Quantitative Evaluation of Tight Shale’s Pore Configuration: Mathematics and Experiments

The pore configuration of shale has always been a contentious topic in shale gas exploration research due to its complexity, aperture size and dispersion varies from nanometers to millimeters. To investigate the pore configuration of shale, this study selected the Longmaxi Formation shale in the Sichuan Basin as the research subject and conducted high-pressure mercury, cryogenic liquid nitrogen and cryogenic carbon dioxide adsorption experiments. By employing a combination of characterization methods and fractal dimension analysis, the study delved deeply into the nano-level pore features of the Longmaxi Formation shale. The experimental results demonstrated that the pores of the Longmaxi Formation shale samples could be classified into three types, of which the first and second types indicated good pore connectivity, while the third type showed poor connectivity. Moreover, the capacity and particular surface area of the minuscule pores were predominantly distributed at pore sizes of 0.3-0.5 nm. Additionally, mesopores could provide a substantial amount of pore volume, while micropores played a crucial role in controlling the total specific surface area and serving as the key location for gas adsorption and storage. Furthermore, the pore configuration of the Longmaxi Formation shale adhered to fractal laws, and the fractal dimension of pores larger than 50 nm was 2.9176, indicating that larger pores were more complex than medium and small pores. In conclusion, this study offered valuable insights into the pore architecture of the Longmaxi Formation shale and underscored the significance of considering pore configuration in shale gas exploration.