Medyn-Saremboy Anticline zone Lochkovian reservoirs structure and petroleum potential

Mironcheva E.Y.

LARGEO, Moscow, Russia; Moscow State University, Moscow, Russia

mironcheva@mail.ru

The investigated Medyn-Saremboy anticline zone is associated with the north-east of Varandey-Adzva structural zone. Geographically it is situated in Nenets Autonomous Area of the Arkhangelsk Region, on the territory of the Medyn Peninsula and in water area of Khaypudirskaya and Perevoznaya bays of Pechora Sea.

Toboy, Myadsey, Medyn, Perevoznoe, Varandey-Sea, Medyn-Sea fields are of some interest here. Lochkovian carbonaceous, Pragian terrigenous, Eifelian terrigenous, Timanian terrigenous, Frasnian carbonaceous and Tournaisian carbonaceous deposits are producing.

Stratigraphy

An object of current investigation are the most geologic low and deeply buried Lochkovian deposits, that are productive also on the larger part of Timan-Pechora basin. The section is considered to be a stratotypic for the whole north-eastern part of the basin, therefore the research subject is now becoming new urgent due to the fact of new fields discovery.

Lower Devonian Lochkovian stage contains the deposits of Ovinparmskiy and Sotchemkyrtinskiy horizons. The most dismembered of them is Ovinparmskiy horizon. The maximum thickness falls to the northern part of the territory (up to 800 m).

Four members are stood out as a part of Ovinparmskiy horizon (bottom-up members I-IV).

Member I (thickness 50-70 m). Basic. Clayey deposits, marls, loamy limestones. Sequence is characterized by enhanced gamma-ray activity and lower resistivity.

Member II (thickness 110-145 m). Four thick (15-35 m) producing carboniferous layers (bottom-up A, B, C, D, E) with clayey limestone (5-10 m) delimiters. Could be good reference mark. Producing layers are formed by limestones and dolomites. The member is characterized by the high resistivity with lower radioactive background.

Member III (thickness 90-125 m). Sequence is formed by clayey marls with loamy limestones sublayers. The member could be a good seal for collector layers of Member II.

Member IV (thickness 45-95 m) is formed by limestones, secondary dolomites and marls. Dolomites are dominated in the upper part of sequence.

Sotchemkyrtinskiy horizon is presented by the alternation of sedimentary dolomites and anhydrites with subordinate sublayers of secondary dolomites and claystones. From lithological point it is subdivided into two complexes: clayey-carbonate and anhydrites-carbonate.

The lower clayey-carbonate complex (thickness 75-90 m) is presented by sedimentary dolomites, dolomitic marls, with minor sublayers of argillites and secondary dolomites. Differently oriented fractures filled with anhydrite are observed. The sublayers of porous oil-saturated carbonates occur.

The upper anhydrite-dolomite complex (thickness 295-305 m) is presented by alternation of sedimentary sulfates, dolomites, anhydrites, dolomite marls. Rare sublayers of siltstones occur.

Tectonic

Tectonically the studied area is located at the junction zone (tectonic contact) of the Pechora plate and the external part of the Paykhoy-Novozemel'sky fold-and-thrust belt. In the central part the Ordovician-Triassic rocks (autochthon) are tectonically overlapped by the allochthon rocks, which were formed as result of an overthrust during the pre-Jurassic time. In the eastern part the autochthon rocks are overlapped by the allochthon rocks formed as results of a blanket appeared during the Late Cretaceous time.

Structure of the Medyn-Saremboy anticline zone is complicated in the north-eastern direction, to the zone of the Vashutkinsko-Talotinsky overthrust. By the Vashutkinsko-Talotinsky overthrust, the Silurian – Lower Devonian deposits composing the Chernova range are thrust over on the Carboniferous-Devonian deposits of the Medynskaya-Saremboyskaya zone. The the Vashutkinsko-Talotinsky overthrust has deep underlay, and it is clearly seen in the magnetic field and may be traced north-westwardly to the aquatory of the Pechora Sea. The frontal plane of the overthrust is inclined to the north-east on the angle 35-40^о. In the sedimentary cover it represents a series of overthrusts and upthrow-overthrusts.

Petroleum potential

Lochkovian stage productivity is associated mainly with ovinparmian limestones and dolomites. Oil pools of Medyn, Toboy, Myadsey and Perevoznoe fields falls to the layers A, B, C, В and E of carbonate member II. Abnormal high pressure is typical.

Clayey-carbonate deposites of member III are working as a seal.

Also a carbonate layer of the member IV, formed by the secondary dolomites, could be a good reservoir. It is producing on North-Saremboy fields and Medyn and Perevoznoe fields gave oil-shows.

Structural and tectonically screened traps are predicted due to the trust-belt structure development.

References:

1. Timonin, N.I. (1998). Pechora plate: history of geologic development in Phanerozoic. Ekaterinburg, 240 pp.

2. Zhemchugova, V.A. (2002). Natural reservoirs in carbonate formations of the Pechora oil-gas bearing region. M., MSTU. 241pp.