Licensing Priorities for the West Siberian Petroleum Basin
Within the West Siberian basin, most of the promising oil and gas areas are licensed and allocated. The unallocated regions are steadily shrinking and the question regarding the optimal choices for the remaining license areas is becoming more and more acute. In order to identify the promising license areas, we will consider the regional oil and gas content of West Siberian basin and the location patterns of the hydrocarbon fields. It is known that the distribution areas of the deposits are determined, first of all, by geological factors, such as: the presence of reservoirs, seals, traps of various types, as well as hydrocarbon systems that provide generation, migration, accumulation of hydrocarbons and the safety of the formed deposits. It is obvious that the outer limits of these factors is the boundary beyond which the formation of oil and gas fields is impossible. Taking this paradigm into account, considering the map of the West Siberian Oil and Gas Fig. 1. The green line here shows the boundary of the sedimentary basin, within which the aforementioned geological factors that determine the possibility of the existence of hydrocarbon deposits exist, the identified hydrocarbon deposits and the administrative boundaries of the territories and regions adjacent to the Tyumen region are also plotted.
As can be seen on the map, most of the identified deposits are concentrated in the central part of the basin, the geology here is well studied. Obviously, the less studied lands in the eastern part of the Tyumen region and the adjacent territories in Krasnoyarsk and the Urals, including the northeastern lands of the Sverdlovsk Region, are of the greatest interest in terms of the prospects for discovering new deposits. These territories represent the marginal parts of the West Siberian sedimentary basin and have significantly lower geological and geophysical studies and lower densities of predicted resources. Nevertheless, there is a high probability of discovering small and medium-sized hydrocarbon reserves. The identification of larger clusters cannot be ruled out, if they are controlled by a series of closely spaced lithological traps, as is the case in the Shaim oil and gas region, which is located in the western part of the Tyumen region and extends westward towards Sverdlovsk. Oil fields have been identified here right up to the administrative boundary, which, obviously, cannot be the boundary of the distribution of the deposits (Fig . 2).
Territories of the Trans-Urals
Geological exploration work in the northeast of the Sverdlovsk region began in the 1930’s, in the 60’s they resumed, but did not last long, until the discovery of large deposits in the Shirotnoye Ob region. The geologists focused on these large deposits.
In the early 2000’s, the Tyumen Oil Company was awarded the Chernorechensky license area in the northeast of the Sverdlovsk Region. The territory of the site was directly adjacent to the administrative boundary, and several reconnaissance seismic profiles and gravimetric surveys were conducted. After this geological exploration work ceased, the company concentrated its efforts on larger objects. Nevertheless, a comprehensive interpretation of the work performed showed that there are promising zones for development in the Vogulkinskaya strata. The seismic data revealed, sandstone in the stratum are clearly traced in graben-like submerged areas, where they stick to the basement protrusions.
Single exploration wells drilled in the 60’s gave negative results, however, the analysis showed that they were in unfavorable geological conditions, and the tests performed were not reliable enough. The prospective trap, identified by seismic and gravimetric data, is characterized by increased sandstone thicknesses, which, as a rule, is accompanied by increased reservoir porosity.
The available geological and geophysical data indicate that the area under consideration is the southwestern end of the Shaim-Krasnoleninsk oil and gas accumulation zone and is very promising for licensing in order to identify and develop hydrocarbon deposits.
Yenisei-Khatanga Oil and Gas Region
As noted earlier, the marginal parts of the West Siberian Basin that have all the necessary geological factors that determine the possibility of formation and preservation of deposits, are of increased interest from the point of view of acquiring new license areas. The most promising in this respect, in our opinion, is the territory of the Yenisei-Khatanga regional trough, which, as can be seen in the tectonic diagram (Fig. 3), is a «branch» of the West Siberian basin and has an identical geological sections and depth. Within its limits, there are two main oil and gas areas: the Yenisei-Khatangskaya in the western part and the Anabar-Khatangskaya in the eastern part of the saddle (Fig . 4).
Geological and Geophysical Study of the Yenisei-Khatanga Trough
Geophysical Research:
The Yenisei-Khatanga trough began being studied with geophysical solutions in 1930 by the Mining and Geological Administration of Glavsevmorput. Since the mid-fifties, geophysical exploration of the region was acquired systematically. During the sixties and seventies, the entire territory was covered with aeromagnetic surveys.
