## 1 Introduction  
Shale gas is a self-generating and self-storing natural gas system [1, 2], which is one of the most important petroleum resources of recent years. The Sichuan Basin is a key target for shale gas exploration in China [3, 4, 5, 6, 7, 8]. Numerous studies have significantly revealed the tectonic, petrological, geochemical and petrophysical characteristics of this gas shale section [9, 10, 11, 12, 13, 14, 15, 16]. Among the numerous findings, it is a well-known fact that total organic carbon (TOC) in shale gas systems is positively correlated with shale gas content [17, 18, 19]. [PERSON] et al. obtained a moderately positive correlation (R\({}^{2}\) = 0.667) between shale gas content and TOC content in the Fuling field in the Sichuan Basin [19]. The exploration and development of shale gas in China has made major breakthroughs in recent years. The shale gas of the Wufeng-Longmaxi Formation in Changing and the Zhaotong, Weiyuan and Jiaoshiba blocks in Sichuan Basin has been commercially produced, and the daily shale gas production of the Jiaoshiba block reached 3.1 \(\times\) 10\({}^{6}\) m\({}^{3}\) in May 2014 [20; 21]. Nevertheless, no other blocks in the Sichuan Basin have obtained commercial gas flow except the four blocks mentioned above. Comparison shows that the four blocks are all in regions with a simple structure [22; 23; 24], while the exploration and development of shale gas in complicated structural areas has not yet realized a breakthrough. With the rapid development of China's economy, the demand for oil and gas resources is increasing. Therefore, in recent years, China has put forward strategic requirements for vigorous development of gas (especially shale gas) and improvement of domestic oil/gas supply capacity. In recent years, China's shale gas industry has been developing rapidly, and major breakthroughs have been made in the exploration of two sets of organic-rich marine shale widely developed in the Lower Palaeozoic in the south. Land-phase shale oil and gas, on the other hand, is another important new area for shale oil and gas exploration and development in the Sichuan Basin. The Northeast Sichuan area has been proven to have developed a number of stratigraphic formations with marine-land superposition, and industrial gas flow has been obtained in a number of stratigraphic systems, which are key areas for natural gas exploration in the Sichuan Basin [25; 26; 27]. The development of high-quality hydrocarbon source rocks in the marine phase is the necessary material basis for the formation of large oil and gas fields. With regard to the geochemical characteristics and developmental environments of several marine hydrocarbon source rocks in Northeast Sichuan, a lot of research work has been carried out in the past, mainly focusing on the Cambrian and Permian hydrocarbon source rocks. In recent years, the hydrocarbon source rocks of the Upper Permian Dalong Formation, Wujiaping Formation, and Maokou Formation have received more and more attention [28; 29; 30]. Organic matter serves as the main carrier of shale hydrocarbons, and the hydrocarbon potential of hydrocarbon source rocks is in turn related to organic matter abundance, organic matter type and organic matter maturity. A large number of exploration studies have shown that the marine shales in the Sichuan Basin have a large hydrocarbon potential, so the organic matter characteristics of the Permian shales in Northeast Sichuan studied in this paper are of great significance. This shale has high organic matter abundance; the organic matter type is mainly I-II\({}_{2}\), and the organic matter is in the high-overmature stage, which is fully consistent with the characteristics of high-quality hydrocarbon source rock.