准噶尔盆地东部二叠系平地泉组烃源岩富集规律与主控因素

Enrichment Patterns and Main Controlling Factors of Source Rocks in the Permian Pingdiquan Formation Eastern Junggar Basin

准噶尔盆地东部(准东)油气勘探成效差,是否发育规模有效烃源岩是必须回答的关键科学问题。通过地球化学法、ΔlgR法、井震结合对准东地区二叠系平地泉组烃源岩进行识别和评价,探讨烃源岩的空间分布。研究表明,平地泉组烃源岩以暗色泥岩为主,丰度为中等-好,以半深湖-深湖相泥页岩为优,优质烃源岩在平二段富集。平面上烃源岩富集在准东北部的克拉美丽山前带和南部的博格达山前带,中间被奇台凸起所分割。南、北带内部烃源岩的丰度受次级凹陷分割,表现出西高(TOC>1.5%)东低(0.5%<TOC<1.5%)的特征。这种分带分块特征受北天山岛弧、东准噶尔岛弧两大体系和断裂活动控制。沉积期湖水古盐度分析表明北带为彼此分割的小型凹陷,而南带为彼此联通的裂谷盆地。研究成果启发北带的油气勘探应遵循自西而东的勘探思路,而南带则宜东西并重。

To determine whether effective source rocks are developed in the eastern Junggar Basin is crucial to oil and gas exploration in the Junggar Basin. Through geochemical analysis, ΔlgR method and integration of logging and seismic data, we identified and evaluated the source rocks of the Permian Pingdiquan Formation in the eastern Junggar Basin(Zhundong), and delineated the source rock spatial distribution by combining with seismic facies. The results show that the source rocks of the Pingdiquan Formation are mainly dark mudstone, and the abundance of organic matter is medium to high. The mud and shale of semi-deep lacustrine facies is the high-quality source rocks, which is enriched in the Pingdiquan Formation(2member). On the plane, the source rocks are concentrated in the Kalamali piedmont zone in the north and the Bogda piedmont zone in the south, separated by the Qitai uplift. The source rock abundance in the southern and northern zones is divided by secondary sags, characterized by high TOC(>1.5%) in the west and low TOC(0.5% to 1.5%) in the east. The zoning and block characteristics are controlled by two systems and fault activities of the North Tianshan and East Junggar island arcs. Paleosalinity analysis of lake water during the depositional period shows that the northern belt is a small divided depression, while the southern belt is a connected rift basin. The results suggest that oil and gas exploration in the northern belt should be conducted from west to east, while in the southern belt should have equal importance from east to west.