Oil & Gas Geology ›› 2020, Vol. 41 ›› Issue (2): 270-283.doi: 10.11743/ogg20200204

• Petroleum Geology • Previous Articles     Next Articles

The impact of thermodynamics and kinetics of feldspar dissolution-precipitation on reservoir quality: A case study from the Es3, Bonan Sag, Bohai Bay Basin

Zhenhuan Shen1(), Bingsong Yu1, Chenyang Bai1, Shujun Han1, Zhihui Yang1, Zhibin Fei2   

  1. 1. School of Earth Sciences and Resources, China University of Geosciences(Beijing), Beijing 100083, China
    2. Yunnan Institute of Geology&Mineral Resources Exploration, Kunming, Yunnan 650051, China
  • Received:2018-03-28 Online:2020-04-28 Published:2020-04-03

Abstract:

Feldspar dissolution along with the formation of secondary pores has a great impact on sandstone reservoir qua-lity.In order to study belts favorable for pore development in the Bonan sag, Bohai Bay Basin, we mainly focused on the research of secondary pores of feldspar in the Es3, by means of thermodynamics and kinetics calculation of feldspar dissolution-precipitation, combined with petrologic characteristics such as thin section observation, porosity and permeability data.The results show that formation water nowadays is favorable for the precipitation of feldspars, with feldspars in some areas having dissolved.According to the horizontal distribution of porosity and the thin section observation under microscope, we may conclude that the areas of better porosity are characterized by K-feldspar dissolution, fast dissolution of anorthite (ΔG < -15 kJ/mol) and slow precipitation of albite (ΔG < 15 kJ/mol).In addition, the reservoir permeability decreases as clay minerals (including kaolinite) precipitate in those secondary pores with feldspar dissolution.Meanwhile the reservoir porosity decrease accelerates significantly when SiO2 (aq) precipitation in the formation water in areas is triggered at a burial depth of over 3 000 m.In all, the feldspar dissolution has a great contribution to the formation of secondary pores in burial.However, the contribution may be compromised if by-products from feldspar dissolution are not removed, and higher clay content also tends to undermine the reservoir permeability.The study is a positive demonstration of a new way to predict reservoir quality by thermodynamics and kinetics models.

Key words: formation water, feldspar dissolution-precipitation, thermodynamics, kinetics, reservoir quality, Bonan Sag, Bohai Bay Basin

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