Effect of in-situ hydrocarbon generation over geochemical properties of the reservoired natural gas: A case study from the Ordos Basin, China

In a few wells, natural gas in the Permian Taiyuan Formation limestone (Pt-L) has the most depleted ethane carbon isotope. Saturated hydrocarbon gas chromatography (SH-GC), element and carbon isotope analysis of kerogen were conducted to investigate the source and sedimentation environment of the Pt-L, and its influence on the geochemical characteristics of gases. Compositions and carbon isotope values of gases produced in the Permian Taiyuan Formation limestone development area (Pt-LDA) were also studied for comparison with the Pt-L. The Pt-L is mixed source of marine and terrestrial provenance. The sedimentary environment is mainly reducing, which promotes the preservation of organic matter. Natural gas produced in the Pt-LDA is dominated by coal-derived gas generated from the Carboniferous-Permian coal strata. Gases from a few wells with more depleted carbon isotopic values may have generated from marine algae and bacteria in the Pt-L.