This article presents the results and interpretation of the compositional and isotopic analysis of carbon in 14 gas samples derived from oil and gas fields and structures (Liman, East Makat, North Kotyrtas, Zholamanov, S. Nurzhanov and West Prorva) of the southern part of Pre-Caspian basin. According to the results of this study, all gases have a thermogenic source and their organic matters were deposited in the marine environment, which is also consistent with the results of biomarker analysis of oils from these studied fields. A sharp enrichment of propane with heavy carbon isotope in gas №55 of East Makat field suggests its biodegradation, which is also confirmed by the results of gas chromatographic analysis of oil from this well. A star diagram of gases was plotted based on normalized values of carbon isotopic composition of C1-C5, according to the results of which the studied samples can be divided into 5 genetically different groups. The identified groups based on results of this gas analysis are also consistent with the results of «fingerprinting» of oil from these fields. Keywords: gas composition; gas isotopic composition; Rayleigh fractionation; Bernard diagram; Clayton diagram; Laurent diagram; Chung diagram; enrichment in heavy isotope.

A b s t r a c tKeywords:

This paper presents the results of biomarker analysis of 183 oil samples derived from 19 oil and gas fields and Rock-Eval pyrolysis performed on 93 core samples from 12 fields in the South Mangyshlak basin. According to the biomarkers, oils of studied fields were formed from shaly OM and can be divided into 3 groups: the first group includes Oymasha, Ashiagar, Atambay-Sartobe, Alatyube, Karagie North and Akkar North, which have OM of marine origin, while the second group includes oils from the Pridorozhnoye, Airantakyr, Burmasha and Bekturly fields, which have OM of lacustrine origin. The third group includes oils from rest fields, within each of which there are at least two sources: the oils of the lower pay zones have shaly OM of marine origin, and the OM of the oils of the upper horizons was formed in the lacustrine environment. Rock-Eval pyrolysis revealed that some fields can be considered synclinal. Keywords: chromatography; biomarkers; steranes; hopanes; Rock-Eval pyrolysis; South-Mangyshlak.

No abstract

No abstract