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Russian Geology and Geophysics

2001 year, number 11-12

Scientific heritage of A. A. Trofimuk

V. S. Vyshemirskii, A. E. Kontorovich, and G. S. Fradkin
Pages: 1703-1716

Petroleum resources and production

N. A. Krylov
Keywords: Petroleum reserves, explored reserves, production rate, prediction
Pages: 1717-1723

Abstract >>
The relationship between oil reserves and annual oil production is considered. The correlations between the Russian and American resource classes are discussed in the context of the difference in this relationship in Russia and USA.
The notions of quality of explored reserves (reserve concentration, well production rate, and recovery of initial reserves) and inferred resources (concentration of the initial total resources and degree of their exploration) are considered. Depauperation of residual resources of various classes during their development is inferred.
The main results of prediction of petroleum production in Russia in the 21st century are reported. The peak of oil production is expected to be in 2020, and of gas production, in 2030. A decrease in oil production to 2.0-1.8 108 tons and in gas production to 3.5–1011 m3) is expected by 2100.

Geodynamic types of global petroleum-bearing belts and their characteristics

V. E. Khain and L. E. Levin
Keywords: types, thermal regime, rate of sedimentation, petroleum potential
Pages: 1724-1738

Abstract >>
main petroleum-bearing belts are confined to the passive margins of continents – recent and ancient. The recent margins form three global belts which can be considered subtypes differing in time and rifting-spreading stages: Indooceanic-Atlantic, Circum-Arctic, and Mediterranean-Persian.
Sedimentary basins of the three subtypes are characterized by a high rate of sedimentation, up to 5-10 cm/ka, but differ in recent thermal regime. One subtype has an increased thermal regime with a depth of 100 oC isotherm of 2-2.5 km in separate basins. The other two subtypes are characterized by a different thermal regime, with 100 oC isotherms established at depths of 5-7.5 km.
In the case of ancient passive margins, large fields are connected with rift massifs. The post-rifting stage of these belts can be finished by thrusting emerged near orogen and accompanied by formation of molasse foredeeps and multilayer nappe structures. The second type of petroleum belts is confined to active margins, mainly to the Circum-Pacific belt and Western Mediterranean region. Associated with different-age zones of subduction, the basins of the Caspian-Black Sea region can be distinguished as a specific subtype. Subsidence at the last stage is accompanied by an avalanche rate of sedimentation, up to 30 cm/ka. The increased thermal regime (except for the basins of the Caspian-Black Sea subtype) with 100 oC isotherms at depths of 1.5 to 2.5 km contributed to quick generation of organic matter and the most complete realization of petroleum potential.
The third is intraplatformal type of petroleum-bearing belts associated with continental platforms. It is subdivided into subtypes - rifting and epirifting. In the first case, thermal regime is rather high, with the depth of 100 oC isotherm ranging from 1.5 to 0.5 km; in the second case it is low with the depth of 100 oC isotherm of about 5 km.
The forth type includes basins of intermontane troughs of orogens. The basins of this type are rather small but with thick sediments and high sedimentation rate of 3-6 cm/ka at the Cenozoic stage. The thermal regime is characterized by the depth of 100 oC isotherm of to 5 km in intermontane basins of young orogens and to 1.5-2.5 km in rejuvenated orogens.
The sedimentary fill of active-margin basins and intraplatformal and intermontane troughs of young orogens is subject to tangential stress caused by collision of lithospheric plates and is characterized, especially along the periphery, by fold-thrust strains, often with stripping of sedimentary units off the basement or along the plastic horizons in the cover.
To estimate petroleum potential in each type of basins, it is necessary to take into account some endogenic factors: thermal regime, deep-level fluids, lateral stress, rate of sedimentation, etc.

Giant deposits: regularities in distribution and forecast potentialities

M. D. Belonin and Yu. N. Novikov
Keywords: HC deposit, giant deposit, oil and gas basin, regularities, distribution, stock structure, organization levels, self-organization, induction, deduction, static approach, forecast
Pages: 1739-1751

Abstract >>
The problem of forecast of the largest (giant) oil and gas deposits arises not from insufficient empirical knowledge (most recoverable HC resources of the world have been prospected) but from the necessity of its generalization and theoretical justification. Transition from empirical to theoretical level of knowledge requires a deeper integration of oil geology as a special study into the general structure of natural sciences, which requires formalization of a special knowledge in accordance with general principles and laws of the natural science. Inductive analysis traditionally used in oil geology in the context of historical and genetic approach must be complemented with deductive analysis based on static approach. Particular methodological forms of the latter approach are techniques of mathematical simulation, based on regularities in distribution of HC resources of oil and gas basins (OGB) among deposits of various sizing classes, and techniques of analogous structurization, based on regularities of distribution of giant deposits in the planetary system of OGB.

