Ksenija Stojanović

Maturity assessment of oils from the Sakhalin oil fields in Russia : phenanthrene content as a tool

A correlation analysis of maturation parameters was carried out on 14 crude oil samples from nine oil fields on Sakhalin Island (Russia). The oils were taken from reservoir rocks of Miocene age at depths ranging from 73 to 2841 m. On the basis of GC analysis of the alkane fraction (n-alkanes and the isoprenoid alkanes pristane and phytane) as well as on the basis of the abundance of demethylated hopanes (GC–MS analysis, m/z 177), it is assumed that the oils are either biodegraded or are a mixture of biodegraded and nonbiodegraded oils. Therefore, their maturation is assessed on the basis of the distribution and abundance of tricyclic aromatic hydrocarbons that are more resistant to biodegradation than alkane-type biological markers. The oils may be classified into three groups on the basis of the well-established maturation parameter MPI 3: highly mature (group I), moderately mature (group II) and immature (group III). The correlation analysis shows that the percentage of phenanthrene [P] in the tricyclic aromatic fraction of the oils of the Sakhalin oil fields can be used as a maturation parameter. The highly mature oils (group I) were found to have a [P] value of more than 14%; the moderately mature oils (group II) have values of 7–14%, and the immature oils (group III) a value of less than 7%. The very good correlation between MPI 3 and [P] also indicates that parallel to methylphenanthrene isomerization, dealkylation also occurs in the reservoir rocks. By correlation analysis it is shown that these reactions are, to a great extent, determined by the depth of the reservoir rocks.

New maturation parameters based on naphthalene and phenanthrene isomerization and dealkylation processes aimed at improved classification of crude oils (Southeastern Pannonian Basin, Serbia)

Aiming at improved classification of crude oils, naphthalene and phenanthrene isomerization and dealkylation processes were considered in detail as a possible basis to select new maturation parameters. Crude oils originating from the Banat depression (Southeastern Pannonian Basin, Serbia) were used as objects of our study. Four new maturation parameters are proposed in this paper. Two of them are based on dimethylnaphthalene (DMN) and trimethylnaphthalene (TMN) isomerization reactions: DNx = (1,3-DMN + 1,6-DMN)/(1,4-DMN + 1,5-DMN) and TNy = (1,3,6-TMN + 1,3,7-TMN)/(1,3,5-TMN + 1,4,6-TMN). The other two are based on demethylation of dimethyl-and trimethylphenanthrenes (DMP and TMP) into corresponding methylphenanthrenes (MP): MDR = ΣMP/ΣDMP and MTR = ΣMP/ΣTMP. The new parameters’ advantageous applicability was demonstrated by factor analysis, comparing them with maturation parameters known from literature.

The influence of pyrolysis type on shale oil generation and its composition (Upper layer of Aleksinac oil shale, Serbia)

The influence of pyrolysis type on shale oil generation and its composition was studied. Different methods such as Rock-Eval pyrolysis, thermogravimetric analysis (TGA) and pyrolysis in the open and closed systems were applied. Samples from the Upper layer of Aleksinac oil shale (Serbia) were used as a substrate and first time characterized in detail. The impact of kerogen content and type on the shale oil generation in different pyrolysis systems was also estimated. Majority of the analysed samples have total organic carbon content > 5 wt. % and contain oil prone kerogen types I and/or II. Therefore, they can be of particular interest for the pyrolytic processing. Thermal behavior of analysed samples obtained by TGA is in agreement with Rock-Eval parameters. Pyrolysis of oil shale in the open system gives higher yield of shale oil than pyrolysis in the closed system. The yield of hydrocarbons (HCs) in shale oil produced by open pyrolysis system corresponds to an excellent source rock potential, while HCs yield from the closed system indicates a very good source rock potential. The kerogen content has a greater impact on the shale oil generation than kerogen type in the open pyrolysis system, while kerogen type plays a more important role on generation of shale oil than the kerogen content in the closed system. The composition of obtained shale oil showed certain undesirable features, due to the relatively high contents of olefinic HCs (open system) and polar compounds (closed system), which may require further treatment to be used.

