E. Poludetkina

Unsaturated hydrocarbons of thermocatalytic origin in some oils and bitumens from the southern part of Anadyr basin

Unsaturated hydrocarbons (UHCs) of thermocatalytic origin (0.3–1.3 wt %) generated directly from the heteroatomic components of organic matter (OM) of source rock strata were first discovered in Mesozoic-Cenozoic oils. In addition, radiogenic UHCs (∼1.5 wt %) were found for the first time among hydrocarbons from bitumens of dispersed OM. It was shown that their presence can be attributed to natural radiation due to radioactive isotopes occurring in the rock. Thus, it was demonstrated that noticeable effects of radiation-induced processes on the composition of rock OM should be taken into account in young (Neogene) deposits as well. Unsaturated hydrocarbons were generated under conditions in which processes involving the carbocationic mechanism did not play a noticeable role. In the samples from Neogene deposits from the southern Anadyr basin, UHCs experienced to a small extent the effect of secondary aging processes, which resulted in reduction in the relative concentration of the least stable components. Dimensionless parameters were proposed such that their numerical values make it possible to differentiate UHCs of different origins and to assess the severity of their aging processes.

Geochemical technique of organic matter research in deposits enrich in kerogene (the Bazhenov Formation, West Siberia)

The international interest in shale oil has recently provoked special attention to the Russian unconventional oil-source formations, including the Bazhenov Formation of West Siberia, domanik deposits in the Volga–Ural region, and the lower Maikop Group of the Cis-Caucasus. High contents of para-autochthonous soluble organic matter (bitumen) in clayey–carbonate, clayey–siliceous, carbonate–clayey–siliceous rocks with low filtration–capacity properties results in significant uncertainties in the identification of the generation potential of organic matter (OM). Examination of a large database on the OM of the Bazhenov Formation allowed us to propose an optimum complex technique for study of the source rock potential and assessment of the amount of produced hydrocarbons in the kerogen-rich sediments. The investigations include a combination of Rock Eval pyrolysis prior to and after extraction with different solvents, the comparison of bituminological and pyrolytic characteristics, and the determination of the group composition of soluble organic matter, as well as chromatography and chromato-mass spectrometry.

A 13C NMR study of crude oils: Identification of compounds with nonisoprenane k,(k + 3)-dimethylalkyl moieties in oils and bitumenoids from the southern part of Anadyr basin

A group of saturated nonisoprenane dimethyl-branched, alkyl-substituted hydrocarbons of the R-CCCCCC(C)CCC(C)CCCCC-R′ type has been found for the first time in crude oils and dispersed organic matter (DOM). Their concentration in the saturated hydrocarbon fractions of crude oils and DOM from the southern part of the Anadyr basin is 1–2 wt % and is well above that of their structural isomers with the closest structure in the same samples. Some ideas about possible sources of these hydrocarbons have been advanced. In the methodological aspect, the simplicity and efficiency of 13C NMR spectroscopy as applied to searching for previously unidentified alkyl structures in crude oils and DOM have been demonstrated, using as spectral parameters coefficients that determine the dependence of chemical shift on the recording temperature and the concentration of the fraction in the solution.

Comparative 13C NMR analysis of the composition of saturated petroleum and bitumenoid hydrocarbons: Potentialities and outlook

The informativity of 13C NMR spectroscopy as applied to solving the class of problems based on the data of comparative analysis of objects has been evaluated using a material from the southern part of the Anadyr oil-and-gas basin (saturated-hydrocarbon fractions of crude oils and bitumenoids). A set of 27 parameters measured from 13C NMR spectra has been proposed to characterize the composition of the samples with different degrees of detailing the structure of all components of the fractions. Methods for the determination of the degree of closeness of the sample composition have been considered, and it has been shown that not all of them satisfy the natural requirement of transitivity. A simple comparison procedure has been proposed for the case of multiparameter description of the fractions, with the values of the parameters lying in a wide range that has the property of transitivity on the material in question. It has been shown that 13C NMR radically extends the capabilities of the comparative analysis of the composition of crude oils relative to the conventional methods (GLC, GC-MS). In contrast to the results of study of the individual composition of saturated hydrocarbons (including the presumably most informative data on the composition of cyclic biomarkers), the 13C NMR data for the given material revealed a regular change of oils from the bottom up the section and to establish that the bitumenoids from its lowest part has nothing in common with the crude oils examined. The analytical parameters derived from the 13C NMR spectral data are not, in this case, too sensitive to inevitable variations in composition associated with sampling procedures or other insignificant factors. Thus, the generally accepted view on 13C NMR as a technique useless for tackling this class of problems can be regarded as refuted.

Proof of formation of organic matter in upper Devonian carbonate and carbonate-siliceous sediments of the South-Tatar uplift in constant photic layer anoxia

Samples of carbonate and siliceous-carbonate deposits of Semiluk—Sargaev horizons of the N‒NE slope of the South Tatar uplift, Volga-Ural petroliferous basin, have been studied. Specific feature of the source rocks—high concentration of compounds—anoxia testifiers in the photic layer has been identified. That is, organic matter has been deposited under the conditions of the constant presence of anoxia in the photic layer of the sedimentation basin at sufficiently high thickness of the water column contaminated with hydrogen sulfide. Since by the composition of saturated hydrocarbons the studied samples are typical for deposits of the Semiluk horizon of the central part of the Volga-Ural basin, we can assume a fairly wide prevalence of such conditions within the South-Tatar arch. Changes in the concentrations of the components—anoxia markers—show cyclical changes in output layer contaminated with hydrogen sulfide or its bioproduction within the studied time.