The dependence of geological and biological processes on the position of the sun in its galactic orbit

S. G. Neruchev
Keywords: Periodicity, galactic year, climatic seasons, glaciations, transgressions, vegetations, coal, oil
Pages: 1752-1763

Abstract >>
Astronomical and geochronological substantiation of galactic years and the orbital geochronological scale are considered. Climatic seasons of Phanerozoic galactic years are recognized. The dependence of various geochemical and biological phenomena and events, as well as formation of mineral deposits, on the position of the Sun in its galactic orbit and the related galactic climatic seasons is discussed.

Theoretical foundations of predicting the petroleum potential of sedimentary basins with intense manifestation of trappean magmatism

E. Kontorovich and A. V. Khomenko
Keywords: Trappean magmatism, prediction of petroleum potential
Pages: 1764-1773

Abstract >>
The paper considers the criteria of influence of trappean magmatism on the petroleum potential of sedimentary basins. Particular emphasis is placed on the thermal effect of intrusive bodies on organic matter and hydrocarbons. The principles of classification of sedimentary basins are presented based on the degree of maturity by the time of the most intense stage of trap intrusion. The foundations of the technique of calculation of the predicted hydrocarbon resources are given for the basins of different types.

Role of past earthquakes in formation of oil and gas accumulation zones.

K. I. Mikulenko
Keywords: Past earthquakes, autochthonous, allochthonous, and transit traps, zones of oil and gas accumulation
Pages: 1774-1784

Abstract >>
Studies of the traces of Riphean and Phanerozoic earthquakes in the Caucasus, West Siberian Plate, and Siberian Platform, as well as their comparison with the geological evidence of modern earthquakes, show that they may have played a role in the formation of oil and gas traps and accumulation zones. The seismogenic zones of oil and gas accumulation, which are of three main varieties (autochthonous, allochthonous, or transit), are considered in terms of their formation mechanisms and prediction. For such zones in the Caucasian foredeep, West Siberian Plate, and Siberian Platform, probable stratigraphic levels, locations, and types are outlined and example predictions are suggested.

Geologic and geophysical prerequisites for the existence of gas hydrates in the Turonian deposits of the East Messoyakha deposit

S. E. Agalakov, A. R. Kurchikov, and A. N. Baburin
Keywords: Gas, gas hydrates, permafrost rocks
Pages: 1785-1791

Abstract >>
In many regions of the world, including West Siberia, deposits of hydrocarbons in hydrate state are considered to be petroliferous formations. As to methods of search, prospecting, and exploitation of this kind deposits, however, the state-of-the-art is not satisfactory.
In Russia, the problem of existence of gas hydrate deposits is usually discussed in the context of hydrate saturation of the Cenomanian gas pool at the Messoyakha deposit. One more producing horizon has been recognized in the north of West Siberia, which is related to the Gazsalin Member of the Kuznetsov Formation of Turonian-Coniacian age, lying above the Cenomanian deposits and having more favorable PT-conditions for hydrate formation.
Analysis of specific features of geologic structure, temperature regime of the section, gas composition, mineralization of formation waters, logging data, seismic prospecting materials, and sampling suggests that gas hydrates can exist in the Gazsalin Member of the East Messoyakha deposit.
One of the possible directions of further study of genesis of natural gas hydrates and estimation of the effect of gas hydrate processes on the structure of gas deposits and gas resources is study of the hydrocarbons accumulated in the Gazsalin Member of the East Messoyakha deposit with sampling of core by a sealed thermostatically controlled corer.

