Study and application of dynamic inversion model of coal seam gas pressure with drilling

Abstract

The determination of gas pressure is a prerequisite for preventing coal and gas outburst. The traditional measurement method has some shortcomings, such as few test points, long test time and complicated process. In this paper, after analyzing the gas emission law of coal particle and the radial gas flow rule of borehole wall, a real-time and fast method for calculating gas pressure with drilling is proposed to establish gas pressure dynamic inversion model based on gas emission quantity of borehole, which is applied to inversion calculation of gas pressure in the directional drilling process. The results show that: (1) Inversion of gas pressure shows that the physical properties of coal seam and the characteristics of gas adsorption affect the amount of gas emission, resulting in different calculation results of gas pressure, which proves the uneven distribution of gas pressure the in coal seam; (2) According to the comparison results, the error range between the theoretical value and the measured value of gas pressure is from 3.6% to 18.1%, which indicates the correctness and reliability of the new model. The error is mainly influenced by the gas emission quantity of coal particle and the permeability coefficient of coal seam after gas desorption; (3) Field application results show that there are many abnormal regions of gas pressure in the coal seam because of geological structure existence. The research results have important practical significance for the analysis of distribution law of coal seam gas and the identification of gas outburst risk.