Oil & Gas Geology ›› 2006, Vol. 27 ›› Issue (2): 180-186.doi: 10.11743/ogg20060207

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Restoration of eroded thickness and its influence on thermal evolution of Upper Paleozoic source rocks in Ordos basin

Gao Shengli1,2, Ren Zhanli1   

  1. 1. Department of Geology, Northwest University, Xi'an, Shaanxi, 710069;
    2. Exploration and Development Research Institute, Changqing Oilfield Company, PetroChina, Xi'an, Shaanxi, 710021
  • Received:2005-12-10 Online:2006-04-25 Published:2012-01-16

Abstract:

The eroded thickness of Mesozoic in Ordos basin is restored by using vitrinite reflectance-depth profile(Ro-H),and the thermal evolution of the Upper Paleozoic is comprehensively studied based on thermal simulation experiment of source rocks.The Ro-H profile models can be divided into 3 types:single segment,double segments and three segments.The eroded thickness in the eastern part of the basin is large,in the range from(1 400m) to 2 200m;while that in the western part is relatively small,in the range from 400m to 1 000m.Isothermal-complementary thermal evolution simulation experiments of source rocks show that the Ro increases with time,but the incremental rate decreases when heating the rock samples to a certain temperature and then cooling them;in the same time interval,the larger the temperature drop is,the lower the hydrocarbon-generating capacity would be and the hydrocarbon generating capacity would be getting very low with time when the temperature lowers to a certain value.These results show that temperature plays a key role between the time scale of heating and thermal effects of source rocks.In the eastern and middle parts of the basin,the erosion thickness is much larger than the minimum erosion thickness causing the stagnation of thermal evolution of source rocks, which indicates that the thermal evolution of source rocks in these areas would have been in stagnation.While in the western part,the thermal evolution of source rocks might have lasted slowly till the Cenozoic in the area from Bu1 to Tian1 wells where the erosion thickness is relatively thinner.

Key words: vitrinite reflectance, thermal event, erosion thickness, Ordos basin

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