Oil & Gas Geology ›› 2022, Vol. 43 ›› Issue (3): 582-596.doi: 10.11743/ogg20220308

• Petroleum Geology • Previous Articles     Next Articles

“Three-factor” driven microbial carbonate reservoirs and their distribution

Anjiang Shen1,2(), Anping Hu1,2(), Jie Zhang1,2, Xiaofang Wang1,2, Hui Wang1,2   

  1. 1.Hangzhou Institute of Petroleum Geology,PetroChina,Hangzhou,Zhejiang 310023,China
    2.Key Laboratory of Carbonate Reservoirs,CNPC,Hangzhou,Zhejiang 310023,China
  • Received:2021-04-17 Revised:2022-03-10 Online:2022-06-01 Published:2022-05-06
  • Contact: Anping Hu E-mail:shenaj_hz@petrochina.com.cn;huap_hz@petrochina.com.cn

Abstract:

Microbial carbonates are very important hydrocarbon reservoirs. Stromatolite and thrombolite carbonates are commonly suggested to be better hydrocarbon reservoirs than other microbial and no-microbial carbonates. To check the truth of the suggestion, this study characterizes some modern microbial deposits and salt lake deposits, and performs simulated experiments of early degradation and buried pyrolysis of microbial organic matter, and genesis of dolomites by early precipitation and replacement. The results confirm the suggestion and reveal the uniqueness of microbial carbonate reservoirs with their special sediments and depositional setting. Three factors that control the formation of the reservoir are also proposed. (1) Compared with other microbial and no-microbial carbonates, stromatolite and thrombolite carbonates contain more original pores and microbial organic matter and therefore have a better material basis for becoming hydrocarbon reservoirs. (2) The production of organic acid by early degradation and later pyrolysis of microbial organic matter helps preserving and enhancing the original porosity, serving as a key factor for the development of stromatolite and thrombolite carbonate reservoirs. (3) Early dolomitization favors the preservation of pre-burial porosity and two types of low-temperature dolomitization (early deposition and replacement) tend to occur in carbonate-evaporite sedimentary sequences, which result in the development of stromatolite and thrombolite reservoirs in these sequences. The understanding is of great significance to the prediction of distribution of microbial carbonate reservoirs, based on which stromatolite and thrombolite zones are suggested to be promising hydrocarbon reservoirs in carbonate-evaporite sedimentary sequences.

Key words: early low-temperature degradation, late pyrolysis, early dolomitization, carbonate-evaporite sedimentary system, microbial carbonates

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