Origin, organic geochemistry, and estimation of the generation potential of Neogene lacustrine sediments from the Valjevo-Mionica Basin, Serbia

This paper reports an investigation of 60 samples of lacustrine sedimentary rocks of Neogene age lying at depths of 0–400 m in the Valjevo-Mionica Basin, Serbia. The goal of the study was to determine the origin and type of primary organic matter (OM), the degree of thermal alteration, the generation potential of OM from the rocks of this basin, and conditions in the sedimentation environment during the formation of the rocks. The potential of OM of the rocks was estimated on the basis of the thermolysis of a representative sample after its preliminary debituminization.Using data on Corg and bitumen contents and S1, S2, and HI Rock-Eval pyrolysis parameters, the samples were divided into three groups. The first and second groups include rocks recovered from depths up to 200 m, and the third group comprises samples from depths of 200–400 m. The investigation of the inorganic constituents of the rocks and biomarker composition showed that the samples of each of these groups were formed under significantly different climatic conditions, which influenced both the composition of primary organic matter and the conditions of the sedimentation environment, which eventually affected the abundance and quality of OM in the rocks.The yield of the liquid fraction and concentration of hydrocarbons obtained during the thermolysis of the debituminized sample of the first group (showing the highest Corg content), the character of n-alkane and sterane distribution in the saturated fraction of thermolysis products, and the thermal maturity indices calculated from the composition of steranes supported the high generation potential of OM from these rocks.

Study of pyrolysis of high density polyethylene in the open system and estimation of its capability for co-pyrolysis with lignite

Pyrolysis of high density polyethylene (HDPE) in the open system was studied. A plastic bag for food packing was used as a source of HDPE. Pyrolysis was performed at temperatures of 400, 450 and 500 °C, which were chosen based on thermogravimetric analysis. The HDPE pyrolysis yielded liquid, gaseous and solid products. Temperature rise resulted in the increase of conversion of HDPE into liquid and gaseous products. The main constituents of liquid pyrolysates are 1- n -alkenes, n -alkanes and terminal n -dienes. The composition of liquid products indicates that the performed pyrolysis of HDPE could not serve as a standalone operation for the production of gasoline or diesel, but preferably as a pre-treatment to yield a product to be blended into a refinery or petrochemical feed stream. The advantage of a liquid pyrolysate in comparison to crude oil is the extremely low content of aromatic hydrocarbons and the absence of polar compounds. The gaseous products have desirable composition and consist mainly of methane and ethene. The solid residues do not produce ash by combustion and have high calorific values. Co-pyrolysis of HDPE with mineral-rich lignite indicated positive synergetic effect at 450 and 500 °C, which is reflected through the increased experimental yields of liquid and gaseous products in comparison to theoretical ones.

Petrographic and biomarker analysis of xylite-rich coal from the Kolubara and Kostolac lignite basins (Pannonian Basin, Serbia)

Abstract The maceral and biomarker characteristics of 4 sublithotypes of xylite-rich coal (SXCs), pale yellow, dark yellow, brown and black, originating from the Kolubara and Kostolac lignite basins were determined. Based on these results, differences in sources and changes of organic matter (OM) resulting in formation of 4 SXCs were established. Conifers (particularly Cupressaceae, Taxodiaceae and Pinacea) had a significant impact on the precursor OM of all SXCs. The contribution of gymnosperm vs. angiosperm vegetation decreased in order pale yellow SXC>dark yellow SXC>brown SXC>black SXC. The distribution of non-hopanoid triterpenoids indicates that change of SXC colour from yellow to black is associated with reduced input of angiosperm plants from the Betulacea family. Differences in hopane distribution, bitumen content, proportion of short-chain n-alkanes and degree of aromatization of di- and triterpenoids of pale yellow SXC are controlled by microbial communities which took part in the diagenetic alteration of OM. The content of total huminites increased from black to pale yellow SXC, whereas contents of total liptinite and inertinite macerals showed the opposite trend. SXCs differ according to textinite/ulminite ratio, which sharply decreased from pale yellow to black SXC, reflecting increase in gelification of woody tissue. Regarding the composition of liptinite macerals, the SXCs mostly differ according to resinite/liptodetrinite and resinite/suberinite ratios, which are higher in yellow than in brown and black SXC. This result along with values of TOC/N ratio and Carbon Preference Index indicate that the contribution of well preserved woody material, including lignin tissue vs. the impact of epicuticular waxes decreased from yellow to black SXC.

