REAMER

摘要

The invention relates to a borehole underreamer, in particular for a hole below a well casing in the field of oil exploration, comprising a longitudinal body, a drilling fluid conduit, which is disposed longitudinally in the body and which is provided with a fluid flow section having an internal radius i, and at least two underreaming arms (5) which are supported by the body and which are provided with an active part (7) that is equipped with cutting means (8). The underreaming arms are arranged so as to slide between a rest position inside the body and partially outside the body in an active position (10). Said arms are guided and supported for this purpose in the body over a distance g and, when in the active position (10), project from the body by a length o, wherein values i, g and o are selected to satisfy conditions i + g + o = s simultaneously; 0.30 < i/s < 0.45, 0.40 < g/s < 0.60, 0.07 < o/s < 0.20.