Pore structure evolution of organic-rich shale induced by structural deformation based on shale deformation experiments

Abstract

The effect of structural deformation on shale pore structure is a key scientific problem in the development of shale gas resources in structurally complex areas. In this study, we investigated the evolution rules and mechanisms of pore structures in organic-rich shale subjected to structural deformation of varying mechanisms and intensities, by conducting whole-aperture pore structure characterization on experimentally deformed shale rather than naturally deformed shale. Results showed that brittle deformed samples developed more mesopores, macropores, and fracture pores. The inter-granular pores between mineral fragments and the inter-layer pores and micro-fractures were the primary sources of the increased pore structures. The ductile deformation of shale promoted large-aperture transitional pores, mesopores, and small-aperture macropores but was adverse to small-aperture transitional pores, large-aperture macropores, and fracture pores. The primary contributors to the enhanced pore structures were inter-granular pores and inter-layer micro-fractures formed during crumpled deformation and inter-layer sliding of clay minerals, and inter-granular pores caused by the grinding, rounding, and rotation of mineral fragments under the flow deformation of the shale matrix. The irreversible compression of organic matter pores, mineral-related pores, and pre-existing large-aperture pores and fractures was the main reason for the reduction in small-aperture transitional pores, large-aperture macropores, and fracture pores.