准噶尔盆地乌尔禾地区二叠系风城组碱湖烃源岩中C_(30)-C_(32)羊毛甾烷的检测及其地球化学意义

The detection and geochemical significance of C_(30)-C_(32) Lanostane from Permian alkaline source rocks in the Fengcheng Formation, in Wuerhe, Junggar Basin

本次研究通过对乌尔禾地区二叠系佳木河组、风城组和乌尔禾组3套烃源岩的萜类化合物、甾类化合物和C_(30)-C_(32)羊毛甾烷系列等生物标志物的对比分析,发现上述3套烃源岩的萜类化合物、甾类化合物分布特征相似,常规的分子地球化学指标难以满足精细油源对比需要。但C_(30)-C_(32)羊毛甾烷系列化合物在风城组烃源岩中分布完整,而在佳木河组和乌尔禾组烃源岩中则基本不含有此类化合物,展示出其在该地区精细油源对比的潜力。此外,生物降解原油中的C_(30)-C_(32)羊毛甾烷系列分布完整,表明此类化合物在油气运移和成藏中具有较高稳定性。风城组烃源岩生物来源以褐藻、蓝绿藻等菌藻类水生生物为主,以富含C;规则甾烷和C_(30)-C_(32)羊毛甾烷系列为特征。定量分析结果表明,C_(30)-C_(32)羊毛甾烷浓度与姥植比成负相关,与伽马蜡烷指数和C;升藿烷指数成正相关,表明C_(30)-C_(32)羊毛甾烷系列可能形成于高盐度、强还原和水体明显分层的沉积环境进而说明风城组烃源岩沉积时湖泊水体含盐度很高,从分子标志物角度证明风城组为一套碱湖优质烃源岩。

In this paper,we compare the terpenoid,steroid,and C_(30)-C_(32) lanostane biomarkers in the source rocks of the Permian Wuerhe,Fengcheng,and Jiamuhe Formations from the Wuerhe area of the Junggar basin.Based on the analytical results,we found that the distribution characteristics of the terpenoids and steroids in the above three sets of source rocks are similar,and conventional molecular geochemical indicators cannot meet the needs of fine oil source correlation.However,the C_(30)-C_(32) lanostane series of compounds are completely distributed throughout the source rocks of the Fengcheng Formation,whereas the source rocks of the Jiamuhe and Wuerhe Formation basically do not contain such compounds,showing a potential for oil source correlation in the area.In addition,the distribution of the C_(30)-C_(32)lanostane series in biodegraded crude oil is complete,indicating that these compounds have high stability in oil and gas migration and accumulation.Organic matter in the source rocks of the Fengcheng Formation consists mainly of aquatic organisms,such as brown algae and blue-green algae,and is characterized by abundant C;regular sterane and C_(30)-C_(32)lanostane series.The quantitative analysis results suggest that the concentration of C_(30)-C_(32)lanosterane is negatively correlated with the Pr/Ph ratio and positively correlated with the gammacerane index and C;homohopane index,indicating that the C_(30)-C_(32)lanosteranes may be formed in a sedimentary environment with high salinity,strong reduction,and obvious delamination in the water body.The results show that the lake water salinity was very high when the source rocks of Fengcheng Formation were deposited,thereby,implying that the Fengcheng Formation is a set of high-quality source rocks from alkaline lakes from the perspective of molecular marker compounds.