Abstract: In view of the difficulties to obtain the clastic coal core when using the direct method to determine gas content of coal seam, the mathematic model of gas diffusion in taking clastic coal core was proposed in this paper, and the compensation for the methane desorption model was established by step-fitting calculation. In addition, the direct and rapid measurement method of original coal gas content has been achieved by using deep-hole coring technique and gas desorption method. The practice results show that the measured related factors of gas desorption volume and are basically above 0.99 when using step-fitting method to calculate gas diffusion. Moreover, the gas content and pressure of No.7th, 9th and 10th coal seam in Tongzi coal mine were measured, and the results accord well with the real situation of outbursts occurred many times in these coal seams. Thus, the theoretical and experimental studies mentioned above can accurately calculate gas content in coal seam, and provide a basis for predicting coal and gas outburst when using the prediction index of gas content.

Key words: clastic coal core, gas content, desorption, direct measurement method, compensation