渤海湾盆地东濮凹陷文留地区储层烃类地球化学特征

渤海湾盆地东濮凹陷文留地区东营组埋藏较浅,储层中的烃类受到不同程度的生物降解.储层孔隙中自由烃、矿物表面吸附烃和矿物有机包裹体中烃类的气相色谱、色质资料对比分析揭示,在未遭到生物降解井段,同一油砂样品中3种相态的烃类组成特征具有相似性,但某些指标存在差异.相似性主要反映在γ蜡烷含量高(γ蜡烷指数为0.28~0.81),姥/植比相对较低(0.21~0.51),表明生烃母质主要为低等水生生物,形成于强还原性的盐湖沉积环境.差异性则表现为自由烃的饱和烃主峰碳数相对较低(在C₂₂—C₂₄之间),包裹烃的甾烷C_29ααα20S/(20S+20R)成熟度指标为0.25~0.35.在遭到生物降解井段,包裹烃的正构烷烃分布基本完整,但自由烃和吸附烃的正构烷烃基本消失,反映储层中的油气是不同期次充注的产物. 

GEOCHEMICAL CHARACTERISTICS OF THE HYDROCARBONS IN DONGYING FORMATION RESERVOIR OF WENLIU AREA, THE DONGPU SAG OF THE BOHAI BAY BASIN

The hydrocarbons in Dongying Formation reservoir in Wenliu area,the Dongpu Sag of the Bohai Bay Basin,have undergone various degrees of biodegradation as the results of being relatively shallowly buried.The comparison analyses of the gas chromatography data and the chromatography-mass spectrometry data of the free hydrocarbons in the pores,the adsorbed hydrocarbons on the mineral grain surfaces and the wrapped hydrocarbons in the organic mineral inclusions show that,in the same oil sand sample from the unbiodegrated sections,the above 3 states of hydrocarbons have similar component characteristics with only some indicators being different.The similarities are reflected by the high contents of gammacerane(the gammacerane/C30 hopane ratio is about 0.28 to 0.81) and the relatively low Pr/Ph ratio(about 0.21 to 0.51),indicating that the parent materials are mainly from aquatic orga-nism,which were formed in a kind of saline-lacustrine deposition environment under a strong reduction condition.The differences are reflected by the relatively low carbon number of the highest chromatographic peaks of free saturated hydrocarbons(between C22 to C24),and the unique values of the sterane maturity indicator C29 aaa20S/(20S 20R) of the inclusion hydrocarbons(0.25 to 0.35).Whereas in the sections being biodegrated,the distribution of the normal alkanes in the inclusions are generally intact,while the normal alkanes in free hydrocarbons and adsorbed hydrocarbons are almost disappeared,indicating that the hydrocarbons in the reservoir are the results of different phases of recharge.