Rapid measurement and its calculation of coal seam permeability coefficient under the condition of gas injection

The coal seam permeability coefficient is the main index to evaluate the effect of gas drainage, and also the most direct technical parameter to evaluate the effect of coal seam permeability.The rapid determination method of coal seam permeability coefficient and its corresponding calculation method were studied to solve the problem of its long measurement time.The mobile quick measuring instrument of the permeability coefficient of the coal seam was developed, and the measurement method of “drilling along the seam+mobile measuring instrument+gas injection” was proposed based on the principle of “in situ, dense, and fast” measurement.The inversion equation of the permeability coefficient of the coal seam was built based on the Darcy's law for the specific condition of measurement by “gas injection”,and the analytic equation of permeability coefficient of the coal seam in actual drill hole with the mathematical and physical method was derived, and the characteristic curve equation of the drill hole pressure was determined.The reproducibility of the rapid measurement method of coal seam permeability coefficient was verified by field measurement, and compared with the traditional calculation method of permeability coefficient of the coal seam.The results show that the variation law and basic characteristics of borehole pressure characteristic curve can be obtained by short time measurement and the rapid measurement method of coal seam permeability coefficient is feasible.The results of repeated measurement of the same borehole and the same measuring point are basically the same, which has good reproducibility, and the rapid measurement method proposed in this paper is reliable.The characteristic curve obtained from the measured borehole pressure curve is linear through coordinate transformation, which is completely consistent with the characteristic curve equation derived in this paper, and it is correct to solve the permeability coefficient of coal seam according to the characteristic curve.The permeability coefficient of coal seam is only related to the slope of borehole pressure characteristic curve, and the calculation method is simple.The calculation result of the method developed is basically consistent compared with the traditional permeability coefficient of coal seam calculation method, and it can meet the needs of practical engineering application.