Catagenesis Of Organic Matter Research Articles

Organic Geochemistry of Carbonate Rocks, Silicites and Black Shales of the Vendian (Ediacaran) Khatyspyt Formation, Northeastern Siberia

Abstract —The paper presents the results of the study of organic geochemistry of carbonate rocks, silicites, and calcareous mudstones of the Vendian (Ediacaran) Khatyspyt Formation in the northeast of the Siberian Platform. The distribution of dispersed organic matter (OM) is shown to be uneven. The formation comprises carbonate-dominated intervals depleted in OM, with total organic carbon content (TOC) < 0.1%, or weakly enriched in OM (TOC up to 0.4%), interstratified with carbonate-shale, carbonate-shale-siliceous, carbonate-siliceous and siliceous intervals enriched in OM (TOC up to 1–4%). There is also a thin-layered calcareous mudstones anomalously enriched in OM (black shales with TOC at 10%) cropping out in the Khorbusuonka River valley (unit thickness 10 cm). The redox conditions in the water column varied during deposition of the Khatyspyt Formation. Certain intervals characterize a stratified water column and euxinic bottom water conditions. During the study, the assessment was conducted of the OM catagenesis and the generative potential of the Khatyspyt Formation. Based on the results of geochemical study and the synthesis of information on the geological structure of sedimentary succession in the northeastern Siberian Platform, the Khatyspyt Formation has been evaluated as one of the hydrocarbon sources for the territory.

Organic Matter and Generation Potential of Paleozoic Deposits in the Tal’bei Block of the Chernyshev Ridge (Timan–Pechora Petroleum Province)

Abstract—The study area is located within the Chernyshev Ridge, a fold–thrust structure, which is a promising area for oil and gas exploration in the Timan–Pechora province. Petroleum source rocks of Paleozoic (from Upper Ordovician to lower Carboniferous) deposits stripped by the Vorgamusyurskaya-1 well in the Tal’bei block of the Chernyshev Ridge were studied by lithological, petrographic, organic-petrology, and organic-geochemistry methods. Most of the section is characterized by low values of Corg (<0.5%), genetic potential (S1 + S2 < 0.5 mg HC/g rock), and hydrogen index (HI < 100 mg HC/g Corg). Petroleum source rocks with elevated values of Corg (up to 0.9%), S1 + S2 (up to 2.1 mg HC/g rock), and HI (up to 277 mg HC/g Corg) were identified at different stratigraphic levels of the section: Upper Devonian (D3tm–sr), upper Silurian (S2gj), and Upper Ordovician (O3mt). The maceral composition of organic matter (OM) and the distribution of hydrocarbons in the saturated fraction of bitumens indicate that petroleum source rocks include only marine OM (type II kerogen). The degree of catagenesis of OM was estimated based on the bituminite reflectance (RVeq), Rock-Eval pyrolysis (Tmax), and conodont color alteration index (CAI). The available RVeq (0.63–0.84%), Tmax (430–443 °C), and CAI (1.5–2.0) data indicate that the entire Paleozoic well section is in the oil window (MC1–MC3). The new data refined the catagenetic zoning of the sedimentary section, according to which the OM reached the following gradations: MC1 in the lower Carboniferous and Famennian deposits, MC2 in the interval from the Frasnian to the upper part of the lower Silurian, and MC3 in the lower part of the lower Silurian and in the Upper Ordovician. The results of the study of petroleum source rocks and the type and maturity of OM will be the basis for basin modeling, which will increase the reliability of reconstructions of oil and gas formation at the Chernyshev Ridge.

