Abstract
ABSTRACTCharacterization of coal micro-structure and the associated rock mechanical properties are of key importance for coal seam exploration, coal bed methane development, enhanced coal bed methane production and CO2 storage in deep coal seams. Considerable knowledge exists about coal chemical properties, but less is known about the nanoscale to the micro-scale structure of coals and how they change with coal strength across coal ranks. Thus, in this study, 3D X-ray micro-computed tomography (with a voxel size of 3.43 µm) and nano-indentation tests were conducted on coal samples of different ranks from peat to anthracite. The micro-structure of peats showed a well-developed pore system with meso- and micro-pores. The meso-pores essentially disappear with increasing rank, whereas the micro-pores persist and then increase past the bituminous rank. The micro-fracture system develops past the peat stage and by sub-bituminous ranks and changes into larger and mature fracture systems at higher ranks. The nano-indentation modulus showed the increasing trend from low- to high-rank coal with a perfect linear relationship with vitrinite reflectance and is highly correlated with carbon content as expected.
Highlights
Coal is naturally heterogeneous, composing of different components which are originally derived from various plant organs
A minor detrital or crystalline mineral phase occurs that is dispersed through the plant material or trapped in the cell lumens
Coal micro-structure and coal rock mechanical properties are extremely important for coal utilization, for instance in mining, coke production, deep drilling, coal bed methane (CBM)/enhanced coal bed methane production (ECBM) and CO2 geo-sequestration (Karacan and Okandan 2001; Busch et al 2019; Li et al 2017)
Summary
Coal is naturally heterogeneous, composing of different components (or coal macerals) which are originally derived from various plant organs. Coal porosity, pore size distribution or pore throat size distribution has been investigated by traditional invasion techniques such as helium pycnometer, low pressure gas adsorption or mercury injection capillary pressure (MICP) method (Liu et al 2016). These methods are limited, which require the assumptions about pore shape, the encounter problems at low ranks with moisture, and could cause particle breakdown at high pressure invasion (Mahajan and Walker 1978). Scanning electron microscopy (SEM) is adequate for directly imaging the coal micro-structure and in situ analysis with nanoscale resolution, but it is essentially restricted to 2D (Predeanu et al 2016)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
