SIMPLE ANALYSIS ON THE EFFECTIVENESS OF THE MIDDLE AND LATE　YANSHANIAN TECTONIC TRAPS IN THE WEST SICHUAN DEPRESSION

The tight sandstone tracts of the West Sichuan Depression are rich in natural gas resources.Exploration reveals that there are 16 sets of gas-bearing assemblages composed of 40 gas layers in K₁-T3x² formations at the depth from 200m to 4500m.The gas layers are scattered and overlapped,and connect into zones.Their space distribution shows the key effect of the Middle and Late Yanshanian tectonics.As the Middle and Late Yanshanian periods were peak time of gas generation from major hydrocarbon source rock in the West Sichuan Depression and most sandstone reservoirs had not been compacted yet and still remained in the porous stage with effective accumulation,main hydrocarbon accumulation belts formed along the normal tectonic belts at that time.Therefore,the research of the Middle and Late Yanshanian tectonic traps should be reinforced in the course of exploration in the West Sichuan Depression.