INVESTIGATION ON LAW OF METHANE GAS FLOW IN COAL WITH COAL-GAS OUTBURST HAZARD AND LOW PERMEABILITY

For knowing the law of methane gas flow in coal with coal-gas outburst hazard and low permeability (CCOHLP),an experimental study of methane gas flow in coal samples,produced by raw CCOHLP from a coal mine at Nantong coalfield,is performed with self-developed triaxial load system and by way of steady-state flow under different confining pressures. It presents the comparison of test data on methane gas flow in CCOHLP processed by the traditional method of computing permeability and the method of fitting permeability with Klinkenberg effect. It is proved by experiments and numerical simulation that:(1) the Klinkenberg effect of methane gas flow in low permeability coal is especially prominent;(2) for the low permeability coal,the Klinkenberg coefficient b and the absolute permeability is related to a power function;meanwhile,the absolute permeability and bulk stress is related to a quadratic polynomial function;(3) the Klinkenberg coefficient b increases gradually with the decreasing absolute permeability;meanwhile,the absolute permeability decreases gradually with the increasing bulk stress;(4) the processing results of test data are with reason by the method of fitting permeability considering Klinkenberg effect;and (5) the algebraic expression on effective permeability of low permeability coal obtained by this experiment reflects the combined impact of gas pressure and stress on methane gas flow and it is able to simulate the methane gas flow in CCOHLP.