Section types and oil prospects of the Bazhenov Formation in the Nadym-Ob interfluve

The article presents the results of studying the geological structure of the Bazhenov Formation in the Nadym-Ob interfluve of Western Siberia with the aim of predicting the oil content of this black shale stratum. As a result of interpretation of a wide range of well logging represented by electric, radioactive and acoustic logging, with subsequent matching of these results with paleontological definitions of micro- and macrofauna, the distribution of the Salym, Nizhnevartovsky and Tarkosalinsky types of sections of the Bazhenov Formation was clarified, transitional areas between them were identified. It has been established that the Tarkosalinsky type is more widespread in the western direction than was shown earlier and is also distinguished in the Vengayakhinskaya, Yaraynerskaya and other areas. The Nizhnevartovsky type, on the contrary, has a narrower distribution and stands out directly within the same name arc and to the south by the Variegasky-Tagrinsky megahigh. On the basis of geological, geochemical, geophysical criteria and the results of an inflow test in deep wells, a map of the oil potential prospects of the “classical” sections of the Bazhenov Formation has been compiled. Regional prerequisites (high catagenesis of organic matter, significant modern concentrations of organic carbon, etc.) for the discovery of industrial accumulations of oil in the Bazhenov Formation in the southern regions of the Yamalo-Nenets Autonomous Area are identified. The results of the test for the inflow of the Bazhenov Formation in this area in the 70–90s XX century were analyzed; repeated, interval testing of these deposits using modern methods of stimulation of the inflow is recommended. The necessity of laboratory lithological, petrophysical, geochemical study of the core of the Bazhenov Formation in the southern part of the Yamalo-Nenets Autonomous Area is substantiated with the aim of determining its lithological composition, identifying oil source and oil productive intervals, studying the reservoir structure and the nature of saturation of its void space, developing recommendations for calculating oil reserves and creating technology for its cost-effective production.

The Gol’chikha Formation (Upper Bathonian–Lower Boreal Berriasian) of the Yenisei–Khatanga Depression (West of the North Siberian Lowland)

Abstract —The uppermost Bathonian–lowermost Boreal Berriasian clay horizons (Gol’chikha Formation) of the Yenisei–Khatanga regional depression are regarded as probable oil source strata. Considerable core recovery in the Middle Jurassic to Lower Cretaceous sections from the boreholes drilled in the Paiyakhskaya well site and the presence of oils in the overlying strata of the Shuratovo Formation permit us to carry out integrated stratigraphic (bio-, litho-, chemo-, and seismostratigraphic) and geochemical (organic matter and oils) studies of the entire section of the Gol’chikha Formation and boundary beds, to reveal oil-producing horizons, and to compare the genotype and maturation level of their oils with those of the potentially oil source organic matter (OM) of the rocks. A detailed biostratigraphic zonation of the sections of the Gol’chikha Formation based on microfossils has been carried out. Comparison of δ13Corg variations in the Volgian and in the lower beds of the Boreal Berriasian with those in the Barents Sea shelf and in the northeast of East Siberia provided the basis for more accurate definition of the boundaries of stages and substages in the intervals free of fossils in the Paiyakhskaya area. The studied section of the Gol’chikha Formation has been divided into eight lithologic members calibrated with bio- and seismostratigraphic units. The distinctive features allowing the definition of the upper boundary of the Gol’chikha Formation are proposed using GIS data. Analysis of bio- and chemostratigraphic data allowed the correlation of the seismic reflecting horizons defined in the Gol’chikha Formation and its boundaries with the geologic section and relevant litho- and biostratigraphic units. It has been established that the strata with the highest content of organic matter consist of the upper part of the Gol’chikha Formation (the Upper Volgian and basal Boreal Berriasian). According to the vitrinite reflectance data, the OM catagenesis in the Upper Volgian interval corresponds to the oil window, which is confirmed by pyrolysis data. Thus, these strata can be considered oil-producing. The low δ13Corg values confirm the predominantly marine OM composition. Analysis of oils from the Cretaceous productive strata of the Paiyakhskaya area shows that they formed from the marine OM of the upper part of the Gol’chikha Formation at the same accumulation stage. The comprehensive studies of the Gol’chikha Formation in the Paiyakhskaya well site and complete stratigraphic coverage of the sections confirm that they can be considered a hypostratotype.

