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 degrees 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 degrees 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 degrees 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 alkalies. 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 5 alpha(H)14 alpha(H)17 alpha(H)20(R)-steranes --> 5 alpha(H)14 alpha(H)17 alpha(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 degrees 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 degrees C, which is caused by the different coordination properties of these metal ions.