西藏羌塘盆地侏罗系膏盐岩与油气成藏

Characteristics of the Jurassic saline deposits and its significance to hydrocarbon accumulation in Qiangtang Basin of Tibet area

石油地质调查与研究表明,羌塘盆地在中生代前陆盆地形成演化阶段广泛地发育了膏盐岩沉积,其中中侏罗统雀莫错组、布曲组和夏里组膏盐岩最发育。受前陆盆地北部冲断带和前陆隆起的制约,膏盐岩主要沿中央隆起和盆地北部边缘展布。膏盐岩形成于干旱气候条件下的封闭—半封闭泻湖和萨巴哈环境,具有较好的封闭性,为盆地最重要的盖层。同时,膏盐层变形产生了多种类型的盐相关构造圈闭,这些圈闭构造主体形成于侏罗纪末—白垩纪初,与盆地主力烃源岩的生烃高峰在时间上具有一致性,为盆地油气聚集成藏提供了有利场所。

The geological investigation of Qiangtang Basin in Tibet area indicated that the saline deposits were well developed during the generation and evolution period of the Qiangtang foreland basin in the Mesozoic. The saline deposits with larger thickness mainly occurred in Quemoeuo Formation, Buqu Formation and Xiali Formation of the Middle Jurassic. Under control of the northern thrust zone and uplift in the Qiangtang foreland basin, the saline deposits were distributed mainly along the central uplift and the northern edge of basin and formed in the lagoon and sabaha circumstances. Good sealing reveals that the saline deposits are the best cap rocks in Qiangtang Basin. The different salt-related traps were formed during the period from the Late Jurassic to the Early Cretaceous, which is coincident with the peak of hydrocarbon generation. Therefore, these salt-related structures are good traps in the basin and can provide the favorable conditions for hydrocarbon accumulation.