Quantitative Identification and Distribution Pattern of Macrolithotype of Coal in Deep Coal Seams of the Daji Block

The construction of a logging response model for macrolithotypes in coal has been successfully completed. This model has enabled delineation of vertical and planar distribution patterns of coal macrolithotypes within the #5 and #8 coal seams of the Daji block, as well as to forecast the distribution of favorable reservoir conditions. Our findings indicate that semibright coal is predominant in the deep layers of the Daji block, with semidull, bright, and dull coals occurring less frequently. There is a strong correlation between the content of vitrain and clarain and the logging parameters of AC, DEN, GR, and M2RX. The accuracy of the logging response model for coal macrolithotypes is as high as 80%. Vertically, in both the #5 and #8 coal seams, the Yichuan–Hedong area is characterized predominantly by bright and semibright coals, while semidull coal is the dominant type in Yanchuan. Specifically, within the #8 coal seam, the Yichuan–Hedong area is largely composed of semibright coal, whereas the eastern part of Yanchuan is dominated by semidull coal. In terms of planar distribution, the #5 and #8 coal seams exhibit a development of semibright and bright coals in the Yichuan–Hedong and northern Yanchuan regions. Notably, the combined content of bright and semibright coal in the #8 coal seam exceeds that of the #5 coal seam. Based on the proportion of bright coal plus semibright coal as an index, the reservoirs have been categorized into three types. The middle and upper sections of the #8 coal are identified as the primary reservoirs, while the areas adjacent to the dirt band and the lower sections are considered less favorable for reservoir development. The favorable areas for both the #5 and #8 coal seams are predominantly concentrated in the central region of the Hedong area.