珠江口盆地白云凹陷原油双杜松烷分布特征及地球化学意义

Distribution patterns and geochemical implication of bicadinanes in crude oils from Baiyun Sag, Pearl River Mouth Basin

珠江口盆地白云凹陷原油中双杜松烷(W和T)含量丰富。基于35个原油样品系统的色谱—质谱(GC-MS)分析,对白云凹陷双杜松烷分布特征及地球化学意义进行了研究。白云凹陷原油双杜松烷相对含量分布明显呈现“北高东低”的特点。双杜松烷相对含量在成熟—高成熟原油中基本不随成熟度变化,也不受气洗作用的影响,而主要受油气来源的控制。双杜松烷相对含量与姥鲛烷/植烷(Pr/Ph)及三环萜烷(C19TT+C20TT)/C23TT均呈现正相关关系,偏氧化及高陆源输入的环境有利于双杜松烷的富集。双杜松烷相对含量是指示生源、沉积环境及油源分析的良好指标。此外,双杜松烷T/W比值是有效的成熟度参数,适用于低—中等成熟度的原油和有机质。

Bicadinanes(W,T)are abundant in crude oils in the Baiyun Sag of the Pearl River Mouth Basin.The distribution patterns and geochemical implication of bicadinanes in crude oils from the study area were investigated based on the gas chromatography-mass spectrometry of 35 oil samples.The relative content of bicadinanes in crude oils is relatively higher in the north but lower in the east of the sag.Maturity and gas washing exert a minor impact on the relative contents of bicadinanes in mature to high-maturity crude oils,while hydrocarbon sources play an important role.The relative content of bicadinanes is positively related to Pr/Ph and tricyclic terpane(C 19 TT+C 20 TT)/C 23 TT ratios,which shows that an oxidizing environment with high terrestrial input is more favorable for the enrichment of bicadinanes.Therefore,the relative content of bicadinanes can be used to define biological source,depositional environment and oil-source correlations.In addition,bicadinane T/W ratios may serve as an index for evaluating maturity in low to medium-maturity crude oils.