[Music] the core drilling process includes three major operations the actual drilling the retrieving of the core sample and resuming of the drilling together this is called a round trip and for each round trip the drill hole is extended by the length of one or two drill rods there are two core drilling methods conventional and wire line the main difference lies in the method used for bringing up the core samples to the surface once the inner tube is full in conventional core drilling the entire drill string has to be pulled out of the drill hole in
each round trip in a 150 meter deep drill hole this could mean that the drill rod threads need to be broken and joined back again up to 50 times for each core sample in wire line core drilling a so-called overshot is sent down to release the inner tube the overshot and inner tube are then hoisted up to the surface with a wire a new inner tube is lowered down and locked in place this method is much more productive efficient and safe during the drilling process a drilling fluid is flushed down the drill string to cool
the drill bit and to transport the cuttings to the surface when the drill bit is worn out the whole drill string has to be taken out of the drill hole regardless of drilling method therefore choosing the right drill bit for the formation is extremely important for high productivity between each round trip the driller stores the core samples in core boxes the driller logs the time and date of the drilling as well as depth core recovery and possible losses these high quality core samples are the final goal of the core drilling process
