Energy Fuels 2010, 24, 4357–4368 Published on Web 07/07/2010
: DOI:10.1021/ef100466f
Pyrolysis and Catalyzed Pyrolysis in the Investigation of a Neogene Shale Potential from Valjevo-Mionica Basin, Serbia Ksenija Stojanovic,*,†,‡ Aleksandra Sajnovi c,‡ Tibor J. Sabo,† Anatoly Golovko,§ and Branimir Jovancicevic†,‡ † Faculty of Chemistry, University of Belgrade, Studentski trg 12-16, 11000 Belgrade, Serbia, ‡Center of Chemistry, IChTM, Studentski trg 12-16, 11000 Belgrade, Serbia, and §Institute of Petroleum Chemistry, 3 Academichesky Avenue, 634021 Tomsk, Russia
Received April 13, 2010. Revised Manuscript Received June 24, 2010
The generative potential of a Neogene shale from Valjevo-Mionica Basin (Serbia) was investigated using conventional pyrolysis and pyrolysis in the presence of Pt(IV)- and Ru(III)-ions at temperatures 250 and 400 °C. Total liquid pyrolysate and hydrocarbon yields obtained in pyrolytic experiments, group composition of liquid pyrolysates, and distributions of saturated biomarkers and alkylaromatics in pyrolysates showed that the shale is in a catagenetic stage and may be a source of liquid hydrocarbons. It was estimated that similar shales found at a depth of 2300-2900 m would become active oil generating source rock where the minimum temperature necessary for catagenetic hydrocarbon generation is between 103 and 107 °C. The used metal ions, demonstrated significant positive effects on the yields of total liquid pyrolysate and corresponding hydrocarbons, at both temperatures 250 and 400 °C. Comparison of the results of alkylaromatics maturity parameters with maturity ratios calculated from distribution and abundance of saturated biomarkers showed that the metal ions had much greater influence on maturity changes on planar aromatic systems than on isomerizations in the molecules of polycyclic alkanes. The influence of Pt(IV)- and Ru(III)-ions on the distribution of saturated biomarkers in liquid pyrolysates is the same at both temperatures. The used metal ions have greater impact on kerogen degradation, which directly reflects on the increase in the quantity of hydrocarbons, than on isomerization reactions: moretanes f hopanes, hopanes f neohopanes and 5R(H)14R(H)17R(H)20(R)-steranes f 5R(H)14R(H)17R(H)20(S)-steranes. Interactions between the used metal ions and aromatic systems during pyrolysis depend on temperature. Pt(IV)- and Ru(III)-ions demonstrated significant catalytic effect on maturation changes in both naphthalene and phenanthrene isomers during pyrolysis at 400 °C. Catalytic effects of Pt(IV)-ion on maturation changes in alkylnaphthalenes and Ru(III)-ion on maturation changes in alkylphenanthrenes were observed at 250 °C, which is caused by the different coordination properties of these metal ions. and thermal maturity level.9-14 Apart from the mentioned analyses, full characterization of the organic matter of sedimentary rocks also requires investigation of kerogen. In the case of an immature sample, its potential might be estimated by simulation of organic matter maturity changes under the laboratory conditions, using different pyrolytic experiments on bitumen-free shale.15,16 In some cases, degradation techniques are used to also remove the mineral part of the shale in order to isolate pure kerogen.17 However, kerogen maturity under geologic conditions occurs in a mineral environment so that pyrolysis of bitumen-free shale may be considered as a
1. Introduction Organic rich shales have been the subject of many studies, primarily because of their potential economic value.1,2 In that sense, organic geochemical investigations have special significance. First of all, they include the determination of the quality and type of organic matter, its composition, origin, and thermal maturity level.3-6 Rock-Eval pyrolysis is used as a rapid and preliminary method to examine the type and origin of the organic matter.7,8 Nevertheless, for more reliable examination of the organic matter of sediments it is necessary to isolate bitumen, determine its quantity and composition, and on the basis of a great number of group and specific geochemical parameters to more precisely estimate the origin
(9) Katz, B. J. Org. Geochem. 1983, 4, 195–199. (10) Radke, M. Organic Geochemistry of Aromatic Hydrocarbons. In Advances in Petroleum Geochemistry; Radke, M., Ed.; Academic Press: London, 1987; pp 141-205. (11) Strachan, M. G.; Alexander, R.; Kagi, R. I. Geochim. Cosmochim. Acta 1988, 52, 1255–1264. (12) Al-Arouri, K. R.; McKirdy, D. M.; Boreham, C. J. In Advances in Organic Geochemistry 1997, Part 1; Horsfield, B., et al., Eds.; Pergamon Press: Oxford, U.K., 1998; pp 713-734. (13) van Aarssen, B. G. K.; Bastow, T. P.; Alexander, R.; Kagi, R. I. Org. Geochem. 1999, 30, 1213–1227. (14) George, S. C.; Ruble, T. E.; Dutkiewicz, A.; Eadington, P. J. Appl. Geochem. 2001, 16, 451–473. (15) Huizinga, B. J.; Aizenshtat, Z. A.; Peters, K. E. Energy Fuels 1988, 2, 74–81. (16) Parsi, Z.; Hartog, N.; G orecki, T.; Poerschmann, J. J. Anal. Appl. Pyrolysis 2007, 79, 9–15. (17) Nzoussi-Mbassani, P.; Khamli, N.; Disnara, J. R.; LaggounDefarge, F.; Boussafir, M. Sediment. Geol. 2005, 177, 271–295.
