Wireline core drilling
In conventional core drilling jobs, the whole drill string needs to be pulled out of the bore holes to recover the core samples; while in wireline core drilling, no needs to remove the drill rods to recover each core sample. An overshot is sent down the hole to retrieve the inner tube, the overshot and inner tube are then brought up to the surface using a wireline hoist, allowing the rods and core bit to remain in the hole.
A complete set of wireline core drilling tools include drill rods, drill bits, core barrel assembly, overshot assembly, holding dog, hoisting plug, circle wrench etc. Wireline core drilling method is more common nowadays due to its' high penetration rate, high core recovery ratio and long bit life, hole drilling depth is increased clearly with these advantages, which makes core drilling jobs more efficient and safe.