| Abstract: | Qiangtang Basin is located in the middle of Tethys, which is the famous oil and gas accumulation belt of the world. one of the few exploration areas in our continental petroleum industry at present. Previous studies show that this basin is a “composite basin" which has experienced, from Late Paleozoic to Cenozoic, a long time geological evolution. The major of this basin formed at Late Permian to Early Cretaceous, and its deformation generated after Late Cretaceous. The present part is just the remnants of the proto basin.Qiangtang Basin, about 180000km\+2, is located in the west part of Qiangtang\|Qamdo Terrane with Triassic Jurassic system as the main exploration systems.The tectonic framework of the basin displays the characteristic of one central uplift between the northern and the southern depressions, among of which the maximum burial depth of the substratums is 7km deep at Tubocuo in the northern depression. The deformation of the basin developed different kinds of structural styles, including compressive, wrench and extensive as well as inversive structures.The thickness of effective hydrocarbon source rocks (mudstone and carbonate rocks) is over 1500m, and the organic matter types are mainly of type I and type Ⅱ. In general the abundance of organic matter of the carbonate rocks is 0 1%～0 3%, the hydrocarbon generating potential (S1+S2) being 0 01～0 195mg/g. The abundance of organic matter of mudstone is generally over 0 5%, with the maximum over 2%. Its hydrocarbon generating potential is 0 018～28 1mg/g, and the organic matter is mainly at the mature to highly mature stage. More than 30 oil seeps have been found in the area, of which three are oil liquid ones and the others are solid bitumen and soft bitumen. Oil bearing rocks are concentrated in the Middle Upper Jurassic and Upper Triassic. Oil to source correlation analysis shows that the liquid oil is derived from the strata with oil reserves.The oil and gas shows, especially liquid oil seeps, indicate that the area experienced a history of hydrocarbon generation and migration. Preliminary prospecting shows that there exist two kinds of reservoirs: clastic rocks and carbonate rocks. The porosity of some carbonate reservoirs is up to 15%, which is favorable to the storage of oil and gas. Gypsum layers (single layer is generally 20～40m) are extensively distributed in Middle Jurassic of the Qiangtang Basin. Since Mesozoic marine strata in the basin has been strongly deformed and exposured on the surface of the earth during the Cenozoic, compared with other general bearing hydrocarbon basins, the preservative condition of Qiangtang Basin appears to be poor, but there still has a good prospects of exploration because of the Mesozoic strata containing abundant pliable layers such as gypsums and shales. |