Areal gravimetric surveys have been carried out since the early sixties. Between 1977-1978, in the territory adjacent to the east and west to the Khatanga Bay, gravimetric and aeromagnetic surveys of 1: 200,000 and 1: 50,000 scales were carried out. In 1991, a detailed airborne geophysical survey was carried out on the right bank of the Anabar Bay, in 1995 – aeromagnetic surveys were conducted in the Leno-Anabar trough.
The reflection seismic survey of the MOV began in 1962. During the sixties and seventies, about 42 thousand linear meters were worked on in the TaimyrAutonomous Okrug and in adjacent areas kilometers of seismic profiling of MOV. Structures of the I and II orders have been identified, and almost all the large anticlinal structures of the III order with an area of 100 km2 and more have been found. The study of the structural plan of Paleozoic deposits has begun within the Anabar-Khatanga saddle.
The seismic exploration of the Yenisei-Khatanga region began in 1972, when the main large structural elements of the depression were mapped. In the second stage, between 1981-1989, about 5500 linear meters were worked out. km of CDP seismic survey (Common Depth Point), however, it can be stated that this territory is poorly studied, and its vast areas have not been studied at all by modern seismic exploration surveys.
At present, a new stage of regional CDP seismic work has begun in Taimyr. This is to prepare a highly promising hydrocarbon region for licensing but which has been poorly studied. The regional geophysical studies are being continued by the State Research Center of the Federal State Unitary Enterprise «Yuzhmorgeologiya» on the Anabar-Khatangskaya saddle, a total of 1200km of profiles were surveyed using a complex of geophysical methods, including CDP seismic exploration and Magnetotellurics (MT) electrical exploration.
Drilling Works:
The geophysical work was accompanied by a core and deep drilling program. A total of 40 deep wells were drilled with a total meterage of more than 66,000m. As a result of the drilling, the material composition and stratigraphy of the Upper Paleozoic, Mesozoic and Cenozoic deposits were studied, large swell-like uplifts and 22 small local structures were identified, and the presence of salt domes was established.
The main result of the exploration work was the identification of four oil fields: Nordvikskoye, Yuzhno-Tyaginskoye, Ilyinsky and Kozhevnikovskoye. The deposits contained in these fields are small in size with low production rates.
In 1954, oil exploration work was stopped and resumed only in 1974, when the forces of the Nizhne-Yenisei exploration expedition continued deep prospecting drilling in the region. The work was focused on local uplifts identified and prepared for drilling by the seismic surveys carried out by Yeniseigeofizika. The first six wells were drilled in the Balakhninskaya area in the eastern part of the Yenisei-Khatanga trough. As a result of prospecting drilling, a commercial gas deposit was discovered in the Vymskaya suite of the Middle Jurassic.
Research peaked in the 1980’s and early 90’s. During this period, the Taimyr geophysical expedition regularly (in each field season) worked with significant volumes of CDP profiles using 2-3 seismic crews, and a specially createdKhatanga oil exploration expedition drilled one or two deep wells a year. The work was concentrated in the eastern part of the Yenisei-Khatanga trough and on the Anabar-Khatanga saddle in order to search, primarily, for oil and gas deposits in the Jurassic-Cretaceous sediments, and in the Upper Paleozoic in the second.
In the Yenisei-Khatanga oil and gas field, deep drilling began in 1978. In the late 70-80’s, a number of parametric and exploratory wells were drilled. The wells penetrated the Cretaceous, Jurassic and, partially, the Permian-Triassic sediments.
In the Anabar-Khatangskaya oil and gas field, a new stage of oil exploration began in 1979. The drilling was carried out on the right bank of the Khatanga Bay. During 1979-1986, the Khatanga oil exploration expedition drilled three parametric and ten prospecting wells. The total volume of deep drilling was 37,500m. The depth of the wells did not exceed 3.5km. The core studies established there were high oil-generating properties of organic matter in the Permian-Triassic sediments, but no hydrocarbon deposits have been found.
By the early 1990’s all geological exploration work was completely stopped due to the onset of the crisis in the industry. Thus, exploration work carried out to date within the eastern part of the Yenisei-Khatanga depression has not led to the discovery of commercial hydrocarbon accumulations. However, valuable factual data were obtained on the deep structure of the territory, as well as direct evidence of the productivity of the permeable horizons of the Middle Jurassic (Vymskaya Formation) and the Lower Permian (Lower Kozhevnikovskaya Formation) in the eastern parts of the Yenisei – Khatanga and Anabar-Khatanga oil-and-gas province, respectively.