New Geochemical Data on the Organic Matter in Rocks of the Lower and Middle Cambrian Kuonamka Complex, the Lena–Amga Interfluve Area, Southeastern Siberian Platform

Saturated hydrocarbon biomarkers were studied in bitumens from organic matter (OM) in the Lower and Middle Cambrian Kuonamka Complex in the Lena–Amga interfluve of East Siberia. Their contents and distribution were analyzed. It was established that OM of siliceous and carbonate rocks from the lower part of the sequence differs from OM of overlying mainly mixed siliceous–carbonate rocks in terms of distribution of alkanes, steranes, tricyclanes, hopanes, and ratios of their homologs. It was concluded that the peculiarities of molecular composition of OM in the rocks are related to the biochemistry of microorganism communities, the remains of which were accumulated in sediments of Cambrian sea. It is possible that the microbiota changed its composition in response to a sharp change of sedimentation settings, which follows from biomarker proxies. It is suggested that sediments in the lower part of the sequence were formed under conditions of H2S contamination. Catagenesis of OM and contribution of the Lower and Middle Cambrian potentially oil-generating rocks in naphthide generation on the northern slope of the Aldan anteclise are discussed.

Organic geochemistry of the Lower Cambrian Sinyaya Formation (northern slope of the Aldan anteclise)

We investigated organic matter (OM) of the Lower Cambrian Sinyaya Formation in the southeast of the Siberian Platform. The studied collection of rocks was divided into groups according to the contents of organic carbon, bitumens, and sulfur and lithologic characteristics. The content and distribution of saturated biomarkers were examined. Lanostanes C30, norlanostanes C29, 28,30-bisnorhopanes, and 2α- and 3β-methylhopanes have been identified in the bitumens. Relationships between the content of organic carbon and the distribution of hopanes, hopane ratios, and 2α-methylhopane index have been established. The conditions of sedimentation, diagenesis, and catagenesis of OM and the generation potential of the rocks have been estimated. It is shown that lanostanes, 28,30-bisnorhopanes, and methylhopanes can be used as biomarkers of the source rocks of the Sinyaya Formation and thus can help to determine the source of bitumens on the northern slope of the Aldan anteclise of the Siberian Platform.

Organic geochemistry of rocks of the Mesoproterozoic Malgin Formation and their depositional environments (southeastern Siberian Platform)

Organic matter (OM) and rocks of the upper member of the Mesoproterozoic Malgin Formation in the southeastern Siberian Platform have been studied by modern research methods. Analysis has revealed homologous series of alkanes, tricyclanes, and hopanes in the bitumens. Leiosphaeridia crassa, L. minutissima, cf. Leiosphaeridia tenuissima, cf. Glomovertella, and Oscillatoriopsis sp. have been identified among the rare microfossils preserved in mudstones. Geochemical, lithological, and paleontological studies have shown that bacterial microcommunities and, to a lesser extent, eukaryotic microorganisms were the main source of OM. Based on results of sedimentological analysis and study of biomarkers, the depositional environment has been reconstructed. A model for the accumulation of black shales and carbonate rocks of the Malgin Formation is considered. The hypothesis that the highly carbonaceous rocks formed in uncompensated depressions of shallow epicontinental marine suboxidation environments is substantiated. The petroleum potential and degree of OM catagenesis of the Malgin Formation rocks are evaluated. Pyrolysis, bitumen analysis, and hydrocarbon composition study have revealed autochthonous and parautochthonous bitumens in the oil shales, mudstones, and carbonate rocks. The obtained data show that the Malgin Formation rocks might have participated in petroleum generation in the Uchur-Maya region.

