Depending on the conditions used, either nucleation or crystal growth may be predominant over the other, leading to crystals with different shapes and sizes. ![]() Many compounds can exist in multiple crystal structures – a phenomenon known as “polymorphism” – and can have different physical properties (melting point, shape, dissolution rate, etc.). The control of the nucleation phase is difficult but is the key to process control crystallization chemists usually aim to achieve goals of high purity and high yield by solely using controlled cooling crystallization techniques. Supersaturation and supercooling are two of the most common driving forces behind crystal formation.ĭevelopment of crystallization processes represents a complex and challenging issue, requiring simultaneous control of various product properties, including purity, crystal size and shape, and molecular level solid structure. Crystal growth is a dynamic process, with atoms precipitating from solution and becoming redissolved. Crystal Growth – Nuclei that have successfully achieved the “critical cluster size” begin to increase in size.It is this point in the crystallization process that defines the crystal structure. Clusters need to be stable under current experimental conditions to reach the “critical cluster size” or they will redissolve. Nucleation – Molecules gather together in clusters in a defined manner.The crystallization process consists of two major events: BACKGROUNDThe pore characteristics of shale are one of the key parameters for evaluation of the shale reservoir capacity.How does the crystallization process occur? Scanning Electron Microscopy (SEM) has been widely used to describe the pore characteristics of shale. However, the classification of micro-pore types in mud shale reservoirs in the literature was relatively diverse, and the quantitative characterization of pore based on SEM was relatively lacking. OBJECTIVESTo classify the pore types and quantitatively characterize these pores in shale. METHODS18 shale samples were selected as the research object in this study. Based on the form, position and origin of pores observed by argon ion polishing and Scanning Electron Microscopy, the types of different pores in the sample were classified. By using JMicroVision image analysis software, the pore characteristics including the number of pore types, pore size, face rate, shape coefficient, probability entropy and other parameters were quantitatively described. RESULTSThe inter-crystal (particle) pores and organic pores were the most developed, followed by intra-crystal (particle) pores and crystal gap inter-crystal (particle) pores. The probabilistic entropy of intra-crystal (particle) pores and organic pores were mainly distributed between 0.5 and 0.7, with a different shape coefficient distribution. The shape coefficients of organic pores were mainly distributed between 0.6 and 0.7, and their shape were mainly oval or nearly circular. The shape coefficient of intra-crystal (particle) pores and inter-crystal (particle) pores were mainly between 0.3 and 0.7, which were mainly affected by the original pore morphology, compaction and dissolution.ĬONCLUSIONSThe combination of SEM and JMicroVision is an effective means to quantitatively study the development characteristics of different types of micropores. This work has laid a foundation for the study of the genesis and evolution of micropores. Mastalerz M, Schimmelmann A, Drobniak A, et al.Porosity of Devonian and Mississippian New Albany Shale across a maturation gradient:Insights from organic petrology, gas adsorption, and mercury intrusion.AAPG Bulletin, 2013, 97(10):1621-1643. Wang X Z, Zhang J C, Cao J Z, et al.A preliminary discussion on evaluation of continental shale gas resources:A case study of Chang 7 of Mesozoic Yanchang Formation in Zhiluo-Xiasiwan of Yanchang.Earth Science Frontiers, 2012, 19(2):192-197. Wu S T, Zhu R K, Cui J G, et al.Characteristics of lacustrine shale porosity evolution, Triassic Chang 7 Member, Ordos Basin, NW China.Petroleum Exploration and Development, 2015, 42(2):167-176. Li J N.Study on Pore Structure Characteristics and Connectivity of Shale Reservoir.Nanjing: Nanjing University, 2017.
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