Comparative study on pore structure of marine and terrestrial shales:A case study of Longmaxi Formation and Lucaogou Formation
The pore structures of shale formed under different sedimentary backgrounds are different.Taking the marine shale of Longmaxi Formation in Northwest Hunan Province and the terrestrial shale of Lucaogou Formation in Jimushar Depression,Xinjiang Province,were taken as the objects of study,and the quantitative methods such as elemental geochemical analysis,mineralogical analysis,gas adsorption experiment,high-pressure mercury intrusion experiment,and the qualitative methods such as field emission scanning electron microscopy observation were combined.Then,the differences in the pore structures of shales in different depositional backgrounds were clearly defined,and the controlling factors for the differences in pore structures between the marine and terrestrial shales in the study area were revealed in combination with the study of the depositional environments.The results show that Longmaxi Formation marine shale develops a large number of organic pores,and the pore sizes range from micropores to mesopores;the organic pores of the terrestrial shale of Lucaogou Formation are less developed,and the inorganic pores distributed in the mesopore-macroporous scale are the main contributors to the pore system.The marine shales of Longmaxi Formation have high primary productivity and good bottom water preservation conditions,with high organic matter maturity,and the organic matter abundance is the main factor controlling pore development;.However,the terrestrial shales of Lucaogou Formation deposit in anoxic environments and have high productivity conditions,with a high organic matter content but a low maturity and limited development of organic pores.The clay mineral content is the main factor controlling the development of pore space.By studying the differences in pore structures between marine and terrestrial shales and the main controlling factors,we hope to provide a theoretical basis for the subsequent shale oil and gas exploration and development work in the study area.
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