Paleogeographic reconstruction of the West Siberian basin during the Jurassic is based on a variety of criteria used to evaluate the depositional environments (paleontological, sedimentological, geochemical, etc.). Extensive geochemical data on the hydrocarbon biomarkers in bitumen from organic matter are first used to constrain the depositional setting of this large region over a span of about 45 Myr. The study provides a detailed description of paleogeographic maps compiled for the main epochs of the Jurassic period with the reconstruction of paleorelief and differentiation of potential external and internal sources of terrigenous material. The paleogeographic reconstructions of the basin are considered with implications for the formation of regional seals and reservoir units. A special emphasis is given to interpretation of organic matter type and depositional setting of the major oil and gas source rocks. The study infers a paleogeographic control on the stratigraphic and areal distribution of hydrocarbon accumulations in the basin.

This study provides a comprehensive sedimentologic analysis of the J2 prospective horizon (Middle–Late Bathonian) in the central West Siberian Basin. Based on the extensive dataset, it was established that structural complexity of this horizon is largely caused by a variety of depositional environments. Sedimentary facies of this horizon pass upward from widespread continental at the base, through deltaic or coastal-continental, to marginal-marine at the top. Change in the paleohypsometry of the study area reflects the distribution of depositional environments, in terms of the proportions of continental, transitional, and marine deposits. The study also shows that facies variability and change in depositional settings can have a significant control on reservoir quality, as well as its vertical and lateral distribution. Using a combination of detailed GDE reconstructions, structure contour mapping on the top and base of the J2 horizon, analyses of well test data, probability of reservoir presence, distribution of average porosity and permeability within different subenvironments, a composite map showing variations in the reservoir effectiveness in the J2 horizon was generated.

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We have studied Jurassic sections in the Predyenisei subprovince of the West Siberian petroleum basin, which were penetrated in the Vostok-1, Vostok-3, and Vostok-4 stratigraphic wells. The Urman, Togur, Ilan, Peshkovo, Tyumen’, Naunak, and Mar’yanovka Formations are described from a detailed comprehensive core analysis and log data. The depositional environment for these sediments was predominantly continental. There is evidence for short transgressions in the Ilan (Lower Toarcian) and Peshkovo (Upper Toarcian) Formations, as well as the Upper Urman (Upper Pliensbachian) and the Upper Tyumen’ (Bajocian) Subformations. In the Upper Naunak Subformation (Oxfordian), there was a change of facies from continental to littoral continental and littoral marine. The Mar’yanovka Formation developed in normal marine shallow- or moderately deep-water environments. Although good reservoirs are common throughout the Jurassic section in the southeast of West Siberia, only small, lithologically screened deposits are predicted here.