Experimental study on rapid determination of critical value of drilling cutting gas desorption index K1

The field measurement for critical value of drilling cutting gas desorption index K is not accurate due to high gas loss caused by personnel operation , equipment performance , process defect , exposure time and borehole layout.The measurement error for K, could be as high as 30% .To solve this problem , this paper conducted laboratory experiments to study the correlation between the initial gas radation velocity index (△P) and( K, x P) .153 coal samples were collected from 59 coal mine of six regions , including Anhui , Shanxi , Guizhou, Henan , Chongqing , and Yunnan.The coal samples were tested to determine the critical value of measured ( K;) a.74.The power function of the undetermined cofficient A and the value of the undetermined cofficient B were also analyzed. Then the relationship between dilling cutting gas desorption index K; and gas radiation initial velocity index△P in six regions were analyzed. Furthermore,a mathematical model for( K)a.74-OP when gas pressure is 0.74 MPa for the six regions was established. The result shows that, compared to the measured ( K) 0.74 ,the maximum error of the modeled ( K) 0.74 is 17.87% and the minimum error is 0.53% .The maximum error less than 30% indi- cates that utilizing the model to determine the critical value of drilling cutting gas desorption index ( K) 0.74-△P critical value is accurate and reliable.The test results also show that under the same gas pressure ,K critical value mainly depends on△P which can be determined in laboratory in four hours.The ( K) 0.74-AP critical value model can rapidly and accurately determine the sensitive indicators of working face outburst ( critical value K) for coal seams in the same regions.This paper provides scientific basis and theoretical guidance for deter- mination of the critical value to evaluate effect of outburst prevention measures and outburst risk prediction.