The evolution law of pore characteristics and pore bulk modulus for overpressured coal-bearing formation in Yuwang Minefield

The abnormal high pressure in coal and coalbed methane exploitation will bring danger to exploitation, thus threatening the safety of personnel and property.Six coal samples collected from Yuwang colliery in Yunnan province were analyzed by CT scanning and low-temperature liquid nitrogen adsorption experiment.Analysis reveals the characteristic parameters of pore radius, pore throat radius and pore volume-pore diameter differential distribution of overpressured coal samples.Meanwhile, the pore bulk modulus of overpressured coal samples under different confining pressures is derived based on the mechanism of the Gassmann model.The results show that the porosity of Yuwang colliery overpressured stratum can reach 10 %, and the mesoporous pore shape is mainly spherical and cylindrical.The shear wave velocity of dry coal samples increases nonlinearly with confining pressure.The pore bulk modulus of saturated coal sample remains proportional to confining pressure, but increases rapidly when the water saturation exceeds 90 % with the same confining pressure.