黔北坳陷过成熟海相烃源岩中的25-降藿烷系列  

25-Norhopanes in the post-mature marine source rocks in the North Guizhou Depression

作　　者：包建平[1] 张润合 蒋兴超[1] 王鹏万 朱翠山[1] 马立桥 

机构地区：[1]长江大学油气资源与勘探技术教育部重点实验室,地球化学系,湖北荆州434023 [2]中国石油杭州地质研究院,浙江杭州310023

出　　处：《地球化学》2015年第4期360-369,共10页Geochimica

基　　金：中国石油天然气股份有限公司科技项目(2012B-0504);国家自然科学基金(41272169)

摘　　要：25-降藿烷系列是常用来指示原油遭受深度生物降解作用的可靠生物标志物,但在黔北坳陷几个露头和钻井剖面上的前寒武-下古生界高、过成熟海相烃源岩抽提物的饱和烃馏分中普遍检测到了这类生物标志物,且丰度较高,说明25-降藿烷系列在高、过成熟烃源岩中的存在是个客观现象,它应该与生物降解作用无关。不同样品中25-降藿烷同系物与相应碳数17α(H)-藿烷同系物的比值间存在较好的正相关性,但这一相关性与层位之间没有内在联系,表明样品自身的特征决定了25-降藿烷系列的组成。与17?(H)-藿烷系列相比,25-降藿烷系列具有较高的热稳定性,这是它们出现在高演化烃源岩中的内在因素。尽管其确切的形成机理目前并不清楚,但推测它们可能源于键合在干酪根结构中具有藿烷骨架的结构单元在高演化阶段发生断裂后的产物。换言之,高温热裂解作用可能是这些地质样品中25-降藿烷系列的重要形成机理,此时它们可能与正常藿烷系列一样具有相似的地球化学意义。25-Norhopanes are usually used as a reliable biomarker indicator for indicating the severe biodegradation of crude oil. However, they can be widely identified in the saturated hydrocarbon fractions of all extracts from the Precambrian-Lower Palaeozic post-mature marine source rocks from several outcrops and cores of the North Guizhou Depression. The presence of more easily biodegraded n-alkanes and a complete distribution in the same source rocks suggest that 25-norhopanes are possibly not just produced from biodegradation. In addition, a good positive correlation is observed between homologues in different samples, and this correlation is not the ratios of 25-norhopanes and 17α（H）-hopane influenced by the stratum age of drilling core and outcrop samples. This phenomenon suggests that relative abundance of 25-norhopanes depends on geochemical features of the post-mature source rocks. Compared to 17α（H）-hopanes, 25-norhopanes are thermally more stable. It may be an important factor resulting in their common occurrence in the post-mature source rocks. Although exact formation mechanism for 25-norhopanes in the post-mature source rocks remains unknown, it is inferred that they may be derived from thermal cracking of the hopane-like structure units bound in kerogen at high thermal evolution stages. Therefore, 25-norhopanes may have a similar geochemical significance with 17α（H）-hopanes in these samples.

关 键 词：25-降藿烷系列 前寒武-下古生界 海相烃源岩 过成熟作用 抽提物 黔北坳陷 

分 类 号：P593[天文地球—地球化学]