Investigation of Intermingled Fractal Model for Organic-Rich Shale

Abstract

Organic-rich shales have abundant micronanopores and slits. Most micronanopores exist in organic matter and pyrites. Pore size distribution significantly influences shale gas flow. In micronanopores of organic matter and pyrites, pore size distribution has a self-imitating or fractal property. This property is helpful in upscaling calculation. In this work, intermingled fractal model for organic-rich shale is investigated. First, on the basis of scanning electron microscopy (SEM) images of shale samples in Longmaxi shale formation, fractal units are built-in representative elementary surfaces of organic matter and pyrites. Second, intermingled fractal models (IFMs) are then built considering the organic matter fractal pore units, the pyrite fractal pore units, and slits. Influences of fractal parameters on apparent gas permeability of IFMs are investigated. Third, an upscaled shale model is successfully built using the mirror image method. This upscaling method is verified by comparing the apparent gas permeability between upscaled models and experimental results. The upscaling method based on fractal theory can significantly shorten the calculation time and provide a promising way for apparent gas permeability calculation in the upscaled model.</p