Sedimentary conditions for good coal reservoir development in the Carboniferous and Permian,Qinshui Basin

In the Carboniferous and Permian of the Qin-shui Basin, coal reservoirs are well developed. But different coal reservoirs are obviously different in distribution, thickness and reservoir performance, etc. This paper studies the factors controlling the development and distribution of good coal reservoirs from the viewpoint of sedimentology and sequence stratigraphy. The study shows that good coal reservoirs are mainly formed in marsh environments on tidal flats and delta plains. The coal reservoirs formed on tidal flats are more continuous laterally than those on delta plains. The fluctuation of sea level shows important control over the vertical and lateral distribution of coal reservoirs. Generally speaking, the coal reservoirs formed in the highstand system tracts are more abundant, thicker and more widespread, and thus the highstand system tracts are more favorable to the formation of good coal reservoirs. The coal reservoirs formed in the transgressive system tracts are lower in abundance, thinner and much less widespread, and thus the transgressive system tracts are not favorable to the formation of good coal reservoirs.