Oil & Gas Geology ›› 2020, Vol. 41 ›› Issue (2): 316-327.doi: 10.11743/ogg20200208

• Petroleum Geology • Previous Articles     Next Articles

Diagenesis and physical properties of subsalt dolomite reservoirs of the Cambrian, Bachu-Tazhong areas, Tarim Basin

Lijuan Cheng1,2(), Zhong Li1,2,*(), Jiaqing Liu1,2, Jingbo Yu3   

  1. 1. Institute of Geology and Geophysics, Chinese Academy of Sciences(CAS), Beijing 100029, China
    2. University of Chinese Academy of Sciences, Beijing 100049, China
    3. Hebei GEO University, Shijiazhuang, Hebei 050031, China
  • Received:2019-05-05 Online:2020-04-28 Published:2020-04-03
  • Contact: Zhong Li E-mail:chenglijuan211@163.com;lizhong@mail.iggcas.ac.cn

Abstract:

The effective subsalt dolomite reservoirs in the Tarim Basin are characterized by great spatial heterogeneity.The reservoir distribution therein is under the influence of both high-energy sedimentary facies belts such as grain shoal and organic reef facies, and diagenetic modification.To further understand the restriction mechanism of diagenetic modification on dolomite reservoirs, we thoroughly described the subsalt dolomite characteristics through microscopic observation, geochemical analysis and logging data interpretation of drilling core samples taken from Bachu-Tazhong areas.The results indicate that the Lower Cambrian subsalt dolomites are dominated by micrite dolomite, grain dolomite, microorganism dolomite and fine-crystalline dolomite.The reservoirs mainly evolved from early-stage diagenetic modification by meteoric water, middle-stage porosity preservation, to continuous improvement of reservoir properties at later stages.The high-quality subsalt dolomite reservoirs are the combined products of proper dolomitization, shielding effect of the overlying gypsolytes on the underlying intervals, and dissolution by thermal fluids in the later periods.Vertically, there are five diagenetic zones in the reservoir under tectonic-hydrothermal modification:hydrothermal mineral developing zone, hydrothermal brecciation zone, fracture developing zone, dissolution zone, and hydrothermal dolomite zone of cementation.Among them, the dissolution zone is the most significant contributor to reservoir improvement, followed by the fracture developing zone.

Key words: reservoir, diagenesis, hydrothermal dolomitization, subsalt dolomite, Cambrian, Tarim Basin

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