Review of diagenetic facies in tight sandstones: Diagenesis, diagenetic minerals, and prediction via well logs

摘要

The tight sandstones are characterized by low porosity, low permeability, complex pore structure and strong heterogeneity due to the extensive diagenetic modifications they experienced. Understanding of the impact of diagenetic alterations on reservoir quality is crucial to the hydrocarbon exploration and production in tight sandstones. Diagenetic facies, which is the comprehensive description of the diagenesis and diagenetic minerals, determines the formation and distribution of sweet spot. By correlating the diagenetic facies to well log responses, the subsurface distribution of porosity and permeability can be predicted. However, the prediction of diagenetic facies and reservoir quality via well logs in tight sandstones remains a challenging task. This paper critically reviews the impact of diagenesis and diagenetic minerals on reservoir quality in tight sandstones, and establishes a model for prediction of diagenetic facies via well logs, as assessed from peer reviewed papers in the literature as well as from the authors' personal experiences. This review begins with reviewing the impacts of compaction, cementation, dissolution and various types of diagenetic minerals on reservoir quality evolution. The definition and classification schemes of diagenetic facies are then discussed, and the reservoir quality as well as diagenetic evolution sequence of various diagenetic fades is summarized. The same diagenetic fades commonly display similar compositional and textural attributes, matrix and cement, as well as porosity systems. The well log responses (GR, AC, DEN, CNL, and RT) of various diagenetic facies are summarized by the calibration of log values with cores and related thin sections. By translating the diagenetic facies to conventional well logs, a predictable model, which can be used for subsurface reservoir quality prediction, is established. Then the theory of ECS logs is reviewed, and the application of ECS logs in diagenetic facies evaluation is discussed. At last, the quantitative characterization for various type and degree of diagenesis is reviewed, and the subsurface diagenetic facies is predicted by quantitative calculation of the compactional porosity loss, cementational porosity loss and dissolution porosity content via well logs. Correlating the diagenetic facies to well logs provides a powerful tool to predict the distribution of high quality reservoirs in tight sandstones. This review will provide insights into the reservoir quality evaluation and sweet spot prediction via well logs in tight sandstones.