A Rapid Method for the Determination of Coal Seam Gas Pressure Based on Raw Coal Adsorption

ABSTRACT The residual gas pressure of pre‐pumped coal seams is one of the key indices to check the effect of regional outburst prevention. The success rate in direct measurement is low, and it is generally obtained indirectly by use of the Langmuir equation, but it requires many test parameters, is time consuming, and prone to significant errors. To obtain the residual gas pressure of pre‐pumped coal seams more accurately and quickly, based on the theoretical analysis, an adsorption and desorption experimental device built by the authors was used to ascertain the gas adsorption constants of raw coal and applied to the calculation of coal seam gas pressure. The calculated gas pressure value was compared with the experimental gas pressure and the field measured gas pressure. The results show that under the constant temperature (consistent with the temperature of the coal seam) and natural recovery of gas pressure of coal samples, the adsorption constants a and b of raw coal gas are quickly measured by the adsorption/desorption and degassing equilibrium experiment. The relative errors of the calculated values of coal seam gas pressure with those measured by experiments and measured on site are 4.67%–9.43% and 2.78%–5.56%, respectively. Compared with the indirect method using the Langmuir equation, this method can exclude the influences of temperature and moisture on the pressure measurement results, requiring fewer test parameters and less time. Compared with direct pressure measurement in downhole drilling, this method does not require sealing of the hole and is not limited by the location of pressure measurement. The results offer a new method for coal mines to obtain the residual gas pressure in a pre‐pumped coal seam more accurately and quickly, and provide technical support for mining engineers who need to grasp situation around coal seam gas extraction situation and regional outburst prevention, and do so timeously.