This system consist by bringing up mud and debris through the rods and swivel head, from the bottom to the top of the borehole.
In this way, the fluid flows between the walls of the hole and the drill pipe and, along with the debris, generated by the bit, goes back to the surface, passing inside the pipes and trough the swivel head. Then drilling fluid and debris arrive to the sedimentation tank that is in direct communication with the borehole, in which they go down again and start a new cycle.
The reverse circulation system allows large diameter wells (up to 1000 mm or more) at average depth (400/600 m) without particular problems, preferably in alluvial soil, although it is also usable on a compact ground with smaller diameter (200 mm).
The drilling fluid used can be made of water and mud alone or mixed with bentonite with low viscosity and density, with the ultimate benefit for purging and development of the wells.
Major part of Ethiopia, for example, is provided with drinking water thanks to this working method, performed by Massenza drilling rigs.
With the first Massenza MI28 arrived in Bahir Dahr (Ethiopia), it was performed a hole with an initial diameter of 540 mm and 430 mm final diameter. These dimensions have led to the 294 mm rods installation along the entire depth of the hole. This large diameter allowed the use of the 196 mm submersible pump.
Massenza Drilling Rigs Company is one of the leading manufacturer of rigs in Europe and produces high quality and highly reliable machines since 1921, which are now present all over the wall.