Implication of Alkane Carbon and Hydrogen Isotopes for Genesis and Accumulation of Over-Mature Shale Gas: A Case Study of Longmaxi Formation Shale Gas in Upper Yangtze Area

To clarify the implication of alkane carbon and hydrogen isotopes for genesis accumulation over-mature shale gas, we carried out a comparative study on Longmaxi gases from eight blocks in Upper Yangtze area. The results show that δ 13 C CH4 , C2H6 C3H8 gas are all positively correlated with Ro. According to distribution model thermal maturity, lies reversal stage. Shale is mixture kerogen cracking secondary mixing ratio two can be estimated by isotopic fractionation experiments thermogenic gas. proportion Formation ranges 33 72%. increase lower would reduce isotope have acute sensitivity occurrence hence they used as potential indicators content. decline generation capacity, reduction micropores, destruction tectonic movement considerable factors leading decrease content high-maturity shale.