Occurrence characteristics of Carboniferous-Permian tar-rich coal and its influencing factors in Northern Shaanxi

The rational development of tar-rich coal is of great significance to promote clean and efficient utilization of coal, improve the independent guarantee ability of oil and gas, and achieve carbon emission peak and carbon neutrality. In order to find out the occurrence characteristics of tar-rich coal in the typical mining areas of Carboniferous-Permian coalfield in Northern Shaanxi, based on coal exploration data and sample test results, this paper compares the tar yield of mineable coal seams, summarizes the spatial-temporal distribution rules of tar-rich coal, and discusses the occurrence influential factors. The results show that the average tar yield of mineable coal seams is higher in the north than that in the south, with 9.22%-11.6%, 8.49%-11.02% and 5.15%-6.89% in Gucheng, Fugu and Wubu Mining Areas respectively. Tar-rich coal mainly distributes in Gucheng-Fugu Mining Area, with tar-rich coal seams mainly of circle-belt pattern in Gucheng Mining Area, and tar-containing coal seams primarily scattered between tar-rich coal seams in Fugu mining area. Wubu mining area is dominated by tar-containing coal, with a small amount of tar-rich coal distributed and high-tar coal undeveloped. No.7 coal seam in Fugu Mining Area belongs to rich-high tar coal, with the distribution area of high-tar coal accounting for 23%, and the distribution area of tar-rich and high-tar coal of No.3, No.4 and No.8 coal seams all exceeding 94%. The developmental frequency of tar-rich coal decreases with the increase of coalification degree, and distribution regions of low and middle rank coal are greatly favourable areas for tar-rich coal occurrence. Coal tar yield positively correlates with the content of reactive component, hydrogen, oxide of calcium, magnesium and sulfur in ash composition, V/I, H/C atomic ratio and volatile matter, while negatively correlates with the content of inertinite, quartz, clay minerals and ash yield. The higher the degree of occlusion, reduction and alkalinity in depositional environment, the more favourable for tar-rich coal development. Coalification degree, coal-forming material, depositional environment and inorganic deposition act together on the tar-rich coal occurrence. As tar-rich coal has great potential in Gucheng-Fugu Mining Area, it is suggested to strengthen the protective mining and efficient utilization of the special coal resource.