The Improved Research On The Method To Determine The Emissions Radius Based On The Gas Flow Theory

Based on the theoretical of the coal seam gas flow, this paper systematically studied coal seam gas flow pattern and radial flow of gas drilling pattern. Referencing comparatively mature bottom-hole pressure calculating method of the reservoir development theory, this paper then calculated the drilling gas pressure change in periods of emission and hole sealing pressure measuring. On this basis, combining with radial flow theory of gas pressure, and transforming the solution of the two periods'calculation formulas, we got the calculating method of gas emissions radius. This method considers the original gas pressure coal seam, permeability coefficient or Permeability, Viscosity of gas mixture, isothermal compression coefficient and other parameters. As research shows, coal bed gas emission will increase in a certain extent along with the extension of observing time, but the effect is limited, and coal seam pressure, permeability coefficient or permeability have very apparent effect on the emission radius. First, since permeability coefficient and permeability have different dimensions, they are different in the process of computation. If the permeability coefficient is adopted, it is unnecessary to consider the viscosity of gas mixture, lots of verification results indicate that the isothermal compression coefficient of gas is very close to that of the ideal gas. So when the coal seam temperature is not so high (generally not higher than 40 degrees centigrade) and the gas pressure is not so large( often equals to or under 10 MPa),the coal seam gas can be considered as ideal gas.This paper also gives practical investigation to the calculation method of gas emissions radius, through a number of verification, the results show that this calculating method of the coal bed gas emission radius is of quickness and reliability.