Abstract
The aim of this study is to conduct a geochemical investigation to assess the maturity and genetic type of oil from the Nuraly oil field in the Aryskum depression. To achieve this goal, the following tasks were carried out: a geological characterization of the study area; geochemical analysis of collected oil samples; and interpretation of the obtained results. The objects of the study are oil samples taken from the Lower Neocomian, Upper Jurassic, Middle Jurassic, and Jurassic horizons of the Nuraly oilfield, located in the Aryskum depression. The individual composition of alkanes, n-alkylbenzenes, naphthalenes, phenanthrenes, cheilanthanes, pentacyclic triterpanes, and steranes has been determined. Geochemical parameters reflecting the specific conditions of oil-source rock formation were calculated. The obtained data demonstrated the genetic unity of oils from the Lower Cretaceous and Proterozoic of the Akshabulak Graben, as well as a common genesis of oils from the Lower Cretaceous and Paleozoic of the Aksai Horst, and differences in the facies conditions of oil-source rock deposition in these areas. Based on the composition of steranes and pentacyclic triterpanes, the source rocks that generated the oils within the Akshabulak Graben are characterized by a higher carbonate content. These rocks accumulated in deeper marine environments and under less oxidative conditions compared to the Aksai Horst, where the oil-source rocks contained more clay components and were likely deposited in a saline lagoon environment. Oil from the Lower Jurassic of the Bozingen Graben was generated by deposits formed in a freshwater deltaic zone.