*Corresponding author. E-mail:
[email protected]. (1) Ercegovac, M. Geology of Oil Shales; Gra{evinska knjiga: Belgrade, Serbia, 1990; pp 105-115, 142-147 (in Serbian). (2) Tissot, B. P.; Welte, D. H. Petroleum Formation and Occurrence, 2nd ed.; Springer-Verlag: Heidelberg, Germany, 1984; pp 225-237. (3) Liu, L.; Lee, Y.-J. J. Pet. Sci. Eng. 2004, 41, 135–157. (4) Peters, K. E.; Walters, C. C.; Moldowan, J. M. The Biomarker Guide; Cambridge University Press: Cambridge, U.K., 2005; pp 73, 500, 612. (5) Li, M.; Stasiuk, L.; Maxwell, R.; Monnier, F.; Bazhenova, O. Org. Geochem. 2006, 37, 304–320. (6) Stojanovic, K.; Jovancicevic, B.; Vitorovic, D.; Golovko, J; Pevneva, G.; Golovko, A. J. Pet. Sci. Eng. 2007, 55, 237–251. (7) Johannes, I.; Kruusement, K.; Palu, V.; Veski, R.; BojesenKoefoed, J. A. Oil Shale 2006, 23, 110–118. (8) Sari, A.; Aliev, S. A. J. Pet. Sci. Eng. 2006, 53, 123–134. r 2010 American Chemical Society
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more realistic simulation of organic matter maturation in the natural conditions compared to thermal decomposition of pure kerogen.4,18 Certainly, there is no ideal pyrolysis, as during these simulations the conditions are different from the natural ones.19 Neogene shale from Valjevo-Mionica Basin (Serbia) was investigated in this study. On the basis of group and specific organic geochemical parameters, the sample was shown to contain a significant amount of organic matter composed primarily of kerogens type I or I/II that have good liquid hydrocarbon generation potential and is at a low maturity level. The objective, on the one hand, was a detailed estimation of the potential and prediction of the conditions necessary to attain catagenesis using pyrolytic experiments on the bitumen-free sample. On the other hand, bearing in mind that some metal ions (e.g., Al(III)-ion in clay minerals)13,20-23 have catalytic influence on most of the maturation processes and that Pt(IV)- and Ru(III)- ions are often components of catalysts in many laboratory investigations and industrial procedures,24,25 the pyrolytic experiments were performed also in the presence of simple inorganic salts, H2[PtCl6] and RuCl3, to investigate if their presence changes the yield and hydrocarbon composition of liquid pyrolysates. 2. Samples and Methods 2.1. Samples and Geological Settings. The genesis of oil shales in Serbia is connected with lacustrine depositional environments in several periods since the Upper Carboniferous period and most prominent during the Paleogene and Miocene periods.1 Geological occurrences of oil shales in Serbia is spatially connected with the eastern, the southern, and the western parts of the country. Figure 1 shows the locations of the investigated area and the other important oil shale deposits in Serbia. After the Aleksinac Basin, which represents the most important oil shale deposit by quality and geological reserves, ValjevoMionica Basin is one of the major deposits of this energy producing material. Valjevo-Mionica Basin stretches from the northwest to the southeast. The oil shale deposit in Valjevo-Mionica Basin cover an area of approximately 40 km2 and is designated as the Mionica Formation. These shales were the subject of a number of studies that frequently disagree in their stratigraphic identity because of a lack of paleontological benchmarks and the extraordinary lithological similarity and cyclic repetition of marly deposits.26 Some authors consider the Mionica Formation with oil shales as the oldest registered formation in the Valjevo-Mionica Basin and assign it to Lower Miocene, Egger-Eggenburgian, or Eggenburgian-Ottnangian. The
Figure 1. Locations of the most important deposits of oil shale in Serbia. 1, Aleksinac; 2, Goc-Devotin; 3, Vlase-Golemo Selo; 4, Vranjski Basin; 5, Babusnicki Basin; 6, Raca; 7, Svrljig; 8, Petnica; 9, Valjevo-Mionica Basin.
depth of the formation ranges between 150 and nearly 300 m depending on the paleorelief.27,28 The Mionica Formation is found at a depth of 200 m and is characterized by relatively rare thinner beds or interbeds of sandy aleurolites and laminated shales, marlstones (dolomitic, sandy, and clayey as well as tuffous), tuffs, lenses enriched with searlesite, and analcite and limestone with chert concretions. The organic matter is mainly concentrated in bands or laminas of different thicknesses, which indicates specific conditions of sedimentation with very pronounced seasonal changes in a lacustrine environment. Mionica Formation corresponds to intrabasin facies of a shallow lake, whose bottom was gradually sinking during the geological past. Valjevo-Mionica lake was uplifted by the movements of the II Stajerska tectogenesis, when the lake development was completed. The Mionica Formation Neogene shale sample investigated in this study originated from the most interesting exploratory well (Val-1) from an organic geochemical point of view. In the former investigations, 60 sedimentary rock samples from the Val-1 exploratory well were examined in detail. On the basis of the analysis of the organic matter and inorganic part of samples, the well was divided into 4 zones according to depth intervals. The most interesting zone with oil shale laminas is found at a depth of up to 75 m.29 The investigation in the present study
(18) Gordzadze, G. N. Termolysis of Organic Substance in Geochemical Prospection Explorations of Oil and Gas; I.G. and R.G.I.: Moscow, 2002; pp 79-80 (in Russian). (19) Yoshioka, H.; Ishiwatari, R. Geochemical Journal 2002, 36, 73–82. (20) Waples, D. W.; Machihara, T. Biomarkers for Geologists: A Practical Guide to the Application of Steranes and Triterpanes in Petroleum Geology; The American Association of Petroleum Geologists: Alexandria, VA, 1991; pp 20, 47. (21) Jovancicevic, B.; Vitorovic, D.; Saban, M.; Wehner, H. Org. Geochem. 1992, 18, 511–519. (22) Jovancicevic, B.; Vucelic, D.; Saban, M.; Wehner, H.; Vitorovic, D. Org. Geochem. 1993, 20, 69–76. (23) Bastow, T. P.; Alexander, R.; Sosrowidjojo, I. B.; Kagi, R. I. Org. Geochem. 1998, 28, 585–595. (24) Hu, J.; Venkatesh, K. R.; Tierney, J. W.; Wender, I. Appl. Catal. A: General 1994, 114, L179–L186. (25) Kawaguchi, T.; Sugimoto, W.; Murakami, Y.; Takasu, Y. J. Catal. 2005, 229, 176–184. (26) Jovanovic, O.; Grgurovic, D.; Zupancic, N. Geology, Series A, B (Hydrogeology and Engineering Geology) 1994, 46, 207-222 (in Serbian with a summary in English).
(27) Dolic, D. Protocol SGD 1984, 1, 63-67 (in Serbian with a summary in German). (28) An{elkovic, M.; An{elkovic, J. Annales G eologiques de la P eninsule Balkanique 1985, 49, 1-9 (in Serbian with a summary in English). (29) Sajnovi c, A.; Stojanovic, K.; Jovancicevic, B.; Cvetkovic, O. CHEMIE der ERDE GEOCHEMISTRY 2008, 68, 395–411.
