Far Eastern Federal University, Vladivostok, Russia:

T. V. Selivanova, Associate Professor, Candidate of Geological-and-Mineralogical Sciences, Selivanova_d@mail.ru
V. S. Pechnikov, Associate Professor, Candidate of Physico-Mathematical Sciences

Real-time monitoring of the combustion face advance is an important aspect of operational reliability and economic efficiency of thermochemical coalbed treatment. The current methods of the combustion face control are expensive and technically complicated. In-situ coal is a weakly magnetic rock. Considering that matrix of coal and its mineral component undergo substantial thermomagnetic changes under thermal treatment, it is assumed possible to use the magnetic survey method in the real-time remote monitoring of the combustion face advance along the strike of a coalbed under thermochemical treatment. In order to check on the assumption, measurements of magnetic moment of coal samples taken from Urgal deposit of Bureinsk Coal Field were carried out in the constant magnetic field at the varied heating temperatures using a vibrating magnetometer. The magnetic moment and temperature dependences were determined on the prepared powdered coal specimens. During the tests, the specimen and air contact time was reduced to a minimum in order to eliminate oxidation of coal. Magnetic moment of a specimen was measured at a set temperature. The heating temperature of a specimen was changed by stages, starting from room temperature and finishing at 800 °C. The tests showed that under such temperature conditions, a specimen was uniformly heated throughout the volume in 3–5 min. The measurement of magnetic moment of a specimen at a set temperature was carried out in the constant magnetic field with the induction up to 125 mT. This article gives the analysis of change in magnetic properties of coal specimens depending on exposure temperature. It is found that the change in magnetic properties of the tested coal specimens under influence of high temperatures is conditioned by polymorphic transformation of sulfide minerals (pyrite) in the composition of coal matrix, with the further oxidation of sulfi de minerals and generation of ferromagnetic material that, even if present in a small amount, considerably enhances magnetic susceptibility of thermally altered coal. The research findings are applicable to validation of usability of the ground geophysics methods in the combustion front positioning and advance monitoring in the course of Urgal coal mining with thermochemical treatment.

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