The lack of industrial discoveries is partly due to the fact that the drilling was concentrated in the most favorable areas, from an organizational point of view, but seismologically complex in the right-bank part of the Khatanga region, on low-amplitude uplifts identified at the limit of the seismic data’s accuracy.
In general, it can be stated that the knowledge of seismic exploration and deep drilling of the Yenisei-Khatangskaya and Anabar-Khatangskaya oil and gas fields is extremely low, but the geological and geochemical prerequisites identified here indicate a real possibility of discovering large industrial hydrocarbon accumulations here.
Yenisei-Khatanga Oil and Gas Sedimentary Basin
The Yenisei-Khatanga oil and gas sedimentary basin covers the extreme northwestern part of the Siberian. As can be seen in the regional seismic section, it has a geological section identical to the West Siberian basin (Fig. 5) and belongs to the areas with potential for oil and gas.
In terms of oil and gas, the Yenisei-Khatanga basin corresponds to the oil and gas bearing area of the same name, the eastern border of which runs along the western slope of the Anabar-Khatanga saddle, the western border is conventionally drawn along the western slopes of the Taimyr uplift and the Tanamo-Malokhetsky mega-swell (Fig. 6, 7).
16 hydrocarbon fields have been discovered in the Yenisei-Khatangskaya oil and gas field, of which 15 are located in the western part of the region, the largest of which are the Messoyakhskoye, Pelyatkinskoye and Deryabinskoye gas condensate fields.
In the eastern part of the Yenisei-Khatangskaya OGO (remove OGO – should be Oil and gas region) along the Jurassic and Cretaceous complexes, there are 2 provinces that could be highlighted – Balakhninsky oil and gas region with the only field “Balakhninsky” with gas deposits in the sandstones of the Vymskaya suite of the Middle Jurassic, as well as possibly the Zhdanikhinsky field.
The Balakhninskoye field is confined to the mega-swell of the same name, within which, in addition to the Balakhninsky uplift, four more local folds are distinguished, which, in our opinion, are the most promising in this area for identifying new gas fields.
In the most studied western part of the Yenisei-Khatangskaya Oil and Gas, 15 oil and gas fields have been discovered, deposits have been identified in the Lower Cretaceous, Middle and Upper Jurassic. The nature of the distribution of the reservoirs and traps, as well as oil and gas occurrences, in the section of the Jurassic-Cretaceous deposits of the Yenisei-Khatangskaya Oil and Gas Region, 7 regional oil and gas complexes (OGC – oil gas complex) were identified (Fig. 8): Zimniy, Dzhangodsky, Vymsky, Malyshevsky, Lower Cretaceous, Dolgan and Nasonovsky, which productivity is identified in the western part of the Oil and gas region. In the eastern, poorly studied, part of the Oil and gas region, gas shows are confined only to the Zimniy and Vymsky complexes.
The estimate of the total initial geological resources in the Yenisei-Khatangskaya oil and gas field made by FSUE SNIIGGiMS is 19.2 billion tons of conventional hydrocarbons (HC), including recoverable resources: oil 1.6 billion tons, free gas 11.3 trillion m3.
Despite such a large assessment of the hydrocarbon potential, only a small part of its territory is licensed, which is obviously due to its remoteness and severe climatic conditions. As can be seen from the map we have compiled (Fig. 9), the license areas are mainly located on the western lands adjacent to the offshore water area of the Yenisei Bay. The rest of the promising oil and gas territory still belongs to the unallocated subsoil fund.
Our analysis of the available geological and geophysical information has shown that on the territory of the Yenisei-Khatangskaya oil and gas bearing area, with a high degree of probability, will identified numerous fields with large reserves as in all adjacent areas of the Arctic sector of the West Siberian oil and gas province (Fig. 10). Our specialists, having the necessary knowledge and a database of the necessary data, can select the most promising areas for licensing, while making a probabilistic assessment of their resource base, calculating geological risks, and recommending an optimal exploration program.
Anabar-Khatanga Oil and Gas Region
The territory of the Anabar-Khatag Oil and Gas Region includes both on and offshore areas of the Khatanga Bay (Fig. 11). As noted earlier, it has been poorly studied with field geophysical methods, and vast areas have not been studied at all by modern seismic surveys (Fig. 12).
As for the adjacent Laptev Sea shelf and the offshore area of the Khatanga Bay, seismic surveys of the CDP began here in the mid-eighties of the last century. The first ariel seismic studies were carried out by Sevmorgeologiya PGO between 1985-1986 in the offshore area of the Khatanga Bay. In 2005, the marine integrated studies of the southwestern part of the Laptev Sea were resumed: 3000km of seismic profiles of CDP in combination with gravimetry and hydromagnetometry. In 2006-2007, the network of profiles was continued to the west: 2,250km of reflection seismic survey were conducted in combination with gravity and magnetic exploration.
