Investigation of Tectonically Disturbed Zones of Coal Seams of the Kuznetsk Coal Basin Using SANS
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nvestigation of Tectonically Disturbed Zones of Coal Seams of the Kuznetsk Coal Basin Using SANS T. Vasilenkoa, *, A. Islamovb, A. Kirillovc, **, A. Doroshkevichb, and N. Doroshkevichb aSt.
Petersburg Mining University, St. Petersburg, 199106 Russia Institute for Nuclear Research, Dubna, Moscow oblast, 141980 Russia c Institute for Physics of Mining Processes, National Academy of Sciences of Ukraine, Dnipro, 49005 Ukraine *e-mail: [email protected] **e-mail: [email protected] bJoint
Received July 21, 2019; revised August 27, 2019; accepted September 5, 2019
Abstract—Small-angle neutron scattering (SANS), low-temperature nitrogen adsorption (Brunauer– Emmett–Teller method, or BET) and Raman spectroscopy are used for a comparative analysis of the structural characteristics of the coals of the two seams, Boldyrevsky and Polenovsky, of the Kuznetsk coal basin. SANS measurements show that the microstructure of coal is characterized by surface fractal dimension close to three. The calculated specific surface area of the pore space makes it possible to distinguish the zones of disturbances from the calm areas of the same coal seams. The most sensitive method for the analysis of tectonic disturbances is the Raman spectroscopy, which allows tracing the characteristics of the type of deformation (brittle or ductile) in the disturbed zones. The BET and SANS methods are necessary to understand the dependence of coal Raman spectra on disturbances. Thus, an increase in specific surface area and surface fractal dimensions indicates the potential danger of outbursts in the area of the tectonic disturbances. Keywords: coal, fractal dimension, hazardous seam, Raman spectroscopy, neutron, small-angle scattering, specific surface, tectonically disturbed coal DOI: 10.1134/S1027451020070496
INTRODUCTION The study of structural organization of coal substance is a relevant objective because the mechanisms of sorption and mass transfer of fluids within the pore space are realized at the nanoscale level. Structure features are factors determining the tendency of coal seams to dangerous sudden outbursts of coal, rock and gas. Coal structure is able to vary along the coal seam. Substantial changes are found in the zones of tectonic disturbances where the conditions advantageous to free methane accumulation are formed. When the excavating mechanisms approach the zone of tectonic disturbances, the probability of geodynamical events and incidents increases. The testing of structural organization of coal substance by atomic force microscopy, nuclear magnetic resonance, methane desorption, impedance spectroscopy [1–5] allowed making a conclusion about hierarchical structure of pore organization and fractal properties of coal matrix that is heterogeneous with respect to the physical properties. The methods of small-angle X-ray scattering and Raman spectroscopy detect fine effects that characterize the coal structure at the nanolevel; so, they are able to provide reliable forecast of sudden outbursts of coal and gas, as well as the degree
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