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Application of Biomarkers and Oil Fingerprinting for Genetic Classification of Oil and Prediction of Petroleum Migration Pathways of Aryskum Downfold of South-Torgay Depression


 This article presents the results of fingerprinting and biomarker analysis of 254 oil samples derived from 11 different fields and structures in Aryskum downfold of the South-Torgay depression for genetic classification of oils and prediction of petroleum migration pathways. According to the oil fingerprinting results based on patented Shell technology, 12 groups of oils were found: oils in reservoirs of central part of Nuraly field form the first group, while oils in the producing horizons of Western Nuraly, Southern Khayrgeldy, Akshabulak East and fluvial beds of Central Akshabulak fields form the second group. The oils related to the third group were found in the wells exploiting producing horizon I in the north dome of Central Akshabulak, while the oils from wells penetrating lower producing horizons(III-IV-V) of Central Akshabulak, upper producing horizons in South dome of Central Akshabulak and of all producing horizons of the north dome of Akshabulak South constitute the fourth group.
 The fifth group includes only one oil sample of different genesis from well № 37, which penetrates the paleo-channel №13 at South Akshabulak. The genetic difference of this oil from other oils was also confirmed by its biomarker composition. Most of oil fingerprinting star plots in Aksay field are identical and form the sixth group, although the seventh group comprises only one oil № 47 in Aksay. Sample set with №8 was discovered in the pay zones of Taur field and well № 75, exploiting the same horizon in the northern part of Aksay. The ninth oil group was identified in cretaceous producing layers of the Khairgeldy South-West field and Jurassic beds of the Khargeldy North field, while the identical composition of the cretaceous oil from the Khairgeldy North and Khairgeldy fields forms the tenth group. The last eleventh group includes oil from well №. 12 on South-west Khairgeldy, although it has some similarities with Taur oils.
 For 20 oil samples was carried out biomarker analysis, according to the results of which all studied oils were formed in terrigenous (shaly) OM, deposited in lacustrine environment. Oils from central Nuraly are more thermally mature and lighter in density than those from western Nuraly. Oils of Akshabulak East are thermally less mature than oils of Central Akshabulak and Akshabulak South despite its deeper deposition.
 Based on the performed analysis, in the conclusion were presented 5 prospective hydrocarbon accumulation zones for increasing hydrocarbon reserves in the future. But the results of the performed studies provide valuable information only when integrated with confirmed geological and seismic data.