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was performed with the representative sample of Neogene shale originated from this zone, at a presentday depth of 52 m. 2.2. Methods. Organic carbon content in the initial shale was determined by elemental analysis after the removal of carbonates from the sample with diluted hydrochloric acid (1:3, v/v). The measurements were performed using a Vario EL III, CHNOS Elemental Analyzer, Elementar Analysensysteme GmbH. Rock-Eval pyrolysis was performed on the Rok-Eval II apparatus according to the method JUS ISO/IEC 17025. For the analysis, 50 mg of sample was used and for calibration 100 mg of standard IFP 160000. Soluble organic matter (bitumen) was extracted from the shale by Soxhlet’s method with an azeotrope mixture of methylene chloride and methanol for 42 h. The saturated, aromatic, and NSO-fractions (polar fraction, which contains nitrogen, sulfur, and oxygen compounds) were isolated from bitumen using column chromatography (adsorbents: Al2O3 and SiO2). The saturated hydrocarbons were eluted with n-hexane (at the rate of 0.5 cm3/ min), aromatics with n-hexane, mixture of n-hexane/benzene = 3:1, v/v, and benzene, whereas the NSO-fraction was eluted with a mixture of methanol and chloroform 1:1, v/v. A UNICO 2804 UV/ vis double beam spectrophotometer was used to determine the separation of the saturated and aromatic fractions. Elemental sulfur from the saturated fraction was removed by the method suggested by Blumer.30 Pyrolyses were performed on soluble organic matter (bitumen) free shale, which contained kerogen with native mineral matrix. The pyrolytic experiments also were performed on bitumenfree shale in the presence of H2[PtCl6] and RuCl3 under the same conditions. The initial mass of bitumen-free shale was 4.55 g, and the organic carbon to catalyst mass ratio was 10:1. Pyrolyses were performed in an autoclave under nitrogen for 4 h at two temperatures: 250 and 400 °C. Liquid pyrolysis products were extracted with hot chloroform. Gaseous products were not analyzed, although the production of gaseous products was indicated by the pressure change in the autoclave. Liquid pyrolysates were separated into saturated hydrocarbon, aromatic hydrocarbon, and NSO fractions using the same method as that applied for the fractionation of extracted bitumen. Saturated and aromatic fractions isolated from the initial bitumen and pyrolysates were analyzed by gas chromatography-mass spectrometry (GC-MS). A gas chromatograph Shimadzu GC-17A gas chromatograph (DB-5MS þ DG capillary column, 30 m 0.25 mm, He carrier gas 1.5 cm3/min, FID) coupled to a Shimadzu QP5050A mass selective detector (70 eV) was used. The column was heated from 80 to 290 °C, at a rate of 2 °C/min, and the final temperature of 290 °C was maintained for an additional 25 min. Saturated fractions were analyzed for n-alkanes and isoprenoids from the m/z 71, steranes from the m/z 217, and terpanes from the m/z 191 ion fragmentogram. Methyl-, dimethyl-, and trimethylnaphthalenes in the aromatic fractions were identified from the m/z 142, 156, and 170 ion fragmentograms, whereas phenanthrene, methyl-, and dimethylphenanthrene isomers were analyzed from the m/z 178, 192, and 206 ion fragmentograms. The individual peaks were identified by comparison with the literature data19,31,32 and on the basis of the total mass spectra (libraries: NIST 107, NIST 121, PMW_tox3 and Publib/Wiley 229).
Table 1. Values of Group and Specific Organic Geochemical Parameters of the Initial Shalea group parameter
value
Corg (%) S1 (mg/g rock) S2 (mg/g rock) bitumen (ppm) bitumen/Corg (%) hydrocarbons (ppm) HC/Corg (%) HI (mgHC/gTOC) Tmax (°C)
3.40 3.40 20.92 5054 14.86 256 0.0075 600 428
group composition of bitumen saturated and aromatic HC þ NSO-compounds and asphaltenes (%)
5.07 þ 94.93
specific parameter
value
CPI Pr/Phyt Pr/n-C17 Phyt/n-C18 Sq/n-C26 C30M/C30H C29M/C29H Gx100/C30H C29RRR(S)/ C29RRR(S þ R)
3.38 0.29 0.04 0.94 3.73 5.44 1.03 47.53 0.20
a S1, free hydrocarbons; S2, pyrolysate hydrocarbons; HC, hydrocarbons; HI, hydrogen index; CPI, carbon preference index determined by the equation of Bray and Evans for full amplitude of n-alkanes C16-C32. CPI = 1/2 [Σodd(n-C17 - n-C31)/Σeven(n-C16 - n-C30) þ Σodd(n-C17 -- n-C31)/Σeven(n-C18 - n-C32)]. For peak assignments, see legend, Figure 2.
content (Corg) of 3.40%, a Hydrogen Index (HI) of 600 mgHC/ gTOC, and a Tmax of 428 °C (Table 1). These values are consistent with the presence of immature to marginally mature, oil-prone organic matter composed primarily of kerogens type I or I/II. Soxhlet extraction of the shale with an azeotrope mixture of methylene chloride and methanol yielded 5054 ppm of bitumen (Table 1). The relatively high bitumen content in an immature sample may be explained by the presence of a significant amount of polar fraction (94.83%), which is not readily expelled from the kerogen or did not incorporate into the kerogen matrix during late diagenesis. The n-alkane distribution in bitumen extracted from the shale is characterized by pronounced n-C17 domination, typical for organic matter of predominantly algal origin, which is in agreement with the value of the hydrogen index, obtained by Rock-Eval pyrolysis (Figure 2a, Table 1). The CPI value for the full amplitude of n-alkane range of 3.38 indicates low maturity, which has also been confirmed on the basis of the values of group organic geochemical parameters (Tmax and group bitumen composition; Table 1). Pr/Phyt ratio in bitumen extracted from the initial shale is 0.29 (Table 1), which indicates reducing conditions during deposition of the organic matter that contributed to its preservation. This fact is in accordance with the results of previous investigations of the inorganic part of the sediment, which showed that increased salinity and arid climate were conducive to the formation and preservation of the organic matter.33 The presence of squalane supports this inference (Figure 2a and Table 1). Distribution of terpane biomarkers in bitumen isolated from the initial shale is characterized with the domination of thermodynamically less stable βR- and ββ-isomers, the most abundant being C30 βR-moretane (C30M/C30H ratio >5; Figure 2b and Table 1). Terpanes typical for extracts of more mature source rocks and crude oils, such as Tm, Ts, C29Ts, and a series of 22(S)-homohopane isomers, were not identified with the exception of C31(S), which is a minor component that coelutes with 2-gammacerene (Figure 2b). C29 and C30 Rβ-Hopanes are present in small quantities, as well as a thermodynamically less
3. Results and Discussion 3.1. Characteristics of Organic Matter in the Shale Sample. Group organic geochemical parameters obtained by elemental analysis and Rock-Eval pyrolysis indicate the shale has significant generative potential with a total organic carbon (30) Blumer, M. Anal. Chem. 1957, 29, 1039-1041. (31) Philp, R. P. Fossil Fuel Biomarkers. Applications and Spectra; Elsevier Press: Amsterdam, The Netherlands, 1985; pp 164-174, 246-257. (32) George, S. C.; Lisk, M.; Summons, R. E.; Quezada, A. R. In Advances in Organic Geochemistry 1997, Part 1; Horsfield, B., et al., Eds.; Pergamon Press: Oxford, U.K., 1998; pp 631-648.
(33) Sajnovi c, A.; Simic, V.; Jovancicevic, B.; Cvetkovic, O.; Dimitrijevic, R.; Grubin, N. Acta Geol. Sin. (Engl. Ed.) 2008, 82, 1201–1212.
