Rosneft: The Final Frontier, Hydrocarbon Potential in the Eastern Arctic
N. A. Malyshev, Dr. of Geology and Mineralogy,
V.V. Obmetko, PhD Geology and Mineralogy,
A.A.Borodulin (Rosneft)
Introduction
Today, Rosneft’s activities cover most of the hydrocarbon producing regions of Russia: the Timano-Pechora oil and gas basin, the Volga territory, Northern Caucasus, East and West Siberia and the Far East. Along the shelf of Russian Federation and the adjacent countries, activities are underway in the waters of the Okhotsk, Caspian, Black and Azov seas. As per the company development strategy entitled – Rosneft’s Development Program of Offshore Hydrocarbon Resources (HC) until 2030 – They are planning to commence operations in the offshore areas of the Arctic sea [1]. This makes it very important to evaluate the hydrocarbon potential of little-explored sedimentary basins of the Eastern Arctic, where recoverable resources of hydrocarbons, based on an assessment of the Russian Ministry of Natural Resources (MNR), exceed 12 billion tonnes of fuel equivalent.
Addressing Existing challenges
Estimations of hydrocarbon potential in the East Arctic seas vary depending on data from different sources – from 1.9 bln.toe estimated by USGS [2] to 12.2 bln.toe forecasted by the Russian MNR (as of 01.01.2002). This is both due to differences in resource evaluation methods and a different understanding of the basins’ structure and formation history. This is why, since 2007, the company’s technology block has been working on special research to establish modern regional geological models of sedimentary basins for the entire Russian Arctic, including the East Arctic, as well as basin modeling with an independent evaluation of resources and that of geological risks.
The East Arctic is severely underexplored with little siesmic exploration being done – less than 0.01 km2 per squared kilometer in the East Siberian Sea and 0.08 km2 per squared kilometer in Laptev Sea – and also has an absence of deep wells. Sedimentary cover within the shelf basins is represented by formations of varying ages with basement blocks of multiple aged ancient cratons and folded formations [3, 4]. Continuation of the latter in the offshore area is uncertain, and basement highs and folded areas do not often allow for an unambiguous correlation of reflecting seismic horizons, traced in the East Arctic shelf with those distinguished on the Siberian platform, in the American sector of Chukchi Sea and tied to the drilling results.
To confirm the stratigraphic completeness of the section, forecast the development for oil and gas source rock (OGSR) and hydrocarbon generation centers, reservoirs and seals, allocating prospective objects and resource evaluation, the authors have used the basin analysis, which allows for the determination of a formation (genesis) features, modern structure and geological evolution of sedimentary basins, as well as establishing the conditions of oil and gas generation and accumulation [5]. This integrated methodological approach had included (figure.1):
» collection and generalization of all accumulated geological and geophysical information for East Arctic basins and their margins (drilling results, geological survey and thematic research);
» re-interpretation of seismic data (over 30000 km), aimed for stratification of reflecting horizons, determination of interruptions in precipitation accumulation, seismic-facial analysis, construction of modern structural-tectonic model and reconstruction of the geological development history for the basins;
» multi-variant modelling of HC-systems;
» structural-tectonic and oil and gas geological zoning;
» selection of prospective areas, evaluation of resources and geological risks; preparation of recommendations for selection of most favorable areas for licensing and further study.
Multi-variant modeling on the formation of HC-systems was undertaken due to the absence of shelf wells and corresponding drilling results which are necessary for models calibration. Considering numerous uncertainties in initial data, the parameters of subsoil temperature conditions, the number of OGSR and their potential production features, fault conductivities in time and etc, the data was altered. Evaluation of the resources was done using the volumetric method (with the possibility of separating localized objects within the basin) and by the” geological analogies” method. The North-Alaskian basin was selected as the analogous basin (for the Chukchi and East-Siberian seas).
Geological structure
Laptev Sea
There are presently two principal viewpoints regarding the age of the basement and stratigraphic completeness of sedimentary mantle of Laptev Sea.