The subsidence and thermal history of the Baikit anteclise sedimentary basin

The Riphean rocks of the Baikit anteclise have been examined using pyrolysis Rock–Eval 6 to evaluate the subsidence history and erosion level. The studied Riphean rocks have the МK3–МK4 catagenesis grade. Based on the catagenesis of organic matter we propose a model of maximum burial before the beginning of the accumulation of Vendian deposits. Estimated calculations of subsidence and erosion have shown that the assessed catagenesis grade could be reached at a depth of 7 km, while the erosion level was approximately 5–7 km.

Subsidence and thermal history of Baikit anteclise sedimentary basin

Riphean rocks of Baikit anteclise are examined using pyrolysis RockEval 6 to evaluate subsidence history and level of erosion. Investigated Riphean rocks show МК 3 -МК 4 catagenesis rate. Based on catagenesis of organic matter we propose a model of maximum burial before the beginning of Vendian stratum sedimentation. Supplied calculations of subsidence and erosion shown that estimated catagenesis rate could be reached at 7 km depth; erosion level was about 5 to 7 km.

Modeling of catagenetic transformation of organic matter from a Riphean mudstone in hydrous pyrolysis experiments: Biomarker data

The catagenesis of organic matter (OM) was modeled by the hydrous pyrolysis of a Riphean mudstone. Microscopic observations of the processes operating during kerogen heating to 600°C were conducted in a diamond anvil cell. The results of pyrolysis in an aqueous environment were used to calculate the activation energies of kerogen cracking and derive chemical kinetic models for OM catagenesis. Isothermal experiments were carried out for 3 days at temperatures of 300, 310, …, 360, and 370°C. The maximum bitumen yield was obtained at 330°C followed by thermal cracking at higher temperatures. The aromatic and saturated hydrocarbons from rock bitumen, hydrous pyrolyzates, and kerogen flash pyrolyzates were analyzed by chromatography-mass spectrometry. We also discuss the problem of extrapolation of high-temperature pyrolysis results to geologic observations under the conditions of regional catagenesis.

The geochemistry of Cambrian organic matter from the Cis-Yenisei subprovince ( evidence from the wells Vostok-1 and Vostok-3)

The paper presents the first comprehensive geochemical data, obtained by modern techniques, on the dispersed organic matter (OM) of Cambrian sediments in the Upper Proterozoic–Paleozoic Cis-Yenisei sedimentary basin (parametric wells Vostok-1 and Vostok-3). The carbonaceous rocks of the Churbiga and Paidugina Formations are the most OM-enriched in the studied Cambrian sections. The OM in these sections is of aquagene (bacterial, plankton-derived) origin. A detailed description of biomarker hydrocarbons has been given for the fraction of saturated hydrocarbons. Also, the high degree of OM catagenesis (apocatagenesis) has been established. Finally, geochemical criteria for predicting the petroleum potential have been considered.

Realization of the oil-generation potential in the estimated source rocks of the sedimentary basin in the shelf of northeastern Sakhalin: Numerical simulation

The numerical simulation of the subsidence history and heat flux of sedimentary rocks in the northeastern part of the Sakhalin shelf was applied to evaluate the variation in the level of catagenesis of organic matter and the realization of the hydrocarbon potential in the course of subsidence of major sedimentary formations in the Sakhalin 5 Kaigan-Vasyukan area. Our simulations demonstrate that, according to the parameters of OM maturity and the realization of the HC potential, the oil-generating source rocks in the northeastern shelf of Sakhalin could be those of the upper part of the Upper Cretaceous complex, Eocene, Machigan, and the lower part of the Uininskii complexes, whereas the rocks of the upper part of the Uininskii, Dagin, Okobykai, Lower and Upper Nutov complexes can be interesting only as those possibly hosting traps for oil and gas generated in underlying rocks. The broadest time span of the generation of liquid hydrocarbons was typical of the rocks of the Upper Cretaceous complex, while the Eocene and younger rocks generated hydrocarbons mostly in the Pliocene-Pleistocene.

