Lithologic Reservoirs >

2013 , Vol. 25 >Issue 3: 9 - 16

DOI: https://doi.org/10.3969/j.issn.1673-8926.2013.03.002

Influencing factors of reservoirs for Ordovician Majiagou Formation in the surrounding area of paleo-uplift in Ordos Basin

  • YANG Hua ,
  • WANG Baoqing ,
  • SUN Liuyi ,
  • LIU Baoxian ,
  • WANG Hongwei ,
  • MA Zhanrong
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  • 1. PetroChina Changqing Oilfield Company， Xi’an 710018， China； 2. State Engineering Laboratory of Low-permeability Oil/Gas Fields Exploration and Development， Xi’an 710018， China； 3. School of Earth Sciences and Engineering，Xi’an Shiyou University， Xi’an 710065， China； 4. Research Institute of Exploration and Development，PetroChina Changqing Oilfield Company， Xi’an 710018， China

Online published: 2013-06-01

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Abstract

Based on the analysis of tectonic setting, petrology characteristics, biologic criteria and saline minerals, The Ordovician Majiagou Formation in the surrounding area of paleo-uplift in Ordos Basin deposited in a carbonate platform of restricted epeiric seas. The fifth member of Majiagou Formation deposited in gypsodolomite flat and gypsic saline lake where water cycle was restricted and salinity was high. The sedimentary environment of the fourth member of Majiagou Formation was relatively broad. Due to the compaction, porosity of the original carbonate sediments decreased greatly.The degrees of order for dolomite display low and changeable values. The dolomites are characterized by high δ18O values, Fe2+ contents and Sr87/Sr86 ratios, low Sr2+ and Na+ contents, and stable δ13C values comparing with original sedimentary values. The dolomites precipitated through microbial activity in the restricted environments with high salinity, and reformed by the karstification latter. The dissolution created different types of pores,caverns and fractures. The karstification formed karst geomorphic unites, such as karst highlands, karst platforms, eroded slopes and karst basins. The dolomitization and karstification are constructive processes, while compaction,cementation and dedolomitization are destructive processes. Abundant anhydrite nodules deposited in the anhydrite dolomite flats near anhydrite salt lakes,which is favorable for the creation of anhydrite nodule mold pores. The karstification developed well in karst eroded slopes, where abundant horizontal strata-bound dissolved pores and vugs were easily formed. In the transitional zones of slopes and basins, karstification was weak, while dedolomitization and cementation developed well. Because of the influence of sedimentation,diagenesis and karstification, the formation and evolution of the carbonate reservoirs are complicated.

Key words： sedimentation; diagenesis; karstification; Majiagou Formation; surrounding area of paleo-uplift; Ordos Basin

Cite this article

YANG Hua , WANG Baoqing , SUN Liuyi , LIU Baoxian , WANG Hongwei , MA Zhanrong . Influencing factors of reservoirs for Ordovician Majiagou Formation in the surrounding area of paleo-uplift in Ordos Basin[J]. Lithologic Reservoirs, 2013 , 25(3) : 9 -16 . DOI: 10.3969/j.issn.1673-8926.2013.03.002

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