Application of quick sampling technology in deep hole at fixed point to test K₁ value of drilling cuttings gas desorption index

The K₁ value of drilling cuttings gas desorption index is an index that comprehensively reflects the gas content of coal seam and the gas desorption speed at the initial stage of pressure relief.It is a key parameter to determine the risk degree of local coal seam outburst, and plays an important role in preventing and controlling coal and gas outburst disasters.This paper aims at the problems existing in the process of sampling and testing K₁ value by using the sampling method of mechanical slag discharge of the drill pipe in coal mine, such as the inability to accurately determine the sampling location and exposure time of coal sample, the shallow effective testing depth, and the large error between the field measurement value and the actual situation.The reasonable and effective sampling depth of K₁ value is studied by using the deep hole quick sampling technology and equipment developed based on the reverse circulation drilling principle.The results show that the deep-hole fixed-point rapid sampling technology uses the central pipe of the double-wall drill pipe to discharge the coal sample at the bottom of the borehole quickly.The coal powder on the borehole wall is not mixed in the coal sample, which meets the requirements of fixed-point sampling and ensures the effectiveness of coal sample measurement.In addition, the time of obtaining sufficient number of coal samples is less than 2 min, which effectively reduces the exposure time of coal sample.The effective measurement depth of K₁ value and the accuracy of measurement results can be effectively improved.The effective testing depth of K₁ value of drill cuttings desorption index can be increased to 30 m by using deep hole quick sampling technology in Zhongheng Coal Mine and Wantian Coal Mine.