METHOD FOR CORE DRILLING Russian patent published in 1995 - IPC

FIELD: mining. SUBSTANCE: if drill pipes are installed above downhole motor, assembly of inserted tool is added with device 5 for its fastening. After adding insert tool, it is lowered onto bottom hole, core drilling is proceeded of pilot hole, and further on, repeated are operations: pulling out, extraction of core, change of drilling head and making connections. Total deepening of pilot hole with core extraction is effected through length larger than even number of footage per bit during reaming. After drilling of pilot hole, the latter is reamed. For this purpose, run to bottom hole by means of drill string 4 is inserted reamer with downhole motor 3. It is installed in shoe 7 of drill string 6 and drilling is continued. As the main hole is deepened, drill string is added. After work with reamer is over, it is pulled out to the surface by means of mud reverse circulation or by rope. Reamer is replaced, and reaming operation is repeated. Reaming of pilot hole is carried out through its entire depth and only part of hole equalling its five diameters is left not reamed. Core is continued to be extracted with periodic reaming. After the last reaming, full-hole drilling is undertaken. So, periodic motions of drill string 6 prevent it from sticking for the period of core drilling. EFFECT: higher efficiency of drilling due to prevention of drill string sticking. 3 dwg