The presence of substantial accumulations of bitumen is critically significant as they serve as direct indicators of oilbearing regions. However, in the context of environmental studies, their existence complicates the assessment of technogenic soil contamination by oil and petroleum products. The objective of this research was to identify informative geochemical parameters that would facilitate the differentiation between natural surface seepages and technogenic hydrocarbon fields resulting from commercial oil spills. This study examined natural surface oil seepages in the Amga River Basin and technogenic oil contamination near the Amga Oil Depot. Employing classical bituminology, Fourier transform infrared spectroscopy, gas chromatography, and mass spectrometry, a comparative analysis of their compositional characteristics was conducted. Notably, significant differences in geochemical parameters, such as the concentrations of hydrocarbons, resins, asphaltenes, and oxygen-containing compounds, were observed when comparing oil pollution to natural surface seepages for the first time. Furthermore, it was demonstrated that genetic parameters for diagnosing soil contamination by oil, based on biomarker composition, could include the presence of 12- and 13-methylalkanes in the hydrocarbon profile of the pollutant. These compounds are recognized as distinctive biological markers of Cambrian and Early Paleozoic oils from the Nepsko-Botuobinsk oil and gas region. Conversely, these biomarkers were absent in the natural surface oil seepages of Amga. The findings of this research may prove valuable in environmental studies, particularly in monitoring efforts aimed at identifying technogenic oil contamination in soils that are not associated with natural oil seeps.

Oil and bitumen shows with previously unknown hydrocarbon biomarkers - 9-methyl, 8-14-secohopanes - were encountered in the sections of hydrogeological wells on the northeastern slope of the Aldan anteclise. Shows of biodegraded asphaltites are confined to the cavernous horizon in the middle Cambrian limestones of the Tankhai Formation. The relatively high residual concentrations of the "new" biomarkers are due to their very high resistance to biologic oxidation processes. Geologic materials and geochemical data on the studied naphthides suggest that in the region under consideration there is a typical oil deposit sealed in the "head" of the cavernous horizon by highly viscous bitumens.

Проведенные исследования и анализ опубликованных данных нацелены на совершенствование высокоразрешающего биостратиграфического расчленения верхней юры и нижнего мела эталонного разреза на п-ове Нордвик, Анабарский залив, море Лаптевых. Это позволило установить в разрезе последовательности из 13 биостратонов по фораминиферам, 9 биостратонов по диноцистам и 8 с палинофлорой в ранге зон и слоев. Полученные новые данные дали возможность обосновать стратиграфическую непрерывность этого разреза в интервале нижнего и средневолжского подъярусов, где ранее предполагался крупный стратиграфический перерыв. Установленные зональные подразделения имеют разный корреляционный потенциал. Рассмотрены разные версии расчленения разреза по аммонитам и обоснована используемая шкала. По кальцисферам/известковым диноцистам выявлен реперный уровень, позволяющий осуществлять глобальные корреляции и увязывать приграничные толщи юры и мела Тетиса и арктических регионов. Обсуждено магнитостратиграфическое расчленение изученного разреза и его сопоставление с тетическими регионами. Показано, что кривая вариаций δ13Cорг в верхней юре и нижней части валанжина отражает фациальные изменения и с учетом биостратиграфических данных может служить инструментом для корреляций в разных регионах Северного полушария. Для верхневолжского подъяруса и бореального берриаса установлена цикличность изменений изотопного состава углерода. В исследованном разрезе определено распределение значений геохимических параметров (Сорг, δ13Cорг и водородного индекса), показана геохимическая стратификация разреза и вариации породообразующих оксидов. В основании паксинской свиты (верхневолжский подъярус) установлена резкая смена значений геохимических параметров. Определен интервал распространения «подповерхностного максимума хлорофилла». Проведенные исследования показывают, что высокие значения Сорг с легким изотопным составом первого диастеренового геохимического подгоризонта формировались за счет высокой биопродуктивности фитопланктона и накопления органического вещества в благоприятных для его сохранности восстановительных условиях. Анализ содержания основных породообразующих оксидов в изученных породах позволил выявить определенные вариации химического состава изученных отложений, отражающие изменения минералого-петрографических характеристик. The goal of this study was to improve the high-resolution biostratigraphy of the Upper Jurassic and Lower Cretaceous in the type section on the Nordvik Peninsula, Anabar Bay, Laptev Sea. The results were used to identify a succession of 13 foraminiferal biostratigraphic units, 9 dinocyst units, and 8 palynofloral biostratigraphic units in the rank of zones and local zones. Based on new data, the stratigraphic continuity of this section is proved for the Lower and Middle Volgian, where a major stratigraphic hiatus was previously assumed. The established zones have variable correlation potential. Different versions of the subdivision of the section based on ammonites are discussed and the proposed scale is justified. A reference level based on calcispheres/calcareous dinocysts is defined providing global correlations and calibration of beds near Jurassic-Cretaceous boundary in the Tethyan and Arctic regions. The magnetostratigraphic subdivision of the studied section and its comparison with the Tethyan regions are discussed. Together with biostratigraphic data, the proposed δ13Corg curve in the Upper Jurassic and lower part of the Valanginian can be a tool for detailed correlations in different regions of the Northern Hemisphere. The cyclicity of carbon isotope composition in the Upper Volgian and Boreal Berriasian and isotope events in the Volgian and Lower Valanginian are determined within the Arctic region. The distribution of geochemical parameters (Corg, δ13Corg and hydrogen index) is determined in studied section, geochemical stratification of the section and variations in major oxide compositions are demonstrated. A sharp change in geochemical parameters is identified at the base of the Paksa Formation (Upper Volgian). The distribution interval of the “subsurface chlorophyll maximum” is determined. The study shows that high concentrations of isotopically light organic carbon in the first diasterene geochemical subhorizon were caused by high phytoplankton productivity and were deposited under reducing conditions favorable for preservation of organic matter. The analysis of major oxide compositions of the studied rocks revealed that variations in the chemical composition of the studied rocks reflect changes in their mineralogy and petrography.

