MICRO-PORE STRUCTURE OF LONGMAXI SHALE FROM SOUTHEAST SICHUAN BASIN

This paper is devoted to the micro-pores of the Longmaxi Shale from the southeast Sichuan basin using SEM and mercury injection combined with nitrogen adsorption method. Based on the derived adsorption-desorption hysteresis curves and FHH fractal model, pore shape and fractal property were studied. The results show that micro-and meso-pores contribute more than 80% of the pore space. Organic-poor shale of the Longmaxi Formation is dominated by plate-like pores with fractal dimension values less than 2.75 as micro-fractures along silt borders and between illite layers. On the contrary, organic-rich shale exhibits ink-bottle like characteristic with fractal dimension values larger than 2.85 which is contributed by organic pores.TOC content is positively related to pore volume,hysteresis capacity and fractal dimension values. It is revealed that with the increase in TOC content, shale pore network changes from plate-like pores dominated inorganic pores to ink-bottle dominated organic pores. This change is not only beneficial for gas storage but also for gas retention and enrichment because of multi-capillary seal and diffusion reduction.