1. The Western part of Laptev sea basin lies in the continuation of the Siberian platform, its basement being of Early Proterozoic age. All rock complexes are present within the sedimentary mantle, from the Riphean to the Cenozoic. The Eastern part of the foundation pertains to Late Cimmerian and the cover consists of Cretaceous-Cenozoic depositions.
2. The basement of the basin in every area of the shelf is of the Late Cimmerian (Early Cretaceous, Pre-Aptian) age and the cover is represented with younger (Cretaceous-Cenozoic) deposits.
Based on the results of our work, the continuation of the Siberian platform in the western part of Laptev sea shelf was established beyond doubt. The sedimentary cover is allocated within the Permian-Cenozoic formations[6]. Underlying Riphean-Carboniferous, primarily carbonate formations, considering pre-Cenomanian uplift and erosion, the height of which in palaeo-elevations reaches 3 km, were submersed to a depth of 15-18 km, and seem to have been transformed considerably. They are currently included into the transient formation complex, or acoustic foundation.
The borderline between the eastern and western part of the shelf lies along the Lazarev fault zone, which are supposed to be palaeo-transform zone. Such interpretation of the geological structure of Laptev sea shelf, by analogue with sections of the Siberian platform at the base of the sedimentary section in its western and central parts; along with the development of thick sedimentary formations of Permian, Triassic and Jurassic periods, significantly increases the possibility of potential discoveries of hydrocarbons in this area.
The sedimentary cover is up to 15 km thick and is comprised of three rock types: Upper Paleozoic-Lower Cretaceous, Aptian-Early Miocene and Middle Miocene-Quaternary. The first one is of pericratonic character, the second is of synrift, and the third is of post-rift (syneclise).
The pericratonic complex is composed of Permian-Triassic carbonaceous-terrigenous and Jurassic-Neocomian terrigenous rocks. Based on the analysis of the drilling data and the descriptions of discoveries on adjacent land, Permian-Triassic formations are represented mainly by shallow marine and continental strata, with possible interlayers of tuff, basalts and dolerites within the Triassic interval of the section. Development of deeper subsea rock is forecasted in a land-to-shelf direction, up to condensed depression facies. The Jurassic-Neocomian formations are represented by the interlaying of siltstone, sandstone and argillites, with layers and lenses of limestone and conglomerates, interlayers of coal in the upper part and sandstone-clay turbidite stratum in Stolbovoy and Maly Lyakhovsky islands. Shallow marine sandstone-clay formations are forecasted as the dominant layers on the the shelf. The thickness of the deposit complex for the Laptev shelf based on seismic data varies from 1-2 km to 8 km.
The Synrift complex is divided into two strata – the Upper Cretaceous, that is represented exclusively by a continental coal-bearing molasse, and Paleogene-Early Miocene terrigenous stratum with the development of marine facies (from shallow-marine to depression type) in the central part of the basin. Cretaceous formations consist of conglomerates, gravelite, sandstone, siltstone and argillites with interlayers of coal at the Novosibirsk islands – with volcanic rock of various composition. Paleogene formations consist of interlaying sandstone, siltstone and argillites, and rare layers of limestone and diatomites. The thickness of the Cretaceous stratum based on seismic data varies from 400 to 3500 m, and in the Paleogene-Lower Miocene – from 600 to 5500 m.
The Post-rift complex is analogous by composition to Paleogene-lower Miocene stratum. The unconformity divides it into Middle-Miocene-Pliocene and Quaternary strata that are 200-1300 m and 175-500 m thick, respectively.
As for tectonics, the Laptev shelf is located in a zone of old Siberian cratons and the following three Mezozoic mountain-folded regions: Early Cimmerian Southern Taymyr, the Late Cimmerian Verkhoyansk-Kolymskaya and the Novosibirsk-Chukotskaya. Generalized structural trends of these regions framing the Laptev shelf, indicate the possibility of a continuation of their folded structures into the shelf area.
