OIL MIGRATION AND ACCUMULATION PATTERN IN THE TAHE OILFIELD

Based on study of geochemical characteristics,fluid inclusion characteristics,reservoir bitumen,reservoir autogenetic clay minerals,ancient and present tidal current fields,ancient and present fluid potentials,petroleum conduction condition related to petroleum migration and accumulation,petroleum charging process in the Tahe Oilfield can be divided into 3 stages and 5 times: late Hercynian(the 1st time),Indosinian-Yanshanian(the 2nd time),and Himalayan(the 3rd,4th and 5th time).The main accumulation stages are late Hercynian and Himalayan.During late Hercynian,petroleum migrates from south to north.During Himalayan,petroleum migrates from south to north and east to west.Huge Cambrian and Ordovician source rocks provide for multistage hydrocarbon charging and accumulation.Favorable tectonic locations on ancient uplifts and slopes are the target for petroleum migration.Large-scale unconformities,karst passage networks and fractures are channels for petroleum migration and accumulation.Sets of reservoirs,sets of reservoir and seal associations, types of traps and the generation of large-scale carbonate rock karst-fracture reservoirs are the key for the generation of large-scale composite oil-andgas field.Ordovician reservoir in the Tahe Oilfield is characterized by early accumulation transformation and late charging adjustment.Generation and evolution of sealing condition control hydrocarbon accumula-tion in the Tahe Oilfield.