渤海海域辽西凸起锦州A构造原油地球化学特征及油源分析

GEOCHEMICAL CHARACTERISTICS AND ORIGIN OF CRUDE OIL FROM JZ-A STRUCTURE ON THE LIAOXI UPLIFT,BOHAI SEA

通过对辽西凸起锦州A构造沙河街组二段原油的地球化学分析,研究了原油的物性、成熟度和生物标志化合物特征。通过对比辽西凹陷和辽中凹陷已发现典型油气田的原油地球化学特征,结合区域地质背景分析了锦州A构造的油源。研究结果表明,锦州A构造西盘为低蜡、低硫凝析原油,而东盘为高蜡、低硫轻质原油。原油饱和烃色谱完整,显示未遭受明显生物降解。油源母质为混合型,沙河街组二段原油陆源有机质输入较少。原油形成于弱还原-还原条件下的微咸水或咸水沉积环境。根据锦州A构造原油的生物标志物特征,利用聚类分析方法划分为2类原油:Ⅰ类原油表现为高伽马蜡烷指数、低-中等四甲基甾烷指数、低藿烷/甾烷、高C27/C29甾烷和高C28/C29甾烷比值,主要来源于辽西凹陷沙一段烃源岩;Ⅱ类原油表现为低-中等伽马蜡烷指数、中等-高四甲基甾烷指数、高藿烷/甾烷、中等C27/C29甾烷和低C28/C29甾烷比值,主要来源于辽中凹陷沙三段烃源岩。

Geochemical analyses of crude oil samples from the 2nd Member of Shahejie Formation of the JZ-A structure on the Liaoxi Uplift were carried out,upon which physical properties,maturities and characteristics of biomarkers of the crude oil were studied.Comparison of geochemical characteristics of the crude oil is conducted for the oil and gas fields discovered in the Liaoxi and Lizhong depressions.The research results show that the crude oil in the western block is dominated by condensate oil with low wax and low sulfur,while the crude oil in the eastern block is characterized by light oil with high wax and low sulfur.The saturated hydrocarbon chromatograms of the crude oil from JZA structure show a complete distribution pattern,indicating a lack of biodegradation.The results also show that organic matters in the 2 nd Member of Shahejie Formation came from a mixed source with minor terrigenous input of organic matter.Crude oils were formed in a reduction to weak reduction and brackish or saline water environment.Two source-related oil classes are identified by hierarchical cluster analysis according to the biomarkers of the crude oil from JZ-A structure.The ClassⅠoil has higher gammacerane index,low-medium 4-methyl sterane indices(4-MSI),low hopane/sterane,high C27/C29 sterane and high C28/C29 sterane,which is most similar with the E2 s1 source rock of Liaoxi Depression.However,the ClassⅡ oil displays low-medium gammacerane index,medium-high 4-MSI,high hopane/sterane,medium C27/C29 sterane and low C28/C29 sterane,mostly similar with the E2s3 source rock of Liaozhong Depression.