| In order to reveal the shale facies characteristics of Dawuba Formation of Lower Carboniferous in Liupanshui
area and its influence on the shale micro-pore structure, a series of experimental testing techniques and methods have
been used, including thin section observation, whole rock X-ray diffraction, field emission scanning electron microscopy,
cryogenic nitrogen adsorption experiment, carbon dioxide adsorption experiment and organic geochemical analysis. In the
process of analysis, different types of shale lithofacies were observed and analyzed at multiple scales, the relationship
between lithofacies type and micro-pore structure was analyzed and the main influencing factors of micro-pore structure
of different lithofacies types of shale were discussed. The results show that: (1) The shale facies types of Dawuba
Formation in Liupanshui area mainly include calcareous shale lithofacies, argillaceous/ siliceous mixed calcareous shale
lithofacies and argillaceous-rich calcareous shale lithofacies. The argillaceous-rich calcareous shale lithofacies is most
favorable lithofacies among them. (2) Shale pores are composed of organic pores, inorganic pores and micro-fractures.
The combination of organic pores and clay mineral interlayer pores in the argillaceous-rich calcareous shale lithofacoes is
beneficial to shale gas enrichment. (3) The pore diameter of shale is 6.27-10.91 nm, with an average of 8.41 nm; the pore
volume of shale is (10.04-24.26)×10-3 mL/g, with an average of 17.93×10-3 mL/g; the specific surface area of shale is
5.20-17.61 m2
/g, with an average of 12.17 m2
/g.The average pore volume and specific surface area of argillaceous-rich
calcareous shale lithofacoes are the highest, followed by argillaceous / siliceous mixed calcareous shale lithofacies and
calcareous shale lithofacies. (4) Organic carbon content and clay mineral content are the main factors affecting the micro
pore characteristics of shale, followed by carbonate mineral content. Organic carbon and clay minerals play a positive role
in the pore development of shale , and carbonate minerals inhibit the pore development of shale. |