Within the Laptev basin, the authors had distinguished large super order tectonic elements – primarily the West-Laptev syneclise and East-Laptev anticlise (figure 2). The northmost part of the Laptev sea is located behind the shelf edge on a continental slope. The West-Laptev syneclise includes the distinguished West-Laptev uplift, Ust-Lensk-Omoloy through (rift system), the Central Laptev brow and the North Laptev depression. The East Laptev anticlise entangles the Belkovsko-Svyatonosskaya graben and horst zone and the Anisin trough.
A large part of the local structures in the western part of the shelf pertains to transtension processes (stretch-and-shift), i.e. uplifts are of shift-related nature. In this part of the aquatory, enveloping structures for basement highs are less common. For all local structures, fault tectonics is very typical (figure 2). Within the borders of the above mentioned large tectonic elements, given the presently existing grid of seismic profiles, over ten structures are distinguished, averaging about 2100 km2 in area.
East Siberian and Chukchi Seas
The East Siberian Sea is the least studied with regards to seismic surveying. Moreover, the vast majority of existing seismic profiles are located in its southern and western parts, thus not allowing for a full understanding of the basement structure and sedimentary mantle for the entire aquatory. Based on general geological perceptions, the structure of the East Siberian shelf is assumed to be similar to that of Chukchi Sea, which has had more study dedicated to it.
In the east Siberian sea, two basins have been discovered – East Siberian basin and the Vilkitsky basin (north of the aquatory), while the Russian sector of Chukchi sea includes the South and North Chukchi basins. They are separated with ledges of the Novosibirsk-Chukotsky folded belt. These sedimentary basins are different in age, formation composition and thickness of sedimentary filling.
No drilling has been done in the East Siberian Sea and the Russian part of the Chukchi Sea, however the formations from Riphean to Cenozoic have been studied in detail on outcropping areas of adjacent land, on the Wrangel and Herald islands, and also in wells drilled in the American sector of Chukchi Sea. We are forecasting the section of sedimentary cover based on seismic data with the consideration of these materials.
The Vilkinsky and North Chukchi sedimentary basins, that are developed in the northern part of the aquatory, lie in the Caledonian (Ellesmerian) folded foundation. The sedimentary mantle is from 6-18 km thick and is in five structural formation complexes: the Lower Ellesmerian (Upper Devonian – Carboniferous-Lower Permian), Upper Ellesmerian (Upper Permian – Middle Jurassic), Rift (Beaufortian, Upper Jurassic-Neocomian), Lower Brookian (Aptian-Upper Cretaceous) and Upper Brookian (Cenozoic), and are divided into a series of regional surfaces.
The Lower Ellesmerian is presumably composed of terrigenous rocks similar to the Endicott group and carbonaceous Lisburne group in Alaska, and the Upper Ellesmerian is predominantly terrigenous formations corresponding to the Sadlerochit group (formations Echuca, Kaviik and Ivishak) and Shublik, Sag River and Lower Kingak formations. In the Vilkitsky and North Chukchi sedimentary basins, the total thickness of Ellesmerian complex in this section varies from
6 km in the south to 4 km in the north of the basins.
The Rift (Beaufortian) complex is represented with similarities of the Upper Kingak, Kuparuk and Pebble Shale formations on the Alaskian shelf being predominantly terrigenous, and within Chukchi peninsula it has interlayers of coal and volcanic rock of various composition. The thickest part of this complex in the Vilkitsky and North Chukchi basins exceeds 6 km.
The terrigenous coal-bearing Lower Brookian complex distinguishes three stratigraphic subdivisions that are similar to the Torok formation, the Nanushuk group and Colville formation. On Chukchi peninsula, age-related analogs of this complex are predominantly granitoid. The formations of the complex have a thickness of over 6 km in the Vilkitsky and North Chukchi basins and up to 3.5 km in East Siberian and South Chukchi basins.