Катагенез органического вещества юрско-меловых отложений юго-запада Енисей-Хатангского регионального прогиба1 Институт нефтегазовой геологии и

goal of this study was to improve the high-resolution biostratigraphy of the Upper Jurassic and Lower Cretaceous in the type section on the Nordvik Peninsula, Anabar Bay, Laptev Sea. The results were used to identify a succession of 13 foraminiferal biostratigraphic units, 9 dinocyst units, and 8 palynofloral biostratigraphic units in the rank of zones and local zones. Based on new data, the stratigraphic continuity of this section is proved for the Lower and Middle Volgian, where a major stratigraphic hiatus was previously assumed. The established zones have variable correlation potential. Different versions of the subdivision of the section based on ammonites are discussed and the proposed scale is justified. A reference level based on calcispheres/calcareous dinocysts is defined providing global correlations and calibration of beds near Jurassic-Cretaceous boundary in the Tethyan and Arctic regions. The magnetostratigraphic subdivision of the studied section and its comparison with the Tethyan regions are discussed. Together with biostratigraphic data, the proposed delta 13Corg curve in the Upper Jurassic and lower part of the Valanginian can be a tool for detailed correlations in different regions of the Northern Hemisphere. The cyclicity of carbon isotope composition in the Upper Volgian and Boreal Berriasian and isotope events in the Volgian and Lower Valanginian are determined within the Arctic region. The distribution of geochemical parameters (Corg, delta 13Corg and hydrogen index) is determined in studied section, geochemical stratification of the section and variations in major oxide compositions are demonstrated. A sharp change in geochemical parameters is identified at the base of the Paksa Formation (Upper Volgian). The distribution interval of the "subsurface chlorophyll maximum" is determined. The study shows that high concentrations of isotopically light organic carbon in the first diasterene geochemical subhorizon were caused by high phytoplankton productivity and were deposited under reducing conditions favorable for preservation of organic matter. The analysis of major oxide compositions of the studied rocks revealed that variations in the chemical composition of the studied rocks reflect changes in their mineralogy and petrography.

