The multilayer structure is a superposition of several different types of basins, which is mainly developed in large basins with a long development history. It is characterized by different times, different sedimentary types of coal-bearing rock systems and many different types of sedimentary systems superimposed on the formation of different types of archetypal basin superposition, each sedimentary system represents a particular stage of development. For example, in the Sichuan Basin, there are four sets of coal-bearing rock systems belonging to different types of basins: the Lower Permian Liangshan Coal System, the Upper Permian Longtan Coal System, the Upper Triassic "Shushita Basin" (lower part of the T3) and "Shushang Basin" (upper part of the T3) coal-bearing rock systems, with the Aurignacian - Carboniferous, Middle Permian Carboniferous, Middle Permian Qixia Formation-Maokou Formation, Upper Permian Changxing Formation biotite -Lower Triassic Feixianguan Formation-Jialingjiang Formation-Middle Triassic Leikoupo Formation, Jurassic-Cretaceous -Cenozoic terrestrial facies. -Cretaceous -Cenozoic terrestrial clastic sedimentary system between each other, forming a thick more than 10,000 meters of sedimentary cover.
The four sets of coal-bearing rock systems are in the Sichuan Basin at the beginning of a certain stage of tectonic development, for example, after the late Caledonian uplift of the region as a whole and the Hercynian Carboniferous Yunnan movement, the Yangzi Plateau has begun a new development cycle, the Lower Permian Liangshan coal system is the early stage of the development of the cycle of sediments, although the thickness of the small, small prospect of coal gas, but the representative of the tectonic significance of the great; The Upper Permian Longtan Coal System deposited after the Dongwu Movement (Emei Rift Movement) in the Hercynian Period is the sediment at the beginning of another new development cycle in southern China and the Sichuan Basin area; after the tectonic movement in the middle of the Indo-Chinese Period and the overall uplift of the whole region in the Late Triassic, the Sichuan Basin area entered the stage of development dominated by the terrestrial clastic sedimentary system, and the "Shushita Basin" (Shuxia Basin) (the "Lower Permian Coal System") developed in the Sichuan Basin area. The "lower basin" (T3 lower) coal-bearing rock system, Anxian movement after the development of the formation of the "upper basin" (T3 upper) coal-bearing basin, so that the Sichuan Basin completely into the inland lake basin development stage.
It is obvious that the possibility of transforming the coal-bearing basins into gas-bearing basins in the form of a single structure is the smallest; the coal-bearing basins with a double-layer structure generally have better prospects for coal gas formation; the coal-bearing basins with a multilayered structure consist of coal-bearing rock systems of different eras and different depositional types superimposed on several sets of sedimentary strata of different types, and the coal-bearing rock systems represent different tectonic environments and different sedimentary depositional modes, which reflect different evolutionary sequences of the basins, and each set of coal-bearing rock systems has a different evolutionary sequence. Because the coal-bearing rock systems represent different tectonic environments, different sedimentary depositional methods, and reflect different evolutionary sequences in the basin, the gas prospect of each set of coal-bearing rock systems is quite different.