The Study On The Features Of The Bottom Cretaceous Unconformity And Its Controlling Affect On The Hydrocarbon Accumulation In The Hinterland Of Junggar Basin

Junggar Basin experienced four tectonic movements, including Hercy movement,Indosinian movement, Yanshanian movement and Himalayan movement, which formedeleven regional unconformities and three local unconformities, and the unconformitylocating on the bottom of Cretaceous formation is a regional one which formed during themidium-term of Yanshan Movement(Main act of Yanshan Movement). The multihydrocarbon sources, various kinds of transport systems and kinds of continental depositsprovide material conditions for J-K oil and gas accumulation and the stratigraphic andstratigraphic/lithological oil and gas reservoirs according with unconformities are the maintargets for oil and gas exploration in the hinterland of Junggar Basin. In order to offerstrategic formations and zones for regional exploration, one of sixty-four-dollar questions isto clarify the features of the Bottom Cretaceous unconformity and its controlling effect onthe hydrocarbon accumulation.This paper bases on the conventional geologic research, uses seismic attributetechnique, and synthetically applies multiple disciplines and multi-parameters to identifytraps.Several conclusions are concluded:1. In the hinterland of Junggar Basin, the Cretaceous and Jurassic formation contactunconformable with different formations;2. Based on seismic data, well-logging data, logging data and analysis data, theunconformlty surfaces in vertices are divided into three parts: under-conglomerate,weathering claystone and paleokarst zone,and the structures have different sptial distributionfeatures. Under-conglomerate, depositing under transgressive systems, is a good reservoir;the weathering claystone is a local effective caprock because of suffering long timeweathering-leathing. The paleokarst zone is also a good reservoir because long timeweathering-leathing can develop secondary porosity that improve the characters of reservoir.3. On the base of fine description of the Bottom Cretaceous unconformity, Che-MoPaleo-uplift is timed and located again. The surface of Che-Mo Paleo-uplift is identical ofthe Bottom Cretaceous unconformity's surface, and the Che-Mo Paleo-uplift rised stronglyduring unconformity formed. Recovering denudation thickness by using the tendencyanalysis indicates: the maximum denudation thickness occurs in the shaft of Che-MoPaleo-uplift, where Well Zheng 1 is located vicinaly, and denudation thickness reaches to650 meters and rimland thinner .4. Formation of Che-Mo Paleo-uplift resulted in special diagenesis mode developing,that is sandstone below unconformity suffering diagenesis condition of midway opening,secondary burried, and this mode improved the reservoirs' characters effectively. The threestructures of the unconformity formed kinds of reservoir-seal association, and the surface ofunconformity became effective transport systems combined with the regional fractures,interlayer faults and epigenesist fractures. Unconformity formation provideded condition forformation of stratigraphic/lithological oil and gas reservoirs.In the hinterland of Junggar Basin, unconformities developing in Yongjin area where islocated on the block 3 belong to fault-fold unconformity, and its' bearing is about fromwestsouth to northeast. On the controlling of denudation zone and pinch-out boundary,multitudinous stratigraphic traps are formed. Through seismic attribute technique, thesedenudation zone , pinch-out boundary and traps are fine depicted. From above mentioneddiscussions, it is concluded that the most favorable area for oil and gas prospecting is fromwestsouth to eastnorth of Yongjin area locating on block 3 in the hinterland of JunggarBasin.