STABILIZER FOR A DRILLING STRING

Abstract: A stabilizer for a drilling string comprises a one-piece metal loop (1), stabilizing blades (3), and tightening bolts co-operating with internally threaded bores (9) to draw the end portions (4) and (10) of the loop towards each other. The end portion (4) is formed with an involute camming surface (7) on which the end portion (10) rides to urge the end portion (4) resiliently inwards.

Description: This invention relates to a stabilizer for a drill string US 4,275,935 discloses a stabilizer for a drill string. The stabilizer is of a split configuration having an open slot which extends for the length of the stabilizer. The split stabilizer is slipped over a drill collar and nuts-and-bolts are used to draw the split stabilizer together to clamp the stabilizer to the drill collar. The stabilizer may thus be positioned at any desired axial location on the drill collar and non-rotatably locked thereto by the nuts-and-bolts. The stabilizer is made in one piece of a non-magnetic metal. This stabilizer is designed to bear evenly, in its clamped condition, upon a drill collar of a particular diameter around substantially the whole external periphery of the drill collar. However, differences in the external diameters of drill collars of the same nominal diameter can result in a less than optimum bearing of such stabilizer upon a drill collar, so that a desired immobilizing clamping force on the drill collar may not be obtained. To try to meet this difficulty, US 4,275,935 discloses that a shim of cylindrical form having an axially extending split can be utilized between the stabilizer and the collar. However, such a shim cannot cope optimally with a range of diameters and moreover constitutes not only an additional part but also a part that owing to its thinness is easily damaged in the very rough usage to which drilling equipment is normally subjected. EP0132192, corresponding to US4,611,839 and US4,639,020, discloses a segmented coupling for use in sealing adjacent pipe ends. The coupling includes two semi-circular coupling segments having bolting pads at their ends, the ends of each coupling segment including inclined, planar end faces for cooperation with correspondingly inclined planar end faces of the other coupling segment to produce self-adjustment of the coupling and firmer clamping of the pipe ends upon tightening down of the coupling. EP0194034, corresponding to US4653782, discloses a pipe repair clamp of a similar construction. According to the present invention, there is provided a stabilizer for a drilling string, comprising a one-piece metal loop having first and second opposite end portions, stabilizing blades fixed relative to the loop and projecting outwardly therefrom, and tightening means operable to displace the end portions towards each other, wherein the first end portion is formed with a curved camming surface inclined to the tangential sense of the loop, and having the curvature of an involute form of a circle whose constant is 1/π, the second end portion is arranged to ride on the camming surface, and the tightening means is operable to displace the end portions towards each other to cause the second end portion to ride on the camming surface, thus to cause one of the end portions to be urged resiliently inwards by the other of the end portions. An advantage of this present stabilizer is that tightening of the tightening means produces a clamping displacement of the loop not only in the direction of tightening of the tightening means but also in the substantially radial direction perpendicular thereto, so that improved bearing of the stabilizer upon a drill collar, for example, can be obtained and the use of shims can be avoided. An advantage of the use of a camming surface of such curved form is that, compared to a planar camming surface, a given clamping displacement in the direction of tightening produces a more nearly equal clamping displacement in the substantially radial direction perpendicular thereto. In order that the invention may be readily understood and readily carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:- Figure 1 shows a perspective view from one end of one embodiment of a stabilizer for a drilling string, Figure 2 shows a half elevation of the other end of a slightly different embodiment of stabilizer, and Figure 3 shows a half elevation of one side thereof. Referring to the drawings, the stabilizer comprises an open loop 1 of steel, which has an internal cylindrical surface 2 and which externally is formed integrally with stabilizing blades 3, which may be either rectangular-ended as shown in Figure 1 or radiused-ended as shown in Figure 3. One end portion 4 of the loop 1 is in the form of one of the blades 3 with a cut groove 5 in the free longitudinal