**5. Conclusions**

There are di fferences in the molecular and carbon isotopic composition and noble gas abundance and isotopic composition in the Longmaxi shale gas sourced from the Weiyuan (WY) and Changning (CN) areas. This could be accounted for by the intense tectonic activities of the Sichuan Basin and secondary reactions in the shale gas reservoir. Additionally, the di fferential e ffect on WY and CN of the complex burial history and Emeishan super mantle plume activities in the Sichuan Basin has resulted in di fferent thermal histories and hydrocarbon generation processes of Longmaxi shale in these two areas. The carbon isotope fractionation e ffect during the processes of shale gas generation results in di fferent molecular and carbon isotopic compositions in the primary gases generated from kerogen compared with the secondary gases cracked by oil and/or gaseous hydrocarbons. The di fferent partial mixing of primary and secondary gases is a governing factor for the di fferences in the gas geochemical characteristics between WY and CN. In addition, the di fferent geotectonic movements have caused

different fault and fracture systems in the WY and CN Longmaxi shale strata, which have led to various amounts of shale gas loss and consequently carbon isotope fractionation in the gas loss processes. Furthermore, water–rock interactions could enhance the molecular and carbon isotope composition differences, and the heterogeneity of the shale could bring about the different noble gas abundances and isotope compositions.

**Author Contributions:** Conceptualization, C.C.; funding acquisition, C.C. and Z.L.; investigation, C.C., L.L., Y.L.; methodology, C.C. and L.L.; project administration, C.C.; resources, C.C., L.L., L.D., and J.H.; supervision, C.C., and L.L.; writing—original draft, C.C.; writing—review and editing, C.C. and L.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by National Natural Science Foundation of China, gran<sup>t</sup> number 41502143, and Key Laboratory Project of Gansu Province, gran<sup>t</sup> number 1309RTSA041.

**Conflicts of Interest:** The authors declare no conflict of interest.

**Data Availability:** The shale gas geochemical data used to support the findings of this study are included within the supplementary information file(s). Previously reported shale gas geochemical data were used to support this study, and are available at: https://doi.org/10.1016/j.marpetgeo. 2017.01.023, https://doi.org/10.1016/j.marpetgeo.2017.01.022, https://doi.org/10.1016/S1876-3804(16)30092-1, https://doi.org/10.1016/j.petrol.2018.04.030. These prior studies are cited at relevant places within the text as references: [15,16,21,22,27].
