哈拉阿拉特山西部地区生物降解原油地球化学特征及来源分析

Geochemical characteristics and source correlation of biodegraded oils from the Western Halaalate Area

生物降解原油的来源识别在国内外一直是难点、热点课题。哈拉阿拉特山(以下简称为哈山)西部地区石炭系原油样品的βα构型C20~C21~C23三环萜烷构型呈上升型,符合风城组烃源岩供烃特征,而在哈山西本地及其东南方向玛湖凹陷地区均存在成熟可供烃的风城组烃源岩,但是通过色谱-质谱分析发现,原油普遍遭受过不同程度的生物降解作用。本次研究针对生物降解原油的常规生物标志物特征,应用抗降解能力较强的生物标志物参数,例如成熟度、盐度参数及新伽马蜡烷指数和芳烃参数等对两套烃源岩进行“细微化”区分,并结合国内外最新研究发现,通过运移参数论证油气运移的可行性,最终综合确定了哈山西石炭系原油来源于本地风城组烃源岩。本研究一方面确定了石炭系降解原油的来源,为下一步勘探工作提供理论依据;另一方面积累了哈山西地区生物标志物参数因生物降解而呈现的蚀变规律,补充和丰富了生物降解原油油源对比认识,为后续判定浅层侏罗系底层严重生物降解原油的来源奠定了理论基础。

Biodegraded oil-source correlation is a difficult and hot topic at home and abroad.Crude oil samples found in Carboniferous strata of the Western Halaalate Area(Hashanxi for short)ascend in the configuration ofβαtricyclic terpenes C20-C21-C23.This is in accordance with the characteristics of the Fengcheng Formation source rocks,which can be found in both the Hashanxi Area and Mahu Sag.These crude oils have undergone slight to moderate biodegradation,according to chromatography spectrometry analysis.Based on our study of conventional biomarker characteristics of biodegraded oil and the application of biomarkers that are resistant to biodegradation(such as maturity parameters,salinity parameters,a new gammacerane index,and aromatic hydrocarbon parameters),we conclude that Carboniferous oil originated in the local Fengcheng Formation source rocks.This study has been combined with the latest research in the field and an analysis that demonstrates the feasibility of oil migration.This study determines the source rock of Carboniferous degraded crude oil and clarifies the alteration rules of biodegradation in the Hashanxi Area.Thus,this study supplements the regional understanding of biodegraded oil-source correlation.It lays a theoretical foundation for a subsequent study on the source of severely biodegraded crude oil in shallow strata.