The exploration prospect of non-structural traps of Jurassic in Junggar basin

There are many unconformities in the Jurassic of Junggar basin, which laid a good foundation for forming stratigraphic traps. The non structural traps have been the consequential selection for the exploration of the Jurassic in Junggar basin. The most favourable type is the onlap trap, which is mainly developed at the margin of the basin, the sides of Luliang uplift and in the sequences of Ⅰ to Ⅳ near the slope break inside the basin. There is large down cutting stream valley on the upper slope break in sequences Ⅱ and Ⅲ, which would possibly open up for forming incised valley trap. In major areas, the rocks in the bottom of each sequenence are too coarse to form unconformity trap. But in some places, the rocks in the bottom of the Cretaceous or Toutunhe Formation are fine grain, being favorable for forming unconformity trap. The Jurassic formations of the Junggar basin are dominated by fluvial deltaic system. Among them, the sand shale ratio in meandering stream and meandering stream delta in the upper part of sequence Ⅲ and in sequences Ⅳ and Ⅴ is relatively low so it is favorable for the development of lithologic traps. There are huge pressurized fluid compartment from south edge of the basin to Luliang uplift, which would open up for forming a great diagenetic trap under given conditions. The exploration for non structural traps should be facused on stratigraphic traps putting lithologic trap in the second and preparing for diagenetic trap as well. Special attention should be paid to the conditions for petroleum migration and accumulation in the evaluation of non structural traps.