The Upper Brookian complex is thought to be represented by terrigenous coal-bearing strata and similar, age-wise, to the Sagavanirktok formation. In the sedimentary basins of Vilkitsky and North Chukchi the deposits are over 4 km thick, and up to 1.4 km in East Siberian and South Chukchi basins.
The basic structural elements of the North Chukchi sedimentary basin are the North-Wrangel ledge and the North-Chukchi trough, which is separated from the former with a hinge fault zone (figure 3). In south-eastern and south-western parts of the basin, along the overlap zone of the Wrangel-Herald, fragments of a trough are traced, which, unlike that of the Colville trough in Alaska, occupies a considerably smaller area and is less evident both structurally and thickness-wise. This must be due to development of large ledges in the Russian part of the shelf (North Chukchi zones of grabens and horsts and Mammoth uplift), that served as barriers during the formation of the foredeep in front of the folded area. Apart from this, in the Early Paleogene age the Wrangel-Herald ledge underwent an intensive uplift, which caused the sediments of the foretrough to develop therein to be subject to erosion processes, and were completely denuded in the central part.
Similar to the highly promising oil-bearing Barrow swell in Alaska, the sublateral bordering uplift in the Russian sector of Chukchi sea shelf in the present structural plan can only be traced near relict depressions of the foredeep. In the areas where these depressions are absent, bordering uplift is inclined northward and is practically unexpressed due to the North Chukchi trough forming from the north.
In the base of the Ellesmerian complex, the authors made the first discovery of the Central Chukchi riftogenic trough of submeridianal extension, consisting of deposits of Early Carboniferous age (similar to the Endicott formation). This downfold is similar to the Hanna trough, traced in the foundation of the sedimentary mantle in the western part of the American sector of Chukchi Sea.
The North Chukchi trough entangles structures of a smaller order: The Andrianov uplift, Western brachyanticline, Western, Central and Eastern trough bends. Within the North-Wrangel ledge, the following secondary structures can be distinguished: Mammoth stage, Wrangel-Herald niche, Academian and Linear-1 and Linear-2 stages, and Linear horst. The majority of prospective local structures are located within the Mammoth, Academian and Linear stages. The Mammoth stage by its composition is most similar to Barrow swell, and the unique deposit of Prudhoe Bay in Alaska (see figure 3 b, c).
For both the East-Siberian and South Chukchi basins, that were both formed on a younger (Late Cimmerian) folded basement, development of sedimentary cover is assumed to be up to 7 km thick and including the following complexes:
» lower synrift Cretaceous (post-Neocomian) complex with developments of grabens, semi-grabens and their separating uplifts;
» average post-rift complex (Pg-N1) with numerous manifestations of long transtension structures extending N-W;
» upper syneclise complex (N2-Q), deposited sub-horizontally and blanketing lower complexes and basement rock.
The basic structures of South-Chukchi basin are Wrangel-Herald zones of horsts and grabens, the Onman ledge, Schmidt depression, Ushakov ledge, Sredinny trough and the South-Chukchi monocline (see figure 3, a). All noted localized prospective objects are located within the Sredinny trough, the Onman and the Ushakov ledges.
In view of poor exploration, sedimentary basins of the East Siberian Sea are not discerned in any greater detail.
The formation of the structural plan of South Chukchi and East Siberian sedimentary basins was greatly affected by transtension processes, which resulted in a wide development of shift-related structures, separated with numerous faults. In the central part of South Chukchi basin, along the main shear zone dividing the basin into two large trough – Schmidt and Spedinny – at the area of its knee-fold, the shift deformations have led to the formation of the Ushakov anticline zone with pop-up type structures, which may be of interest for exploration.
Hydrocarbon Potential
Laptev Sea
Up to now, due to the lack of deep drilling on Laptev shelf, commercial hydrocarbon reserves have not been found. However, the close proximity of Yenisey-Khatanga oil and gas field and the presence of fields of natural bitumen in Lena-Anabar downfold (Olenekskoye etc), as well as numerous bitumen deposits on the Laptev sea coast, the islands of the Novosibirsk archipelago, and oil and gas finds in deep wells of Anabaro-Khatanga anticlinal fold and Lena-Anabar trough give hope that there is a good possibility of discovering commercial deposits of oil or gas reserviors on the Laptev sea shelf.
