Studies On Oil/gas Reservoir-forming In The Thrust Belt On The West Part Of The Northern Margin In The Qaidam Basin

The northern margin in the Qaidam Basin has a wider exploration prospect, however ,the extent of exploration is lower because of the limition of varied facters, so that the geological understanding for the north region is limited in some extent , especially,the sedimentary and evolutionary rule for Mesozoic have not been known clearly, as a result it has confined the people to realize the oil/gas-forming conditions in the front-mountain belt, furthermore ,the oil/gas exploration in the thrust belt of the front-mountain cannot be run smoothly.In this paper ,the exploration history and present circumstances in the northern margin of the Qaidam Basin are concluded , the update exploration achievements and progresses made in recently are introduced .Based on oil/gas resources condition in the northern margin of the Qaidam Basin, it is realized that the northern margin of the Qaidam Basin is characterized by abundant oil/gas resources, lower exploration extent, large exploration potential, and good prospect of exploration .On the basis of the present circumstances in the northern margin of the Qaidam Basin, four key viewpoints on the basic geology in the northern margin of the Qaidam Basin have been put forward: that is ,the division and distribution of Jurassic strata, the tectonic evolutionary history, the cause-forming and the age-forming of tectonic. According to these viewpoints, the finial title and the researches being made in this paper are detemined.Based on the characteristics of distribution and sedimentation of Jurassic basin in the western region of China, the background of tectonic evolution of the Qaidam Basin and regional geology in the northern margin of the Qaidam Basin have been studied. It is suggested that the northern margin of the Qaidam Basin is a subsidence-uplift- subsidence-uplift basin. During the Early Jurassic and early stage of Middle Jurassic, the sedimentary envoiroment of Jurassic belonged to the type of weak-extension and extension fault-depression, then it switched to depression during the middle stage of Middle Jurassic and a large-scale movement happened after the Early Cretaceous, which made the early paleo-tectonic forming. At the end of Cenozoic, the Qilian Mountains was pushed back to the basin because of the effect of the late stage of Himalayas event, and overturned tectonic are formed, thus become the favorable exploration target. In addition, on the basis of the data of Dameigou profile, division of the stratigraphical sequence for the northern margin of the Qaidam Basin has been studied, meanwhile according to the distribution characteristics ofJurassic remains strata , the auther puts forward that two-large subsidence belts had been formed during the Jurassic, Jurassic strata get deep along the front of Mountain, thus provide the source rocks for the reservoir-forming of the thrust-belt at the front of mountain. Finally, based on the detailed researches , six main characteristics on Mesozoic and Cenozoic petroleum geology of the northern margin of the Qaidam Basin can be concluded, also,the auther suggests that the thrust-fault belt at the front-Saishiteng Mountains, hidden structure belt in Saishiteng depression and Lenghu-Nanbaxian structure belt could become the key favorable exploration targets, it will play significant role in guiding the next step of exploration.