Biodegradation of saturated cyclic chemofossils

V. A. Kashirtsev, A. E. Kontorovich, R. P. Philp, O. N. Chalaya, I. N. Zueva, I. K. Ivanova, and N. P. Memetova
Keywords: Crude oil, natural bitumens, biomarkers, biodegradation, steranes, hopanes, cheilanthanes
Pages: 1792-1800

Abstract >>
The paper deals with the problem of bacterial oxidation (biodegradation) of crude oil hydrocarbons. The review of the literature on natural biodegraded oils and laboratory experiments suggest that the normal and branched alkanes are susceptible to microbiological degradation, as well as polycyclic saturated biomarker hydrocarbons (steranes, hopanes, and cheilanthanes). The homologous series of demethylated hopanes are assumed to be of different genesis: 28-norhopanes have the precursors in membranes of prokaryotes, i. e., they are "primary" biomarkers, while 25-norhopanes result from bacterial oxidation of regular hopanes in oil pools. Homohopanes close to "biological" structures (22R) are the first to be assimilated by bacteria. At the final stages of biodegradation, demethylation of cheilanthanes occurs at C-10. All this allows construction of the stage scale of hydrocarbon biodegradation.

Petroleum potential of Precambrian and Paleozoic deposits of the southern Uralian region

A. Kamaletdinov, T. T. Kazantseva, Yu. V. Kazantsev, and D. V. Postnikov
Keywords: Overthrust, thrust, tectonics, structure, Archean, Proterozoic, Riphean, Vendian, Paleozoic, oil, gas
Pages: 1801-1807

Abstract >>
The history of investigation into the petroleum potential of deep-seated horizons of the Uralian region is reviewed. Two major objects for oil and gas prospecting are considered: 1) Late Precambrian (Riphean and Vendian) deposits in the platform part of the Bashkir Autonomic Republic and 2) Paleozoic and Precambrian underthrust series in the fold-nappe zone of the Urals. The petroleum potential is justified by numerous oil shows on the territory of Bashkiria and in adjacent areas and by the world data on the presence of abundant underthrust petroleum deposits in many countries.

Catagenetic zoning and petroleum potential of the sedimentary cover of the Barents Sea shelf

S. Gramberg, N. K. Evdokimova, and O. I. Suprunenko
Keywords: Catagenetic zoning, modeling, prediction, vitrinite, reflectance, Barents Sea megatrough, petroleum potential
Pages: 1808-1820

Abstract >>
The maturity of organic matter (OM) has been investigated according to vitrinite reflectance (Ro). This index has been modeled within the sedimentary cover. The depth dependence of Ro has been studied for the first time in the region. Model curves of OM maturation have been constructed for prospecting and test boreholes. This allows prediction of Ro at depths of to 10-12 km. Maps of OM maturity have been compiled for three OM-rich sequences: Carboniferous-Permian terrigenous-carbonate, Upper Triassic and Upper Jurassic terrigenous. The degree of OM conversion varies from protocatagenesis (PC) in the Cretaceous and Upper Jurassic deposits to apocatagenesis (AC) in the Permian ones. Structural and catagenetic levels are conformable in depressions, whereas mismatches of structural and catagenetic surfaces are observed in the terrigenous-carbonate complex and Lower-Middle Triassic deposits on uplifts, particularly, on the western flank of the Barents Sea megatrough and, to a lesser extent, on the Admiralteiskii megarampart.
The catagenetic model suggests a large-scale hydrocarbon generation in the sedimentary deposits of the deep-seated Barents Sea megatrough from Early Paleozoic to Late Mesozoic. During the last 250 Ma, the greatest petroleum catchment area has occurred in the zone of uplifts on the western flank of the Barents Sea megatrough. The potential of this area is comparable with that of the structures of the Shtokman-Lunin megasaddle, proven by exploration drilling.

Formation and distribution of lithological oil and gas traps in the Devonian fill of the Pripyat' paleorift

S. M. Obrovets, A. M. Sinichka, and R. E. Aizberg
Keywords: Pripyat' basin, Devonian, intersalt and uppersalt deposits, petroleum potential, lithological traps, hydrocarbon pools and deposits
Pages: 1821-1831

Abstract >>
The Famennian intersalt and uppersalt petroliferous deposits in the Pripyat' basin (Byelorussia) formed during the main rifting stage of its evolution. The related lithologically and facially diverse sections, cut by synsedimentary and postsedimentary faults, contain a broad variety of oil and gas traps and pools, including lithologically confined ones. All lithologically confined traps in the Pripyat' paleorift are grouped into zones; eleven zones have been discovered to date, and economic oil pools were found in four of them.