Potential oil and gas source rock in the region developed in the Permian-Paleogene section. On the edges of Laptev sea, within Lower-Permian deposits, numerous interlayers of clay are present, where organic matter (OM) of mixed (humus-sapropelic) and sapropelic types varies from 2.4 to 3.7%. In the Lower Triassic deposits of the Lena-Anabar region on land, the content of sapropelic OM in argillites makes up 0.5-2.7%, and on Novosibirsk islands it reaches 11-16% [7]. In the Lower and Middle Jurassic deposits, OM is of mixed composition, and is contained in argillaceous interlayers, reaching 0.5-2%. Development of the abovementioned types of oil and gas source rock is expected on Laptev shelf, and it is presumed to be thicker in the aquatorial part and has higher oil generation potential.
In the Cretaceous-Paleogene rocks, the TOC varies from 0.26 to 19.54%, and is of mixed composition, primarily humus type. On this basis we can presume that the Cretaceous-Paleogene complex will be gas-producing.
The Eocene deposits on the Lomonosov ridge (the oceanic part of the Arctic) have interlayers of argillic-silicious rock (the so-called Azolla interval) with TOC of up to 3%. Considering the extensive development of marine deposits in the Paleogene section on Laptev shelf, and based on results of seismic analyses, similar oil-source rock may be developed there.
To evaluate the maturity of OGSR, the conditions for generation, migration and accumulation of hydrocarbons on Laptev shelf, 2D and 3D modelling of oil and gas formation was done using TemisSuite software. As mentioned earlier, multi-variant modelling was carried out for various features of the strata including heat flow and conductivity of fault disturbances in time.
The lithological models of sedimentary cover were made for carbonate-terrigenous (Permian-Jurassic) and terrigenous (Cretaceous-Cenozoic) types of sections based on conducted palaeographic alterations with consideration of gradual decrease of precipitation grain size in transition from continental to depression facies. Values of heat flow were accepted by analogies with the existing measurements from land and north-east part of Laptev sea [8]. The calculations were made using both constant heat flow values (45, 65 and 85 MWt/m2) and values differentiated in time (20 MWt/m2 during pre-rift stage, 100 MWt/m2 during active rifting and 65 MWt/m2 during post-rifting time).
All models calculated so far indicate HC-saturation for the larger part of the section. Based on modelling results, and depending on the value of heat flow, the Permian oil and gas bearing rock started fulfilling its generation potential during mid-Triassic and late Jurassic time, early Triassic rock – in Jurassic and late Cretaceous time, and overlying OGSR – during the rifting stage (late Cretaceous – Cenozoic).
The pre-Cenomanian uplift had a significantly negative effect on the oil and gas accumulations. Due to erosion and, at a later stage, the absence of a reliable cap rocks, the destruction and then reformation of hydrocarbon accumulations may have occurred. This can be especially noted on models with a high value of heat flow. However, the models with a better distribution of heat flow show that the basic oil-source rock fulfilled its generation potential after an increase of heat flow, and during an active downwarping in the rifting process, which allows us to estimate that most of the hydrocarbon accumulation have been preserved. Influence of other, less significant uplifts and erosion in the region were not considered during the modelling due to their insignicicant effects.
Modelling with various conductivity of the faults in time shows HC-saturation of structure crests even during a constant high conductivity of faults, starting from late Cretaceous and to the present time. This is related to the fact that the largest fault disturbances are found on structures flanks. Their crests are, as a rule, less dislocated and the uplifts are enourmous. From this we can conclude that all necessary conditions were present for the formation and preservation of hydrocarbon accumulations, regardless of active fault tectonics.