Limited available data on molecular geochemistry indicate the predominance of terragenous organic matter in the source material of the Lower Cretaceous deposits of the Ozhoginskaya suite, which allows it to be considered gasgenerating. However, based on the mixed nature of the source material, this suite could possess potential for liquid hydrocarbon generation. The geochemical features of the organic matter were studied using classical bituminology, Fourier transform infrared spectroscopy, gas chromatography, and mass spectrometry. The results showed a regular distribution of alkanes with a predominance of low-molecular-weight homologues with a maximum at nC15-19 and low values of ∑n.c.-nC 20 /∑nC 21 -c.c., vanadylporphyrin complexes. Thus, the contribution of algal material could be significant to the composition of the fossil organic matter of the Lower Cretaceous Ozhoginsky suite with different ratios of terrigenous and aquatic components in the section. Our results on the Ozhoginskaya suite showed the similarity of geochemical parameters with the Upper Bastakh suite of the Upper Jurassic, the features of bitumoid composition, which were mainly due to the predominance of planktonic-algal material capable of generating a large amount of liquid hydrocarbons. This established similarity raises the estimate of the oil generation potential of the organic matter of the Lower Cretaceous deposits of the Ozhoginskaya suite, along with the high gas generation potential inherent in terragenous organic matter.

РаботапосвященагеохимическимисследованияморганическоговеществапородпоразрезуверхнейюрыИлинь-Тасскогоантиклинорияпоестественнымобнажениямикерновомуматериалуиззоныфорланда,

Results of a geochemical study of brines and oil occurrences in the Udachnaya kimberlite pipe are presented. Like other intrusions in the Daldyn-Alakit diamondiferous region, this diamond deposit is a unique cryohydrogeologic microstructure differing from the host sedimentary rocks and other diamond pipes of the Yakutian diamond-bearing province. Two waterlogged zones distinguished in the section of orebodies at the explored depths of the deposit correspond to the upper and middle Cambrian aquifers. Predominantly acidic (average pH = 5.5) Cl-Ca and Cl-Ca-Na brines with TDS from 94.3 to 391.3 g/dm(3) are widespread within the orebodies and host rocks. The brine mineralization and contents of major salt-forming components increase with depth, to the horizon at the -365 m elevation, where TDS reaches 391 g/dm(3), while below, at the -650 m level with noted hydrogeochemical-field inversion, TDS is 253 g/dm(3). The mineral-ization of Cl-Ca, Cl-Ca-Na, Cl-Ca-Mg, and Cl-Ca-Mg-Na brines in the upper Cambrian rocks varies from 102.9 to 192.9 g/dm(3), and the pH values, from 4.9 to 6.2, averaging 5.6. Among the microcomponents, the highest average concentrations (mg/dm3) are found for Br-1292.8 > S-875.7 > Sr-453.7 > Fe-79.7 > Li-53.4 > B-32.7 > I-13.3 > Si-10.8 > Mn-6.4 > Se-3.6 > Rb-2.3. The values of genetic coefficients vary widely: The rNa/rCl coefficient ranges from 0.18 to 0.31; rCa/rMg, from 1.03 to 3.60; Ca/Cl, from 0.2 to 0.3; and the integrated metamorphism index S (according to S.L. Shvartsev) varies from 193 to 277. The middle Cambrian rock complex, containing more saline brines, has been ex-amined in much more detail. It hosts Cl-Ca, Cl-Ca-Na, Cl-Ca-Mg, and Cl-Na-Mg brines with TDS from 94.3 to 391.3 g/dm(3) and high average concentrations (mg/dm3) of microcomponents: Br-2224.9 > Sr-1024.9 >S-500.1 > B-202.9 > Li-147.1 > Fe-97.0 > I-33.2 > Rb-11.4 > Si-9.6 > Se-9.5 > Mn-3.6 > Ni-1.7. As compared with brines in the overlying rocks, the middle Cambrian brines show a wider variation in element ratios: rNa/ rCl from 0.14 to 0.34, rCa/rMg from 0.66 to 9.71, and Ca/Cl from 0.03 to 0.45. These brines are also characterized by a significantly higher metamorphism grade, which is indicated not only by the rNa/rCl and rCa/rMg ratios but also by the S index varying from 278 to 316. The composition of stable isotopes (delta D and delta O-18) and dissolved inorganic carbon (delta C-13) of the brines was investigated. The studied waters are assumed to be of sedimentary-metamorphic origin. Their isotopic composition reflects the climatic conditions existing at the time of their burial, which were probably aggravated by the contribution of the oxygen isotope exchange with water-bearing rocks. The delta C-13 values of carbon dioxide dissolved in water allow an inference about its biogenic origin. The biogenic carbon isotope exchange is governed by the relationship between methanogenic and SMT processes. Analysis of the Rb-87/Sr-86 and Sr-87/Sr-86 isotope ratios of the studied brines has revealed affinity between the isotopic compositions of waters in the Cambrian deposits and in ancient seawaters. The mass chromatograms of saturated-hydrocarbon (HC) fractions show at least two individual types of oils and malthas (naphthides). The third variety resulted from their mixing at different stages of migration. The fourth is from the contact zone; it changed during the explosion of kimberlites. The first, most common, type of naphthides ("postexplosive") is similar in all geochemical parameters to oils from the Nepa-Botuobiya anteclise, in particular, to those from the Mirnyi arch. Oils of the second (pre-explosive) type are found only in the Udachnaya Formation, within the depth range 1130-1430 m.