Tectonic structure and history of evolution of the West Siberian geosyneclise in the Mesozoic and Cenozoic

V. A. Kontorovich, S. Yu. Belyaev, A. E. Kontorovich, V. O. Krasavchikov, A. A. Kontorovich, and O. I. Suprunenko
Keywords: West Siberian geosyneclise, seals, structural maps, classification of tectonic elements, tectonic maps, tectonic history, faults, petroleum potential
Pages: 1832-1845

Abstract >>
The results of generalized regional studies of the West Siberian geosyneclise are presented. The structural maps for the bottom of the plate complex and top of the Jurassic and Cenomanian complexes were compiled at the modern informative and technological level. The refined classification of the tectonic elements allowed comilation of tectonic maps for these levels, in which the tectonic elements and faults differentiated by the time of their formation and depth of occurrence are shown.
The structural and tectonic maps for the top of the Jurassic structural stage are presented and briefly.
Analysis of the structural and tectonic maps, isopach maps, and seismic profiles enabled description of the tectonic history of the West Siberian geosyneclise during the Cretaceous and Cenozoic in relation to its petroleum potential.

The geothermal regime of hydrocarbon pools in West Siberia

A. R. Kurchikov
Keywords: Geothermal regime, deep heat flow, temperature, hydrocarbon pool
Pages: 1846-1853

Abstract >>
A map of deep heat flow of West Siberia has been compiled on the basis of over 6000 heat flow determinations, and the present temperature field has been analyzed in terms of the role of various factors forming the geothermal regime.
Analysis of local temperature fields in the vicinity of 340 hydrocarbon pools shows that almost 80% of them are associated with considerable heat flow variations, of which some are positive anomalies.

Methodology and experience of main petroliferous objects in northern West Siberia at the present stage of petroleum field exploration

A. M. Brekhuntsov, V. S. Bochkarev, V. N. Borodkin, and N. P. Deshchenya
Keywords: West Siberian geosyneclise, basin, Paleozoic cover, ranking of tectonic structures, petroleum potential
Pages: 1854-1863

Abstract >>
Integral methodology of geological survey, exploration, and production for Russia as a whole is in progress. Criteria for recognition of petroliferous megacomplexes and their basic elements are described. It is demonstrated that oil pools of Jurassic and older deposits are confined to large "hot" fields (regions), whereas gas accumulations exist under more moderate bed temperatures. This regularity is used for predicting oil and gas deposits.

Petroleum-bearing complexes in the Lower-Middle Jurassic and Lower Cretaceous clinoforms of the West Siberian basin

V. S. Surkov, L. V. Smirnov, F. G. Gurari, A. M. Kazakov, V. P. Devyatov, A. E. Ekhanin, and O. V. Serebrennikova
Keywords: Petroleum potential, Lower-Middle Jurassic complxes, West Siberia
Pages: 1864-1874

Abstract >>
The West Siberian basin formed as a result of the Early Triassic rifting and downwarping of the Earth's crust during the Mesozoic and Cenozoic. Three stages are recognized in this process: early (postrift, Middle Triassic-Middle Jurassic), middle (platform, late Middle Jurassic-Eocene), and late (neotectonic, late Eocene-Quaternary). In this paper, the regularities and conditions of sedimentation are described concisely, and the potential of Lower-Middle Jurassic petroleum-bearing complexes (Zimnii, Sharapov, Nadoyakh, Vym', and Malyshev) and Neocomian cllinoforms is estimated. The conclusion is made that the further increase in reserves of hydrocarbons in the West Siberian petroliferous province in a sufficient volume is possible at the cost of these two petroleum-bearing stories. A program of their further study on a regional scale is proposed. This program will be a base for a more complete estimation of resources of the complexes under study, for determination of areas for detailed seismic prospecting and parametric drilling, and for their geological and economical estimation aimed at a necessary licence.

