Oil & Gas Geology ›› 2020, Vol. 41 ›› Issue (1): 209-222.doi: 10.11743/ogg20200119

Previous Articles     Next Articles

Characteristics and origin of dolostones in the Miocene Meishan Formation in Well Xike 1, Xisha Islands, South China Sea

He Yin1(), Yahui Wang2, Juan Liu2, Zhiqiang Shi1,*(), Daojun Zhang2   

  1. 1. Institute of Sedimentary Geology, Chengdu University of Technology, Chengdu, Sichuan 610059, China
    2. Zhanjiang Branch of CNOOC(China), Zhanjiang, Guangdong 524057, China
  • Received:2019-08-01 Online:2020-02-01 Published:2020-01-19
  • Contact: Zhiqiang Shi E-mail:717819782@qq.com;szqcdut@163.com
  • Supported by:
    国家科技重大专项(2017ZX05026-005-003)

Abstract:

Cenozoic carbonate platform was well developed in South China Sea, and dolostones are quite common in carbonate sequences of Xisha Islands. The characteristics of the Miocene Meishan dolomite is described by studying the macro-and micro-scopic features of dolostones, the carbon and oxygen isotopes, and main/trace elements in Well Xike 1. Mainly four categories of dolostones were developed in the Meishan Formation in Well Xike 1, which are different in thickness, color and porosity. Sucrosic dolomites, commonly distributed under the ancient exposed surface, can be seen in thick-bedded dolostones. While thin-bedded dolostones feature loose consolidation and incomplete dolomitization.The dolomite crystals are dominated by subhedral-idiomorphic flat surfaces, and bright edge and foggy center are seen in some dolomites of very fine to fine-crystallized crystals. The carbon and oxygen isotopes of carbonate rocks in the Meishan Formation show certain correlation, while the correlation of carbon and oxygen isotopic values in the dolostones is insignificant. The paleosalinity value of dolostones is calculated to be slightly higher than that of contemporaneous seawater. The oxygen isotopic value of dolostones is positive, indicating that the dolomitization was not affected by magmatic hydrothermal fluids and organic acid solution.Most thin-bedded dolomites in the Meishan Formation are calcareous dolostones, low in Fe, Sr and Mn concentrations, suggesting that the source of magnesium ions is mainly seawater. The rare earth elements (REE) are characterized by low Ce and Eu. In conclusion, the dolomitization in the study might have been caused by seepage reflux, and is characterized by high porosity and permeability as a result of geothermal warming, implying good reservoir potential.

Key words: geochemistry, petrological characteristics, dolostone, Meishan Formation, Miocene, South China Sea

CLC Number: