西藏羌塘盆地中生界海相烃源岩特征

Characteristics of the Mesozoic marine source rocks in the Qiangtang Basin,Tibet

伍新和 张丽 王成善 伊海生

Wu Xinhe Zhang Li Wang Chengshan Yi Haisheng

羌塘盆地海相地层发育,沉积厚度大(最厚处可达万米),其中以侏罗系厚度最大。羌塘盆地中生代具有广泛分布且发育良好的三叠系肖茶卡组、侏罗系布曲组、夏里组和索瓦组4套烃源岩。烃源岩主要为灰岩和泥岩,最厚处超过3000m。上三叠统的肖茶卡组、中侏罗统布曲组烃源岩厚度大、有机质类型主要为Ⅱ型、有机碳含量平均1.5%以上、成熟度从成熟到过成熟均有分布,而且埋藏较好,生烃量大,是盆地油气的主要来源;索瓦组烃源岩虽然厚度大、有机质类型主要为Ⅰ型和Ⅱ型,但出露较多。烃源岩有侏罗纪晚期至白垩纪早期和新近纪早期两次生烃高峰。

Qiangtang Basin has well-developed thick marine deposits with the Jurassic as the thickest(ten thousand meters).Four sets of high quality source rocks,namely the Triassic Xiaochaka Formation,the Jurassic Buqu,Xiali,and Suowa formations,are extensively distributed in the Mesozoic Qiangtang basin.These source rocks are mainly composed of limestone and mudstone with a maximum thickness over 3000 m.The source rocks in the Upper Triassic Xiaochaka Formation and the Middle Jurassic Buqu Formation have larger thickness and their organic matters are mainly of type Ⅱ with maturity varying from mature to over-mature,and average is over 1.5%.They have favorable burial conditions and are the main hydrocarbon source in the basin.The Jurassic Suowa Formation is also rather thick and its organic matters are of mostly type Ⅰ and Ⅱ,however,the formation was over exposed and not favorable for hydrocarbon generation.There were two peaks of hydrocarbon generation:late Jurassic-early Cretaceous and Neogene.

10.11743/ogg20080310