BASIC CONDITIONS OF MARINE HYDROCARBON ACCUMULATION IN NORTHWEST SICHUAN BASIN-HIGH GUALITY SOURCE ROCKS

The prospecting degree of oil and gas is low and basic research about conditions of hydrocarbon accumulation is weak.Based on comprehensive study of regional geology,conditions of hydrocarbon formation,organic geochemistry and petrology,the developmental conditions of marine hydrocarbon in the north sector of Longmenshan structural belt were discussed.There were fair source rocks for hydrocarbon generation,mainly including muddy source rocks of Qiongzhusi and Dalong Formations and carbo-nate source rocks of Qixia and Maokou Formations.But the Devonian source rocks were limited in terms of their distribution.There was no qualified source rocks in the Ordovician-Silurian.It underwent large scale of hydrocarbon migration,accumulation and late destruction in the Longmenshan belt.Ana-lysis of this process may be helpful for marine petroleum exploration.Based on geological data,it was predicted that there were favorable target zones with better exploration prospects in the thrust-nappe tectonic belt and deepest depression of the northwest Sichuan Basin.