Research Advances on Characteristics of Nanopore Structure of Organic-rich Shales

Key words: 
• organic matter /
• shale gas and oil /
• pore structure /
• highly envolution stage /
• sedimentary environment

Abstract: A full understanding of the properties of the pore structure in organic-rich shales is beneficial for determining the shale oil and gas accumulation mechanism,and thus is significant in guiding exploration and exploitation. Methods of characterizing the pore structure of organic-rich shales embody quantitative analysis and qualitative description,both of which should be combined during investigations. Factors such as total organic carbon(TOC),thermal maturity,origin of organic matter,mineral constituents and tectonism have considerable impacts on the nature of the pore structure in organic-rich shales. Of these,the origin of organic matter determines the potential for organic pores formation;TOC and mineralogy control the types of nanopores;and thermal maturity influences nanopore evolution. Tectonism has a secondary effect,in that it may modify the nanopore structure. Pyrolysis experiments play a crucial role in investigating the evolution of pore structure in shales,since the factors are controlled artificially;however,experimental conditions should match the actual geological conditions. At present,pore structure evolution in shales is still inconclusive and controversial. Due to the diverse origins of organic matter,the evolution of the pore structure in organic-rich shales may differ from one sedimentary environment to another,and thus require further separate study. Dilemmas such as the impacts of TOC on the characteristics of pores in shales,the mature stage of the development of secondary organic pores and the evolutionary scenarios and mechanisms of pores at the envolution stage (R_o>3%) need to be further explored. In addition,the methods identifying the microscopic compositions of organic matter using scanning electron microscopy need to be established,and the usage of some terminologies should be standardized to reduce the confusion that is currently caused by researchers who engage in different fields.