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Figure 2. GC-MS ion fragmentograms of n-alkanes and isoprenoids, m/z 71 (a), terpanes, m/z 191 (b), and steranes, m/z 217 (c) from a saturated fraction of bitumen isolated from the initial shale. Pr, pristane; Phyt, phytane; Sq, squalane; C27βH, C2717β(H)-22,29,30-trisnorhopane; C29H, C2917R(H)21β(H)-30-norhopane; C29M, C2917β(H)21R(H)-moretane; C30H, C3017R(H)21β(H)-hopane; C30M, C3017β(H)21R(H)-moretane; C31(S), C3117R(H)21β(H)22(S)-hopane; C31(R), C3117R(H)21β(H)22(R)-hopane; G, gammacerane; C30ββH, C3017β(H)21β(H)-hopane; C31ββH, C3117β(H)21β(H)-hopane; C27βRR(R), C275β(H)14R(H)17R(H)20(R)-sterane; C27RRR(R), C275R(H)14R(H)17R(H)20(R)-sterane; C28βRR(R), C285β(H)14R(H)17R(H)20(R)-sterane; C28RRR(R), C285R(H)14R(H)17R(H)20(R)-sterane; C29RRR(S), C295R (H)14R(H)17R(H)20(S)-sterane; C29βRR(R), C295β(H)14R(H)17R(H)20(R)-sterane; C29RRR(R), C295R(H)14R(H)17R(H)20(R)-sterane.
stable epimer of C31-homohopane with biological 22(R)-configuration. These observations are in agreement with the low maturation degree of the organic matter indicated by group parameters and CPI ratio. The relatively high value of the gammacerane index of 47.53% is in agreement with the fact that organic matter was deposited in the reducing hypersaline environment (Figure 2b and Table 1). Sterane distribution of the saturated fraction of the extracted shale bitumen is characterized by the predominance of homologues with unstable RRR(R)- and βRR(R)-configurations (Figure 2c), which again confirms a low maturity. Among them, C27- and C28-steranes are in higher proportions, which is in agreement with the predominantly algal origin of the organic matter. Steranes with Rββ(R)-, Rββ(S)configuration and typical geoisomers, βR- and Rβ-diasteranes, were not identified, and only C29 sterane with RRR(S)-configuration is present in low amounts (value of C29RRR(S)/ C29RRR(S þ R) ratio = 0.20; Table 1). Components of aromatic fraction, methyl-, dimethyl-, and trimethylnaphthalenes, as well as methyl- and dimethylphenanthrenes (m/z 142, 156, 170, 192, and 206) typical for more mature source rock bitumens and oils, were not identified or are present in traces in the shale extract, with the exception of phenanthrene (m/z 178). The observation is consistent with the low maturity of the organic matter since the main quantity of alkylaromatics is generated during catagenesis. The examined immature shale has sufficient organic richness to be a potential source of hydrocarbons when exposed to
higher thermal stress. Rock-Eval pyrolysis is only a rapid and preliminary method for characterizing the potential of this shale. In order to estimate more precisely its potential and to predict the conditions necessary for attaining catagenesis, pyrolytic experiments at 250 and 400 °C on bitumen-free samples were conducted. Metal ions were added to determine if their presence assists kerogen pyrolysis and whether catagenesis simulation can be conducted at a lower temperature.4,34 3.2. Characteristics of Liquid Pyrolysates. 3.2.1. Group Organic Geochemical Parameters. Yields of liquid pyrolysates and hydrocarbons, as well as group compositions of liquid pyrolysates, obtained by pyrolyses of bitumen-free shale, both pure (S250 and S400) and added with of H2[PtCl6] (SPt250 and SPt 400) and RuCl3 (SRu250 and SRu400) at 250 and 400 °C, are given in Table 2. Temperature is the dominating factor influencing the pyrolysate yield (Table 2). Total liquid pyrolysate generated at 250 °C is ∼30 to 40% that observed at 400 °C, and the amount of hydrocarbon is ∼22%. These observations are not surprising since it is known from the literature that significant production of saturated biomarkers requires a temperature above 300 °C for this heating time.34 Heated at 400 °C for 4 h, the shale generated a total liquid pyrolysate and hydrocarbons of 1700 ppm and 692 ppm, (34) Jaeschke, A.; Lewan, M. D.; Schouten, S.; Sinninghe Damste, J. S. Book of Abstracts, 23rd International Meeting on Organic Geochemistry, 2007, Torquay, England; Farrimond, P., et al., Eds.; Integrated Geochemical Interpretation Ltd.: Bideford, U.K., 2007; pp 999-1000.
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Figure 3. GC-MS ion fragmentogram of n-alkanes and isoprenoids, m/z 71 (a), terpanes, m/z 191 (b), and steranes, m/z 217 (c) from a saturated fraction of pyrolysate SPt250, typical for all pyrolysates obtained at 250 °C. For peak assignments, see the legends for Figures 2 and 4.
groups, and the aromatic systems in the so-called sandwich compounds.35-37 Apart from the liquid pyrolysate, the pyrolytic experiments also produced gaseous products that may be generated by direct degradation of kerogen or as secondary products of the degradation of liquid hydrocarbons. Gaseous products were not analyzed. However, their presence is proved by measuring pressure in the autoclave at the end of pyrolysis in relation to the initial pressure, which typically was ∼4.5 atm. The increase in pressure ranged between 2.13 and 32.56% and, as expected, was greater after heating at 400 °C than at 250 °C (Table 2). As in case of liquid products of pyrolysis, the increase of pressure/yield of gas products was somewhat more pronounced for Ru(III)ion compared to Pt(IV)-ion at both temperatures. The more pronounced influence of Ru(III)-ion may be explained by the fact that the Ru(III)-ion forms exclusively octahedral complexes, while Pt(IV)-ion forms both octahedral and squareplanar complexes, because of which the Ru(III)-ion has greater capacity for forming complexes with organic substance.35-37 3.2.2. Specific Organic Geochemical Parameters. 3.2.2.1. n-Alkanes and Isoprenoids. All of the six pyrolysates have similar n-alkane distributions in which n-alkanes C17-C23 are predominant, typical of the organic matter of algal origin (Figures 3a and 4a). CPI values for all of the pyrolysates are close to 1, typical of a mature oil distribution (Table 3). The above observation suggests that the effect of temperature at pyrolysis is reflected in the increased amount of hydrocarbons, while the distribution of n-alkanes in pyrolysates primarily depends on the precursor material. Unlike bitumen in the immature shale, squalane is absent in the 250 and 400 °C pyrolysates (Figures 2a-4a). Values of the Pr/Phyt ratio are higher than that in the initial bitumen, which may be explained by the fact that degradation of
Table 2. Values of Group Organic Geochemical Parameters in Liquid Pyrolysates group composition of liquid pyrolysates saturated þ NSO þ yield of liquid aromatic asphaltenes pyrolysatesa yields of a (ppm) HC (ppm) HC (%) (%) p0 sample S250 SPt250 SRu250 S400 SPt400 SRu400
700 900 1000 1700 2700 2700
154 301 312 692 1266 1376
21.88 29.76 33.87 40.85 47.63 51.35
78.12 70.24 66.13 59.15 52.37 48.65
/ 4.7 4.7 4.5 4.5 4.3
p / 4.8 5.0 4.9 5.0 5.7
a
Relative to the bitumen-free sample; HC, hydrocarbons; p0, initial pressure; p, pressure in autoclave at the end of pyrolysis; /, not measured
respectively (Table 2). The yields are consistent for source rock with good potential and support the assumption derived from an analysis of the immature shale.4 The presence of Pt(IV)- and Ru(III)-ions significantly increases the yields of liquid pyrolysate and hydrocarbons, at both temperatures, with a bit more pronounced effect of Ru(III)-ion. The catalytic effect of the used metal ions is based on them acting as Lewis acids and their high affinity for forming complexes with organic matter, both with the functional groups, such as carboxylic, hydroxyl, and amino (35) Filipovic, I.; Lipanovic, S. General and Inorganic Chemistry; Skolska knjiga: Zagreb, Croatia, 1988; pp 335-337, 1055-1065 (in Croatian). (36) Hagen, J. Industrial Catalysis. A Practical Approach; Wiley-VCH Verlag GmbH & Co.KGaA: Weinheim, Germany, 2006; pp 63-81. (37) Sheldon, R; Arends, I; Hanefeld, U. Green Chemistry and Catalysis; Wiley-VCH Verlag GmbH & Co.KGaA: Weinheim, Germany, 2007; pp 49, 109, 164.
