确定有效烃源岩有机质丰度下限的一种新方法——以鄂尔多斯盆地陇东地区上三叠统延长组湖相泥质烃源岩为例

A new method for determining the lower limits of the organic matter abundance parameters of effective source rock:taking the Triassic dark mudstones of Yanchang Formation in Longdong region,Ordos Basin as an example

以鄂尔多斯盆地陇东地区三叠系上三叠统延长组长4+5、长6、长7和长9段暗色泥岩为例,利用有机碳与氯仿沥青"A"转化率、热解有机质相对生烃量(IHC=S1/w(TOC),%)的关系,建立了适合研究区的湖相有效泥质烃源岩的有机质丰度下限值.热解S1和氯仿沥青"A"含量代表烃源岩中的已生烃量,在不排烃情况下,随有机碳含量增加而增大,当其减小时则表明有烃类的排出.代表有机质相对生烃量的热解参数IHC和沥青转化率(w(A)/w(TOC),%)随有机碳含量增加而开始降低的转折部位对应的有机碳含量即为有效烃源岩的下限值,研究区的有机碳质量分数为1.1%,相应的热解S1+S2下限值为2.2 mg/g,氯仿沥青"A"质量分数下限值为0.03%,总烃质量分数下限值为150×10-6.该下限值主要适合于研究区湖相有效烃源岩的识别,不同含油气盆地不同层段的有效烃源岩有机质丰度下限值应根据相应的分析数据加以确定.

Taking of the member 4+5,6,7 and 9 as an example,the lower limits of the organic matter abundance parameters of the effective source rock in the studied region are determined by using the relationship between organic matter abundance and hydrocarbon-generating transformation ratio.Pyrolysis parameter S1 and trichloromethane bitumen 'A',representing generated hydrocarbon amount in source rocks,increase with organic carbon content rising when there is no hydrocarbon expelling from source rocks.They will decrease with organic carbon content raising when hydrocarbons blow out of source rocks.Pyrolysis parameter IHC(IHC=S1/w(TOC),%) and bitumen transformation ratio(w(A)/w(TOC)),representing relative hydrocarbon generating amount in source rocks,increase firstly and then decrease with organic carbon content rising,while the lower limits of the organic matter abundance parameters of effective source rock are corresponding to the organic carbon content at the turning point.In the studied area,the organic carbon mass fraction is 1.1%,the corresponding lower limit of pyrolysis parameter S1+S2 is 2.2 mg/g,the lower limit of trichloromethane bitumen A content is 0.03% and the lower limit of total hydrocarbon content is 150×10-6.The lower limits of organic matter abundance parameters mentioned above suit mainly to Longdong region of Ordos Basin.To other petroleum basins,the lower limits of organic matter content should be analyzed according to corresponding organic geochemical data of source rocks.