ABOUT OIL AND GAS POTENTIAL OF THE ARYSKUM DEPRESSION OF THE SOUTH TORGAI SEDIMENTARY BASIN

Abstract

The article discusses laboratory studies carried out to compare the composition of oils from Mesozoic and pre-Mesozoic formations: a comprehensive analysis of the molecular composition of oils by chromatography-mass spectrometry; separation and identification of the composition of alkanes by gas-liquid chromatography; NMR-spectroscopic determination of the fragment composition of oils; mass spectrometry was used to determine the isotopic composition of carbon, which identifies the genesis of hydrocarbons in relation to the zones of oil and gas formation. As a result of the study, the laboratory data were obtained, which made it possible to reveal the similarity between oils from deposits of different ages within the graben-synclines, namely, close values of geochemical parameters and the relative content of individual classes of biomarkers made it possible to assume the genetic unity of oils from the Lower Cretaceous and Proterozoic of the Akshabulak graben-syncline and genetic unity of oils from the Lower Cretaceous and Paleozoic of the Aksai horst anticline. The value of the pristane/ phytane ratios indicates a common environment for the formation of the initial organic matter within the structures - suboxidizing conditions in the Akshabulak graben syncline and oxidizing conditions in the Aksai horst anticline, and the existence of a higher redox potential in the Bosingen graben-syncline. Gas- liquid chromatography data showed a slight difference in the thermal transformation of the studied oils, which were classified as "mature". The results of NMR spectrometry in combination with other methods indicate the genetic unity of oils from the Lower Cretaceous and Proterozoic of the Akshabulak graben- syncline and the genetic unity of oils from the Lower Cretaceous and Paleozoic of the Aksai horst anticline. A comparative analysis of the carbon isotopic composition of oils from the Jurassic and Cretaceous deposits of the Aryskum depression and oils from various basins of the world showed a similar range of their variations and a possible genetic relationship of these oils with organic matter of the sapropel type.