G. N. Gordadze

Distribution features of biomarker hydrocarbons in Asphaltene thermolysis products of different fractional compositions (using as an example oils from carbonate deposits of Tatarstan oilfields)

Asphaltenes of two types, A1 (propagators) and A2 (terminators), have been isolated by fractional precipitation from oil samples, collected from Bashkirian and Vereiskian deposits of carbonate reservoirs of the Akanskoe oilfield in Tatarstan, and subjected to thermolysis at 330°C. For each oil sample, a comparative analysis of the distribution of biomarker hydrocarbons (n-alkanes, isoprenanes, steranes, and terpanes) in the original crude oil and the products derived by thermolysis of its initial asphaltene fraction and asphaltenes of both types A1 and A2 has been performed. Hydrocarbon (HC) biomarkers have been analyzed by capillary gas-liquid chromatography and gas chromatography-mass spectrometry. It has been found that the maturity of organic matter (OM) evaluated in terms of the distribution of regular C29 steranes decreases in the order: initial oil → thermolysis products of initial asphaltenes → thermolysis products of type A1 asphaltenes → thermolysis products of type A2 asphaltenes. It has been shown that except for the OM maturity, geochemical conclusions based on the biomarker parameters of the thermolysis products of asphaltene fractions A1 and A2 coincide with the geochemical findings based on the distribution of biomarkers in the thermolysis products of the initial asphaltene fraction and in the crude oils.

Modeling of formation of petroleum biomarker hydrocarbons by thermolysis and thermocatalysis of bacterium biomass

Thermolysis and thermocatalysis of the insoluble part of chemoorganoheterotrophic aerobic bacteria Arthrobacter sp. RV and Pseudomonas aeruginosa RM have been performed. The thermolyzates and thermocatalyzates of these bacteria contain the hydrocarbon biomarkers n-alkanes, isoprenanes, steranes, and terpanes. Of n-alkanes, the C9-C35 hydrocarbons with unimodal distribution formed in the products of or C9-C39n-alkanes with bimodal distribution are produced by thermolysis or thermocatalysis, respectively. n-Alkanes with odd number of carbon atoms in the molecule prevail over the even counterparts (n-C9, n-C11, n-C15, and n-C17) in the thermolysis products of both strains, whereas n-alkanes with even number of carbon atoms (n-C16, n-C18, and n-C20) dominate in the thermocatalyzates. Isoprenanes of the C13-C20 composition are generated. It is noteworthy that regular C17 isoprenane has been found for the first time among isoprenanes. The cyclic biomarker hydrocarbon steranes and terpanes are simultaneously generated, with the distribution of C27-C29 regular steranes resembles that in marine oils generated in argillaceous strata. At the same time, the adiantane to hopane ratio (H29/H30) is characteristic of the organic matter generated in carbonate strata.

Bacterial synthesis of n-Alkanes with an odd number of carbon atoms in the molecule

Abstractn-Alkanes with an odd number of carbon atoms in the molecule and respective unsaturated even-chain fatty n-acids have been found in native biomass of Arthrobacter sp. RV and Pseudomonas aeruginosa RM hemoorganoheterotrophic bacteria. In addition, C8 and C10n-alkanes with an even number of carbon atoms in a much lower concentration compared with odd-numbered alkanes have been found within native biomass of the bacteria under investigation. Both strains have synthesized an unsaturated irregular isoprenane, squalene (2,6,10,15,19,23-hexamethyltetracosa-2,6,10,14,18,22-hexaene). It has been supposed that the prevalence of odd-over even-carbon-number alkanes in low-maturity oils is due to not only high-temperature decarboxylation of the relevant acids with an even number of carbon atoms, but also bacterial synthesis.

Petroleum C15 polyalkyl substituted bicyclo[4.4.0]decanes (sesquiterpanes) as oil maturity indicators (illustrated by the example of Jurassic and Cretaceous oils of Kalmykia)

It has been found that along with traditional biomarkers (steranes and terpanes), petroleum C15 polyalkylated bicyclo[4.4.0]decanes (sesquiterpanes) can be used for the determination of maturity of crude oils.

