Abstract:

There are two overpressure systems,lower and upper overpressure systems,in Kuqa foreland basin.The former was closely related with rapid and large gas generation,and thus the gas generated from Mesozoic source rocks mainly took the form of water-soluble gas.The upper overpressure system has the characteristics of reservoiring at normal pressure.When gas in the lower overpressure system migrated upward along faults in the form of miscible fluids into the upper normal pressure environment,degasification would occur and then accumulated in reservoirs.At a later stage,the upper overpressure system was formed under further compression of tectonic movement.Dina 2 gasfield is the final results of gas accumulation in the upper overpressure system.Based on analysis of trap development history and hydrocarbon generation history,in combination with fluid inclusion in the reservoir and K/Ar dating of authigenic illite,it is believed that Dina 2 gasfield had been charged in three different stages.In the first stage,liquid hydrocarbons were charged at the end of Paleogene and destroyed later.In the second stage,mixed liquid and gaseous hydrocarbons were charged in early-middle Kuqa stage.In the third stage,natural gas was charged in late Kuqa and early Xiyu stages,which was the key reservoiring stage of the field.

Key words: reservoiring period, reservoiring mechanism, dual overpressure systems, water-soluble gas, Dina 2 gasfield