Based on 2D and 3D modelling, formations of the Permian and Early Cretaceous has, by now, completely fulfilled its generation potential (in areas of downwarping), or is in the main zone of gas generation (gas window) (in uplifts). With that, major oil generation was occurring in the main zone of oil generation (oil window). Late Cretaceous-Cenozoic rock deposits, in areas of downwarping, are located in oil window or at the beginning of gas window and, in fact, had just started to fulfill its potential.
The results of structural plan analysis show that the major part of traps had formed either before active migration of HC from oil source rock, or, sometimes, at the same time. On the whole, this is a favorable factor in the formation, and preservation, of hydrocarbon accumulations.
Based on 2D and 3D modelling, and also considering the features of distribution, types and maturity of OGSR, predominant oil accumulations of the Permian and Lower Cretaceous part of the section have been forecasted, along with a predominance of gas deposits in the Upper Cretaceous and Cenozoic formations.
Based on the modelling results, the structural plan analysis, the thickness of the sedimentary cover, understanding of reservoirs and OGSR distribution and amount of pre-Cenomanian scouring on palaeo-uplifts, the authors have started to zone the oil and gas geology for the shelf. The distinguished areas are West Laptev, Central Laptev, Anisin, Omoloy and East Laptev and promising oil and gas bearing zones (POGBZ) of the continental slope (behind the shelf edge). With that in mind, the best potential zones expected for the West Laptev and Central Laptev POGBZ, located near large centers of hydrocarbon generation and featuring very thick sedimentary mantle. POGBZ’s of the continental slope, Anisin and Omoloy, are of great interest for oil and gas prospecting, but do require a great deal of additional study. The East Laptev zone is considered to be lacking in potential. Comparing the resource evaluation performed by the authors with the estimations of MNR, it should be noted that MNR had somewhat underestimated the oil constituent due to it’s disregarding of the HC potential of the Permian and Low Cretaceous formations.
Chukchi Sea
The North Chukchi basin is very promising based on a structural similarity with the North Alaskian basin lying eastward, where over 20 oil and gas fields have been discovered to date, including the unique Prudhoe Bay field with oil resources of 3 to 5 bln tonnes [9].
To estimate the potential in this section of the North Chukchi basin, already published geochemical research data for rocks sampled on Wrangel Island, the Chukchi peninsula, and from wells of the American sector of Chukchi shelf and Alaska’s North Slope was used.
Oil and gas source rock had been confirmed in the entire mantle section from the Carboniiferous to Paleogene. The Lower Carboniferous formations (Kekiktuk) have interlayers of argillites with an organic material content of 0.5-1% and kerogene of humus-sapropel and humus mixed types. In the Upper Carboniferous – Lower Permian Lisburne formation in Alaska, argillites and marlstone have been detected with an organic material content of 0.5-1% and type-2 kerogene. Upper Permian deposits on Wrangel Island have numerous interlayers of black argillites and marls [10]. These have not undergone geochemical analysis, but considering the predominant development of depression facies in this area, high organic material content of sapropel type is expected. Argillites from the Ivishak formation are full of sapropel and humus-sapropel type organic material (0.5-3% content).
Marlstones and argillites of the Shublik formation are the main oil producing stratum in the region. Their organic material content reaches 8%, and the kerogen is mostly of sapropel type. The Lower Cretaceous argillites of the Pebble Shale formation also bear good oil-source potential. Their organic matter varies from 1.6 to 5.5 %, with kerogen type 2 and 3. The youngest oil-bearing rock known in the area are the Lower Cretaceous argillites of the Torok formation (Aptian-Albian). TOC is 0.6-2.2%, with kerogen of mixed humus-sapropel type. The Middle and Upper Jurassic argillites of the Kingak formation have a varying TOC from 0.5 to 6.47%, with kerogen type 2 and 3. Rock deposited higher on the section is of the Upper Cretaceous – Paleogene complex and is primarily gas-bearing. TOC reaches 5-6% (up to 12.3% in individual samples) primarily due to humus constituent.