Applicability of Calculated Vitrinite Reflectance for Assessment of Source Rock’s Organic Matter Maturity in Hyperthermal Basins (Banat Depression, Serbia)

Middle and Upper Miocene petroleum source rocks from the Banat Depression, SE Pannonian Basin (Serbia) were investigated. These rocks contain organic matter (OM) in a relatively wide range of maturity (from early to late stage of liquid hydrocarbons generation). OM consists predominantly of Type II kerogen and was deposited under variable redox conditions. This prolific oil and gas production area, as a part of the hyperthermal Pannonain Basin, is characterized by high geothermal gradients (4.0–7.5°C/100 m) and high heating rates (9–22°C/Ma) of the Miocene sediments. Considering complexity of the vitrinite reflection measurements in the source rocks containing Type I and/or Type II kerogen, in this study the values of the measured vitrinite reflectance were compared to calculated vitrinite reflectance, based on maximal palaeotemperature and numerous geochemical maturity parameters. The objective of the study was to assess the applicability of calculated vitrinite reflectance for the Type II kerogen source rocks from a hyperthermal basin. The correlation analysis was performed according to Spearman and Pearson tests. The obtained results showed that calculation of vitrinite reflectance and determination of thermal maturity of OM of the source rocks in hyperthermal basins with high heating rates is best done when based on geochemical parameters calculated from compositions of steranes and methyldibenzothiophenes, and as expected-on maximal palaeotemperature.

Geochemical and Sedimentation History of Neogene Lacustrine Sediments from the Valjevo-Mionica Basin (Serbia)

Valjevo-Mionica Basin is one of the numerous lacustrine Neogene basins in Serbia. After Aleksinac Basin, according to the quality and amount of oil shale, it is one of the main deposits of this raw material in Serbia. The most important oil shale deposits in ValjevoMionica Basin are located in the central part of the basin (Bela stena series, Suseocka and Radobicka Bela Stena). The kerogen content in oil shales ranged from 8 16 %. The average oil yield of 6.3 % is of economical value.

Validation of data on polycyclic biomarkers, naphthalenes, phenanthrenes, and alkyldibenzothiophenes obtained by gas chromatographic-mass spectrometric analysis of hydrocarbon concentrates

The possibility of using the data on the hydrocarbon composition obtained by analysis of hydrocarbon concentrates for geochemical studies has been shown on the example of Pannonian Basin (Serbia) crude oils of different genetic types and different degrees of thermal maturity and biodegradation. A high convergence of the values of geochemical parameters calculated on the basis of the composition of steranes and terpanes, alkylnaphthalenes, phenanthrenes, and dibenzothiophenenes in hydrocarbon concentrates and chromatographic fractions isolated from them has been found by correlation analysis.

Studying of liquid thermolysis products of various types of immature kerogen in sedimentary lacustrine rocks from the valjevo-Mionica basin, Serbia, and the effect of Pt4+ and Ru3+ ions on their yield and the hydrocarbon composition

Liquid thermolysis products of various types of immature kerogen from sedimentary lacustrine rocks from the Valjevo-Mionica basin in Serbia were studied to evaluate the generation potential of kerogen contained in the organic matter (OM) of the rocks, determine the composition of the biomarkers and alkylaromatics in the liquid thermolysis products, and elucidate the effect of Pt4+ and Ru3+ ions (which were added in the form of inorganic salts) on the yield and hydrocarbon composition of the liquid thermolysis products. For this purpose, representative bitumen-free samples A and B of the sedimentary rocks were subjected to thermolysis under various conditions. Rock A contains high amount of immature organic matter, which is dominated by kerogen type I/II and was generated under strongly reduced sedimentation conditions at a high salinity. Sample B is poorer in immature OM than sample A, and the OM of the former contains kerogen type II/III and was generated predominantly in a reduced environment. The content of the liquid products and the concentrations of hydrocarbons obtained in the course of thermolysis of bitumen-free sample A and the typical oil distribution of the biomarkers and alkylaromatics in the thermolysis products confirm a high generation potential of OM in this rock. In all of our experiments on the thermolysis of bitumen-free sample B, the yield of liquid products and hydrocarbons is low. According to the kerogen type, the thermolysis of this rock generates much gases. The Pt4+ and Ru3+ ions (added in the form of simple inorganic salts) increased the yield of liquid (kerogen type I/II) and gaseous (kerogen type II/III) products. During the thermolysis of various type of immature kerogen in the lacustrine sedimentary rocks at a temperature of 400°C, the OM attained maturation corresponding to the early catagenesis level. Saturated biomarkers and alkylaomatics in the thermolysis products of both samples display typical oil distributions. The type of the source OM most strongly affects the composition of n-alkanes and alkylnaphthalenes. The metal ions used in this research served as catalysts for the methylation process during the thermolysis of immature kerogen, regardless of its type. The effect of the Pt4+ and Ru3+ ions on other transformations of the hydrocarbons, for example, the destruction of high-molecular n-alkanes to low-molecular ones and on isomerization reactions in molecules of polycyclic biomarkers and alkylaromatics to thermodynamically more stable isomers in the thermolysis products is controlled, first of all, by the type of the source OM.