The Pyrolysis Simulation Of Source Rock From Ordos Basin And Western Sichuan Depression At The Upper Triassic

As the Ordos Basin and the Sichuan basin are the two largest petroleum systems in central China,it is essential to research the source rock in these two basines.For the Ordos basin,in terms of the contribution of source rock,there has been existed a question about the oil source in the different members of Yanchang Formation.What's more,as the shale oil and gas has been the focus of petroleum field,it should be emphasis on the study of source rock.For Sichuan basin,the gas source has also existed question,even though it can be confirm the major source rock formation is the Xujiahe Formation.So as to evaluate the hydrocarbon-generation potential of the source rock at The Upper Triassic of the Ordos Basin and the western Sichuan Depression and their production feature,seven samples were collected from outcrops and wells for pyrolysis simulation.In the Ordos basin,four samples were selected: a shale stone and a mudstone in the 7th member of Triassic Yanchang Formation,a shale stone and a mudstone from the 9th member of Triassic Yanchang Formation.In the western Sichuan Depression,three samples come from outcrops at the Upper Triassic Maantang Formation,the 3rd member of Xujiahe Formation and the 5th member of the Xujiahe Formation.In a closed pyrolysis system with hydrous conditions,autoclave and gold tube,the amount of production of the source rock cracking can be quantitative calculate and then definite the excellent source rock.The pyrolysis products were fractionated as gas liquid and solid.By analysing the stable carbonate isotope composition and the biomarker feature,excellent source rock can be confirmed.Based on the Kinetic studies on the hydrocarbon generation of source rock,biomarker analysis and carbon isotope composition analysis were used to confirm the oil/ gas potential identification for the Ordos basin and the western Sichuan Depression.All of this study could provide a data fundamental of resource potential assessment and petroleum-source correlation.The results from the pyrolysis simulation indicate that,the source rock in Ordos basin is oil preference,while the samples from western Sichuan depression is gas preference,the mudstone from Maantang Formation and the 5th member of the Xujiahe Formation can also produce oil.In the thermal maturation process,there exist two hydrocarbon generation peaks,the one corresponding oil generation peak,and the other corresponding to dry gas stage.The maturity can affect the stable carbon isotope composition of methane and ethane,but it is more obvious for methane.The stable carbon isotope would be heavier as the maturity increase.As a result,determining the origin and identification of natural gas should consider the influence of maturity.