| The formation and evolution processes of high quality source rocks deposited in Mesozoic-Cenozoic petroliferous basins are always companied with direct or indirect effect of volcanic activities.Although the close spatial relationship between volcanic rocks and source rocks has aroused the attention of many scholars,the study of volcanic materials' effect on the hydrocarbon generation process is mostly limited to basic theory research and specific experiment research is far from enough.The catalytic mechanism of volcanic materials is still open to question.Due to the composition complexity of volcanic materials and there could be materials promoting hydrocarbon generation and inhibiting the process as well,it is biased to take it as a whole to discuss the effect of volcanic materials on kerogen hydrocarbon generation.Therefore,it has a great significance to carry out the related pyrolysis experiments with specific inorganic component to evaluate the effect of volcanic materials on the hydrocarbon generation process of kerogen.Considering the fact that volcanic rocks and source rocks coexist in the same basin,the author has made a lot of investigation and research work and found out that different types of volcanic rocks within many petroliferous basins are characterized by high contents of Cr2O3,which was neglected in previous study.Therefore,pyrolysis experiments added with Cr2O3 catalytic were carried out in order to reveal the influence of volcanic materials rich in transition metal elements on the hydrocarbon evolution of kerogen.The experiment results showed that the influence of Cr2O3 on the generation of hydrocarbon gas was limited.Cr2O3 could improve the gas hydrocarbon productivity of type ? kerogen during low temperature stage(360~450?),and had no obvious effect on type ? and ? kerogens.It is indicated that the catalytic effect of Cr2O3 has a certain relationship with temperature and organic type.And the catalytic effect of Cr2O3 was more obvious on chain structure(type ?)than ring structure(type ? and ?).At the same time,the effect of Cr2O3 on the generation of non-hydrocarbon gas of type I kerogen was stronger than that of type ? and ? kerogens.The Cr2O3 could inhibite the generation of H2,CO2 and H2 S of type ? kerogen during low temperature stage and increase the productivity of H2,CO2 and H2S during high temperature phase,indicating that the Cr2O3 has a certain promoting effect on the oxidation of hydrocarbon and the crack of sulfur-containing organic matter during high temperature stage.The influence of Cr2O3 on the generation of C6-14 and C15+ was much more obvious than that on the gas hydrocarbon.The results showed that,Cr2O3 had obvious catalysis effect on the generation of light hydrocarbon of type ? and ? kerogen and only showed catalysis effect on the generation of light hydrocarbon of type ? during high temperature stage.With the existence of Cr2O3,the yield of light hydrocarbon of type ?,? and ? kerogens could be increased by 42%(450?),50%(450?)and 23%(500?),respectively.The pyrolysis experiment results indicated that Cr2O3 could promote the saturated hydrocarbon yield of type ? kerogen and inhibit the generation of aromatics,non-hydrocarbons and bitumen.It means that the quality of liquid hydrocarbon can be greatly improved by the existence of Cr2O3 since Cr2O3 is favorable for the generation of the petroleum with high saturated hydrocarbon abundance and high fluidity.During high temperature stage,Cr2O3 could reduce the productivity of saturated hydrocarbons,aromatic hydrocarbons and non-hydrocarbons and reduce the ratios of saturated hydrocarbon/aromatic hydrocarbon and non-hydrocarbon/bitumen in liquid hydrocarbon products.The productivity of C15+ from type ? kerogen decreased greatly with the existence of Cr2O3 during low temperature stage,this may be due to the fact that Cr2O3 improves the generation of light hydrocarbons from heavy hydrocarbons that have already been generated,resulting in lower yields of heavy hydrocarbons and higher yields of light hydrocarbons during low temperature stage.Gas chromatographic analysis of saturated hydrocarbons showed that Cr2O3 could catalyze the cleavage of long chain n-alkanes during the pyrolysis of three types of kerogens,resulting in the increase of low carbon number n-alkanes and the decrease of high carbon number n-alkanes.The n C21-/n C22+ ratios could as well be enhanced.At the same level of thermal maturity,the ratios of Pr/n C17 and Ph/n C18 yielded from kerogen with Cr2O3 were all decreased,indicating that Cr2O3 can promote the formation of n-alkanes.Gas chromatography-mass spectrometry analysis of liquid hydrocarbon showed that Cr2O3 could increase the ratios of C29 sterane 20S/(20S+20R)and Ts/Tm in saturated hydrocarbon products,indicating that Cr2O3 could accelerates the isomerization of biomarker compounds and promote the conversion of organic matter.The pyrolysis experiment results have a certain reference value to the organic-inorganic interaction theory and also important significance to the oil and gas exploration in Mesozoic-Cenozoic faulted basins that are companied with strong volcanic activities in the eastern China.Under the same conditions,the intervention of volcanic material could promote the formation of middle-low molecular compounds with relatively strong fluidity.This intervention is favorable to the exploitation of shale oil.It means that in the eastern faulted basins,the layers that are abundant with organic matter and volcanic materials are favorable sections for exploration and exploitation of shale oil,which is worthy of attention. |
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