Microstructure characteristics and sedimentary environments of clay sediments

Key words: 
• shale /
• sedimentary microstructure /
• flocculation /
• physical and chemical factor /
• micro-environment

Abstract: As an important component of unconventional oil and gas resources, the basic research of shale oil and gas resources has gradually attracted attention. Microstructures of clay sediments have an impact on shale foliation and lamination structure, thus influencing the shale reservoir capacity and development effect. In addition to being affected by physical action, clay particles also undergo chemical adsorption and flocculation to form floccules with varying degrees. The basic unit of floccule is tabular particles or domains, further forming flocs or chains, and finally forming a card house structure under the action of electric charge. In the sedimentary stage, the physical and chemical factors affecting the flocculation include particle size, particle content, external hydrodynamic strength and flow properties, climate, electrolyte concentration, ion type, pH value, organic matter, etc. By studying the physical and chemical factors affecting the microstructures of clay sediments and analyzing the other components of mudstone composite particles such as volcanic rock fragments, shale lithics, muddy intraclasts and fecal pellets, the sedimentary environments of mudstone and shale can be identified and described. This study is still in its infancy and a perfect geological model has not been established; The quantitative research of floccules and other components of mudstone composite particles is insufficient, and big data technology has not been used well; The study on the sedimentary micro-environment and internal association characteristics of marine black shale in western China needs to be deepened; The research technology and method are slightly single. Based on the qualitative and quantitative description of microstructures of clay sediments and demonstration of sedimentary environments of mudstone composite particles, it can achieve fine description of complex and changeable sedimentary micro-environment, deepen understanding of the differentiation characteristics of sedimentary environments of shale such as lakes and seas, and further reveal the differences in shale reservoir quality within the high-precision range, laying a foundation for the selection and development of geology and engineering "desserts" in shale.