Oil & Gas Geology ›› 2006, Vol. 27 ›› Issue (2): 233-238,243.doi: 10.11743/ogg20060214

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Effects of hydrocarbon migration and dissipation in later reformation of a basin:formation of Mesozoic bleached sandstone in northeastern Ordos basin

Ma Yanping, Liu Chiyang, Wang Jianqiang, Zhao Junfeng, Fang Jianjun, Gui Xiaojun, Yu Lin   

  1. Key Laboratory of Continental Dynamics, Northwest University, Xi'an, Shaanxi, 710069
  • Received:2005-12-01 Online:2006-04-25 Published:2012-01-16

Abstract:

Study on bleaching of sandstone of different ages in the world indicates that the formation of bleached sandstone is relevant to organic fluid flows.It can provide some clues to hydrocarbon migration,accumulation and dissipation,thus can be used as an evidence for predicting the existence or destruction of oil/gas reservoirs(or fossil oil/gas reservoirs) in nearby areas.The occurrence of oil and gas in Ordos basin would have been altered during the later reconstruction of the basin.Based on analysis of the major elements,rare-earth elements and petrologic characteristics of Mesozoic bleached sandstone in the northeastern Ordos basin,it is preliminarily believed that the bleached sandstone in the study area would have been formed in an acidic and reducing environment.The bleached sandstone is characterized by its relatively high content of kaolinite and pyrite,and the color of ferric oxide minerals on the edge is lighter than that in the center.The major element analysis of sandstone samples shows that they have relatively high Al2O3 content and low Fe3+/Fe2+ ratio;the REE analysis shows that the Eu contents in both core and outcrop samples are negative;all these indicate a reducing environment.At the same time,the geochemical characteristics of oil sand in the northern part of the basin indicate that the oil is exactly condensate as a result of the migration and dissipation of Permo-Carboniferous humic gas in the south to the surface.In a word,the comprehensive study suggests that the bleaching of Mesozoic sandstone in the study area indicates dissipation of natural gas.

Key words: bleached sandstone, gas dissipation, Mesozoic, Ordos basin

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