Oil and Gas Reserves of West Siberia

Located in the arctic regions of Siberia, the Yenisei-Khatanga regional trough is one of the few underexplored areas in Russia, highly promising in terms of oil and gas deposits. Geographically, the study area is situated in the southern part of the Taimyr Peninsula, Krasnoyarsk Krai.

Targeted geological and geophysical investigations of the Yenisei-Khatanga regional trough were carried out mainly in the 1950s—1980s. Significant contributions to these studies were made by I. S. Gramberg, A. E. Kontorovich, V. D. Nakoryakov, L. L. Kuznetsov, V. N. Saks, V. G. Sibgatulin, B. А. Sokolov, D. S. Sorokov, and D. B. Talvirsky. At that stage of investigations, the scientists revealed the main geological and tectonic structural characteristics of the Yenisei-Khatanga Trough, determined its interaction with the fringe structures, and made the first estimates of petroleum and gas potential. During the following decades, exploration works in this region were sporadic and fragmentary, and the collected geological and geophysical data were not analyzed using state-of-the-art methods.

Currently, geological survey of Siberian arctic regions has been resumed. Seismic exploration operations in the Yenisei-Khatanga regional trough are supported by the Russian Federal Agency on Mineral Resources. Active participants in the study of this area are the biggest national oil producers OAO Rosneft and OAO Gazprom. In 2009 Rosneft discovered in this region the Baikalovskoye oil and gas condensate field.

Geological, geochemical, lithologic, petrophysical and other investigations, including a comprehensive analysis of the geological and geophysical data collected in the area of the Yenisei-Khatanga regional trough were carried out by the Institute of Petroleum Geology and Geophysics (IPGG) SB RAS in 2008 and 2009. This composite survey is the most comprehensive synthesis of the region’s geology and oil and gas potential performed in the last 40 years.

The trough itself is traditionally considered to be a part of the Siberian Platform, on which the major part of the Krasnoyarsk Krai, Irkutsk Oblast, and Sakha Republic (Yakutia) are located. According to the existing tectonic maps, the trough borders in the west on the West Siberian geosyneclise, in the north on the Taimyr fold belt, in the south on the Kureika syneclise, and in the east on the Anabar-Khatanga saddle.

Oil and gas reserves of the Siberian Platform are localized in the Riphean, Vendian and Lower Cambrian deposits, whose age is 540—850 million years. The traps controlling these reservoirs are connected with sand and carbonate horizons and have an extremely complex geological structure. Search, prospecting and exploitation of the Vendian-Cambrian oil and gas deposits require the development of new, non-conventional approaches and technologies.

In terms of the oil-and-gas potential, the Yenisei-Khatanga regional trough is part of an eponymous oil and gas-bearing area (OGA) bounded on the west by the Gydan OGA belonging to the West Siberian oil and gas bearing province (OGP). At present, 17 oil and gas deposits have been discovered within the Yenisei-Khatanga OGA. Most hydrocarbon accumulations of the area are concentrated in the Cretaceous sand horizons, which are 95—145 million years old; three accumulations are Middle and Upper Jurassic deposits, formed 145—170 million years ago. The majority of these deposits are gas and gas condensate fields. Oil accumulations were discovered in the Cretaceous deposits of the Payakhskaya, Novosoleninskaya, and Baikalovskaya areas.

So despite the tectonic association of the Yenisei-Khatanga regional trough with the ancient Siberian Platform, of special interest here with regard to the oil-and-gas potential are younger stratigraphic levels, connected with which are the main hydrocarbon deposits of West Siberia.

In the West Siberian OGP, the major part of hydrocarbon deposits is concentrated in the Mesozoic sand formations and controlled by the local uplifts and structural-lithologic traps of a simpler geological structure compared with those of the Siberian Platform. Techniques for the search and prospecting of these objects in West Siberia were developed during half a century. Presently, traps of this kind are reliably revealed with the use of seismic methods. Similar objects with a good oil and gas potential have been explored in the Yenisei-Khatanga Trough.

