鄂尔多斯盆地中东部下古生界奥陶系自生自储气地球化学特征

对鄂尔多斯盆地下古生界气源的争议已有30多年，主要观点包括以上古生界煤成气为主和以下古生界海相油型气为主。近年来学者们通过分区域、分层位研究，认为盆地不同地区由于源储配置情况有异，盆地不同地区下古生界气中上、下古生界来源气混源比例不同，应分别讨论。细化的研究使下古生界气源问题的争议得到了一定程度的调和，但同时混源比例计算等也使得2个前提问题变得尤为重要：①下古生界是否存在自生自储气；②下古生界自生自储气地球化学特征如何。结合测井数据对近年来最新勘探井的下古生界烃源岩进行了评价，证实了下古生界有效烃源岩的存在。通过对奥陶系马家沟组盐下(奥陶系马五₆巨厚膏盐岩以下)天然气地球化学特征与盐上(上古生界及奥陶系风化壳)天然气组分、碳同位素对比，指出下古生界海相烃源岩原生气具有δ¹³C₁<-35‰、δ¹³C₂<-28‰的特征。

Geochemistry of the self-generated and self-accumulated gasof Lower Paleozoic in Ordos Basin,China

There has been dispute on the origin of Lower Paleozoic gas in Ordos Basin for more than 30 years.Two main opinions include the Upper Paleozoic coal-derived origin and the Lower Paleozoic carbonate origin.In recent years,researchers began to study the origin of the Lower Paleozoic gas in Ordos Basin by region or by strata.It is believed that different regions of the basin have different constitution of source rock and reservoir.So the Lower Paleozoic gas in different part of the basin has different percent of gas mixed from the Upper and Lower Paleozoic gas.The deep discussion has made the gas origin more clearly.However,it also raised two questions when it comes to the calculation of the mixing percent from the Upper and Lower Paleozoic gas:(1)Whether the Lower Paleozoic source rock could generate self-preserved gas? If the answer is yes,then;(2)What are the characteristics of the self-generated and self-accumulated gas of Lower Paleozoic source rock? In this paper,we combined the log data into the evaluation of source rock,and the TOC result reveals that effective source rock exists in Lower Paleozoic.Also we compared the geochemistry of Lower Paleozoic gas below salt and gas above salt and found that the gas generated from the Lower Paleozoic source rock all has δ¹³C₁<-35‰ and δ¹³C₂<-28‰.