Catagenesis of organic matter and petroleum potential of the jurassic, triassic, and paleozoic deposits in the northern areas of the west siberian megabasin

A. N. Fomin, A. E. Kontorovich, and V. O. Krasavchikov
Keywords: Petroleum potential, vitrinite reflectance, catagenesis grades, Jurassic, Triassic, and Paleozoic deposits, West Siberia
Pages: 1875-1887

Abstract >>
Based on generalization of 1500 measurements of vitrinite reflectance, deep zoning of organic-matter (OM) catagenesis in Mesozoic deposits has been established, and schemes of catagenesis were constructed for the top and bottom of the Jurassic deposits. The OM catagenesis is within the range of grades PC3 to MC32 in the Upper Jurassic deposits and PC3-AC3 in the basal Jurassic horizons. Throughout most of the West Siberian megabasin, OM reached the end of mesocatagenesis and apocatagenesis. Regionally, the degree of OM catagenesis of the Jurassic deposits increases from the margins to the central and northern, most buried, areas of the West Siberian megabasin. The level of OM maturity ubiquitously increases with depth, but the rate of these changes varies throughout the area. The highest deep gradient of variations in OM catagenesis was identified in the Yamal and Gydan regions. Depth ranges of the main zone of oil generation (oil window) were determined from vitrinite reflectance values in different petroliferous regions. In the Nadym-Pur region, the main zone of oil generation is identified in the depth range 2.9-3.8 km, in the Pur-Taz region, at 2.8-3.6 km, in the Gydan region, at 2.4-3.3 km, and in the Yamal region, at 2.0-2.8 km. The Jurassic deposits to depths of about 4.0 km have not passed out of the oil window yet and can be of interest for oil and gas exploration. Down the section, the sequences are in the zone of intense gas generation, and, therefore, preservation of only dry and fat gas accumulations is possible at great depths. The same is true for the Triassic and Paleozoic sediments, in which the organic matter underwent significant thermobaric changes (grades MC32 – AC3).

Upper Jurassic deltas of West Siberia (by the example of the Vakh oil deposit)

V. B. Belozerov, I. A. Ivanov, and G. I. Rezyapov
Pages: 1888-1896

Lithology of Callovian-Oxfordian deposits in various facies districts of the West Siberian Plate

P. A. Yan, L. G. Vakulenko, O. V. Burleva, T. P. Aksenova, and I. K. Mikulenko
Keywords: Lithology, sedimentation settings, lithofacies zonation, Jurassic, West Siberia
Pages: 1897-1907

Abstract >>
The structure, composition, and formation settings of the Callovian-Oxfordian deposits of the Pur-Irtysh, Taz-Kheta, and Silgin facies districts of West Siberia are considered. In the first of them the Callovian-Oxfordian deposits include the Vasyugan and Abalak Formations; in the second, the Tochino and Sigovsk Formations; and in the third, the Naunak Formation. The variability of the Vasyugan Formation in the southeastern areas of the West Siberian Plate, in the latitudinal Ob' region, and in the Nadym-Taz interfluve has been shown by lithological and mineralogy-petrographical studies invoking production geophysics and geochemical and paleontological evidence. This allows recognition of three facies subdistricts: Ob'-Tara, Ob'-Agan, and Nadym-Pur. In addition, the Yamal-Nadym facies subdistrict, where the Abalak Formation occurs, has been recognized.

Sedimentation in the Early Cretaceous basin of West Siberia and its influence on oil and gas potential

S. V. Ershov, K. V. Zverev, V. A. Kazanenkov, and Yu. N. Karogodin
Keywords: West Siberia, Neocomian, avalanche sedimentation, clinoform
Pages: 1908-1916

Abstract >>
The opinions about the structure of the Neocomian deposits in West Siberia are discussed. We defend the viewpoint of its clinoform structure. According to studies performed, clinoforms are bodies of transgressive-regressive sedimentation cycles (cyclites) formed during avalanche sedimentation. Their structure involves two types of sand-siltstone reservoirs related to shallow-water shelf and distal fairly deep-water sediments, each containing a wide range of traps. Clinoforms are stratigraphic and petroliferous subdivisions calling for independent complex studies.

Comparative analysis of prospects for formation of large hydrocarbon accumulations in the north of the Tunguska syneclise

V. S. Starosel'tsev and T. A. Divina
Keywords: Basalt covers, petroleum potential of Paleozoic deposits, tectonic prerequisites
Pages: 1918-1926

Abstract >>
The prospects for oil and gas potential of the northern Tunguska syneclise are estimated with regard to quantitative oil-geologic characteristics of Riphean-Paleozoic deposits overlapped by Permian-Triassic basalts. These characteristics have been for the first time obtained for the inner regions of this syneclise. On the basis of spatial combination of the deepest (to 10 km and more) large negative structures of platform cover and adjacent uplifts – potential zones of gas and oil accumulation, – the areas of the most probable formation of large accumulations of hydrocarbons were supposed. Two of them, Upper Khugdyakit and Khantai, have been recommended for top-priority studies by parametric drilling to a depth of up to 3.5 km.

