Distribution of early and middle Jurassic tar-rich coal and its geological controls in Northern Xinjiang

The tar-rich coal resources in northern Xinjiang are rich, accounting for about half of the country's tar-rich coal. The rational development and utilization of tar-rich coal resources in this region is an important supplement to Chinese coal resources for coal-to-oil and gas. Previous studies on coal resources in this area have ignored their oil and gas resource attributes, and the characteristics and genetic laws of tar-rich coal are unclear. On the basis of systematically collecting the geological data of tar-rich coal in the six coal bearing belts of Northern Xinjiang, 137 groups of samples were collected and tested, the occurrence characteristics of early and middle Jurassic tar-rich coal was analyzed, and the geological controls of tar-rich coal were further discussed. The tar yield in the northeastern, western and central parts of northern Xinjiang was relatively high, while the high-oil coal was distributed in discontinuous bands in the Badaowan Formation in the northeast region. According to the tar yield of coal from high to low, the six coal bearing belts in northern Xinjiang are Balikun-Santanghu coal bearing zone, Zhunnan coal bearing zone, Yili coal bearing zone, zhunbei coal bearing zone, Turpan-Hami coal bearing zone and Zhundong coal bearing zone, respectively. The formation of tar-rich coal is affected by some factors, such as coal-forming environment, degree of coalification and coal macerals. The tar yield of coal is positively correlated with total sulfur content, volatile matter and vitrinite, and indicates an increasing trend with the increase of the ratio of vitrinite and inertinite (V/I). The reducing water environment provides good conditions for the enrichment of tar-rich coal. The tar-rich coal is mainly developed in the relatively reducing swamp environment. The stronger the reducibility of overlying water, the more conducive to the formation and enrichment of tar-rich coal. There is a positive correlation between maximum vitrinite reflectance and tar yield before the peak of oil generation. The tar yield of coal increases gradually with the increase of coalification degree. The relatively high vitrinite in coal macerals has a significant positive role in promoting tar yield, among these, hydrogen rich vitrinite provides a good material basis for the development of tar-rich coal.