| 摘要 |
<p>Drilling tool with a drill bit assembly, means of rotating this assembly and a tube surrounding part of the length of the bit. Mounted over at least part of its length, the tube has means of limiting the speed of rotation of the extracted mud relative to the speed of rotation of the drill bit assembly so the rotation of the drill bit assembly allows the vertical displacement of the mud into the tube The means of limiting the relative speeds of rotation acts mechanically and comprises an internal coating on the tube to produce a friction coefficient, or a helix with the same axis as the drill bit, placed between the edge of the drill bit and the tube and fixed or driven in rotation in the opposite direction to that of the drill bit. Alternatively, the means of limiting the speed of rotation is roughnesses (protrusions) or grooves on the internal face of the tube. The drill bit assembly has a first upper drill bit whose lower end extends below the lower end of the tube by a length L and a second drill bit with the same axis as the first placed and below the first. The means of rotation are therefore a first means for the first drill bit and a second means for the second drill bit. The length L is at least one pitch of the helix of the first drill bit. The external diameter of the second drill bit is the same as that of the tube. The first and second means of rotation can drive them in opposite directions.</p> |
