Jurassic reservoir development in Fukang Deep Sag, Central Junggar Basin

Jurassic reservoirs were deeply buried in the Fukang Deep Sag, where faults are difficult to identify, and traps are subtle, leading to significant differences in reservoir-forming controls where they are dominated by large structural traps in the uplift zone. The process of oil and gas migration and accumulation and the main factors controlling hydrocarbon accumulation were analyzed based on the study of oil and gas source, migration pathway, migration agent and timing of reservoir development. Geological and geochemical analyses showed that oil and gas in the Fukang Deep Sag mainly came from coal-measure source rocks which were deposited in a freshwater environment in the Badaowan Formation. Combined with the analyses of abnormal pressure, oil and gas migration characteristics and reservoir-forming stages, it was deduced that, after discharge from the Badaowan Formation, oil and gas laterally migrated for a long distance in sand bodies of the Badaowan and Sangonghe formations, and then, through strike slip faults, vertically to traps in the Toutunhe Formation. The analyses of the main factors controlling hydrocarbon accumulation in the Fukang Deep Sag indicated that the formation of oil and gas reservoirs in the Toutunhe Formation was controlled by overpressure, fault, trap and the good matching of them. A reservoir development model of the study area was established.