The Computing Method Of Permeability Of Radial Gas Flow In Coal Seams

Based on the gas radial unsteady flow theory of boreholes in coal seam, a nonlinear second order partial differential equation of the gas radial unsteady flow can be deduced.Then with the help of the Matlab numerical simulation software, using the method of the prediction-correction algorithm, solve this nonlinear second order partial differential equation, and get the law of the gas radial unsteady flow. At the same time, simulate the gas pressure distribution of the boreholes in coal seam under different times and different permeability coefficients. Use the maturational theory of calculating the formation parameters by the method of buildup curve in oil and gas well test for reference, and then deduce theoretically the formulas of gas pressure recovery which are applicable in coal seam. And on this basis, deduce the fundamental formulas of pressure approach and pressure-squared approach which are used to calculate the permeability coefficients of coal seam.Combine with case studies, and compare with the radial flow method. It has been verified by comparing that the fundamental formulas which are deduced by pressure approach and pressure-squared approach are reasonable. And compared with the method of the radial flow method, the result which is got by the pressure-squared approach is more exact than the one which is got by the pressure approach. It is because that the gas pressure in coal seam is usually low(often equals to or under 14 MPa), and under this gas pressure, the gas flow process is more similar to the fluid flow process in gas well,both of them take the compressibility of gas into consideration.