The Structure Characteristics And Trap Formation In Yanqi Basin

Yanqi Basin, which locates in the eastern part of Tianshan Belt, is a Mesozoic-Cenozoic oil-bearing superposition basin. Good progress for petroleum exploration has been made in recent years. In the basin, the geological condition is very complicated because of the multicycle structural movement, so the research on the property of tectonic evolution and the traps is critical for further petroleum exploration.In this thesis, according to Nonmarine Petroleum Geology theories and the basin analysis principles "Integrated, Dynamic, Comprehensive", mainly using the 2D and 3D seismic document and the drilling results, the research on the feature of the faults and the traps is emphasized in both the distribution and the development aspects, and the relationship between faults and traps is also discussed.The research shows that the faults in Yanqi Basin takes on the following features: (1) NWW (EW) and NW are two main directions and NE also existed. NWW faults are usually former basal faults with large scale; NW and NE faults are formed in later periods. (2) In the plane, assemble styles include parallel, echelon, "T" form etc. and the dissection and dislocation is not evident. (3) In the section, assemble styles include anti-thrust structure, ramp structure, flower structure, decken structure. In some degree, Strike-slip component is existed in Both NWW and NW faults. (4) The fault activity is dominated by transpression processes, fault separation in the same fault is almost the same and the syngenesis is not clear.There are many kinds of traps such as anticline, fault-nose, fault-block, lithology, buried hill and composite trap. The anticline is the main and vast trap in the basin, which is closely related with oil-bearing traps. The mechanism is that the thrust-drag anticline in accordance with tectonic setting plays the key role and most efficient traps are formed by fault processes.The trap formation can be divided into three stages as following: (1) the traps related with normal faults in lower-middle Jurassic slight extensional period, which is complicated by later reformation processes. (2) The traps in the late period of middle Jurassic to Palaeogene are the rudiments of the main traps at present. (3) After Neogene period, the trap scale is enhanced by reformation and new traps came into being at the same time. Reformations have the duplex effect on the formation of the reservoir, which leads to the escape of the petroleum and the succession accumulation. Structure trap is the oil-bearing trap in potential and transmit floor is the crucial factor for the formation of the petroleum trap. The migration is carrying out through the fault-nose structure between the trap and the source rocks. However, the role of the faults is not ignored in the formation of the reservoir, which is limited and works only in the fault activity stage.