Kerogen from the Cambrian deposits of the Kuonamka Formation ( northeastern Siberian Platform)

Kerogens from the Lower and Middle Cambrian deposits of the Kuonamka Formation in the northeastern Siberian Platform have been analyzed by modern methods. We have determined the pyrolytic characteristics of insoluble organic matter and the contents of C, H, S, N, O, and the stable C isotope. The type and catagenesis of organic matter have been estimated, as well as the generating potential of oil source rocks. It has been found that the composition of kerogens taken from the Molodo River outcrops was affected by supergene processes and that the degree of their alteration is related to the organic content of rocks and their structure.

Catagenesis of organic matter at the top and base of the Jurassic complex in the West Siberian megabasin

Thermal maturation for the top and base of the Jurassic in the West Siberian megabasin was modeled on the basis of the vitrinite reflectance ( R vt 0) data using mathematical modeling and computer simulations. The values of thermal maturation are found to vary within substages PC 3-MC 3 2 for the top (or being equivalent to PC 3-MC 1 2 on the periphery and southern part of the basin, or to MC 2-MC 3 2 in the north) and PC 3-AC 3 for the base of the Jurassic (or being equivalent to PC 3-MC 2 on the periphery and southern part of the basin or MC 3 1-AC 3 in the north). Thermal maturity levels of the Jurassic in West Siberia are controlled by depths of burial and peak temperatures which the source rocks were subjected to during this period. The situation is further complicated by high heat flows superimposed on the regional background, which are observed in deep fault zones and in the proximity of numerous igneous bodies.

Hydrothermal pyrolysis of organic matter in Riphean mudstone

The catagenesis of organic matter (OM) was modeled by the hydrothermal pyrolysis of a source rock (Riphean mudstone from eastern Siberia). Isothermal experiments 72-h long were carried out in an aqueous environment in autoclaves at temperatures of 300, 310, 320,..., 370°. The pyrolysis products were analyzed for yield of extract, organic carbon, and parameters of Rock-Eval pyrolysis. The amount of the generated liquid hydrocarbon (HC) compounds increased to a temperature of 340°C and then decreased. The experimental trend of the hydrogen index (HI) dependence on the T Max temperature generally coincided with that for natural OM maturation. The carbon isotopic composition of the insoluble (in organic solvents) OM remained practically unchanged in the course of the experiments. The carbon structure of the solid remnants of the experimental samples was ordered (after the experiments) with the origin of turbostratic graphite with a spacing of d 002≈3.5 A°. We also conducted pyrolysis in a diamond anvil cell equipped with a digital camera in order to obtain additional qualitative and quantitative information on oil generation and emigration in the source rock and isolated kerogen. Chemical kinetic parameters of kerogen cracking were calculated for pyrolysis in an open system. The extrapolation of the high-temperature experimental results is discussed with reference to natural OM maturation.

Deep subsidence of the early catagenesis zones of organic matter in the sedimentary rocks of Northeastern Sakhalin shelf at high thermal regime of the basin