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Figure 4. GC-MS ion fragmentogram of n-alkanes and isoprenoids, m/z 71 (a), terpanes, m/z 191 (b), and steranes, m/z 217 (c) from saturated fraction of pyrolysate S400, typical for all pyrolysates obtained at 400 °C. Ts, C2718R(H)-22,29,30-trisnorneohopane; Tm, C2717R(H)-22,29,30-trisnorhopane; C29H, C2917R(H)21β(H)-30-norhopane; C29Ts, C2918R(H)-30-norneohopane; C29M, C2917β(H)21R(H)-moretane; C30H, C3017R(H)21β(H)-hopane; C30M, C3017β(H)21R(H)-moretane; C31(S), C3117R(H)21β(H)22(S)-hopane; C31(R), C3117R(H)21β(H)22(R)-hopane; G, gammacerane; C32(S), C3217R(H)21β(H)22(S)-hopane; C32(R), C3217R(H)21β(H)22(R)-hopane; C33(S), C3317R(H)21β(H)22(S)-hopane; C33(R), C3317R(H)21β(H)22(R)-hopane; 1, C275R(H)14R(H)17R(H)20(S)-sterane þ C2813R(H)17β(H)20(S)-diasterane; 2, C275R(H)14β(H)17β(H)20(R)-sterane þ C2913β(H)17R(H)20(S)-diasterane; 3, C275R(H)14β(H)17β(H)20(S)-sterane þ C2813R(H)17β(H)20(R)-diasterane; 4, C275R(H)14R(H)17R(H)20(R)-sterane; 5, C2913β(H)17R(H)20(R)-diasterane; 6, C285R(H)14R(H)17R(H)20(S)-sterane; 7, C285R(H)14β(H)17β(H)20(R)-sterane þ C2913R(H)17β(H)20(R)-diasterane; 8, C285R(H)14β(H)17β(H)20(S)-sterane; 9, C285R(H)14R(H)17R(H)20(R)-sterane; 10, C295R(H)14R(H)17R(H)20(S)sterane; 11, C295R(H)14β(H)17β(H)20(R)-sterane; 12, C295R(H)14β(H)17β(H)20(S)-sterane; 13, C295R(H)14R(H)17R(H)20(R)-sterane. Table 3. Values of Parameters Calculated from Distributions and Abundances of n-Alkanes and Isoprenoids in Pyrolysatesa sample
CPI
Pr/Phyt
Pr/n-C17
Phyt/n-C18
S250 SPt250 SRu250 S400 SPt400 SRu400
1.06 1.08 1.12 1.04 1.03 1.04
1.14 0.99 0.78 1.12 1.29 1.50
0.42 0.37 0.31 0.23 0.46 0.66
0.40 0.51 0.51 0.22 0.37 0.50
general, metal ions showed greater influence on isoprenoids than on n-alkanes. The Ru(III)-ion exhibits a somewhat more pronounced catalytic effect on both n-alkanes and isoprenoids, which also is observed at interpretation of group organic geochemical parameters (Tables 2 and 3). 3.2.2.2. Terpanes and Steranes. All of the six pyrolysates obtained contain a greater quantity of thermodynamically more stable C29 and C30 Rβ-hopanes, compared to that in the corresponding βR-moretanes (C29M/C29H and C30M/C30H below 1; Table 4). In pyrolysates obtained at 400 °C, unstable ββhopanes and unsaturated hopenes were not identified, while in all of the three pyrolysates obtained at 250 °C, 2-gammacerene and C30 and C31 ββ-hopane homologues were present. On the basis of the mass spectra of corresponding peaks, the presence of Tm, Ts, C29Ts, and 22(R and S)-epimer homohopanes was determined in all pyrolyses (Figures 3b and 4b). The values of all of the terpane maturity parameters indicate higher maturity of pyrolysates obtained at 400 °C (Table 4). The values of C31(S)/C31(S þ R)-homohopanes ratio in pyrolysates obtained at 250 °C are lower than the equilibrium values, which indicates that the maturity level of organic matter which corresponds to the beginning of catagenesis was not attained using the pyrolysis at 250 °C. The presence of C30 and C31 ββ-hopane isomers and 2-gammacerene (which is one of the dominant
a CPI, carbon preference index determined by the equation of Bray and Evans for full amplitude of n-alkanes C12-C34, CPI = 1/2 [Σodd(nC13 - n-C33)/Σeven(n-C12 - n-C32) þ Σodd(n-C13 - n-C33)/Σeven(n-C14 - n-C34)].
kerogen during laboratory simulations results in uniform formation of both pristane and phytane (Tables 1 and 3). Compared to the pyrolysate of rock alone, the pyrolysates obtained at 400 °C in the presence of metal ions have greater relative contents of pristane and phytane, which is reflected through the increase in Pr/n-C17 and Phyt/n-C18 ratios, and have higher values of Pr/Phyt ratios (Table 3). Pr/Phyt and Pr/n-C17 ratios have lower values in pyrolysates obtained in the presence of metal ions at 250 °C, compared with pure shale pyrolysate, while the Phyt/n-C18 parameter has the same trend as that in pyrolysates obtained at 400 °C. In 4362
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Figure 5. GC-MS ion fragmentograms of MN, m/z 142 (a), DMN, m/z 156 (b), and TMN, m/z 170 (c) from an aromatic fraction of pyrolysate SPt250, typical for all pyrolysates obtained at 250 °C. MN, methylnaphthalene; DMN, dimethylnaphthalene; TMN, trimethylnaphthalene; PrN, propylnaphthalene; EMN, ethylmethylnaphthalene.
