Stabilizer device for bottom hole assembly

Abstract

A stabilizer device ( 20, 120, 220 ) for a drill stem, in particular for a bottom hole assembly, which is rotatable about a longitudinal axis (X), the device comprising a tubular central body ( 21 ) and connection means ( 22, 23 ) at its axial ends for connecting to elements of the stem, the device being provided with a helical protrusion ( 24, 25, 26 ) on the surface of the body intended to come into contact with a wall of the drilled hole, said helical protrusion turning in the clockwise direction (W) about the axis of the central body viewed from an upstream axial end in the direction of a downstream axial end, characterized in that a crest ( 33, 33′, 33″ ) of the helical protrusion comprises a leading edge ( 35, 35′ and 35″ ) and a trailing edge ( 36, 36′ and 36″ ) defined in the direction of rotation, the leading edge comprising a convex portion such that a first portion ( 38 ) of said convex portion has a radius of curvature of more than 3.5 mm over an angular arc of at least 20°.

1 . A stabilizer device ( 20 ,  120 ,  220 ) for a drill stem, in particular for a bottom hole assembly, which is rotatable about a longitudinal axis (X), the device comprising a tubular central body ( 21 ) and connection means ( 22 ,  23 ) at its axial ends for connecting to elements of the stem, the device being provided with a helical protrusion ( 24 ,  25 ,  26 ) on the surface of the body intended to come into contact with a wall of the drilled hole, said helical protrusion turning in the clockwise direction (W) about the axis of the central body viewed from an upstream axial end in the direction of a downstream axial end, characterized in that a crest ( 33 ,  33 ′,  33 ″) of the helical protrusion comprises a leading edge ( 35 ,  35 ′ and  35 ″) and a trailing edge ( 36 ,  36 ′ and  36 ″) defined in the direction of rotation, the leading edge comprising a convex portion such that a first portion ( 38 ) of said convex portion has a radius of curvature of more than 3.5 mm over an angular arc of at least 20°. 
     
     
         2 . A stabilizer device according to  claim 1 , characterized in that the convex portion is complex and comprises at least one second convex portion ( 39 ) adjacent to the first portion, said second portion having a radius of curvature which is smaller than that of the first portion, said second portion being located ahead of the first portion in the direction of rotation. 
     
     
         3 . A stabilizer device according to  claim 2 , characterized in that the convex portion extends over an angular arc of less than 180° and comprises a third portion, such that the second portion is disposed between the first and the third portion ( 40 ), such that said third portion has a radius of curvature which is greater than that of the first portion. 
     
     
         4 . A stabilizer device according to  claim 1 , characterized in that the parts of the convex portion are linked tangentially. 
     
     
         5 . A stabilizer device according to  claim 1 , characterized in that the crest of the helical protrusion forms an arc of a circle linked tangentially to the convex portion of the leading edge. 
     
     
         6 . A stabilizer device according to  claim 5 , characterized in that the circular arc has a diameter (OD 2 ) which is determined as a function of the theoretical diameter of the drilled hole at the well bottom; in particular, this diameter is determined by reducing the theoretical diameter by a minimum value of 1/64 inch. 
     
     
         7 . A stabilizer device according to  claim 1 , characterized in that the trailing edge comprises a second convex portion ( 41 ,  42 ) such that the crest of the helical protrusion forms a circular arc linked tangentially to this second convex portion. 
     
     
         8 . A stabilizer device according to  claim 1 , characterized in that it comprises a material with a substantially greater hardness than that of the helical protrusion, this material covering the crest and part of at least one of the leading edge and the trailing edge. 
     
     
         9 . A stabilizer device according to  claim 1 , characterized in that a housing ( 250 ) is formed at the crest of the helical protrusion in order to retain a roller which is free in rotation ( 251 ). 
     
     
         10 . A stabilizer device according to  claim 1 , characterized in that the helical protrusion forms a radial foot with a minimum width (Lmin) measured perpendicular to a bisecting line (B) such that this minimum width is smaller than the maximum width (Lmax) of said foot closer to the crest than the minimum width. 
     
     
         11 . A stabilizer device according to  claim 1 , characterized in that it comprises a concave zone ( 37 ,  37 ′,  37 ″) between a leading edge and a trailing edge. 
     
     
         12 . A stabilizer device according to  claim 11 , characterized in that each concave zone comprises a first concave portion ( 44 ) linked tangentially to the leading edge, said first concave portion having a radius of curvature which is smaller than that of a second concave portion ( 45 ) linked tangentially to the adjacent trailing edge. 
     
     
         13 . A stabilizer device according to  claim 12 , characterized in that the helical protrusions are spaced by a developed distance (d) which is less than the axial distance covered by the helix. 
     
     
         14 . A stabilizer device according to  claim 1 , characterized in that the helical protrusion turns through less than one turn about the body, in particular over a half turn. 
     
     
         15 . A stabilizer device according to  claim 1 , characterized in that the downstream axial end is attached directly to the drill bit. 
     
     
         16 . A stabilizer device according to  claim 1 , characterized in that the helical protrusion and the tubular body are produced in an integral manner. 
     
     
         17 . A stabilizer device according to  claim 1 , characterized in that the central body has a bore such that the minimum thickness of the wall of said central body represents more than 25% of the external diameter of said body.