Selection of Supplement Gas for Active Pressure Measuring Method to Measure Gas Pressure of Seam

In order to select suitable gas for the active pressure measuring method to measure the compensation gas in the gas pressure of the borehole seam, fro m the study on the Absorbability of CH4, CO2 and N2 to the seam, the adsorption-desorption of CH4 and N2 to the seam was reversible and the adsorption-desorption of CO2 was irreversible. The paper analyzed that the CO2 as the compensation gas would influence the adsorption-desorption balance of the CH4.Finally, N2 was provi ded as the suitable gas as the compensation gas.The site practices showed that there was a certain error existed in the gas pressure measured with the CO2 as the Co mpensation gas and the error could be at 0.050 .20 MPa. When N2 as the compensation gas, the error is much smaller and the seam in-situ gas pressure could be accur ately measured.