Research On Change Rule Of Initial Velocity Of Gas Emission From Borehole

Initial velocity of gas emission from borehole is one of the most important indexes for the coal and gas outburst prediction. It is related to the gas storage, the position and volume of the measuring chamber, and the airway resistance. The mathematical model of gas flow in the coal seam, gas flow into the measuring chamber, gas pressure change in the measuring chamber, and gas flow out of the chamber through the airway is established. Using the finite difference method, gas flow around borehole with measuring chamber is measured under dynamic boundary conditions. The variation rule of gas pressure in the measuring chamber and the gas flow quantity in borehole with time is obtained. The influence of gas storage and airway resistance on initial velocity of gas emission from borehole is analyzed. Results show that:When airway resistance, original gas pressure and permeability coefficient is not the same, the maximum value and appear time of gas flow quantity is different. Original gas pressure and permeability coefficient has great impacts on the value of gas flow in borehole. Airway diameter has great impacts in airway resistance on the value of gas flow in borehole. When the airway resistance is smaller, the gas flow quantity is bigger, and the initial velocity of gas emission from borehole is bigger too.