Study into gas desorption law of coal in drilling mud during coring

Based on the self-constructed experimental equipment, the gas desorption of coal in drilling mud during coring are simulated. It has been proved that the beginning time of coal gas desorption during coring is related to gas pressure and mud pressure, and the gas desorption of coal in the medium of drilling mud is a nonuniform pressure desorption process with an increased velocity at first and an attenuated velocity afterwards. The gas desorption characteristics and law of coal in the medium of drilling mud is entirely different from those of coal in the medium of air. And it has also been proved that China's desorption method (DM) for coal gas content measurement exists some severe technical shortcomings in calculating gas-lost during coring in drilling mud.