西藏羌塘盆地中侏罗世布曲期及夏里期岩相古地理与油气远景

Lithofacies palaeogeography and oil-gas prospectivity of the Buqu Age and Xiali Age of Middle Jurassic in Qiangtang Basin,Tibet

在露头剖面地层学及沉积学研究的基础上,采用单因素分析多因素综合作图法,编制了西藏羌塘盆地中侏罗世布曲期及夏里期的单因素图和岩相古地理图。布曲期以碳酸盐岩沉积为主,自北而南依次发育局限台地(潮坪、湖)、开阔台地(台盆、浅滩/点礁)、台缘礁/浅滩、台缘斜坡、盆地等沉积(亚)相;夏里期以陆源碎屑沉积为主,发育湖、潮坪、滨岸、陆棚等沉积(亚)相。布曲组台盆和湖相泥灰岩和泥晶灰岩是良好的烃源岩,台缘礁和浅滩相碳酸盐岩是良好的储集岩,而上覆的夏里组湖和潮坪相泥岩和膏盐层是良好的区域性盖层,共同构成良好的生、储、盖组合。该生储盖组合大都被上覆的上侏罗统、白垩系、古近系和新近系覆盖。因此,布曲组是盆地内最好的油气勘探目的层,沿中央隆起带两侧以及北羌塘地区的琵琶湖—半岛湖凸起一带应是油气勘探的有利区带。

Based on the study of outcrop sequence stratigraphy and sedimentology, according to the ＂single factor analysis and multifactor comprehensive mapping method＂, various quantitative single factor maps and lithofacies palaeogeography maps of the Buqu Age and Xiali Age of Middle Jurassic in Qiangtang Basin have been compiled. The Buqu Age was dominated by carbonate rock deposits, and from north to south, the restricted platform （lagoon, tidal flat ）, open platform （platform basin, shallow beach, spot reef ）, platform edge shallow beach （or reef）, platform foreslope, and deep sea basin were respectively developed. In the Xiali Age, the sediments were mainly terrigenous materials, deposited in the environments of lagoon, tidal flat, and shoreline and shelf.The marls and micritic limestones of lagoon and platform basin facies are good source rocks, and the carbonate rocks of platform beach and edge reef facies are good reservoir rocks in the Buqu Formation. The mudstone and gypsum of lagoon and tidal fiat facies in the overlying Xiali Formation are good seal rocks.The source-reservoir-seal combination above is mostly covered by the overlying Upper Jurassic, Cretaceous, Paleogene and Neogene, and thus the Buqu Formation is the best oil-gas exploration target strata in the Qiangtang Basin.The best oil- gas exploration belt is along both sides of the central uplift belt and the belt from Pipa Lake to Bandaohu Lake.