Heat flux measurements in the shelf zone of Northern Sakhalin reveal strong heating of the sedimentary complexes with a temperature gradient of the order of 36 ° C/km along the entire length of the Okhotsk Sea margin of the North Sakhalin basin [2]. However, despite the high thermal regime of the lithosphere in the region, the fact that initial stages of catagenesis gradations PC3‐MC1 ( R o = 0.50‐0.64%) are confined to great depths (3800‐5000 m) is a characteristic property of the deep distribution of the organic matter catagenesis of sedimentary rocks in the boreholes of Northern Sakhalin. It is likely that this fact is related to a high rate of sediment accumulation in the Neogene-Quaternary time. In order to check this supposition and estimate the rate of variations in the degree of transformation of organic matter (OM) in the deeper layers of the basin, we applied the modeling system of GALO basins and reconstructed numerically the history of subsidence and temperature evolution of the rocks of the sedimentary cover in the northeastern part of the Sakhalin shelf in Kaigano-Vasyukanskii area of Sakhalin-5 region (Fig. 1). In addition to the traditionally considered Cenozoic complex, our model of the sedimentary section of the basin includes Upper Cretaceous formations, whose thicknesses were estimated from the seismic data (table). The peculiarity of the shelf region considered here was in the fact that it was located on the one hand within the continental margin of the Okhotsk Sea Plate and on the other hand near the complex of the accretion prism of Eastern Sakhalin [1]. Although the close location of the accretion cline (and consequently the underthrust zone) predetermines the domination of compression stresses over the territory of the basin and consequently the nonisostatic response of the basin lithosphere to the load of water and sediments, there is sufficient evidence of active fracture tectonics in the northeastern shelf of Sakhalin with notable weakening of the lithosphere in the Late Cretaceous and Cenozoic (see below). Therefore, we considered two limiting versions of the basin development. In the first of them, we assumed that numerous fractures and displacements along the fractures significantly weakened the lithosphere strength in the region studied. Under these conditions, the local isostatic response of the lithosphere to the load of water and sediments existed during the entire history of the basin, which we consider started in the Late Cretaceous (and possibly excluded a few relatively short periods). In the second alternative version of the basin formation, we assumed that the local isostatic response of the basin lithosphere to the load of water and sediments existed only during the last 34 Ma starting from the time of the Kuril arc formation, which absorbed the main part of the regional compression stresses. The initial heat flux in the basin in the second version was assumed notably lower than in the first one. Of course, in both versions of the basin development, modern temperature distributions and OM maturity with depth (the values of the reflecting property of vitrinite, R o , %) calculated in the model were close to the values measured in the regions of the basin considered here and in the neighboring regions (Fig. 2). The main modeling results of the thermal history of the basin and variation in the OM maturity are shown in Fig. 3 for the first version of the basin development, which assumed an isostatic response of the lithosphere to the load of water and sediments and consequently high heat flux (approximately 160 mW/m 2 ) in the beginning of the Late Cretaceous. In such a model, intense subsidence of isotherms in the Pre-Cenozioc period of the basin development (Fig. 3) is determined

Artificial Maturation of Organic Matter from Recent Venezuelan Sediments

Laboratory simulation of the catagenesis of organic matter in sedimentary rocks has been used to provide an understanding of the processes involved in petroleum generation. Several of these studies have focused on the thermal evolution of organic matter (OM) present in Recent sediments. This study examines the geochemical characteristics and experimental thermal evolution of primary organic matter from two organic facies that are thought to be major contributors to Venezuelan hydrocarbon source rocks. A third facies, generally considered unimportant for petroleum formation, is used to contrast the experimental results. Hydrous pyrolysis maturation experiments were performed for three intermediate temperatures. The products of the final 330°C stage are shown in this paper because they best illustrate the changes in the OM during catagenesis. Results from the hydrous pyrolysis experiments show that at 280°C and higher all three samples yield liquid hydrocarbons similar in composition to natural crudes and the transformed organic matter is similar to kerogen that occurs in natural source rocks. Chromatograms from the saturated fraction of extracts at 330°C are similar to natural crudes with respect to n-alkane distribution and abundance of αbeta; and beta;alpha; hopanes. The only difference seems to be the relative abundance of 22R over 22S isomers, which indicates immature oil. This is in contrast to indications from the Ro and Tmax parameters measured on the accompanying kerogen.