Identification of tetramantanes in crude oils

Determination of tetramantanes in crude oils is complicated by low concentrations, the lack of information on retention times, and the fact that their characteristic m/z 292 and 291 mass chromatograms typically contain a variety of foreign peaks having the same ions. Since tetramantanes could not be isolated in pure form using separation by thermal diffusion, the catalytic isomerization of the thermal diffusion concentrate of polycyclic hydrocarbons (most likely, prototetramantanes) over aluminosilicate has been carried out; as a result, all the three tetramantane isomers (iso-, anti-, and skew-) and methyltetramantane have been obtained in pure form. Mass chromatograms at m/z 291 and 292 before and after the separation by thermal diffusion and after the isomerization of the concentrate of saturated polycyclic hydrocarbons on aluminosilicate are presented. The retention indices of tetramantanes on HP-5 are as follows: iso-tetramantane (2293), anti-tetramantane (2365), and skew-tetramantane (2431). It is interesting that methyltetramantane, a homologue with a higher molecular weight, elutes before iso-tetramantane, the tetramantane isomer with the lowest boiling point. Its retention index on HP-5 is 2287.

On the origin of petroleum n -alkylbenzenes

The homologous series of C9–C23n-alkylbenzenes has been first identified in the products of thermal and thermocatalytic transformations of the insoluble part of the Arthrobacter sp. RV and Pseudomonas aeruginosa RM bacterial biomass, and their distribution has been revealed; a homologous series of n-alkyltoluenes has been discovered as well. It has been suggested that the n-alkylbenzenes are biomarkers.

Adamantanes C11-C13 in biodegraded and nonbiodegraded condensates

The distribution of n-alkanes, isoprenanes, and adamantanes in biodegraded and nonbiodegraded condensates (of types B and A by Al.A. Petrov’s classification, respectively) of different genotypes has been studied by gas-liquid chromatography (GLC) and gas chromatography-mass spectrometry (GC-MS). It has been shown that the biodegradation does not affect the relative distribution of adamantanes in the condensates.

Identification of triamantanes in crude oils

Concentrates of petroleum triamantanes (heptacyclo[7,7,1,13,15,01,12,02,7,04,13,06,11]octadecanes) have been obtained by thermal-diffusion separation, and triamantane and 9-methyltriamantane have been identified. It has been shown that foreign peaks present in the m/z 240 and m/z 239 mass chromatograms of the paraffin-cycloparaffin fractions of crude oils do not hinder the identification of triamantanes and calculation of their relative concentrations.

The formation of petroleum biomarker hydrocarbons from possible oxygen-containing precursors

Some possible oxygen-containing precursors of petroleum hydrocarbons were subjected to mild thermolysis. It has been first shown that n-alkylcyclohexanes and steranes are formed along with the expected hydrocarbons n-alkanes and isoprenanes, which result from the loss of a functional group, and there is good correlation between the molecular-mass distributions of n-alkanes and n-alkylcyclohexanes. It has been found experimentally that sterane fragments of oxygen-containing compounds are thermodynamically unstable, and this is confirmed by the formation of biological C27–C29 5α,14α,17α,20S- and 20R-, and 5β,14α,17α,20R-(coprostane) steranes as a result of thermolysis.

Formation of Petroleum Hydrocarbons from Prokaryote Biomass: 1. Formation of Petroleum Biomarker Hydrocarbons from Thermoplasma sp. Archaea Biomass

Saturated hydrocarbon biomarkers (n-alkanes, isoprenanes, pregnanes, steranes, cheilanthanes, hopanes) in the soluble part and thermolysis products of the insoluble part of the biomass of Thermoplasma sp. archaea isolated from the Neftyanaya Ploshchadka hot spring of the Uzon volcano caldera (Kamchatka, Russia) have been identified by gas chromatography–mass spectrometry. The distribution of these hydrocarbons resembles that of slightly transformed marine oils generated in argillaceous-carbonate strata, a fact that is confirmed by Rock-Eval pyrolysis data for the biomass of the archaea studied.