西藏改则地区二叠系沉积环境及石油地质特征

西藏地区广泛分布的二叠系地层属冈瓦纳大陆北缘较稳定的浅海碳酸盐台地相沉积,包括了开阔台地、半局限台地、颗粒浅滩、介壳浅滩、生物礁、近岸潮下带等相类型。开阔台地、半局限台地相常发育烃源岩,地表样品有机质处于高成熟-过成熟阶段;属于礁滩相的储集层并不很发育,多属Ⅳ类储层,裂隙是该套地层中油气最可能的储集空间。二叠系地层中盖层亦不发育,在中上侏罗统和下白垩统泥页岩的覆盖下和其它有利条件的配合下,有可能形成一些中小型的、与不整合面有关的油气藏。 

DEPOSITIONAL ENVIRONMENT AND PETROLEUM GEOLOGY OF THE PERMIAN IN GAIZE AREA,TIBET

The widely distributed Permian strata belong to stable c arbonate platform facies near the north edge of the Gondwana Land,in which inclu des several subfacies,i.e.open platform,half restricted platform,grain bank,shel ly bank and reef.Hydrocarbon source rocks were developed in open platform and ha lf restricted platform facies with organic matters in high mature phase or post -mature phase.Reserviors,mostly in reef and banks,were not developed very well and fracture was the most possibel space for hydrocarbon storage.The cap rocks w ere also not developed efficiently.Some middle and small reservoirs related to u nconformity may be formed under co-vering of the Middle and Upper Jurassic and Lower Cretaceous shales.