ISSN 0016-8521, Geotectonics, 2018, Vol. 52, No. 3, pp. 297–311. © The Author(s) 2018. This article is an open access publication. Original Russian Text © N.B. Kuznetsov, V.Yu. Kerimov, A.V. Osipov, A.V. Bondarev, A.S. Monakova, 2018, published in Geotektonika, 2018, No. 3, pp. 3–20. Geodynamics of the Ural Foredeep and Geomechanical Modeling of the Origin of Hydrocarbon Accumulations N. B. Kuznetsova, b, V. Yu. Kerimovb, c, *, A. V. Osipovb, A. V. Bondarevb, and A. S. Monakovab aGeological Institute of the Russian Academy of Sciences, Moscow, 109017 Russia bGubkin Russian State University of Oil and Gas, Moscow, 119991 Russia cOrdzhonikidze Russian State Geological Prospecting University, Moscow, 117997 Russia *e-mail: [email protected] Received November 26, 2017 Abstract⎯We present tectonic implications for hydrocarbon accumulations in the Ural‒Novaya Zemlya Foredeep. Its eastern flank is rich in economical oil and gas deposits mostly localized within the fold-and- thrust belt that was constructed as a result of continent‒continent collision during the Ural Paleoocean closure. On the basis of striking correlation between oil and gas accumulation and fold-and-thrust tectonics we per- formed geomechanical and petroleum systems modelling that allowed us to propose a new geodynamical model for hydrocarbon accumulations in both fold-upthrust and subthrust structural levels of the Ural‒Novaya Zem- lya Foredeep. Keywords: upthrust fault structures, subthrust zones, geomechanical modeling, Ural Frontal Folds, Ural foredeep, fore-Ural/fore-Novaya Zemlya belt of hydrocarbon accumulations, hydrocarbons DOI: 10.1134/S0016852118030044 INTRODUCTION distinguished in terms of hydrocarbon potential and The epi-Paleozoic Ural–Mongolian Fold Belt is geology as the Ural–Novaya Zemlya Forebelt of Oil constrained to the central part of the modern structure and Gas Accumulations [3]. The hydrocarbon poten- of Eurasia. Geographically and structurally, the belt tial of the axial parts of this belt (closer to areas of plat- separates the ancient East European, Siberian, Tarim, form-style structure) is well explored [9, 10, 24, 45], and North China platforms of the single Eurasian con- whereas the potential of parts of the deep closer to the tinent (Fig. 1). Belts as individualized megaregional epi-Paleozoic Ural Fold and Thrust Belt is largely structural units were first recognized by M.V. Muratov uncertain. These parts of the deep host large hydrocar- [19]. Currently, they are referred to as orogenic or fold bon fields, such as the Vuktylskoe gas-condensate belts, e.g., the Central Asian Orogenic Belt [1, 42]. The field in the Northern Ural part of the deep and the westernmost element of the Ural–Mongolian Fold Belt Saratov, Isimovo, Berkut, and other fields in the is the Ural–Novaya Zemlya fold system [29], which Southern Ural part. extends nearly meridionally for more than 4000 km With regard to geological zoning and hydrocarbon from the northern tip of the Novaya Zemlya archipel- potential, relicts of the Ural–Novaya Zemlya Fold Belt ago in the north to the Caspian Depression in the south. are referred to as the Ural–Novaya Zemlya Forebelt of The Ural–Novaya Zemlya Fold Belt is structurally Oil and Gas Accumulations (Fig. 2). V.P. Gavrilov [3] and paragenetically associated with a negative struc- was the first to distinguish this belt of hydrocarbon ture that extends along this fold belt throughout its accumulations, as well as belts of similar genesis and entire length and is referred to as the Ural–Pai Khoi– paragenetic relationships with orogens produced by Novaya Zemlya Foredeep. subduction–obduction and collision processes. Parts of the Ural–Novaya Zemlya Fold Belt closest The Ural–Novaya Zemlya Forebelt of Oil and Gas to the Ural–Pai Khoi–Novaya Zemlya Foredeep are Accumulations extends for approximately 4000 km characterized by fold and thrust structure, with the (Fig. 2) along the southeastern and eastern peripheries pitches of the axial planes of folds and upthrust fault of the East European Platform and, north of the seg- planes predominantly directed away from the fold belt ment of the Pechora suture adjacent to the Urals toward regions with platform-style structure [8, 24– (Fig. 1), along the eastern periphery of the young 27, 36]. The Ural–Pai Khoi–Novaya Zemlya Fore- (post-Timanian) Timan–Pechora–Barents Sea Plat- deep is highly promising as a structure hosting oil and form. The belt is subdivided into four areas of oil and gas accumulations. On this basis, this megastructure is gas accumulations: the Arctic, Pechora, Eastern 297 298 KUZNETSOV et al. 40° 50° 60° 70° 80° 900° 10010 °0 111100° 12012 0° 131300° 141400° 15150° E Youngyoung Timan–Pechora–Timan–Pechor East Mesozoides (in the north) and Paleozoides (in the south) of the Ural–Novaya Zemlya –southern Fold Belt Barentssouthern Sea 70° 60° Platform a– Ancient Siberian Platform ° West- 50 Siberian plate ides ozo es M EuropeanE u r o p e a n AncientPlatformP lEast aEast t f o r m PaleozoidesPale of and