Foam Drilling Tests and Analysis in Soft Coal Mines

Abstract

As coal resources in China are becoming scarcer, development and exploitation of soft coal seam is becoming more important. However, the existing technology of drilling of structurally loose soft coal seams is not well developed. A new technology, in which foamed fluid is injected for drilling, was developed and tested in four drill holes in the Zou coal mine, Huaibei. The problems of borehole collapse or pipe-sticking accidents that may occur in the drilling process and ways of their solution were analyzed. In field tests, drilling of hole 1 could not be completed because of lack of foam circulation perhaps because of resistance to foam flow due to high foam viscosity, small diameter of the triangular drill pipe used, and/or air pressure being too low to overcome resistance to foam flow. Drilling of the other three holes were completed to depths of more than 200 m, which demonstrated that the new foam drilling technology can be used to effectively increase drilling depth with reduced coal dust pollution.