渝南—黔北地区下寒武统牛蹄塘组页岩气成藏的生烃条件

    HYDROCARBON GENERATION CONDITIONS OF THE SHALE IN NIUTITANG FORMATION OF LOWER CAMBRIAN, SOUTHERN CHONGQING AND NORTHERN GUIZHOU

    • 摘要: 渝南—黔北地区下寒武统牛蹄塘组的页岩分布广泛,全区TOC含量>2.0%的页岩厚度总体较大,最厚可达200 m,具有有机质丰度高、类型好、成熟度过高的特征。区内的牛蹄塘组烃源岩在早奥陶世进入生烃门限,早—中志留世时进入生油窗并大量生油,中—晚二叠世时二次生烃,中白垩世时进入过成熟阶段。牛蹄塘组页岩中高含量的γ-蜡烷反映了沉积时期水体的分层,利于有机质保存,是研究区内牛蹄塘组烃源岩发育广泛的主控因素。区内的钻井或钻孔中有着良好的油气显示,牛蹄塘组与灯影组之间存在的热水流体也对油气成藏起着非常积极的作用。综合分析认为研究区下寒武统牛蹄塘组页岩的生烃条件好,资源量巨大,有望成为我国页岩气勘探的突破区。

       

      Abstract: The Niutitang Formation of Lower Cambrian is widely distributed in Southern Chongqing and Northern Guizhou. It is dominated by thick shale with TOC greater than 2.0%. The thickness of the shale may reach 200 m. The shale is rich in organic matter, and the types of organic matter are good for oil generation, but the organic matter is overmatured. In accordance with our study, the organic matters of the Niutitang Formation entered hydrocarbon generation threshold in the Early Ordovician, then fell in oil generation window in the Early-Middle Silurian and as a result of it, a large amount of oil was generated. The second time of hydrocarbon generation occurred in the Middle-Late Permian, and the organic matter became overmatured in the Middle Cretaceous. The high abundance of Gammacerane showed that water was layered during the depositional stage. It was beneficial to the preservation of organic matter. The quality of oil and gas showings obtained from boreholes was good in the study area, and the occurrence of hydrothermal fluid between the Niutitang Formation and the Dengying Formation was helpful to hydrocarbon accumulation. Comprehensive study suggests that the Niutitang Formation shale has excellent hydrocarbon generation conditions, and there is great potential of shale gas resource in the study area. In this regard, exploration and research of shale gas should be reinforced in the region of Southern Chongqing and Northern Guizhou.

       

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