Journal of Tropical Oceanography ›› 2024, Vol. 43 ›› Issue (2): 140-153.doi: 10.11978/2023022CSTR: 32234.14.2023022

• Marine Geology • Previous Articles     Next Articles

The framework, reservoir characteristics and reef formation model of Miocene algal reef dolomite in the Xisha Islands*

CHEN Shu1,2(), XU Hong2,3, LU Shushen3,4, Zhang Haiyang5, MA Yazeng1,2, LUO Jinxiong1()   

  1. 1. Yangtze University, Wuhan 430100, China
    2. The First Institute of Oceanography, Ministry of Natural Resources, Qingdao 266061, China
    3. Qingdao Institute of Marine Geology, China Geological Survey, Qingdao 266071, China
    4. China University of Petroleum (East China), Qingdao 266580, China
    5. Baoding Center Seismic Station, Hebei Earthquake Agency, Baoding 071000, China
  • Received:2023-02-21 Revised:2023-05-25 Online:2024-03-10 Published:2024-03-26
  • Supported by:
    National Key Research and Development Program(2017FY201407); National Key Basic Research and Development Program(2012CB956004); National Key Oil and Gas Project(2011ZX05025-002-04); National Natural Science Foundation of China(41106064)

Abstract:

Traditional bioreef genesis theory either lacks evidences for algae forming strong bioreef anti-wave frameworks or attributes them to an accessory reef biotic community. In this paper, microfocal X-ray (X-CT) scanning imaging technology is used to study the core of the Aethesolithon nanhaiensis reef framework rocks and Halimeda reef proglottid rocks of Miocene age in Wells Xike 1 and Xiyong 2. Through three-dimensional tomography visual perspective images, it was found that the wave resistance structure of algal reef created by calcareous algal organisms, including typical Aethesolithon nanhaiensis reef framework structure, baffle-structure rocks and Halimeda reef proglottid structure. It also verifies that algal reefs are important Miocene oil-gas reservoirs in the South China Sea depositional basins by quantifying the throat, areal porosity and porosity parameters using threshold approach. Besides, the genetic model of algal reef is put forward: the reef-building calcium algal algae adapted to the sea level rise and fall gradually succession-replacement, and after calcification, burial and fossilization, dolomitization, sedimentary algal reef dolomitization, resulting in the growth of the longitudinal sequence of the Xisha Reef in Miocene.

Key words: Xisha Islands, calcareous algae organic framework, algal reef-building, three-dimensional tomography, porosity-permeability layer 3D reconstruction