В органическом веществе современных и слабо литифицированных отложений Сибири и Русской платформы методом хромато-масс-спектрометрии идентифицирована серия гомологических рядов высокомолекулярных диметилалканов (ВДМА) с исключительно нечетным или четным количеством атомов углерода в молекуле в диапазоне от С19-20 до С30-31.Первый гомологический ряд начинается с 3,4-ВДМА с четным количеством атомов углерода в молекуле, далее чередуются: 3,5-ВДМА-с нечетным углеродом, 3,6-ВДМА -с четным и наконец 3,7-ВДМА -нечетным количеством атомов углерода в молекуле.Наибольшим распространением пользуются 3,7-диметилалканы.Микробиальное происхождение высокомолекулярных диметилалканов, по всей видимости, является наиболее вероятным путем их появления в составе ископаемого органического вещества.Предшественниками (прекурсорами) ВДМА скорее всего были тетра-и диэфирные липиды архей и эубактерий.

The similarities and differences in the composition of organosulfur compounds in the organic matter of oil shale from Upper Jurassic, Middle Devonian, and Middle Cambrian deposits were characterized using modern analytical techniques (selective chemical destruction with the use of nickel boride, supercritical fluid extraction, gas chromatography–mass spectrometry, and two-dimensional gas chromatography with a time-of-flight mass spectrometric detector).

—The homologous series of high-molecular weight dimethylalkanes (HMWDMAs) with either odd- or even-numbered carbon chains in the range from C19–20 to C30–31 have been identified in organic matter from recent and partially lithified deposits of Siberia and the Russian Platform by chromatography–mass spectrometry. The first homologous series is represented by even-numbered 3,4-HMWDMAs followed by the alternation of odd-numbered 3,5-HMWDMAs, even-numbered 3,6-HMWDMAs, and odd-numbered 3,7-HMWDMAs. The most abundant are 3,7-dimethylalkanes. The microbial origin of high-molecular weight dimethylalkanes is the most likely explanation for their presence in the fossil organic matter. The precursors of HMWDMAs might have been tetra- and diether lipids of archaea and bacteria. It is assumed that HMWDMAs and other immature hydrocarbons from great depths (SV-27 and SG-6 superdeep boreholes) result from the decomposition of asphaltenes, which occluded the related compounds inside their structure during the early stages of generation and carried them unchanged throughout the “oil window”.

Углеводороды каркасного строения в различных генетических типах нефтей и конденсатов Западной Якутии

—The organic-geochemistry data reveal two levels in the reference Upper Jurassic–Lower Cretaceous section of the lower reaches of the Olenek River: lower (Volgian–lower Boreal Berriasian (diasterene)) and upper (Boreal Berriasian–Valanginian (hopane)). The Volgian beds are composed of clays with abundant prasinophytes Leiosphaeridia and Tasmanites and various dinocyst assemblages and have the highest content of organic carbon (Corg), up to 9%. Isoprenoids, in particular, pristane and phytane, are highly predominant among aliphatic hydrocarbons; their content is more than three times higher than that of coeluting n-alkanes, which is typical of buried chlorophyll-containing plankton (dinocysts and prasinophytes). Sedimentological, biofacies, and paleoecological analyses show that the highly carbonaceous beds of the Buolkalakh Formation formed under oxygen deficit conditions. An integrated analysis demonstrated that the pristane/phytane ratio does not always reliably reflect the reducing or oxidizing conditions of organic-matter accumulation and diagenesis. The discrepancy between the geochemical identification of organic matter according to the pristane/phytane ratio and the biofacies and sedimentological data is due to the low catagenetic maturity of OM. The Volgian was marked by a significant transgression of the Anabar–Lena sea, which was gradually changed by a successive regression of its basin at the end of this stage and in the Boreal Berriasian. The Corg contents in the coastal and subcontinental sediments decreased. Diasterenes and 4-methyldiasterenes disappeared from the balance of biomarker molecules, and the portion of hopanoids increased. Aerobic environments prevailed in the subbottom waters. Earlier, three biomarker horizons were identified according to geochemical criteria in the synchronous sections of Anabar Bay (Laptev Sea coast): terpane, diasterene, and hopane ones. In the section of the Olenek basin, the upper two horizons are well identified by specific biomarkers, and the lower one is absent because of the sedimentation break. Stratigraphic analysis of the location of these geochemical levels in different parts (and bathymetric zones) of the Anabar–Lena basin shows their diachronous formation. According to all geological and geochemical criteria, the Volgian Stage and the lower beds of the Boreal Berriasian Stage of this basin have a high petroleum potential. In the axial zone of the basin and, especially, on the Laptev Sea shelf, there were probably favorable conditions for the generation and accumulation of hydrocarbons genetically related to the Upper Jurassic highly carbonaceous rocks.

