Abstract:

Wuerxun depression is a sag with a high degree exploration in the south of Hailaer basin, Inner Mongolia. It is the main oilgasbearing depression in which the deposit thickness is big, and the stratum grows entirely, and the oilgenerating condition is very superior. The main source rock is Nantun Formation, and the next is Tongbomiao Formation and Damoguaihe Formation. The average paleogeothermal gradient recovered by the fission track method is about 344 ℃/hm, which is close to present geothermal gradient (33 ℃/hm). The results of paleotemperature and thermal history simulation show that Wuerxun depression has been undergone a heating process since Mesozoic Era, and the maturity of the source rock is controlled by present geothermal field. The geothermal history and illite dating results reveal that the formation of oilgas reservoirs have two stages in Wuerxun depression, which are in the late period of Early Creaceous and since Tertiary, and the late period of Early Creaceous is the main stage, and the second stage is since Tertiary. The source rock began to generate oil and gas in a second peak since Tertiary. The second stage is important for the formation and concentration of oilgas reservoirs in Wuerxun depression.

Key words: Hailaer basin;Wuerxun depression, geothermal gradient, apatite fission track, geothermal history