COMPOSITION OF BIOMARKERS AND ORIGIN OF OILS OF THE ARYSKUM DEPRESSION (SOUTH KAZAKHSTAN)

Abstract

Based on the analysis of the individual composition of biomarkers of oils from the Lower Cretaceous, Lower Jurassic, Paleozoic and Proterozoic of the Aryskum depression of the South Torgai oil and gas basin, the conditions for formation of oil source deposits generating oil of the territory under consideration are reconstructed. The study is relevant to justify the search strategy for oil and gas deposits, taking into account the tectonics of the foundation of South Kazakhstan. The aim of the study was to identify similarities and differences between the oils lying in the pre-Jurassic deposits of the Aryskum trough basement and oils from sedimentary strata overlapping them, to determine the features of facies conditions for accumulation of oil source material in this territory. Objects and methods. Oil from the Lower Cretaceous, Lower Jurassic, Paleozoic, and Proterozoic of the Aryskum depression of the South Torgai oil and gas basin was studied. The composition of the oils was analyzed by gas-liquid chromatography and gas chromatography-mass spectrometry. Results and conclusions. The distribution in oils and the individual composition of alkanes, n-alkylbenzenes, naphthalenes, phenanthrenes, cheilants, pentacyclic triterpanes and steranes were determined, geochemical parameters reflecting the peculiarities of the conditions for formation of oil source deposits were calculated. The data obtained demonstrated the genetic unity of the oils from the Lower Cretaceous and Proterozoic of the Akshabulak graben-synclinal, as well as the unified genesis of oils from the Lower Cretaceous and Paleozoic of the Aksai horst-anticline and the difference in the facies conditions of accumulation of source rocks in these territories. According to the data on composition of steranes and pentacyclic triterpanes, rocks that produced oil within the Akshabulak graben syncline are characterized by a high content of carbonates, accumulated in the deeper part of the sea and in less oxidizing conditions than in the Aksai horst anticline, where the oil source layer contained more clay component and deposited, apparently in a salted lagoon. Oil from the Lower Jurassic of the Bosingen graben-synclinal is generated by sediments formed in the desalinated delta zone.

Keywords

• oil composition
• hydrocarbon biomarkers
• source rocks
• pre-jurassic deposits
• aryskum depression
• south torgai basin
• oil source rock