青藏高原东北缘六盘山盆地烃源岩的地球化学特征

Geochemistry of hydrocarbon source rocks in the Liupanshan basin at the northeastern margin of the Qinghai-Tibet Plateau

在前人认识的基础上,依据近年来的勘探成果,对六盘山烃源岩进行了评价分析,发现目前较明确的3套主要烃源岩中,白垩系下统的乃家河组、马东山组和李洼峡组源岩在盆地内分布较广,除北部埋藏较浅的区域未成熟外,大部分已趋于成熟。石炭系也是重要的源岩,由于埋藏较深,后期改造作用大,应以找气为勘查目标。三叠系烃源岩成熟度较好,但分布范围局限,勘探潜力受到影响。盆地的诸多油气显示及地面油气异常响应特征,充分证实了该盆地具有烃类的生成、运移和聚集的过程。整个盆地的油气地球化学异常响应特征明显,油气苗显示丰富,分布广泛。地球化学勘探测量发现了盆地内有3个近东西向展布的油气地球化学异常区带。根据三维荧光光谱图,对油气属性进行了判别,均表现为轻质油的地球化学特性。

The authors have evaluated and analyzed hydrocarbon source rocks in the Liupanshan basin on the basis of previous knowledge and recent exploration results and found that among the three sequences of relatively unequivocal major hydrocarbon source rocks the source rocks of the Lower Cretaceous Naijiahe, Madongshan and Liwaxia formations are relatively widely distributed in the basin. Most of them have tended to be mature except in areas in the northern part where the source rocks are shallow-buried. The Carboniferous hydrocarbon source rocks are also important. Because they are deep-buried and have been subjected to significant late-stage modification, they should serve as the target for gas exploration. Triassic hydrocarbon source rocks have a high degree of maturity but are of limited distribution; so their potential of exploration is affected. Many oil-gas shows and features of surface response to oil-gas anomalies in the basin fully demonstrate that there was a process of hydrocarbon generation, migration and accumulation in the basin. The response features of petroleum geochemical anomalies in the whole basin are conspicuous and oil-gas seepages are abundant and widespread. Geochemical exploration has reveals three nearly E-W-trending petroleum geochemical anomaly areas （zones） in the basin. On the basis of the 3D fluorescence spectra, discrimination of the attributes of oil and gas had been made. All of them have the geochemical properties of light oil.