过成熟碳酸盐烃源岩有机碳含量下限值探讨——以鄂尔多斯盆地奥陶系马家沟组为例

过成熟阶段碳酸盐生油岩中烃类产物的相态已由油相演化到湿气、干气相.过成熟阶段碳酸盐岩作为气源岩时,其有机碳含量下限值不仅决定于本身的吸附烃量、有机质类型和热演化程度,而且排烃机理和排烃条件对它也有一定的影响.该文以鄂尔多斯盆地奥陶系马家沟组过成熟碳酸盐岩为例,首先通过罐装岩屑酸解烃法、残余气饱和度法和全烃地化分析法对吸附气态烃进行定量分析,估算出有机碳含量下限值为0.03%～0.06%,然后结合不同排烃机理对有机碳含量下限值作进一步的探讨. 

AN APPROACH TO THE LOWER LIMIT VALUES OF ORGANIC CARBON CONTENT IN OVERMATURED CARBONATE SOURCE ROCKS-WITH ORDOVICIAN MAJIAGOU FORMATION IN ORDOS BASIN AS AN EXAMPLE

The phase state of hydrocarbons formed in carbonate source rocks at overmatured stage change from oil into wet and dry gases. When the carbonate rocks at overmatured stage act as gas-prone source rocks,their lower limit values of organic carbon content depend not only on the content of absorbed hydrocarbons,organic types and thermal evolution levels,but on the mechanisms and conditions of hydrocarbon expulsion to a certain extent. With the overmatured carbonate rocks of Ordovician Majiagou in the Ordos Basin as an example,first the paper made quantitative analyses on absorbed gaseous hydrocarbons generated,using the methods of hydrocarbon acidolysis from tanked cuttings,residual gas saturation,and geochemical analyses of whole hydrocarbons;then estimated the lower limit values of organic carbon content to be 0.03%-0.06% and further approached on the lower limit of organic carbon content combined with different hydrocarbon expulsion mechanisms.