Direct imaging of micropores in shale kerogen. (December 2022)

• Record Type: Journal Article
• Authors: Liu, Yu; Su, Chi; Shang, Fuhua
• Is Part Of: Marine and petroleum geology. Volume 146(2022)
• Publication Date: 2022-12
• Subjects: Shale gas -- Kerogen -- Micropore -- Molecular structure; Submarine geology -- Periodicals; Petroleum -- Geology -- Periodicals; Géologie sous-marine -- Périodiques; Pétrole -- Géologie -- Périodiques; Petroleum -- Geology; Submarine geology; Periodicals; Electronic journals; 551.468
• DOI: 10.1016/j.marpetgeo.2022.105928
• Languages: English
• ISSNs: 0264-8172

Abstract

Abstract: Although micropores (<2 nm) play an important role in shale gas storage, these pores have not been imaged previously. Aberration-corrected scanning transmission electron microscope (AC-STEM) with a secondary electron detector (SED) has been used here to study such pores in kerogen isolated from Longmaxi shale. In addition, a three-dimensional (3D) kerogen molecular model was constructed based on 13 C Nuclear Magnetic Resonance ( 13 C NMR), Fourier transform infrared spectroscopy (FT-IR) and CO2 adsorption experiments, to further study the relationship between micropores and kerogen molecule. The results show that AC-TEM with SED can directly image pores smaller than 2 nm in the kerogen particle by operating in the scanning transmission electron microscopy (STEM) mode. These micropores can occur everywhere on the kerogen surface, which is consistent with the large micropore volume and surface area determined by gas (CO2 and N2 ) adsorption experiments. The surface of the 3D kerogen model is similar to that observed in the SED-STEM images in terms of surface morphology and scale. This suggests that the 3D model of the kerogen molecule is a good representation of the kerogen sample. This study links the direct images of micropores in kerogen sample and the kerogen molecular models, which is important for further understanding of shale gas storage, as these micropores and molecules provide the sites and surface energy for methane storage. Highlights: SED-AC-STEM is an efficient tool to observe the shapes, sizes, and distributions of micropores in kerogen. Micropores are found everywhere on kerogen, which is consistent with the large micropore volume tested by CO2 adsorption. The surface of a 3D molecular model is consistent with that observed by SED- AC-STEM. The suppose that disordered molecular structures of kerogen form abundant pores is directly verified by SED-AC-STEM.