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

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.