The results of a study of melting the commercial waxes in the composition of asphaltene-resin-paraffin deposits and for comparison of petroleum waxes in multicomponent solvents of various nature are presented. It was found that with an increase in the amount of the aliphatic component in the solvent, the content of the crystalline phase in paraffin wax rises. Patterns in the variation of paraffin melting temperatures depending on the content of the crystalline phase were revealed. Recommendations for choosing an effective solvent for removing deposits under conditions of permafrost influence are suggested.

Preview this conference paper: Geochemistry of the Organic Matter from Lower Cretaceous and Upper Jurassic Deposits in the Olenek River Section (Eastern Siberia), Page 1 of 1 < Previous page | Next page > /docserver/preview/fulltext/2214-4609/2019/P141-1.gif

This paper presents the results of the studies of cyclic aromatic compounds composition in gas condensates of Maloyamalskoye and Myldzhinskoye gas fields of Western Siberia. The composition of aromatic compounds in gasoline cuts of gas condensates was analyzed by GC method. Data on group composition of C-7-C-10 aromatic compounds in gasoline cuts demonstrate that the gas condensates of Maloyamal'skoye gas field are enriched with toluene (C-7) and xylenes (C-8) while in the samples of Myl'dzhinskoye gas field the contents of trimethyl- (C-9) and tetramethyl benzenes (C-10) are high. The composition of aromatic compounds of benzene, naphthalene and phenanthrene series in the non-fractionated condensates was studied using GCMS method. It has been shown that alkyl benzenes of condensates are represented predominately by low-molecular compounds (C-7-C-10), content of long-chain n-alkylbenzenes and n-alkyltoluenes is very low. In addition to alkyl-substituted benzenes the naphthene-substituted benzenes (methyl- and dimethyltetralines) are identified in gas condensates. The relative concentrations of cadalene, retene, ethyl benzene, 1,2,3- and 1,2,4-trimethylbenzenes are used as genetic factors on the composition of aromatic compounds. It has been established that humic organic matter contributed to the formation of the studied fluids. The evidences of that are: higher than usual values of Prystane/Phytane ratio; high content of xylene; increased content of 1,2,5- and 1,2,7-trimethylnaphthalenes and the presence of aromatic hydrocarbons - biomarkers (cadalene, retene). Parameters calculated from the composition of alkyl benzenes and alkyl naphthalenes determine the thermal maturity of condensates. According to the values of ratio (m- + p-xylene)/o-xylene, naphthalenic indexes (MNR, DNR2 and TNR6) and low content of long-chain C11+ alkyl benzenes the catagenic maturity level of the studied fluids corresponds to the main gas generation phase.

According to geochemical hydrocarbon indicators (the concentration ratios for the composition of the C4-C9 hydrocarbons, n-alkanes, C10-C13 adamantanes and acyclic isoprenanes, steranes, terpanes and aromatic compounds) and carbon isotope composition, the condensates of the Maloyamalskoe deposit correspond to the terrigenous genotype. The hydrocarbon maturity indexes (the isomer ratios of steranes and terpanes, maturity indices calculated by aromatic composition) indicate the origination of the hydrocarbon fluids in the conditions of the “oil window”. The adamantan and its alkyl-substituted identified in the studied condensates.