Effect of Liquid Nitrogen Treatment on Poro-Perm Properties of Coal

The article presents the laboratory studies on cyclic treatment of fine-pore and banded bituminous coal with liquid nitrogen. Permeability of coal cores was determined in the mode of nonstationary flow, and porosity was assessed using the methods of nuclear magnetic resonance and optical microscopy. The procedures and design solutions used in the experiments are described. The change in permeability of coal along and across its banding is examined in the conditions of hydrostatic compression. It is found that permeability of test coal grows by one–two orders of magnitude along its banding and by two–three orders of magnitude across the banding. Anisotropy of permeability decreases. This effect intensifies with the increasing hydrostatic compression and water saturation of coal. It is shown that the effect of the liquid nitrogen treatment is mostly associated with different-scale crack growth in coal at a minor change in open porosity.