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

Abstract

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 δ 13C and δD (δ 2H) 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 δ 13C and δD values of the individual n-alkanes are − 29‰ to − 30‰ and − 126‰ to − 140‰. However, for well Konggu 4 oil sandstone, the δ 13C 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 δ 13C 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.