Correlation of basic 1H and 13C NMR-measurable structural group parameters of crude oils of the Volga–Urals oil and gas basin

Among 120 pairwise relations between 16 main 1H and 13C NMR-measurable characteristics of the structural group composition of Volga–Urals crude oils, 10 most consistent relations (correlation coefficients |rs| ≥ 0.9), 13 relations with |rs| in the range of 0.8–0.9, and 33 pairs with loosely related or mutually independent members (|rs| ≤ 0.3) have been revealed. Several relationships are parametric. The main parameter is Car. The overall picture of the relationships is complex; correlation coefficients with the absolute value above 0.7 are observed not only between the parameters characterizing the structure in the same group of entities (aromatic, n-alkyl): it has been found that Car correlates with the total content of n-alkyl structures (rs =–0.76). Having definitely common features, oils from the Volga–Urals and Western Siberia oil and gas basins noticeably differ from one another. To explain the differences, it is necessary to launch an integrated study that is methodologically beyond the scope of contemporary petroleum geochemistry. The paper demonstrates the capabilities of correlation analysis for solving problems to which this method has not been yet applied in petroleum geochemistry: partial correlation coefficients as a means of identifying parametric relationships and Spearman correlation coefficients for nonnumeric values in determining differences in the composition between oils of different structures and from different territories or stratigraphic plays.

The hydrocarbon-generation potential of the Domanik rocks in the Volga–Ural petroliferous basin

The factors that are responsible for the formation of the hydrocarbon-generation potential and its occurrence in the Devonian carbonate sequences (Domanik Formation) of the Volga–Ural petroliferous basin are considered. The rocks of this formation are characterized by a high generation potential that is sufficient for the formation of large oil and gas accumulations. The highly carbonaceous deposits lack reservoirs.

The Characteristics of the Organic Matter of the Upper Devonian Domanik-Type Deposits in the Northern and Central Regions of the Volga-Ural Basin According to Saturated Biomarkers Composition

The composition of saturated biomarkers (alkanes, steranes, and triterpanes) in the Upper Devonian sediments (the Sargaev, Semiluk, and Mendym horizons, the Famennian stage) that belong to the Domanik formation, which is widespread on the territory of the Volga-Ural basin, was studied. The section elongated from N to S that covers the northern and central regions of the Volga-Ural basin was observed. A set of 21 parameters was used to characterize saturated hydrocarbons, including those rarely used in geochemical studies. For each parameter a set of mean values for the considered region as a whole and its individual parts was calculated and distribution-density plots were built. It was established that the most representative parameter for characterizing the Domanik-type deposits as a whole is a highly specific parameter, that is, the ratio of 29,30-bisnorhopane C28 to hopane C29. Most of the characteristics of the genetic composition demonstrate the difference between the organic matter (OM) of the vault part of the region and the Mukhanov- Erokhovsky trough. There are large differences in the parameters that characterize the maturity of OM. The characteristic values of the parameters for both the vault and the depression zone are given; two to three genetic groups of OM were determined for the majority of the parameters in both regions. A method for constructing the distribution-density graphs of the parameters is proposed that makes it possible to take their features fully into account.

Characteristics of Sources of Oils of Romashkino Field by Composition of Saturated and Aromatic Biomarkers

Composition of saturated biomarkers revealed the presence of at least two sources of oils of the Romashkino field with the monotypic conditions. All the studied oils are characterized by presence of a large number of components—anoxia testifiers in the photic layer of sedimentation basin in the fractions of aromatic compounds. These are products full or partial hydrogenation, cyclization and degradation of polyene compounds. Total content of this group of compounds is measured in these fractions for the first time. It is shown that the total content of the anoxia testifiers is high. Thus the specific characteristic of oil source rocks is defined—their formation in the conditions of existence of anoxia in the photic layer during the entire accumulation time of initial organic matter, and the thickness of the layer infected with hydrogen sulphide was significant. On the basis of composition and content of the anoxia testifiers it is shown that the hydrogenation of initial polyenes prevailed in diagenesis over the processes of cyclization.

Geochemical Features of Organic Matter of the Bazhenov Formation

The result of general geochemical investigations and biomarker analyses are present in this paper. Bazhenov Formation is organic matter – enriched formation of Late Jurassic- Early Cretaceous age. It is located within the West Siberian petroliferous basin. The most of authors recognize that the Bazhenov formation is the main source rock of West Siberian basin. Moreover, since the 70s of the last century own oil and gas potential of the Bazhenov formation is known. The detailed biomaker investigations of organic matter of Bazhenov formation allow to suggest pattern of distribution of hydrocarbon accumulations; to ascertain paleofacies depositional environment of Bazhenov formation and characteristics of bioproduce; to clarify the variability of microfacies. The last one allows to predict own oil and gas potential of the Bazhenov formation.