catagenesis using pyrolysis at 400 °C was successfully simulated and confirms the good potential of the investigated sample. All pyrolysates obtained in the presence of metal ions are characterized with higher values of C29M/C29H and C30M/ C30H ratios, and lower values of Ts/(Ts þ Tm) and C29Ts/ C29H ratios compared to those of pyrolysate of pure shale, at both temperatures, especially in the case of the Ru(III)-ion (Table 4). Sterane distributions in all pyrolysates obtained are typical for oils, which confirms once again the good potential of the investigated sample (Figures 3c and 4c). Apart from the regular RRR(R)-steranes, C27-C29 isomers with thermodynamically more stable RRR(S)-, Rββ(R)-, and Rββ(S)-configurations, as well as typical geoisomers, βR- and Rβ-diasteranes, were present. The values of sterane maturity parameters in all pyrolysates obtained at 250 °C are lower than those in the corresponding products obtained by pyrolysis at 400 °C (Table 4). Also, the concentration of these biomarkers in pyrolysates at 250 °C is low (Figure 3c). Values of the most used sterane maturation parameters based on the ratios of C29 sterane isomers, C29Rββ(R)/ (C29Rββ(R) þ RRR(R)) and C29RRR(S)/C29RRR(S þ R), in all pyrolysates are lower than equilibrium values. Bearing in mind that in the previous studies it was noticed that equilibria in the sterane isomerizations are established at the Ro value of approximately 0.80% and taking into consideration the fact that equilibria were attained in homohopane isomerizations 22(R) f 22(S) in all three pyrolysates obtained at 400 °C (Table 4), it may be assumed that during pyrolysis at 400 °C the investigated sample reached the value of vitrinite reflectance equivalence between 0.60 and 0.80%.4 Metal ions did not show any catalytic effect on sterane 20(R) f 20(S) isomerization since the value of C29RRR(S)/RRR(S þ R)
Table 4. Values of Parameters Calculated from Distributions and Abundances of Terpanes and Steranes in Pyrolysatesa sample
C29M/ C29H
C30M/ C30H
C31(S)/ C31(S þ R)
Ts/ (Ts þ Tm)
C29Ts/ C29H
S250 SPt250 SRu250 S400 SPt400 SRu400 E.V.
0.32 0.37 0.43 0.24 0.35 0.52 /
0.34 0.39 0.64 0.26 0.31 0.51 0.05-0.15
0.47 0.57 0.44 0.57 0.59 0.57 0.57-0.62
0.42 0.41 0.39 0.42 0.39 0.33 /
0.19 0.13 0.16 0.52 0.36 0.42 /
sample S250 SPt250 SRu250 S400 SPt400 SRu400 E.V.
C29RRR(S)/ C29Rββ(R)/ Gx100/ 2-Gam./ C30H C29RRR(S þ R) (C29Rββ(R)þRRR(R)) C30H 30.54 32.63 31.87 25.88 23.62 23.10 /
0,48 0,69 0,81 / / /
0.42 0.40 0.37 0.49 0.46 0.43 0.52-0.55
0.44 0.49 0.46 0.52 0.54 0.58 0.67-0.71
a
For peak assignments, see the legend for Figure 4; 2, Gam., 2-Gammacerene; E.V., equilibrium value;4 /, not calculated due to the absence of 2-gammacerene in pyrolysates obtained at 400 °C.
peaks) in all three pyrolysates supports this observation (Figure 3b). Values for C31(S)/C31(S þ R)-homohopanes that are in isomerization, 22(R) f 22(S), the equilibria has been achieved in all 400 °C pyrolysates, which is established in the earliest phase of catagenesis, at Ro ≈ 0.60 (Table 4).4 This result, together with the appearance of terpane distribution in the pyrolysate of pure shale (ion fragmentogram m/z 191; Figure 4b), which is typical for mature source rocks and oils, represents another proof that 4363
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Figure 6. GC-MS ion fragmentograms of MN, m/z 142 (a), DMN, m/z 156 (b), and TMN, m/z 170 (c) from an aromatic fraction of pyrolysate S400, typical for all pyrolysates obtained at 400 °C. For peak assignments, see the legend for Figure 5.
biomarker ratios in pyrolysates obtained at 400 °C showed that when using pyrolysis at this temperature the organic matter attained maturity which corresponded to Ro of 0.6-0.8%, while it was lower using pyrolysis at 250 °C, the reported data may be explained by the fact that the values of these ratios in pyrolysates at 250 °C primarily indicate the origin of the organic matter, not the level of maturity. This especially relates to parameters based on the contents of 2-MN, 1,6-DMN, 1,7DMN, 1,3,6-TMN, 1,2,5-TMN, and 1-MP for which it was proved in the earlier studies that their abundances in geological substrates substantially depend on the precursor material.38-41 The values of naphthalene maturation parameters MNR, DNR 1, DNx, R/βDN 1, TNR 3, R/βTN 1, R/βTN 2, and TNy11,42-44 in pyrolysates at 250 °C indicate a significant influence of Pt(IV)-ion on the isomerization reactions of
ratio is the highest in the pyrolysate of pure shale at both temperatures (Table 4). C29RRR(S)/C29RRR(S þ R) has a lower value in pyrolysate with Ru(III)-ion added in comparison with that of Pt(IV)-ion. The only exception among the sterane and terpane maturation parameters is the C29Rββ(R)/(C29Rββ(R) þ RRR(R)) ratio where Pt(IV)- and Ru(III)-ions have a slight influence on the extent of RRR f Rββ isomerization at both temperatures (Table 4). The reported observations lead to the assumption that metal ions, especially in the case of the Ru(III)-ion have greater impact on kerogen degradation, which directly reflects on the increase in the quantity of hydrocarbons, than on isomerization reactions: C29 and C30 moretanes f C29 and C30 hopanes, Tm f Ts, C29H f C29Ts, and C29RRR (R) f C29RRR (S). This conclusion is not surprising since kerogen contains functional groups for which the used metal ions show much stronger affinity, compared to that of saturated hydrocarbons. 3.2.2.3. Alkylnaphthalenes and Alkylphenanthrenes. Liquid pyrolysis products have alkyl-naphthalene and phenanthrene distributions typical of mature oil (Figures 5-8). The values of naphthalene maturity parameters MNR, DNx, and TNR 3 are higher in pyrolysates of pure shale obtained at 250 °C, while DNR 1, R/βDN 1, and TNy ratios indicate higher maturity of pyrolysate obtained at 400 °C. The values of phenanthrene maturity parameters in pyrolysates of pure shale at 250 and 400 °C are equable and in some cases even higher in pyrolysate obtained at 250 °C (Table 5). Bearing in mind that the distributions of some naphthalene and phenanthrene isomers significantly depend on the origin of organic matter and that the values of group parameters and
(38) P€ uttmann, W.; Villar, H. Geochim. Cosmochim. Acta 1987, 51, 3023–3029. (39) Alexander, E. M.; Larcher, A. V.; Kagi, R. I.; Price, P. L. An OilSource Rock Correlation Study Using Age Specific Plant-Derived Aromatic Biomarkers. In Biological Markers in Sediments and Petroleum; Moldowan, J. M., et al., Eds.; Prentice Hall: Upper Saddle River, New Jersey, 1992; pp 201-221. (40) Armstroff, A.; Wilkes, H.; Schwarzbauer, J.; Littke, R.; Horsfield, B. Palaeogeography, Palaeoclimatology, Palaeoecology 2006, 240, 253–274. (41) Borrego, A. G.; Blanco, C. G.; P€ uttmann, W. Org. Geochem. 1997, 26, 219–228. (42) Radke, M.; Willsch, H.; Leythaeuser, D.; Teichm€ uller, M. Geochim. Cosmochim. Acta 1982, 46, 1831–1848. (43) Stojanovic, K.; Jovancicevic, B.; Vitorovic, D.; Pevneva, G.; Golovko, J.; Golovko, A. Geochem. Int. 2007, 45, 781–797. (44) Golovko, A. K. Alkylaromatic Hydrocarbons in Crude Oils. Ph.D. Thesis, University of Tomsk, Russia, 1997 (in Russian).