PaleozoidesPale of northernnort o and oides TurgaiT u r g a i zoides of the AltAltai–Sayanozoides of hern area and MongoliaM aleoz trought r oKazakhstan u g hcentral ai–Sayan PaleozoidesP and Mesozoides 40° N Turan and of the Mongol–Okhotsk area plate ongolia Paleozoides Tien Shan of Dzhungaria Paleozoides Ancient Ancient Tarim North China PlatformP l a t f o r m (Sino–Korean) Platform 1 2 3 0 500 1000 1500 2000 km Fig. 1. Ural–Mongolian (Central Asian) Orogenic Belt and its surrounding structures (compiled with data from [46]). (1) Outer contour of Ural–Novaya Zemlya Fold Belt; (2) outer contour of Ural–Mongolian (Central Asian) Orogenic belt; (3) Pechora suture. Volga–Ural, and Northern Caspian. These parts of tuses and stratigraphic unconformities. Most impor- the Ural–Novaya Zemlya Forebelt of Oil and Gas tantly, the latter flanks of troughs are characterized by Accumulations host oil and gas fields that are very widespread fold and thrust structures, the vergence of nonuniformly distributed over the area: areas with which is directed from the fold and thrust edifices scattered small hydrocarbon pools are combined with toward areas with platform-style structure. areas with anomalously high hydrocarbon reserves: centers of hydrocarbon accumulation. The latter areas In terms of geological formations and structure, the host uniquely large hydrocarbon fields. Ural–Novaya Zemlya Forebelt of Oil and Gas Accu- mulations corresponds to the Ural–Pai Khoi–Novaya Structurally, this type of hydrocarbon accumulation Zemlya Foredeep. This megaregional structure initially belts pertains to linear troughs (foredeeps). They are evolved as a single foredeep but was later divided into elongate parallel to areas of platform-style structure and to orogenic fold and thrust systems. In cross section, the segments by a number of transverse and diagonal rises deeps are typically asymmetric in terms of structure. (in order from south to north, these are the Karatau Their slopes (flanks) adjacent (structurally and spatially Jut, Polyudov Mountain-Ridge rise, Pechora Tec- related) to platform margins are characterized by rela- tonic Ridge rise, Sobski Transverse Rise, and a rise tively low thicknesses of sedimentary filling of troughs on the north part of the Pechora Sea) and a series of and by a mostly platform character of the structure and depressions in between. From south to north, these composition of these sedimentary sequences. In con- are: the Bel’skaya, Yuryuzan–Sylva, Upper Pechora trast, the slopes of deeps near fold and thrust edifices (Verkhne-pechorskaya), Greater Synya (Bol’she- demonstrate increased thicknesses of sediments filling syninskaya; including its Kos’yu-Rogovskii part), the troughs, much more complete sedimentary Korotaikha, and Pred-Novozemel’skii (West Novaya sequences than in the opposite flanks, and fewer hia- Zemlya) depressions (Fig. 2). GEOTECTONICS Vol. 52 No. 3 2018 GEODYNAMICS OF THE URAL FOREDEEP AND GEOMECHANICAL MODELING 299 24° 30° 36° 42° 48° 54° 60° 66° 72° 78° 84° 90° 96° E 72° 1 N 68° 2 3 64° 4 60° 56° 5 52° 6 48° 7 44° 0 200 400 600 8001000 km Fig. 2. Ural–Novaya Zemlya Forebelt of Oil and Gas Accumulations and schematic map of its longitudinal segments (compiled with data from [32]). Zones and depressions (circled numerals): (1) Novaya Zemlya Fold Belt. Depressions: (2) Korotaikha, (3) Greater Synya (including its northern Kos’yu–Rogovaya part), (4) Upper Pechora, (5) Yuryuzan–Sylva, (6) Bel’skaya, (7) Caspian. We used the term upthrust in reference to a folded This paper presents the results of our geomechani- crustal section that corresponded to a hanging wall of cal modeling (with the Dynel program package [49]), detachment whereas the term subthrust corresponded which made it possible to reproduce the Paleozoic to a foot wall of detachment. structural evolution of the Southern Ural segment of GEOTECTONICS Vol. 52 No. 3 2018 300 KUZNETSOV et al. the Ural–Pai Khoi–Novaya Zemlya Foredeep and tion, and trap origin processes [43]. In modeling phases of the origin of the folded–upthrust fault struc- petroleum systems, the input data are of crucial tural parageneses (upthrust fault structures) and sub- importance. The volume and quality of information thrust structures (structural features overlain by over- govern the accuracy of the models and uncertainties in thrusts) in the Ural Frontal Fold Zone in the eastern the conclusions. The input dataset for modeling petro- wall of the trough. leum systems is specified by the software requirements and quantity and quality of the geological, geophysi- cal, and geochemical exploration data on the area. The METHODS major data blocks are as follows: The main tool employed in this research was geo- geometrical parameters of the basin (structural– mechanical and numerical spatiotemporal basin sim- tectonic background); ulations, which gave an insight into the conditions lithologies and facies of sedimentary complexes; under which hydrocarbon accumulations were pro- duced in the overthrust zones.