Pyrolysis and Catalyzed Pyrolysis in the Investigation of a Neogene Shale Potential from Valjevo-Mionica Basin, Serbia

Abstract

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 → hopanes, hopanes → neohopanes and 5α(H)14α(H)17α(H)20(R)-steranes → 5α(H)14α(H)17α(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.

A comparative study of the molecular and isotopic composition of biomarkers in immature oil shale (Aleksinac deposit, Serbia) and its liquid pyrolysis products (open and closed systems)

“…Regular C25 isoprenoid and squalane (present in initial bitumen of the sample D13), as well as β-and γ-carotane are not identified in liquid pyrolysates. Interestingly, the same results were obtained by pyrolysis of the organic-rich sediments (using the same closed system and pyrolytic conditions) from the Valjevo-Mionica and Kremna basins (Stojanović et al, 2010;Perunović et al, 2014). The absence of these isoprenoids in liquid pyrolysates can be due to the sensitivity of their skeleton to thermal stress.…”

“…In liquid pyrolysates from the CS the Pr/Ph ratio is ~ 1 (Table 1). This might be caused by the increase in maturity (Connan, 1974;Peters et al, 2005) or by the fact that both isoprenoid alkanes are formed at the same rate during artificial maturation (Stojanović et al, 2010). As expected, the Pr/n-C17 and Ph/n-C18 ratios decrease during the thermal treatment of kerogen (Table 1).…”

Heavy Petroleum Composition. 4. Asphaltene Compositional Space

“…Asphaltenes have been referred to as the soluble fraction of kerogen in crude oil, with molecular structures comparable to their geochemical precursor, the kerogens. − Pyrolysates produced from the aromatic fraction of asphaltenes yield a series of multiple polycyclic aromatic hydrocarbon (PAH) compounds that contain 1–5 (or more) rings, because pyrolysis conditions cannot account for carbon–carbon bond cleavage to account for small PAH compounds derived from larger condensed aromatic structures. ,, Asphaltene characterization at the molecular level − is critical to address the asphaltene structural debate.…”

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

“…Values of Pr/Ph ratio are higher than in the initial bitumen, which may be explained by the fact that degradation of kerogen during laboratory simulations results in uniform formation of both pristane and phytane (Tables 2 and 4; Stojanović et al, 2009Stojanović et al, , 2010. Compared to the pyrolysate of sample alone, the pyrolysates obtained in presence of metal ions have greater relative contents of pristane and phytane, which is reflected through the increase in Pr/n-C 17 and Ph/n-C 18 ratios and have higher values of Pr/Ph ratios (Table 4).…”