Patent ID: 8434570

Claim:
An element of a drill string for drilling a hole with circulation of a drilling fluid around the element and in a direction moving from a bottom of a drilled hole towards a surface, comprising: at least one zone for bearing on a wall of the hole during drilling, the bearing zone including externally at least one bearing section with an external diameter greater than the diameter of other portions of the element, and two first and second activation zones substantially adjacent to the bearing zone and disposed upstream and downstream of the bearing zone, respectively, the upstream and downstream being defined with respect to the direction of circulation of fluid around the element, the activation zones comprising a plurality of grooves generally helical in shape about the axis of the element, wherein the bearing zone comprises first and second guide sections in a form of a convex rounded body of revolution, disposed upstream and downstream of the bearing section and adjacent to the bearing section, respectively, the guide sections being externally tangential to the bearing section and to the activation zones, and wherein a diameter of the element adjacent to and upstream of the first activation zone and a diameter of the element adjacent to and downstream of the second activation zone are less than the external diameter of the bearing section.