Abstract:

K-Ar isotopic dating method of authigenic illites is used to estimate the age of the Silurian bituminous sandstone reservoirs in Tazhong uplift of Tarim basin and the results are compareied with that of Kongquehe area.The age of authigenic illites in the Silurian bituminous sandstones in Tazhong uplift and Kongquehe area ranges from 383.45 to 203.96 Ma,indicating that the Silurian ancient oil pools were formed during the late Caledonian-early Hercynian and late Hercynian.For Qiao-1,Kongque-1,Longkou-1 and Yingnen-2 wells,located in the outer part of the basin,the age of authigenic illites is in the range from 383.45 to 271.20 Ma,indicating a late Caledonian-early Hercynian reservoiring;while for TZ-37,TZ-67,TZ-12,and TZ-32,wells located in the central area of the basin,it is about 203.96-235.17Ma,indicating a pooling in the late Hercynian.However,for some of the wells in the central area of the basin,such as TZ-23 and TZ-30,formed 293 Ma and 296 Ma respectively,indicating a pooling in the early Hercynian.The good correlation between the authigenic illite ages and the thickness of the bituminous sandstones suggests that the palaeotectonic framework be one of the main controlling factors and the ancient oil pools located in and around the depocenter,such as Qiao-1 and Kongque-1,be formed relatively early.The isotopic dating results are basically consistent with the results of conventional hydrocarbon accumulation history study and further highlight the differences in accumulation times between oil pools in different parts of the basin.

Key words: K-Ar dating, authigenic illite, accumulation time, Silurian bituminous sandstone, Kongquehe area, Tazhong uplift