Oil & Gas Geology ›› 2012, Vol. 33 ›› Issue (5): 713-719,729.doi: 10.11743/ogg20120507

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Authigenic illite dating for the timing of oil-gas accumulation of the Permian reservoirs in northeastern Ordos Basin

Chen Gang1, Xu Liming2, Ding Chao1, Zhang Huiruo2, Li Shuheng2, Hu Yanxu1, Huang Deshun1, Li Nan1, Li Yan1   

  1. 1. State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi’an, Shaanxi 710069, China;
    2. PetroChina Changqing Oilfield Company, Xi’an, Shaanxi 710021, China
  • Received:2011-07-10 Revised:2012-07-20 Online:2012-10-28 Published:2012-11-15

Abstract:

The K-Ar dating method with authigenic illite(AI)is applied to oil-gas-bearing sandstone core-samples to determine the stages and timing of the Permian oil-gas accumulation in northeastern Ordos Basin.Results show that the Permian oil-gas-bearing intervals all experienced two events of original oil-gas accumulation during the periods of 175-155 Ma and 145-115 Ma,respectively corresponding to two age-peaks at 165 Ma of the Middle Jurassic and 130 Ma of the Early Cretaceous in coincidence with the generation stages of the permian hydrocarbon source rocks in the Early and Middle Mesozoic.Specifically,oil-gas accumulation in the Lower Permian features in a relatively wide time range from 178 Ma to 110 Ma,while that in the Middle and Upper Permian is characterized by a narrow time range from 160 Ma to 108 Ma.The AI dating of(160-125)Ma of the Upper Permian samples indicates a relatively earlier ending time of its oil-gas accumulation.Also,the spatial and temporal distribution of the AI ages shows that the sequence of oil-gas migration to accumulation in the Permian is mainly from south(178-122 Ma)to north(131-108 Ma).Accordingly,it could be speculated that reservoirs in the Permian almost unanimously experienced two stages of original oil-gas accumulation during the Early to Middle Jurassic and the Early Cretaceous;and the current secondary accumulation features of the Upper Permian reservoirs should be mainly caused by the later reformation and adjustment of the original oil-gas accumulation during the Late Mesozoic to Cenozoic uplifting of the basin.

Key words: Permian, oil-gas accumulation, authigenic illite dating, northeastern Ordos Basin

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