HISTORY OF HYDROCARBON ACCUMULATIONS IN BEDS OF THE MALYSHEVKA FORMATION ON THE TERRITORY OF KARA-YAMAL REGION

Abstract

The paper describes the characteristics of source beds, considers the structure of fluid seals and formation stages of anticline structures within Kara-Yamal region, bounded from the south by the Messoyakha inclined ridge. Investigations were carried out on the basis of comprehensive generalization of published geological and geochemical materials. It is shown that all formations of the Lower and Middle Jurassic containing aquagene, terragene and mixed types of kerogen in various proportions, possessed oil and gas generating properties. The significant implementation of generation potential due to the high OM catagenetic transformation in rocks of the Middle and especially Lower Jurassic caused the formation of mainly condensate gas accumulations in reservoirs of the Malyshevka Formation. The stages of formation of clay fluid seal in the process of lithogenesis are considered, it was determined by the feature of subsequent transgressive-regressive sediment filling relative to the deep–sea basin in the Late Berriasian – Early Aptian. The history of the anticline structure formation in the roof of the Jurassic structural stage is analyzed separately. According to the results of this analysis, it was found that hydrocarbon accumulations matured within the structures whose main stages of development coincided with the Jurassic period and Early Cretaceous epoch. The beginning time of filling traps with hydrocarbons was defined on the basis of information comparison about the time of compaction of clay strata of the Late Bathonian – Kellovian to the state of fluid seal and time of implementation of the HC main generation phases by oil –and- gas generating rocks. It is concluded that the lithification asynchrony of the fluid seal clay deposits predetermined the time diversity of the HC accumulation generation in the Malyshevka Formation in geological past.