Investigation of microscopic pore structure variations of shale due to hydration effects through SEM fixed-point observation experiments

This paper conducted the shale hydration experiments by using four different types of shale outcrop samples. The microscopic pore structure variations before and after hydration were recorded, compared and analyzed through Field Emission Scanned Electronic Microscope (FESEM) with fixed-point observation technique. The results showed that higher content of montmorillonite and carbonate minerals would contribute to the form of dissolution pores and looseness of mineral grains; some critical factors also include original alignment and cementation of mineral grains, and distribution of natural microfractures. Hydration doesn't change the organic pore structure. Almost all dissolution pores originated from mineral intergranular and intragranular pores in matrix, and the dissolution of matrix pores also lead to mineral particles to loose and fall off. When the mineral grains are aligned and compacted along with the bedding-parallel planes, the density of dissolution pores and the number of dissolution pores of small size in bedding-vertical specimens are usually larger than that in bedding-parallel specimens. For the shale samples with few natural microfractures, carbonate minerals may contribute to the generation and propagation of microfractures during hydration.