At present, a new stage of regional seismic exploration has begun in Taimyr, aimed at preparing the highly promising, but poorly studied, area for licensing. The geophysical research was continued by Yuzhmorgeologiya: 1200km of survey were conducted using a complex of geophysical methods, including seismic prospecting and electrical exploration.
The prospecting and appraisal drilling stage at the Anabar-Khatanga interfluve began in 1979. Drilling was carried out on the right bank of the Khatanga Bay in order to search for oil deposits in the Upper Paleozoic sediments. During 1979-1986, the Khatanga oil prospecting expedition drilled three parametric and ten prospecting wells. The total volume of deep drilling was 37,500m. The depth of the wells does not exceed 3.5km.
The wells penetrated the Cretaceous, Jurassic and partially the Permian-Triassic sediments, the summary section of the geological section of the considered territory is shown in Figure 13.
As a result of the drilling, numerous oil and gas shows were established, which indicates the sufficiently high oil-generating properties of the organic matter of the Permian-Triassic deposits, the hydrocarbon deposits were not of commercial importance (Fig. 14).
By the early 1990’s all the geological exploration drilling programs were completely stopped due to the onset of the crisis in the industry. Thus, the studies carried out to date have not led to the discovery of commercial deposits of hydrocarbons, but they have made it possible to obtain valuable factual data on the deep structure of the territory, as well as direct evidence of the productivity of permeable horizons from the Cenozoic to the Lower Permian.
On the territory of the Anabar-Khatangskaya oil and gas region, four small oil fields are known in the Upper Paleozoic and Lower Mesozoic formations in the South Tigyanskaya, Nordvikskaya, Kozhevnikovskaya and Ilyinskaya areas; minor hydrocarbon inflows were obtained in the Chaidakh area.
The oil and gas potential of the territory is associated with the large positive structures available here. The conducted seismic works have mapped a system of swell-like uplifts that plunge into the bay and are promising for licensing and prospecting for large hydrocarbon deposits. As can be seen on the map (Fig. 15), these structural formations are associated with the highest densities of initial geological resources.
The results of the analysis of geological and geophysical information indicate the high prospects of the territory. In our opinion, this is evidenced by a number of basic prerequisites for oil and gas shows:
● large, up to 10-12 km thick sedimentary cover, capable of generating a significant amount of hydrocarbons;
● contrasting structure of the cover, which leads to the existence of a large number of structural traps;
● stable immersion of the territory of the region at the later stages of geological history;
● numerous signs of oil and gas obtained in a wide interval of the geological section.
Based on the structural features of the territory, the composition of the constituent rocks, the history of development, the following main promising complexes of the sedimentary cover section have been identified: Upper Proterozoic, Lower Middle Paleozoic (subsalt), Upper Paleozoic and Mesozoic.
Prospects for the oil and gas content of all local uplifts revealed recently by seismic exploration (Belogorskoye, Labaznoye, Zhuravlinoye and others), where reservoir type anomalies were identified according to seismic data, as well as a priori data on open oil deposits, indicate that the Upper Paleozoic oil and gas complex is among the available targets for drilling that can be considered as the most promising for detecting hydrocarbons.
Taking into account the peculiarities of the structure and facies composition of the Upper Paleozoic sediments, it is possible to predict the presence of traps associated primarily with anticlinal uplifts – predominantly of a structural type, lithological and tectonically complicated, near-fault, lateral, near-contact, lithologically screened and combined. Moreover, some of the traps can probably be confined to buried uplifts, which have so far been revealed only by seismic exploration.
Assessing the territory by general geological indicators, it can be noted that the most preferable for licensing and subsequent exploration of hydrocarbon deposits are the most studied structures located on the western coast of the Khatanga Bay.
Yuzhmorgeologiya initial estimates of the geological oil resources Anabaro Khatangsky oil and gas region was 3151 million tons. Recoverable – 789 million tons. Initial resources free gas amounted 1223 bcm3.
Thus, the resource potential of the Anabar-Khatanga oil and gas field is very high, which allows us to expect the discovery of large hydrocarbon deposits here.
Authors
Evgeny Popov – Executive Director
(Nedra-Consult LLC)
Yuri Stovbun – Deputy Chief Geologist
(Nedra-Consult LLC)
