaClO concentration, while aliphatic hydrocarbons decrease. Coal hydrophilicity and aromaticity gradually increase due to enhanced hydrogen bonds and aromatic structures. Four indexes (I, DOC, Hal/H, and A(CH2)/A(CH3)) quantitatively characterize modifications in the four typical functional groups. LF-NMR T2 spectra show an increase of over 50% in mesopore and macropore volume after 10% NaClO stimulation. Multiscale-fractal analysis yields fractal dimensions for adsorption pores, seepage pores, and microfractures. The fractal dimension of seepage pores decreases with rising NaClO concentration, while adsorption pores and microfractures do not exhibit fractal characteristics. Findings indicate that bituminous coal is more suitable than anthracite for NaClO oxidation stimulation to enhance permeability. © 2024 American Chemical Society.