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Figure 7. GC-MS ion fragmentograms of P, m/z 178 (a), MP, m/z 192 (b), and DMP, m/z 206 (c) from an aromatic fraction of pyrolysate SPt250, typical for all pyrolysates obtained at 250 °C. P, phenanthrene; MP, methylphenanthrene; DMP, dimethylphenanthrene; EP, ethylphenanthrene.
methyl groups from R- to thermodynamically more stable β- positions on the naphthalene ring. In the case of Ru(III)-ion, a completely opposite effect was reported since the values of all naphthalene ratios in pyrolysate obtained in the presence of Ru(III)-ion show a lower maturity level compared with the pyrolysate of pure shale at 250 °C (Table 5). Values of the mentioned naphthalene maturation parameters11,42-44 in pyrolysates obtained at 400 °C suggest that the metal ions have a catalytic effect on isomerizations of methyl groups that lead to the generation of more thermodynamically stable naphthalene isomers. Again, the Ru(III)ion exhibits a somewhat more pronounced effect compared to that of the Pt(IV)-ion on the naphthalene maturation ratios, with the exception of parameters DNx and R/βDN 1. In pyrolysates obtained at 250 °C, the catalytic effect on maturation changes in phenanthrene isomers which include reactions of isomerization and methylation10,42,43,45,46 observed only in the presence of Ru(III)-ion. In the case of the Pt(IV)-ion, phenanthrene maturity parameters have lower values than the pyrolysate of pure shale with the exception of the MPI 3 ratio (Table 5). Maturation parameters based on the isomerization of methyl phenanthrene groups from R- to β-positions, as well as on the reactions of methylation of phenanthrene ring,10,42,43,45,46 are higher in pyrolysates obtained in the presence of Pt(IV)- and Ru(III)-ions than in the pyrolysate of
pure shale at 400 °C (Table 5). Thus, Pt(IV)- and Ru(III)ions have a catalytic effect on both processes (isomerization R f β and methylation) at 400 °C. Ru(III)-ion showed a more pronounced effect on the reactions of isomerization of methylphenanthrenes (parameters MPI 1 and MPI 3; Table 5) and Pt(IV)-ion on the methylation processes, especially in the case of MP to DMP transformation (parameters PAI 1, PAI 2, and DMR; Table 5). Interactions between the used metal ions and aromatic systems during pyrolysis depend on temperature. Different influences of Pt (IV)- and Ru-(III) ions on the abundance of naphthalene and phenanthrene isomers in pyrolysates at 250 °C may be explained by the properties of these metal ions. Namely, the Pt(IV)-ion forms both square-planar and octahedral complexes, while the Ru(III)-ion builds exclusively octahedral complexes.35,37 Two naphthalene ligands allow building a square-planar complex with the Pt(IV)-ion, while two phenanthrene rings form an octahedral complex with the Ru(III)-ion (Figure 9). Therefore, at 250 °C, the Pt(IV)-ion has a catalytic effect on naphthalene transformations and the Ru(III)-ion on the phenanthrene ones. At 400 °C, hydrocarbon concentrations are higher, and metal ions are more active, not only in terms of forming complexes with aromatic π-systems, but also in terms of other types of interactions. Pt(IV)- and Ru(III)-ions act as Lewis acids and allow the formation of carbocations on aromatic systems, catalyzing the reactions of electrophilic aromatic substitution (such as AlCl3), on both naphthalene and phenanthrene rings.10,36,47
(45) Radke, M.; Welte, D. H.; Willsch, H. Geochim. Cosmochim. Acta 1982, 46, 1–10. (46) Ishiwatari, R.; Fukushima, K. Geochim. Cosmochim. Acta 1979, 43, 1343–1349.
(47) Vollhardt, K. P. C.; Schore, N. E. Organic Chemistry; Hajdigraf: Belgrade, Serbia, 1996; pp 580-585 (in Serbian).
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Figure 8. GC-MS ion fragmentograms of P, m/z 178 (a), MP, m/z 192 (b), and DMP, m/z 206 (c) from an aromatic fraction of pyrolysate S400, typical for all pyrolysates obtained at 400 °C. For peak assignments, see the legend for Figure 7. Table 5. Values of Maturation Parameters Calculated from Distributions and Abundances of Naphthalene and Phenanthrene Hydrocarbons in Pyrolysatesa Sample
MNR
DNR 1
DNx
R/βDN 1
TNR 3
R/βTN 1
R/βTN 2
TNy
S250 SPt250 SRu250 S400 SPt400 SRu400
0.78 0.93 0.66 0.63 0.73 0.77
1.11 1.94 0.82 1.44 1.82 2.35
2.63 2.92 2.30 2.28 3.09 2.95
2.09 1.58 2.98 1.61 0.99 1.07
1.35 1.53 1.06 1.14 1.31 1.67
0.70 0.58 0.71 0.82 0.70 0.57
3.38 2.92 4.16 4.36 3.44 2.91
2.25 2.24 2.07 2.27 2.31 2.44
sample
MPI 1
MPI 3
Ro
DMPI 1
DMPI 2
PAI 1
PAI 2
DMR
S250 SPt250 SRu250 S400 SPt400 SRu400
0.55 0.56 0.59 0.49 0.62 0.63
0.91 0.98 0.90 0.91 0.97 1.01
0.73 0.74 0.76 0.70 0.77 0.78
0.68 0.58 0.76 0.41 0.75 0.70
0.38 0.36 0.40 0.38 0.45 0.44
1.27 1.23 1.48 1.07 1.45 1.43
1.27 1.07 1.56 0.57 1.49 1.40
1.00 0.87 1.06 0.53 1.03 0.98
a
Explanations of abbreviations are given in Appendix.
Differences in values of alkylaromatic maturity ratios obtained in the presence of metal ions in comparison to pyrolysate of the shale without metals, at both temperatures, are more pronounced in naphthalene, compared to phenanthrene parameters (Table 5). Comparing these results to maturation ratios calculated from distribution and abundance of saturated biomarkers, we conclude that Pt(IV)- and Ru(III)-ions have much greater influence on maturation changes on the planar systems (naphthalene and phenanthrene rings) than on isomerizations in the polycyclic alkanes, steranes, and terpanes (Tables 4 and 5). The above observation is in agreement with the theoretical knowledge, as it is known that transition
metal ions acting as Lewis acids show an affinity for aromatic systems and that they form stable complexes with aromatic ligands in the form of sandwich compounds.10,36,47,48 Applying the equation Ro = 0.6 MPI 1 þ 0.37,49 vitrinite reflectance equivalent of 0.70% for pyrolysate of pure shale at 400 °C is calculated (Table 5). This Ro value is in full agreement with the results obtained at the interpretation of terpane and sterane biomarkers. (48) Lancaster, M. Green Chemistry: An Introductory Text; The Royal Society of Chemistry: Cambridge, U.K., 2002; pp 283-285. (49) Radke, M.; Welte, D. H. In Advances in Organic Geochemistry 1981; Bjorøy, M., et al., Eds.; Wiley and Sons: Chichester, U.K., 1983; pp 504-512.
