鄂尔多斯盆地陕北地区长10油源及成藏条件分析

Origin of Chang 10 oil reservoir in Northern Shaanxi region of Ordos Basin

在鄂尔多斯盆地的陕北志丹地区勘探发现了长10油藏,原油密度为0.8152g/cm3,全烃色谱图的主峰为nC13～nC15,油质较轻。轻烃组分中环烷烃较为丰富,芳烃含量低,呈姥植均势(Pr/Ph为1.21～1.45),原油的δ13CPDB值为-31.78‰,甾萜烷分布与主要参数特征为:重排藿烷类相对丰度很高、伽马蜡烷低,Ts/Tm比值很高(5.54～7.26),C30*/C30藿烷比值高(0.67～0.72),C29Ts/C30藿烷比值高(0.38～0.52),甾烷中重排甾烷较高、αβ和βα构型甾烷丰富,ααα-20R构型甾烷呈不对称"V"型分布,反映了较为典型的湖相油型油特征。油-油、油-源对比显示,该区长10原油来自长7优质烃源岩。石油可能是在湖盆中部长7优质烃源岩发育的地区通过垂向倒灌进入长10油层组、经侧向运聚成藏的。据此,预测盆地长9和长10油层组具备良好的成藏与勘探潜力。

The Chang 10 oil reservoir was discovered through the exploration in the Zhidan region of Ordos Basin, where the crude shows a density of 0.8152 g/cm^3 and a main peak at nC15 in the whole hydrocarbon chromatogram. The crude consists mainly of light hydrocarbons, which include abundant naphthenic hydrocarbons and low content of aromatic hydrocarbons, and has an equilibrial ratio of Pr/Ph, varing from 1.21 to 1.45, and - 31.78‰ of δ^13CPDB for the whole crude. Its terpoane distribution is characterized by relatively abundant rearranged hopanes, low content of gammacerane, and high ratios of Ts/Tm （5.54- 7.26）, C30^＊/C30 hopane （0.67 -0.72）, and C29Ts/ C30 hopane （0. 38 - 0.52）. The steranes in the crude mainly consist of rearranged steranes, and show abundant αβ and βα isomers, while ααα-20R sterane isomers display an asymmetric ＂V＂ type distribution pattern, representing a typical lacustrine-derived oil. The oil-oil and oil-source correlations indicate that the crude oil of Chang 10 oil reservoir is originated from the excellent hydrocarbon source rocks of the Chang 7 member in the center of the basin, and migrated vertically into the Chang 10 oil layer, and then accumulated laterally. Therefore, it can be predicted that the Chang 9 and Chang 10 oil reservoirs in the Ordos Basin have favorable resrvoir-fomling conditions and great potential for exploration.