Perceptions about the modern geological structure and the development history of sedimentary basins in the Russian shelf of Chukchi sea were used to construct 2D models of the hydrocarbon-system formation using TemisSuite software. Due to the absence of actual geochemical material for the Russian aquatory, the authors undertook multi-variant modeling with various geochemical parameters, such as the presence and distribution of OGSR, its thickness, type of kerogen and the concentrations of organic material. The heat flow was accepted at an average for existing measurements (50-60 MWt/m2). The calibration of the heat flow was carried out based on the Klondike well in the American sector of Chukchi sea.
The results of 2D modeling show that the potential of Upper Paleozoic deposits on the Wrangel-Herald ledge had been entirely fulfilled before the Late Jurassic time, with the Mezozoic ones partially fulfilled between Cenozoic and the present time. The potential of Cretaceous-Paleogene OGSR has not been fulfilled so far. In the region’s major center of generation (North Chukchi trough), the potential of the Upper Paleozoic deposits had been fulfilled entirely before Late Jurassic period, with the ones from the Mezozoic period – also entirely before Late Cretaceous, and Cretaceous-Paleogene – partially between the Cenozoic and the present time.
In the sedimentary section of North Chukchi basin, on the Wrangel-Herald ledge, the most promising layers for exploration are the Permian, Triassic, Jurassic and Lower Cretaceous deposits (figure 4).
Gas reserviors may be discovered in Cretaceous-Paleogene formations and in flanks of North Chukchi trough. The major geological risks here are related to development of the terrigenous reservoirs in Permian-Triassic complex, and the preservation of formations from the early Cretaceous and early Paleocene erosions.
With regards to oil and gas geology of North Chukchi basin, a potentially gas-bearing (Andrianov) and a potential oil and gas bearing (Academic) areas are cited, with the latter potentially including Linear, Mammoth and West-Mammoth gas-bearing regions. The greatest oil-bearing potential is related to Academic area, where eight prospective uplifts are distinct.
A total of about 20 prospective objects are distinguished on the shelf of the northern part of Chukchi Sea. Hydrocarbon resources calculated for these objects somewhat exceed the estimations of MNR (without consideration of geological risks). Although there are is great potential for oil and gas finds in this area, the risk to the deposits from scouring is high, and therefore further studies are needed, including structural drilling along the forefront of folding zone at the Wrangel-Herald ridge, where shallow deposition of pre-Upper Cretaceous sediments are found, with a purpose of evaluating the erosion.
The South Chukchi sedimentary basin appears to have less potential than the North Chukchi basin. Key areas here are the Nadezhdin PGBA, Onman and Ushakov POGBA, where the predominatly gas-bearing capacity of the Upper Cretaceous-Paleogene sediments is forecasted, confined to downwarping depocenters and Schmidt and Sredinny troughs. The main risks to the basin are of preserving the hydrocarbons deposits during the pre-Middle-Miocene erosion.
East Siberian Sea
Because of the poor exploration up to now on the western Siberian Shelf, calculating the potential resources can only be done by annalogy. Taking in to account the evaluation of the Vilitsky basin and comparing it to the western part of Alaskan Arctic, our estimations of the total recoverable reserves come very close to those of the MNR. In order to get more reliable estimates however, further study, including seismic surveying and stratigraphic drilling, is necessary.
Conclusion
The analysis of the geological structure and indeed the prospects for oil and gas bearing capacity for the sedimentary basins of Eastern Arctic gives evidence of a great potential for development and allows us to point out the best areas for further study. Each basin that we have examined has certain inherent geological risks however which may affect the initial reserves estimations. To resolve the existing problems, further study of the basins is necessary, including both additional seismic exploration and the drilling of deep stratigraphic wells.
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This article was published in the NK Rosneft Scientific and Technical Newsletter (Nauchno-tekhnicheskiy Vestnik OAO “NK “Rosneft”, No.1, 2010, pp. 20-28; ISSN 2074-2339) and won the 1-st prize in the 2010 competition for the best publication in the newsletter. Printed with permission from the Editorial Board.
