Permeability Characteristics and Controls in Fusinite-Rich Lignite

Inertinite-rich coals are widely distributed, in which fusinite (semifusinite) constitutes the dominant maceral component of inertinite. Studying the pore characteristics of fusinite-rich lignite and their impacts on coal reservoir permeability is key to gaining an objective assessment of lignite reservoir properties. Based on this, this study selects the lignite of the Yimin Formation in the Hailaer Basin to carry out nuclear magnetic resonance experiments and permeability testing, combined with electron microscope observation and maceral quantification, coupling maceral quantitative results with coal reservoir pore structure and permeability results, and analyzing its geological control mechanism. The results demonstrate that the Yimin Formation lignite of the Hailaer Basin is inertinite-rich coal. Porosity decreases with rising huminite content but increases with higher inertinite proportions. The geological control of the above phenomena lies in the small pores developed in the huminite and the mesopores and macropores developed in the inertinite. Consequently, huminite content correlates negatively with movable water saturation and permeability, whereas inertinite content shows positive correlations. Fusinite and semifusinite emerge as the primary controls on permeability variations within the inertinite group. However, fusinite-rich lignite exhibits nonlinear porosity-permeability relationships, and part of the samples show the characteristics of "high porosity and low permeability." This anomalous behavior stems from the complex pore networks of the fusinite-rich lignite, which are characterized by cellular structures with either singular or multiple apertures. Different pore structures limit fluid mobility, which is intuitively manifested as permeability differences. Therefore, reservoir optimization necessitates a differentiated evaluation of high-porosity intervals versus high-permeability zones.