«OIL AND GAS GEOLOGY» № 6/2016
Kontorovich A.E., Aksyutin O.E., Varlamov A.I., Dmitrievskiy A.N., Ermilov O.M., Kashirtsev A.R., Kontorovich V.A., Kurchikov A.R., Nesterov I.I., Safronov A.F. Russian academy of science serving Russia. I.M.Gubkin and A.A.Trofimuk – great soviet and russian 20TH century oil experts
OIL AND GAS GEOLOGY ISSUES OF SIBERIA
The paper considers detailed geological structure of the Hettang-Aalenian deposits of the Ust-Tymskaya megadepression and the adjacent area, laying noncomformably on the Pre-Jurassic basic rocks and bounded in the roof with U10 coal bed. Geological section of the Lower Jurassic and Aalenian deposits is fully presented, Urman, Togur, Peshkov-skaya, Salatskaya formations and Lower Tyumen subformation are allocated. Within the Hettang-Aalenian deposits two separate oil-gas complexes are considered, they are the Hettang-Early Toarcian (J16-17 sand beds) and the Toar-Aalenian (J15 and J11-14) complexes. Their oil-gas prospects are estimated.
The article presents the results of detailed differentiation of Bazhenov horizon (Bazhenov forma-tion, lower Tutleim formation) based on complex lithological, geochemical, and paleontological data correlated with well logging. The criteria for consistent stratification of the Bazhenov sediments within the boundaries of fields, tectonic and structural-facies areas were worked out. Marking horizons and reper regional intervals were revealed to provide reliable correlation between sections on vast distances. During recent years, many geological research groups worked on areal Bazhenov sediments analysis, match-ing their supply and oil generation intervals to compare different areas of Bazhenov horizon distribution. Thus, that is essential to determine Bazhenov sediments structure and correlation and the work is urgent and demanded.
Paleographic reconstruction and lithologic-facies analysis of potential reservoirs in the Upper Proterozoic-Paleozoic complexes of the Pre-Yenisey sedimentary basin in the east of West Siberian geosyneclise were performed based on a new regional seismic survey and well drilling data. The reservoirs’ zonation was carried out. With geothermal gradients and organic pyrolitic survey data considered, the conducted analysis of sedimentary strata submersion allowed to specify historic conditions of hydrocarbon accumulations generation and conservation.
The work is devoted to paleogeography and sedimentation conditions study of Parphenov horizon of Chorskaya Vendian formation within the central part of the Angara-Lena oil and gas area. Paleogeographic scheme based on production logging data and core description was constructed. Complex criteria allowed to indicate two most promising petroleum zones. Such zones are observed in the vicinity of wells 3 and 6 of the Angara-Lena field as well as in the area of the Kovykta field. A distribution area of alluvial facies to the east and south-east of the Kovykta gas condensate field should also be considered potential zone.
Extensive data collected for the South-Tungusskaya oil-gas area and the adjacent territories includes data on more than 350 deep and core wells and approximately 300 seismic profiles with total length exceeding 20 thousand km. Based on the material regional structural seismic-geological model was constructed which provided basis for trappean body volume estimation in the investigated area and revealed both areal and vertical sills arrangement regularities in the sedimentary cover. The proposed method for the assessment of trapps content in sedimentary cover considers complex polifacies structure of the Cambrian deposits in the studied area. Zones less affected by trappean magmatism are oil-and-gas promising.
The work is devoted to sedimentation conditions study of the V10 Vendian Nepa formation horizon in the central regions of Nepa-Botuoba anteclise. Paleogeographic scheme based on production logging data and core description was constructed. The allocated environments were attributed to alluvial, deltoid and shore-marine complexes. The most promising oil land allocated according to oil-and-gas criteria is about 300 km2 large and it is located in the south-eastern part of the area.
In the course of the research based on a comprehensive analysis of the deep drilling data and structural constructions made according to the results of seismic data interpretation, the boundaries of the lower Vendian terrigenous and platform Riphean rock complexes distribution were refined. Besides, on the basis of the comparative analysis of the fields geological structure localized in Riphean and Vendian complexes Baykitskaya and Nepsko-Botuobinskaya oil-and-gas areas, oil and gas potential objects were revealed in similar deposits in the south-western part of Siberian platform.
GENERAL AND REGIONAL ISSUES OF ORGANIC GEOCHEMISTRY AND LITHOLOGY
Geochemical analysis of composition and structure of the asphaltenes organic matter (OM) with different genetic nature showed that similarly to kerogen they vary significantly depending on whether they belong to aquagene (sea) or terragene (continental) type. That allowed to develop geochemical criteria for OM type diagnostics according to heterocyclic components. The developed diagnostic criteria for organic matter type according to the study of asphaltenes and kerogen could be used for the diagnostics of the oil source beds for different oil-bearing regions of the country.
The paper provides the results of oil-gas-potential study for Tyumen formation in the Karabashsky region of Western Siberia. Organic content of rocks, its maturity and oil-gas potential are considered, source series in the mid-Jurassic section are allocated, hydrocarbon generation kitchens are delineated and the generation scale is assessed.
Lithologic analysis of the Upper-Jurassic – Lower-Cretaceous black-shale Bazhenov formation sections from two facies regions – Purpeisko-Vasiugansky and Silginsky regions – was carried out. Purpeisko-Vasiugansky region corresponds to abyssal part of the basin while Silginsky region is closer to the paleobasin shoreline. The first region’s sections possess high carbonate and silicon content and widespread distribution of authigenous barite which could be related to more active fauna development in the region. The other region’s sections are characterized with relatively high clay content of rocks. The upper North-Surgutsky region is defined to contain a considerable number of comparatively large carbonaceous concretions. It is revealed that the major calcite source for calcic concretions was mainly represented by coccolithophora, and sometimes by bivalve shells relics. According to rocks lithologic composition analysis it could be concluded that regions adjacent to the Upper-Jurassic – Lower-Cretaceous West-Siberian paleobasin coastline (Mezhov region) possessed significantly less supportive conditions for both carbonaceous and silicon skeleton fauna (radiolaria, coccolithophora, bivalves etc.) and redox conditions for organic matter disposal than abyssal regions of its central part.
In the work organic matter of Sektenskaya formation widespread in the north-eastern part of Siberian platform was investigated. For the first time it was shown that the formation contains four levels of organic-rich rocks. Pyrolitic study indicated potential of Sektenskaya formation rocks (which is facies equivalent for Kuonamskaya formation) is nearly exhausted within Chekurov-skaya anticline slopes. Bitumen and molecular parameters reveal organic matter katagenesis is on MK2 stage or on MK2-MK3 border-line. Organic-depleted carbonaceous and silicon rocks are shown to contain migrated bitumoids. The authors suppose that Cambrian and Permian sedimentary deposits within the northern slope of Olenekskoe uplift and the adjacent areas could carry oil or bitumen accumulations genetically related to Kuonamsky complex.
Based on the analysis of rocks organic matter content, pyrolitic parameters, hydrocarbon biomarkers distribution, isotope carbon content of insoluble organic matter of the Upper-Jurassic deposits in the north-eastern part of Western Siberia and the adjacent western part of the Yenisei-Khatanga regional trough, source rocks were allocated. Oil content for overlaying Cretaceous deposits was studied and genetic correlation between oils and rocks organic matter was conducted.