Reservoir Evaluation and Development ›› 2018, Vol. 8 ›› Issue (2): 14-21.

• Reservoir Geology • Previous Articles     Next Articles

Study on composition, carbon and oxygen isotopic characteristics of carbonate cements in Chang-8 reservoir, Ordos Basin

Wang Zhao1,2,3,Qiu Junli1   

  1. 1.Key Laboratory of Petroleum Resources of Gansu Province & Key Laboratory of Petroleum Resources Research, Institute of Geology and Geophysics, Chinese Academy of Sciences, Lanzhou 730000, China;
    2. University of Chinese Academy of Sciences, Beijing 100049, China
    3. Guangzhou Geological Survey,Guangzhou 510440, Guangdong, China
  • Received:2017-07-14 Online:2018-04-30 Published:2018-04-30


Based on the study of the carbon oxygen isotopic characteristics and the observation of thin slices, we systematically studied the carbonate cementation of Chang-8 reservoir in Ordos Basin. According to the observation of the minerals under the microscope, it can be concluded that the carbonate cements were composed of the calcite, dolomite, ferrodolomite, ferrocalcite and siderite. The mineral composition and distribution are strongly influenced by the heterogeneous chemical activity of fluids. The carbonate cementation often damages the porosity and permeability. Meanwhile, the C-O isotope value was determined by the phosphoric acid method. The experimental results show that the range of carbon isotope distribution is -14.8 ‰ to -1.5 ‰, and the distribution range of oxygen isotope is -25.7 ‰ to -9.9 ‰. The Z values of the samples are mostly less than 120, indicating that the carbonate cements in the sample formed in the freshwater-brackish water environment. The paleo temperature was measured from 68 ℃ to 128 ℃ by oxygen isotope value, which shows that the cementation occurred mainly in the early diagenetic stage B to the middle diagenetic stage A. The carbonate cement content in the upper part of Chang-8 is much lower than that in the lower part, indicating that cementation was derived from carbonate deposits which were related to decarboxylation of organic acids. According to the sedimentary subfacies, the study area is divided into three areas, and the oxygen-carbon isotope gradually decreases in accordance with the half deep lacustrine subfacies-gravity flow subfacies-delta subfacies. Finally, the reasons for the present situation of isotope distribution in the basin are concluded: the organic acid moves gradually from the high potential region to the low potential region under the compaction, and the organic carbon is captured by chemical cementation after a series of chemical changes.

Key words: Ordos Basin, carbonate cementation, carbon oxygen isotope, sedimentary environment, paleo temperature, provenance, solute transport model

CLC Number: 

  • TE122.2