Potentially productive zones of lower Jurassic deposits of Surgut and Nizhnevartovsk highs

Kayurov N.

A.A. Trofimuk Institute of Petroleum Geology and Geophysics SB RAS, Novosibirsk, Russia

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Lower Jurassic’s commercial petroleum content in the central part of the West Siberian oil and gas province for the first time was proved by Talin field discovery in the 70-s of last century. This discovery gave an enormous impetus to the study of the Lower Jurassic, aimed at identifying the hydrocarbon accumulation. The main objective of that works has focused on identifying, first of all, large deposits "Talin" type. But so far such deposits were not found more within the West Siberian oil province.

Study area covers the north-eastern part of Khantei hemianteclise, which included Surgut and Nizhnevartovsk highs. According to the scheme geological zoning of oil and gas fields, area is located in the north-eastern part of Middle-Ob oil and gas bearing region. The main hydrocarbon reserves are associated with Neocomian deposits.

The object of research is the Lower Jurassic oil and gas complex, overlain on the pre-Jurassic basement. It presented Kotuhta Formation and its temporal counterparts (Pliensbachian-Aalenian). The formationis divided into two subformations. Lower parts of subformations consist of sand-gravel-aleuritic and sand-silt layers U_11-12 at the lower subformation and U₁₀ (Tyumen classification) at the top subformation. Sand layers overlain by clay formation members - Togur and Pereval`naya, respectively. These formation members have a regional distribution and can serve as a reliable impermeable layer [7].

Using pre-Jurassic basement surface and the roof of the Tyumen Formation network models (created by IPGG SB RAS think tank) in combination with linear relationships between the lower and middle Jurassic sediments have been built structural maps, maps of thickness for clay packs and their underlying sandstones [2,4]. Also, areal extent of the Lower Jurassic deposits was traced on correlation side views and 2D CDP time cross sections. Moreover, using facial interpretation technique of well logging [1,6] were constructed research area paleogeographic maps.

Fig. Structure principal scheme of recognizedand predicted hydrocarbon accumulations are located in Lower Jurassic sediments of the study area.

A detailed analysis of published articles and produce constructions leads to some conclusions:

· Structurally the Pliensbachian-Aalenian deposits clearly traced inheritance of relief from the pre-Jurassic basement. Identifies two major positive structures: Surgut (West) and Nizhnevartovsk (East) highs, as well as a large negative structure - Yarsomovsky megatrough. In structure plan of sandy horizon U_11-12 is a very desiccated, which gradually leveled to younger sediments.

· The highest rates of sedimentation have been confined to the paleotroughs and paleodeeps and located in the southern, central and northeastern parts of area.

· In the area was dominated by erosion and denudation processes, during the formation of permeable beds U_11-12 and U₁₀. The area was an alluvial plain, with developed river system. The lakes and bogs had limited occurrence.Have been widely distributed to local source areas.

Based on the comparative assessment of Talin field [3] with discovered fields in the research area, it was found that the study area does not measure up prediction criterions of "Talin" type oil and gas accumulation. Repose on a joint analysis of structural and paleostructural constructions, paleogeographic reconstructions, and previously published material of permeable layers Pliensbachian-Aalenian sediments, the main prospects are associated with small lithostratigraphic, lithostructural, roof and massive traps (Fig.).

Based on these patterns, were identified the most promising areas for the detection of hydrocarbon accumulation in permeable horizons U_11-12 and U₁₀ in the study area. According these constructions, particular attention should be paid to the central part of the study area, which was distributed to channel deposits. The most good structures are confined to the slopes of the Nizhnevartovsk high.

References:

1. Belozerov V.B., Brylina N.A., Danenberg E.E. (1984) Facial diagnostics of Jurassic continental and coastal deposits of Western Siberian southeast based on well logs.– Problems of geology and oil and gas content of Siberian Upper Paleozoic and Mesozoic deposits, SNIGG&MS, p. 11 – 23.

2. Kazanenkov V.A., Ryzhkova S.V. (2009) Substantiation of lower Jurassic deposits non-paleontological distinguishing of Western Siberian southern areas.– Jurassic System of Russia: stratigraphy and paleogeography problems, Science, p. 72 – 74.

3. Kontorovich A.E., Andrusevich V.E., Afanasyev S.A. et al. (1995) Geologic and formation conditions of giant Talin oil and gas accumulation zone in lower Jurassic continental deposits (Western Siberia), Geology and geophysics, №6 (Vol. 36), SB RAN Publishers, p. 5 – 28.

4. Kontorovich V.A. (2002) Mesozoic and Cenozoic tectonic and oil and gas content of Western Siberian southern areas, SB RAN Publishers, 252 pp.

5. Mukher A.G., Kuzmenkov S.G., Teplyakov E.A. et al. (2007) Contact zone – prospective feature of KMAA Easter areas, Implementation ways petroleum, gas and mining potential of Khanty-Mansi Autonomous Area – Yugra, vol. 1, IzdatNaukaServis, p. 143 – 156.

6. Muromtsev V.S. (1984) Electrometric geology of sands bodies – oil and gas lithological traps, Nedra, 219 pp.

7. 6th Interdepartmental Stratigraphic Meeting decisions on examination and adoption of revised stratigraphic scheme of West Siberia Mesozoic deposits (2004), SNIGG&MS, 114 pp.

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