The semi-closed pyrolysis simulation system under constant pressure was conducted to explore the characteristics and mechanisms of hydrocarbon generation from Xiamaling Formation shale in Xiahuayuan,North China.The experiment results indicate the oil generated by the Xiamaling Formation shale in oil window should be classified as "aromatic-intermediate" type,whereas the decreasing of dry coefficient can be ascribed to the cracking of residual bitumen in source rock in the stage of high to post maturity.The amount of hydrocarbon gas generated from residual bitumen can be up to 1-2 m3 per ton rock in high to post mature stage by calculating hydrogen contents in the kerogen,the expelled hydrocarbon,and the residual hydrocarbon.This reveals the importance of residual bitumen as a gas source during high to post mature stage of the kerogen evolution,and also as the broad exploration prospect of these gases.This research highlights the attention should be paid to oil/gas reservoirs sourced from residual bitumen of organic-rich source rock in high mature stage,even the primary oil/gas reservoirs considered as the main exploration targets in middle-upper Proterozoic sediments of North China.
Due to the importance of the Gloeocapsomorpha Prisca(G.prisca)-enriched source rocks,which belong to Kukersite-type source rocks in the Lower Paleozoic Ordovician strata,it has received great attentions during the petroleum exploration as to whether there are the Kukersite-type source rocks developed in the major hydrocarbon source strata of the Upper and Middle Ordovician in the Tarim Basin.Using pyrolysis-gas chromatography-mass spectrography to analyse kerogens from source rocks in the limemud mound with moderate maturity,study reveals that there are the Kukersite-type source rocks in the Ordovician strata of the Tarim Basin.The pyrolysis products showed a low content of>n-C19normal alkanes with a significant odd-even predominance between n-C13and n-C17,long-chain alky substituted alkylbenzene and alkylthiophene isomers and distinctive distribution of 5-Nalkyl-1,3-Benzenediol and its homologous.Based on the geographic environment characteristics of G.Prisca,the molecular distributions of crude oil from the Lower Paleozoic petroleum systems in the Tarim Basin and characteristics of kerogen pyrolysis products from the Middle and Upper Ordovician source rocks,the results suggested that it is less possible to develop the G.Prisca-enriched Kukersite-type source rocks in the major hydrocarbon source rocks in the Middle and Upper Ordovician strata in the Tarim Basin.However,the benthic macroalga and planktonic algae-enriched source rocks are the main contributors.
SUN YongGeMAO ShengYiWANG FeiYuPENG PingAnCHAI PingXia
