Reverse Circulation Drilling Method
Reverse Circulation (RC) Down the Hole Drilling (DHH) is a percussion drilling system that utilizes a dual-wall drill pipe that conveys the air to the hammer while discharging all soil and rock cuttings through the inside of the drill pipe to the surface. In RC drilling, the bit has holes that permit cuttings to travel up through the center of the drill pipe, rather than around the drill pipe or casing as in conventional down hole hammer drilling. Compressed air is supplied to the DHH through the dual-wall drill pipe, which provides the down hole hammer percussion energy and discharge air flow. The discharge air and the air exhausted from driving the hammer is used to evacuate cuttings from below the bit up to the surface through the drill pipe and discharge hose. (See Illustration.) The RC DHH system is also equipped with a casing driver unit to allow advancement of the casing ahead of the RC bit, should it be required.
