南襄盆地泌阳凹陷西部稠油地化特征及意义

GEOCHEMICAL CHARACTERISTICS AND SIGNIFICANCE OF HEAVY OILS FROM THE WEST AREA OF BIYANG SAG,NANXIANG BASIN

精细刻画稠油地球化学特征,对其油源对比、成因乃至开发都具有一定指导作用。南襄盆地泌阳凹陷西部地区原油均遭受了中等以上级别的生物降解,规则甾烷和藿烷受到不同程度破坏,使得一些反映原油成因、成熟度的常用指标严重失效。通过对该区12个稠油样品地球化学特征的精细分析和研究,发现饱和烃中的伽马蜡烷、Ts、Tm以及长链三环萜烷的抗降解能力高于规则甾烷和藿烷,能较好地反映该区稠油地球化学特征。油源对比表明,该区核三下段原油均来源于核三下段烃源岩,而核三上段原油除来源于核三上段烃源岩外,不同小层段都有核三下段源岩不同程度的贡献。结合芳烃组成特征和参数,可以清楚地将研究区稠油划分成两类,并显示他们可能具有不同的生物降解机制。

It is essential to take a detailed study on the geochemical characteristics of heavy oil,which will be useful to conduct the oil-source correlation,the genesis and the development of heavy oil.The oils,which are from the west of Biyang Sag,have been experienced above middle degree of biodegradation.Furthermore,the regular steranes and hopanes have been suffered biodegradation to some extent,which made the common parameters reflected the genesis and maturity of oil ineffective.However,some parameters,which can resist strong biodegradation,such as gammacerane,Ts/Tm and some tricyclic terpane,still can identify the source of these biodegraded oils based on the GC-MS characteristics of 12 oil samples.It indicates that the crude oils in the lower of the Eh3 formation are derived from the source rock of the lower of the Eh3 formation,while the source of crude oils in the top of the Eh3 formation is the mixture of the top and lower of the Eh3 formation.In addition,some aromatic parameters,which are the component of aromatic hydrocarbon and the relation of triaromatic sterane（C20＋C21） /∑（C20-C28） and triaromatic sterane C20/（C20＋C28R）,can divide biodegraded oils into two types.And this conclusion is also proved by the relation of triaromatic sterane（C20＋C21）/∑（C20-C28） and C24 tetracyclic terpane/C26 tricyclic terpane.Moreover,it suggests that there might have different biodegraded mechanisms for the biodegraded oils in the west area,for the same degraded degree of oils have a different distribution of saturated compounds.