The application of stable carbon and hydrogen isotopic compositions of individual n-alkanes to Paleozoic oil/source rock correlation enigmas in the Huanghua depression, China

The carbon and hydrogen isotopic compositions of individual n-alkanes from the Paleozoic source rocks, oil and oil sand in the Huanghua depression, China, were determined for oil/source correlation purposes. The sedimentary facies of the upper Paleozoic (terrigenous-marine inter-bedded) is in this paper concluded to be different from that of the lower Paleozoic (marine) in the Huanghua depression. As shown by the results of the isotope analyse, the δ13C and δD (δ2H) values of the individual n-alkanes of the lower Paleozoic samples range from − 29‰ to − 33‰ and − 110‰ to − 140‰, respectively, while they range from − 27‰ to − 29‰ and − 140‰ to − 170‰, respectively, for the upper Paleozoic samples. The latter is relatively enriched 13C and depleted in D (2H). For well Konggu 7 crude oil, the δ13C and δD values of the individual n-alkanes are − 29‰ to − 30‰ and − 126‰ to − 140‰. However, for well Konggu 4 oil sandstone, the δ13C and δD values of the individual n-alkanes are − 27‰ to − 29‰ and − 144‰ to − 162‰. This is irrefutable proof that the Konggu 7 oil was sourced from the lower Paleozoic source rocks, while the Konggu 4 oil originated from the upper Paleozoic source rocks. To conclude, data of δ13C values and δD values of the individual n-alkanes may be used to assess the organic facies of source rocks and depositional environments in addition to being of inverse help for correlating oil/oil and oil/source.