三塘湖盆地低熟油的发现及其地球化学特征

三塘湖盆地目前所发现的原油的C₂₉甾烷 20S/(20S +20R)值大部分小于 0.42,属于低 (未 )熟油的范畴。与国内外报道的低熟油相比,三塘湖盆地物性特征也具有高密度、高粘度及高含蜡量等特征,但其物性偏好。经油源分析,这些低熟油主要来源于上二叠统芦草沟组。该组烃源岩演化程度较低,有机质丰度较高,属较好生油岩。通过有机显微组分分析,发现芦草沟组烃源岩以富含腐泥无定形富氢显微组分而有别于三塘湖盆地其它低熟源岩。经热解分析,腐泥无定形是芦草沟组烃源岩主要生烃贡献者,并且其主生烃期Ro 在 0.35 %～ 0.6 %之间。因此,腐泥无定形低熟生烃是三塘湖盆地低熟油的主要生烃机制。另外,在三塘湖盆地原油以及芦草沟组源岩中都检测到 17α(H) 2 5 降霍烷系列化合物,说明三塘湖盆地的低熟油可能与陆源有机质细菌降解改造作用有关。

The Immature Oils in Santanghu Basin

Most of the oiis found in Santanghu basin were regards as immature, mainiy because the vaiues of 20S/（20S + 20R）of C₂₉ sterane are iower than 0.42. Compared with other immature oiis reported in china, they have some speciai characteristics.Through anaiyzes to oii source, these immature oiis mainiy come from Lucaogou Formation of upper Permian which is better source rocks with iow maturity and much abundance of organic matter. Different from other immature source rocks in Santang iake basin, Lucaogou formation abounds with sapropeiic amorphous that content abundant hydrogen. It can be iearned through pyroiysis that the sapropeiic amorphous is the main contributor of hydrocarbon in Lucaogou formation and the Ro of its main hydrocarbon-generating intervai is from 0.35% to 0.6%, which is the main hydrocarbon-generating mechanism of the immature oiis in Santang iake basin. Furthermore, The series of 17α（H）- 25 - norhopane compound was found not oniy in oii, but aiso in Lucaogou formation, which hints that the immature oiis in Santang iake basin may have reiations with the bacteria degradation of terrigenous organic matter.