Abstract:

Six palaeouplifts of the Yanshan period and one anticline of low amplitude at the end of the Paleogene were identified in the Kuqa foreland basin according to strata contact relations,sedimentary characteristics,and seismic reflectance signatures.This paper concludes that the palaeouplifts at the end of the Yanshan period controlled oil accumulation,the anticline of low amplitude at the end of the Paleogene controlled gas accumulation, and the thrust anticline trap at the end of the Neogene was rich of gas.The conclusion suggests that palaeouplifts of foreland basin had a similar controlling effect on hydrocarbon distribution as that of palaeouplifts in craton basin.Two vertical overpressure systems were identified in the Kuqa foreland basin.The deep overpressure system was caused by the generation of a large amount of hydrocarbons under conditions of fast burial,while the shallow overpressure system was the result of a late lateral tectonic compression.A large amount of earlier-generated gas were accumulated in the palaeouplifts,leading to the formation of the deep overpressure systems.The palaeouplifts determined the location of the Neogene thrust anticline and thus the distribution of present gas reservoirs.

Key words: palaeouplift, dual overpressure system, structural compression, hydrocarbon accumulation sequence, natural gas, Kuqa foreland basin