Aryl isoprenoids in crude oils of the Nyurol’ka depression (southeast of Western Siberia)

Composition of crude oils from the Nyurol’ka depression has been studied with the aim to reveal the specifics of the composition and its change along the section. It has been found that the main distinctive feature of oils from the Nyurol’ka depression in the southeast of Western Siberia is the presence in most of them of aryl isoprenoids (trimethylalkylbenzenes bearing an isoprenoid alkyl substituent), which never have been detected in crudes from other oil regions of Western Siberia. It has been shown that aryl isoprenoid-containing oils occur over the entire section of the Nyurol’ka depression from the Paleozoic to the Upper Jurassic. The maximal concentration of these compounds has been found in Paleozoic and Lower Jurassic oils occurring in the east and south of the depression. Their amount is 2.4–3.3 times that of alkylbenzenes. Paleozoic oils that do not contain aryl isoprenoids differ from the other oils by the presence of retene and a lower amount of the tri- and tetramethyl derivatives among naphthalenes.