川中侏罗系原油重排藿烷类化合物的组成及成因探讨

Composition and origin approach of rearranged hopanes in Jurassic oils of cen tral Sichuan basin

川中石龙场油田侏罗系湖相原油中重排藿烷类化合物异常丰富,经GC/MS和GC/MS/MS分析,检出17α(H)-重排藿烷和18α(H)-新藿烷及未知结构的早洗脱重排藿烷三个完整系列。17α(H)-重排藿烷相对含量最高,碳数分布范围为C27、C29～C35,分布模式与正常藿烷相似,C30化合物为主峰,C31以上化合物每个碳数有两个异构体。18α(H)-新藿烷系列含量明显低于重排藿烷,主要有Ts和C29Ts两个化合物,可能还存在C30的同系物。早洗脱重排藿烷系列碳数为C29～C35,C31以上每个碳数有一对异构体,具有与正常藿烷和重排藿烷相似的分布特征。这些化合物的生物先质物可能是细菌藿类物质。其形成过程与氧化性且富含粘土的沉积环境性质有密切联系,高成熟度条件下有利于它们的相对富集。

The Jurassic lacustrine oils from the Shilongchang oilfield in central Sichuan basin were found to be extremely rich in rearranged hopanes. Three series of rearranged hopanes with full carbon number, 17α（H）- diahopanes, 18α（H）-neohopanes and unidentified early-eluting rearranged hopanes, were detected using GC/MS and GC/MS/MS analysis. 17α（H）-diahopanes is present in highest abundance relative to 17α（H）-hopanes in the studied oils, and has carbon number range from C27 to C35 with predominant C30 and double epimers in C31 - C35, showing a similar distribution pattern with regular hopanes. Compared with 17α（H）-diahopanes, 18α（H）- neohopanes exhibits relatively low concentration and contains mainly Ts and C29Ts homologues, and probably a C30 member. The early-eluting rearranged hopanes extend from C29 to C35 in carbon number, and similar to regular hopanes and 17α（H）-diahopanes, doublets appear above C30. The bacterial hopanoids are thought to be biological precursors for these compounds. The formation of rearranged hopanes could be closely related with a sub-oxic and clay-rich depositional environment, and high maturity favor their enhanced abundance.