Structural evolution and hydrocarbon accumulation in Yabulai Basin
Wu Xiaozhi1, Wang Guijun2, Zheng Ming1, Zheng Man1
1. Research Institute of Petroleum Exploration & Development, PetroChina, Beijing 100083;
2. Research Institute of Experiment and Detection, Xinjiang Oilfield Company, PetroChina, Karamay, Xinjiang 834000
Yabulai oil-bearing basin which located in the western part of Hexi Zoulang lies at the transitional zone between North China Craton and Alashan block and it belongs to North Qilian tectonic belt. It experienced basin evolution of Mesozoic strike-slip pull-apart to Cenozoic compression thrusts. In the Early Yanshannian, EW trending extensional faults developed, and the depocenter lies in the southern part of basin mainly controlled by Beidashan normal fault. During the Middle Yanshannian, collision orogeny resulted in a sharp uplift of the northern basin, the Lower Jurassic strata eroded intensely. Alashan block and its northern territory were in extensional tectonic environment during the Late Yanshannian, EW trending extensional faults were generated in front of Yabulai Mountain. Rapid subsidence resulted in new NE trending extensional rift basin. During the Himalayan, affected by the strike-slip and extrusion, NW trending and south-dipping nappe and thrust faults were generated in the southern Yabulai Basin. Which make the Beidashan normal faults occur dislocation collapse, eventually forming the tectonic framework showing "fault in the south, overlap in the north, uplift in the east and depression in the west". The sedimentary sag of Yabulai Basin have, subsidence sag located in the south, the maximum thickness of sedimentary rocks is 5 400 m, the most developed strata is Jurassic. Dark mudstone and coal from the Xinhe Formation and Qinhejing Formation of Jurassic are source rock and the sandstones are reservoir. The seal is interbeded mudstone from the Xinhe Formation. They constitute the main hydrocarbon combination. Yabulai Basin was deep buried in the early, but the late uplift destroyed the tectonic framework, resulted in the Jurassic sandstone reservoir experienced strongly compaction in the early and the Jurassic coal source rock became mature late. Structure development time is mismatched with the time of hydrocarbon explosion. Generated hydrocarbon are accumulated near the source rock or stranded in the situ. So that the source rock and the reservoir come from the same formation. Tight oil exploration should be the main target.