The structure of the oil-and-gas-promising areas in the geological profile of the Yenisei-Khatanga regional trough has its characteristic features. In the Mesozoic sedimentary cover of the area under study, three regional megacomplexes of oil and gas-bearing sedimentary rocks – the Jurassic, Neocomian (Berriasian-Lower Aptian) and Aptian-Albian-Cenomanian (J, K₁ and K₂, respectively) – are distinguished.

All Mesozoic-Cenozoic megacomplexes are controlled in the top by the regionally developed clay cap rocks (impermeable layers), associated with seismic reflectors. Acting as an individual oil-and-gas promising complex are the Paleozoic deposits, represented in the Yenisei-Khatanga regional trough and cross-border regions of West Siberia by normal sedimentary platform deposits.

As a result of investigations performed at IPGG SB RAS with the use of advanced technologies, the structure of the Yenisei-Khatanga regional trough has been analyzed and the recommendations on oil exploration in this region have been given. The output of work is as follows:

• a unique state-of-the-art bank of geological and geophysical data for this region has been developed;
• lithologic, geochemical, petrographic and petrophysical investigations of drill-hole cores have been carried out;
• based on the previous studies and on the paleontological and palynological data obtained within the framework of the project, the stratigraphy of the Paleozoic, Mesozoic and Cenozoic deposits has been considered in detail;
• a set of new-generation electronic structure maps has been developed;
• a series of seismogeological profiles characterizing the geological and tectonic structure of the studied area has been created;
• geodynamic history of the Yenisei-Khatanga regional trough in the Precambrian and Phanerozoic has been considered;
• Mesozoic-Cenozoic history of the tectonic development of the region has been analyzed and connection between the tectonic processes with the oil-and-gas bearing capacity has been determined;
• structure of the Jurassic and Cretaceous impermeable layers has been analyzed;
• geochemical investigations of oils and condensates have been carried out; their physical and chemical properties determined; a genetic classification of oils performed;
• zones of hydrocarbon generation and accumulation have been distinguished and their scale has been evaluated;
• the oil-and-gas source rocks capable of generating gaseous and liquid hydrocarbons have been isolated, and their generation potential has been evaluated

In the northern and arctic regions of West Siberia, a great number of giant gas fields have been developed. At the same time, this province, like other OGPs in Russia, is facing the acute problem of searching for liquid hydrocarbons. As a result of the studies carried out by the scientists of the IPGG SB RAS, strata of high oil-bearing capacity have been revealed in the profiles of the Middle and Upper Jurassic and of Neocomian deposits, located in the western area of the Yenisei-Khatanga Trough. Sources of liquid hydrocarbons have been identified, their migration pathways shown and accumulation zones predicted.

The complex analysis of the data obtained has allowed performing a quantitative evaluation of the oil, gas and condensate resources; drawing a map of hydrocarbon resource densities; assessing the subsurface management situation; and developing recommendations on geological exploration works and subsurface resource licensing.

According to the results of the quantitative evaluation performed by the IPGG SB RAS, the primary geological resources of hydrocarbons localized in the Mesozoic deposits of the Yenisei-Khatanga OGA are 11 billion tons, and recoverable resources are 7 billion tons.

Targeted geologic exploration works to be carried out in this region will help to make these resources commercial, considerably extend the raw materials base of Russia and, already in 10 to 20 years, increase the production of oil and gas in this area to 10 million tons and 30—40 billion m³, respectively.

References
Antsiferov A. S., Bakin V. E., Varlamov I. P. Geology of oil and gas of the Siberian platform. Ed. by Kontorovich A. E., Surkov V. S., Trofimuk А. А. M.: Nedra, 1981. 552 p.
Kontorovich A. E., Grebenyuk V. V., Kuznetsov L. L. et al. Oil-and-gas bearing basins and regions in Siberia (in eight issues). 1994. Issue 3. Yenisey-Khatanga basin. JIGGM SB RAS. Novosibirsk. 71 p.