THE UNCONFORMITY TYPE AND HYDROCARBON MIGRATION RESEARCH IN TAHE OIL-FIELD

The Ta He Oil-field is a sub-order tectonic unit in the northern Tarim Basin.Controlled by several tectonic movements during the long geo-history,there are four main unconformities developed(the top surface of mid-low Ordovician T 7 4、the top surface of Ordovician T 7 0、the top surface of Silurian T 6 0 and the bottom surface of Triassic T 5 0) in work area and can be divided as four types according to the seismic reflection termination.The unconformities present as concordance denudation in uplift area and as onlap-denudation in slope area.The microstructure of unconformities is typical three-layer structure,in which the interconnected pores of basal conglomerate and loading off-weathering network of fracture of decayed rock are the dual passage for the broadside migration in unconformities.Meanwhile,according to the formation lithology、permeability and contact relationship,this research has identified eight types of unconformities,and the I and the V type are most favorable for the migration of petroleum.The research also analyze the through going character and spatial evolution of unconformities and concludes their inherited and differential characters.Finally,by analyzing in detail the unconformities' evolution and petroleum migration model,the paper finally points out that the T 7 4 and T 5 0 are the most important passage for the migration、modifying and accumulation of petroleum.