Application of low-field nuclear magnetic resonance technology in coal petrographic pore structure

Abstract Background: Low-field nuclear magnetic resonance technology, with the advantages of a rapid detection process and no damage to sample, has been widely used in the field of oil exploration, food preservation, building materials. Purpose: The aim of this work is to study the pore structure of the coal samples in different areas and the saturation of the fluid in the pores, which reflects the difference in the lithofacies structure and the distribution of the fluid in the pores. Methods: The porosity, permeability, and fluid saturation of the coal samples before and after saturation of water and manganese were measured by low-field nuclear magnetic resonance. Results and Conclusion: Results show that before saturation the proton relaxation signal of coal samples is dominated by irreducible water, and after saturation the signal of free water in all coal samples appear, and the signal of irreducible water of the coal samples in Yiwu county, Baishi lake and Dongha district are stronger than that before saturation. The saturation of free fluid of samples in Kazakhstan is the highest and that of irreducible water is the lowest. The oil saturation of samples in Kazakhstan is the highest, which is 4-6 times of that in Yiwu county, Baishi lake and Dongba district; the porosity of Kazakhstan coal sample is relatively large and the porosity of Yiwu county is relatively small; after saturation the number of micropores in coal samples of Kazakhstan, Yiwu county, Dongba district and Baishi lake are reduced, and the number of small holes in Yiwu county, Dongba district and Baishi lake coal samples is much higher than that before saturation; the penetration rate of Kazakhstan coal samples is 3-20 times of that of domestic coal samples, which is related to the difference in porosity and pore size of each sample, and is also a reflection of the geological environment and the degree of development. (authors)