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4. Conclusions The objective of this study was a detailed estimation of the Neogene shale potential (Valjevo-Mionica Basin, Serbia) and investigation of the effect of Pt(IV)- and Ru(III)-ions on the changes in yield and hydrocarbon composition of liquid pyrolysate at two different temperatures, 250 and 400 °C. Liquid pyrolysate and hydrocarbon yields obtained in pyrolitic experiments and distributions of saturated biomarkers and alkylaromatics in pyrolysates supported the assumption derived on the basis of the Rock-Eval data and analysis of the initial bitumen that the investigated Neogene shale in its catagenetic phase may be a source of liquid hydrocarbons. Values of terpane and sterane and phenanthrene maturation parameters indicate that through pyrolysis at 400 °C the investigated sample reaches the value of vitrinite reflectance equivalent of approximately 0.70%, while in pyrolysis at 250 °C, it is lower than 0.6%. It was estimated that the investigated Neogene shale should be found at a depth of 2300-2900 m to become active source rock. The calculated minimum temperature necessary for catagenetic hydrocarbon generation is between 103 and 107 °C. Temperature is the dominating factor influencing the liquid pyrolysate yield. Metal ions used in the pyrolytic experiments affect the significant increase of total liquid fraction and hydrocarbon yields at both temperatures. The influence of Pt(IV)- and Ru(III)-ions on the distribution of saturated biomarkers in liquid pyrolysates is the same at both temperatures. The used metal ions have greater impact on kerogen degradation, which directly reflects on the increase in the quantity of hydrocarbons than on transformation at the chiral center of the sterane side chain (20R f 20S) nor on isomerizations of moretane f hopane and hopane f neohopane. Interactions between the used metal ions and aromatic systems during pyrolysis depend on temperature. Pt(IV)and Ru(III)-ions demonstrated significant catalytic effect on maturation changes in both naphthalene and phenanthrene isomers during pyrolysis at 400 °C. Catalytic effects of Pt (IV)-ion on maturation changes in alkylnaphthalenes and Ru(III)-ion on the alkylphenanthrene ones were observed in pyrolysates obtained at 250 °C, which is caused by different coordination properties of these metal ions. The used metal ions had much greater influence on maturity changes on planar systems (naphthalene and phenanthrene rings) than on isomerizations in the molecules of polycyclic alkanes.
Figure 9. Square-planar complex of Pt(IV)-ion with naphthalene ligands and an octahedral complex of Ru(III)-ion with phenanthrene ligands.
Figure 10. Depth vs vitrinite reflectance vs geothermal gradient (according to Suggate51); % of Ro value calculated in this study and corresponding depth are indicated.
3.2.2.4. Assessment of the Conditions for Achieving Early Catagenesis. Pyrolysis at 400 °C of the investigated Neogene shale achieved oil generation at a vitrinite reflectance equivalent of ∼0.7%. Applying a generalized diagram that relates Ro, depth, and a regional geothermal gradient ranging between 40 and 50 °C/km,50 the minimum depth of 2300-2900 m was estimated at which the shale would become a thermally mature source rock (Figure 10). The minimum temperature necessary for catagenetic generation of hydrocarbons (temperature = depth geothermal gradient þ annual mean surface temperature) was calculated at 103 °C (t = 2.3 40 þ 11 = 103 °C).51 Using the basin-independent equation proposed by Barker and Pawlewicz52 (T = (ln Ro þ 1.68)/0.0124), a Ro value of 0.70% is estimated to be at 107 °C. In the presence of metal ions, under the same conditions, the organic matter of the analyzed shale would attain the value of a vitrinite equivalent of approximately 0.8% (Table 5).
Acknowledgment. Investigations within this study were performed in cooperation with the company Rio Tinto Exploration from Serbia. We thank Central Laboratory of NIS-Naftagas, Novi Sad, Serbia for Rock-Eval determinations. This work was supported in part by the Ministry of Science and Technological Development, Republic of Serbia (Project number 146008). We are also grateful to Dr. Clifford Walters and the anonymous reviewer whose comments greatly benefited this article.
Nomenclature MNR = 2-MN/1-MN42 DNR 1 = (2,6- þ 2,7-DMN)/1,5-DMN42 DNx = (1,3- þ 1,6- þ 1,7-DMN)/(1,4- þ 1,5- þ 2,3DMN)43 R/βDN 1 = (1,4- þ 1,5- þ 2,3-DMN)/(2,6- þ 2,7-DMN)44 TNR 3 = 1,3,6-TMN/1,2,5-TMN11 R/βTN 1 = (1,2,4- þ 1,2,5-TMN)/(1,2,6- þ 1,2,7- þ 1,6,7þ 2,3,6-TMN)44
(50) Ercegovac, M.; Kostic, A. Annal. G eol. P eninsule Balkanique 1993, 57, 331–356. (51) Suggate, R. P. J. Pet. Geol. 1998, 21, 5–32. (52) Barker, C. E., Pawlewicz, M. J. Calculation of Vitrinite Reflectance from Thermal Histories and Peak Temperatures. A Comparison of Methods. In Vitrinite Reflectance as a Maturity Parameter: Applications and Limitations; Mukhopadhyay, et al., Eds.; American Chemical Society Symposium Series 570; American Chemical Society: Washington, DC, 1994; pp 216-222
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R/βTN 2 = 1,2,5-TMN/1,2,7-TMN TNy = (1,3,6- þ 1,3,7-TMN)/(1,3,5- þ 1,4,6-TMN)43 MPI 1 = 1,5(2- þ 3-MP)/(P þ 1- þ 9-MP)45 Ro = 0.6 MPI 1 þ 0.3749 MPI 3 = (2- þ 3-MP)/(1- þ 9-MP)10 DMPI 1 = 4(2,6- þ 2,7- þ 3,5- þ 3,6-DMP þ 1- þ 2- þ 9-EP)/(P þ 1,3- þ 1,6- þ 1,7- þ 2,5- þ 2,9- þ 2,10- þ 3,9þ 3,10-DMP)45 DMPI 2 = (2,6- þ 2,7- þ 3,5-DMP)/(1,3- þ 1,6- þ 2,5- þ 2,9- þ 2,10- þ 3,9- þ 3,10-DMP)42
PAI 1 = (1- þ 2- þ 3- þ 9-MP)/P PAI 2 = ΣDMP/P46 DMR = ΣDMP/ΣMP43 MN = methylnaphthalene DMN = dimethylnaphthalene TMN = trimethylnaphthalene P = phenanthrene MP = methylphenanthrene DMP = dimethylphenanthrene EP = ethylphenanthrene
44
46
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