Prediction of the petroleum potential of the Vendian and Lower Cambrian deposits in the center of the Siberian Platform

G. G. Shemin
Keywords: Horizon, formation, bed, correlation, oil, gas, petroliferous zone, first-order object, pool, trap, hydrocarbon migration
Pages: 1927-1944

Abstract >>
Criteria for predicting the petroleum potential of ancient deposits of complicated structure with a long evolution history of hydrocarbon pools are considered. They rest on combined stratigraphic, tectonic, lithofacies, geochemical, and hydrogeological data. Detailed prediction of petroleum potential has been made for the Vendian-Lower Cambrian subsalt terrigenous and carbonate deposits of the Vilyuchan, Lower Nepa, Upper Nepa, Tira, Lower Danilovo, Upper Danilovo, and Usol'e reservoirs. Fields different in potential, petroliferous zones, and first-order prospecting objects have been recognized in the areas of their occurrence. Predominant types of traps, pool volumes, and phase compositions of hydrocarbons are predicted. The results will add to the efficiency of search for petroleum.

Evaporite screens of oil and gas reservoirs in the Siberian and Tarim Platforms

G. S. Fradkin, Jin Zhijun, A. K. Basharin, and S. Yu. Belyaev
Keywords: Evaporites, screen, reservoir, Siberian Platform, Tarim Platform
Pages: 1945-1953

Abstract >>
Vendian-Cambrian and Devonian evaporite and salt sequences have been reliably distinguished in the sedimentary cover of the Siberian Platform, the lower part of which controls the economic petroleum potential of Precambrian reservoirs, and the upper one shows good prospects for productivity of subsalt and intersalt beds. In this context it is suggested that evaporate sequences in the Tarim Platform, which occur in Cambrian, Carboniferous, and Paleogene sections, make a subject of a special study in terms of their screening role in order to refine the prospecting guidelines for hydrocarbon pools in the subsalt reservoirs of the Tarim petroleum province.

Producing horizons of the Chayandinskoe field (Yakutia): structure and genesis

A. F. Safronov, A. V. Bubnov, I. A. Gerasimov, and V. Yu. Mironenko
Keywords: Horizon, facies, reservoir rocks, logging, porosity, permeability, sedimentation conditions, model, inhomogeneity
Pages: 1954-1966

Abstract >>
This paper deals with the structure and genesis of the Talakh, Khamakin, and Botuobiyan Horizons of the Chayandinskoe oil and gas condensate field, located on the north-eastern slope of the Nepa-Peledui dome of the Nepa-Botuobiyan anteclise. It is shown that the models for these horizons are dip-lenticular rather than plane-parallel. The producing horizons are characterized by significant lateral and vertical inhomogeneity related to the sedimentation conditions. The deposits formed in the setting of sea coast, which evolved from rock-type coast with the strongly dissected relief of the sea bottom (Talakh Horizon), gradually acquiring geomorphologic elements typical of open sea coast. This evolution provided a set of facies making up the producing horizons: The Talakh Horizon is dominated by the turbidite facies; the Khamakin Horizon, by the facies of the cis-frontal zone of the beach; and the Botuobiya Horizon, by the facies of the beach and its cis-frontal zone. The lateral and vertical inhomogeneity intensifies in the horizon sequence: Botuobiyan-Khamakin-Talakh.

The regularities of formation of the porosity of Vendian-Cambrian terrigenous deposits in the southern Siberian Platform (from data of complex petrophysical research)

M. M. Mandel'baum and K. S. Turitsyn
Keywords: Porosity, consolidation of rocks, diagenesis, regeneration of quartz
Pages: 1967-1975

Abstract >>
We have studied the main factors that effect consolidation of terrigenous rocks. The porosity of mudstones of the Nepa Formation (Siberian Platform) is shown to reflect the maximum pressures under which the rocks existed throughout their geologic history. It can be used for regional paleotectonic analysis. The porosity of sandstones depends on much more factors operating both on sedimentogenesis and on subsequent catagenesis of the rocks; the major of them are the depths of the maximum burial of sediments, the size of mineral grains, and the intensity and time of secondary cementation of rocks.