Distribution and geological controls of tar-rich coals in Yushen mining area of Northern Shaanxi

The development and utilization of tar-rich coal is of great significance for achieving clean and low-carbon utilization of coal in our country,alleviate the shortage of oil and gas supply,and ensuring national energy security. In view of this,based on the classification of tar yield,the temporal and spatial distribution characteristics of tar-rich coal in the main coal seam of Yan’an Formation in Yushen Mining Area were studied,and the geological factors affecting tar production rate were discussed. The results show that the area is generally dominated by rich-high tar coal.Vertically,coal seam 3-1 has the highest tar yield and the largest distribution area of tar-rich coal and high-tar coal,followed by coal seam 2-2 and coal seam 5-2.On the plane,the tar yield is high in the southeast and low in the northwest. Except for the local distribution of tar-containing coal,other areas are covered by tar-rich coal and high-tar coal. High-tar coal is continuously distributed in the southeastern of the mining area,and sporadically distributed in the northeast. Among them,the high-tar coal in coal seam No. 3-1 has the largest area and the best continuity. The formation of tar-rich coal is mainly affected by factors such as the degree of coalification,coal-forming materials,and coal-forming environment. A low degree of coalification is extremely beneficial to the development of tar-rich coal,and the development ratio of tar-rich coal and high-tar coal reaching more than 96%. The high content of hydrogen-rich vitrinite provides a good material basis for the development of tar-rich coal. The content of hydrogen-rich vitrinite (matrix+homogeneous vitrinite) is high-tar coal>tar-rich coal>tar-containing coal.The hydrogen-rich vitrinite content of tar-rich coal and high-tar coal accounts for more than 50% of the whole rock macerals,and the hydrogen content is more than 4%.The strong reducing environment provides good conditions for the formation and enrichment of tar-rich coal.Tar-rich coal is mainly formed in the depositional environment of delta plains to shallow lakes.The greater the depth of overlying water,the stronger the reducibility,which is more conducive to the formation of coal with high tar yield. High-tar coal is mainly formed in the coastal shallow lake environment with the largest water covering depth and the strongest reducibility in the southeast.