Geological Constraints on Petroleum Generation in the Qingxi Depression (Lower Cretaceous),Jiuxi Basin,Northwest China

The Qingxi Depression, over an area of merely 490 km2, is a petroliferous depositional center within the Jiuxi Basin. Lower Cretaceous source rocks in this depression are a suite of mudstones, dolomitic mudstones and argillaceous dolostones formed in a deep lacustrine environment. Although their distribution area is small, their thickness is sizable. High abundance and favorable types of organic matter provide an important material basis for petroleum generation. The majority of the source rocks in the Qingxi Depression are of maturation conditions for generating significant volumes of petroleum, and with only one peak generation period that commenced in the Neogene. The Himalayan movement results in a northerly overthrusting of the Qilian Mountains nappe to form a series of compressional faults, shear faults and rock fractures, all of which serve as main conduits for petroleum migration from west to east, and, in addition, as the reservoir space of the Qingxi Oilfield. Based on these factors, it is suggested that the future exploration be on the Qingxi low bulge and favorable fracturing zone within this depression.

酒西坳陷青西凹陷窟窿山、柳沟庄油藏应属“源岩裂缝油藏”

剖析了酒西坳陷青西生油凹陷中发现青西油田的地质背景,研究了青西油田窟窿山和柳沟○油藏的形成和分布规律及其控制因素,在此基础上提出了青西油田的窟窿山和柳沟庄油藏属于“源岩裂缝油藏”的新认识。同时论证了“源岩裂缝油藏”形成的特定地质条件和研究价值。提出“源岩裂缝油藏”的特殊意义就在于源岩层中可以找到油藏,其发现和深入研究,将进一步拓宽油气勘探领域,丰富石油地质理论,是一项具有重大科学意义和实用价值的研究课题。

襄城凹陷未熟—低熟油的形成条件

襄城凹陷下第三系油气显示较为广泛,原油性质呈高密度、高黏度、高含硫、高含蜡的特点,为典型的未熟—低熟油。根据襄城凹陷所处的区域构造背景及烃源岩和原油的有机地球化学特征,采用有机显微组分分析、生物标志物检测、有机岩石学研究等方法,对源岩的沉积环境、烃源岩特征以及生烃母质来源进行了深入分析,探讨了未熟—低熟油油藏形成的主要地质条件。研究结果表明,核桃园组多为半咸水—咸水湖相和盐湖相沉积,属于还原—强还原环境;形成未熟—低熟油的主要成烃母质是藻类,陆源有机质中的木栓质体、角质体和各种细菌;应以核二段为主要目的层,以寻找短距离运移、聚集及自生自储油气藏为主。