Study and application on multi branch point sampling drilling technology of coal seam floor borehole

According to the technical requirements of long-distance gas parameter measurement, gas extraction borehole design guidance, and extraction evaluation for broken soft coal seam, the multi branch point sampling drilling method of coal seam floor borehole was proposedand its sampling drilling process was formulated on the basis of analyzing existing problems of sampling and drilling technology. Furthermore, the key drilling technologies such as accurate drilling trajectory control and “mechanical + hydraulic” efficient slag removal were developed. The equipment of drilling and sealed sampling were introduced. The application test was carried out in a coal mine in Suzhou, Anhui Province, in which the sampling borehole with a depth of 301 m was constructed, and spot sealed sampling drilling were carried out for two times, with the depths of 178 m and 238 m, respectively. The coal samples were successfully taken. The gas content of the obtained coal samples were 9.05 m³/t and 10.08 m³/t respectively. Compared with the conventional method, the measured gas content was increased by 12.4% and 25.2%, respectively. The technology can ensure the accuracy of coal seam gas parameter testing, providing a new technical way for broken soft coal seam sampling.