Biomarkers and Geochemical Classification of Oils in Some Basins of the Commonwealth of Independent States

Contemporary geochemical classifications of crude oils are based on the composition and quantitative ratios of individual hydrocarbons, mainly biomarkers. This paper discusses biomarkers whose composition is closely related to crude oil formation factors such as type of original organic matter; degree of catagenesis of organic matter, kerogen, and crudes; degree of biodegradation of the oil; facies conditions of diagenesis; and geological age of the original organic matter. The identification, by mass chromatography, of a large number of biomarkers resulted in classification of crude oils from basins in the Commonwealth of Independent States. Some of the biomarkers thus determined are n-alkanes, isoprenanes, C[sub 21]-C[sub 30] steranes, tricyclic and pentacyclic terpanes, cheilantanes, hopanes, 25, 28, 30- trisnorhopanes, 28, 30- and 25, 30-bisnorthopanes, [gamma] - lupane, [gamma]-cerane, and others. The geochemical conditions for petroleum formation and the geochemical classifications are discussed in light of the following basins and stratigraphical complexes: western Siberia, eastern Siberia, Timano-Pechora and near Caspian. In the four basins, some 200 crudes were studied, in each of which about 20 different correlation ratios of the most important biomarkers were determined. This work has resulted in the elucidation of the effect of the main factors of petroleum formation on the geochemistrymore » and petroleum generation in these basins and stratigraphic complexes. The study of biomarker composition has made possible the determination of the geological and geochemical conditions for petroleum formation, correlation of composition with the geological age, chemical type of the original organic matter, determination of the severity of the oxidizing conditions, the degree of microbiological activity in diagenesis, and provided information on the lithology of source rocks and other geochemical parameters of petroleum formation.« less

Petroleum Basins of Sakhalin and Adjacent Shelf

Sixty-seven oil and gas fields have been discovered on Sakhalin and the adjacent shelf but the distribution of fields is uneven in north Sakhalin, south Sakhalin, and the Tatar basins. The sedimentary cover is composed of sandy, clayey, and siliceous rocks, with volcanogenic and coal-bearing deposits of Upper Cretaceous, Paleogene, and Neogene 8-12 km thick. Marine clayey and siliceous oil source rocks are regionally developed in the section at different stratigraphic levels; the organic matter is of mixed type and the content varies from 0.5 to 1.5%. The upper Oligocene and middle-upper Miocene source rocks in the north Sakhalin basin are typical, and the organic carbon content ranges from 1 to 5%. The level of organic matter catagenesis and conversion into hydrocarbons is high because of the high differential geothermal gradient in the basins, 30-50[degrees]C per km. Porous sandstones in the Miocene form the reservoirs in all fields with the exception of Okruzhnoye, where the pay zone is a siliceous claystone. Growth-fault rollovers and anticlines form the main traps ranging in area from 5 to 300 km[sup 2], with amplitudes between 100 and 600 m. both stratigraphic and structural traps have been identified. Considerable volumes of reserves are associated withmore » the Miocene deposits of north Sakhalin, which are characterized by an optimum combination of oil source rocks, focused migration paths, and thick sequences of reservoirs and cap rocks. Six large fields have been discovered in the past 15 yr. Oil and condensate reserves stand at over 300 million MT, and gas reserves are about 900 billion m[sup 3].« less

An examination of the timing of catagenesis of organic matter using three published methods

Abstract Using the methods of Bostick (1973), Hood et al. (1975) and Lopatin (1976) I have estimated the expected Rmax0 values of vitrinite from 45 profiles of known burial history, the actual geothermic relations and the coalification-degree. The profiles represent mainly Hercynian and Alpine basins of Australia, the Soviet Union, the United States and Western Europe. Taking into consideration the geological age and the burial history, it is remarkable that Bostick's (1973) method is mainly applicable to profiles rapidly buried and lifted up over the Hercynian cycle, whilst the method of Hood et al. (1975) is especially applicable to profiles buried in the Hercynian cycle and them remaining at great depth until the present. In Alpine basins all 3 methods are equally applicable. Examination of measured and estimated value of Rmax0 of vitrinite makes probable the limited additivity of the thermal effect and the theoretical correctness of the method of Hood et al. If, by the method of Hood et al., the error in comparison is acceptable (⩽30%), the reconstruction can be carried out.