edge of its root. Extending from one end to the other of that groove 5 and bounding the radially inner side of that groove is a tongue 6 of constant cross-section defined internally by the surface 2. The outer surface of the tongue 6 is in the form of a camming surface 7 which extends curvedly obliquely to the tangential sense of the loop 1. As can be seen from the drawings, the curved form of the surface 7 is outwardly bowed relative to the axis A of the loop 1, and the angle of inclination of the curved form to the radial direction from the axis A gradually increases as the distance of the curved form from the axis A gradually increases. The curve is of an involute form of a circle whose constant is 1 / π , to give the effect that a given clamping displacement in the direction of tightening of bolts 15 produces a substantially equal clamping displacement in the substantially radial direction perpendicular thereto. The other surface of the groove 5 is a planar surface 8 which extends in the chordal sense of the loop 1 and is formed perpendicularly with five cylindrical threaded bores 9 distributed along the groove 5. The other end portion 10 of the loop 1 is in the form of part of the material from the groove 5 and has an inner surface 11 of a form similar to that of the surface 7, and a planar surface 12 which is substantially parallel to the surface 8. Formed rough the portion 10 perpendicularly to the surface 12 are two internally threaded bores 13 and five oval plain slots 14, the items 13 and 14 being regularly spaced apart along the portion 10. However, the two bores 13 are arranged next inwards from the outermost slots 14. The bores 9 are aligned with the respective slots 14. In the position naturally taken up by the loop 1, there is a gap between the faces 8 and 12, and the face 11 extends to immediately adjacent to the surface 7. To clamp the stabilizer around a sleeve of a drilling string, first of all, and using an Allen key or a torque wrench, two bolts 15 are screwed into the respective threaded bores 13 and rotated to bear against the surface 8 and then to push the end portion 10 away from the end portion 4 to open out the loop 1 slightly. Then the stabilizer is applied co-axially over the end of the sleeve to a desired position longitudinally of the sleeve. Then the bolts 15 are removed and identical bolts (15, but not shown) are inserted through the slots 14 and screwed into the threaded bores 9 to pull the end portions 4 and 10 towards each other, in the process of which the surface 11 rides up the tongue 6 to cause the portion 4 to be urged resiliently radially inwards by the portion 10. The pulling of the portions 4 and 10 towards each other naturally reduces the internal diameter of the loop 1 parallel to the axes of the bolts, whilst the riding of the surface 11 up the tongue 6 reduces the diameter perpendicular to those axes, so to cause the surface 2 to press tightly against the outer surface of the sleeve round substantially its whole periphery. The positioning of the bores 9 and 13 and the slots 14 and their angle of inclination to the central axial plane of the blade 3 constituting the end portion 4 depends upon the outside diameter of the sleeve, i.e. upon the diameter of the loop 1, but the angle is advantageously between about 110° and about 140° for a sleeve outside diameter of between about 8″ and about 20″. It is selected so as to avoid excessive friction between the portion 10 and the camming surface 7 during clamping and to prevent any bending moment on the bolts.

Claims: A stabilizer for a drilling string, comprising a one-piece metal loop (1) having first and second opposite end portions (4,10), stabilizing blades (3) fixed relative to the loop (1) and projecting outwardly therefrom, and tightening means (9,15) operable to displace the end portions (4,10) towards each other, wherein the first end portion (4) is formed with a curved camming surface (7) inclined to the tangential sense of the loop (1), and having the curvature of an involute form of a circle whose constant is 1/π, the second end portion (10) is arranged to ride on the camming surface (7), and the tightening means (9,15) is operable to displace the end portions (4, 10) towards each other to cause the second end portion (10) to ride on the camming surface (7), thus to cause one (4) of the end portions (4, 10) to be urged resiliently inwards by the other (10) of the end portions (4, 10). A stabilizer according to claim 1, wherein the first end portion (4) is in the form of one of the blades (3). A stabilizer according to claim 2, wherein the said one of the blades (3) has a groove (5) in the free longitudinal edge of the root of the blade and the groove (5) is bounded by the camming surface (7) on a radially inner side thereof. A stabilizer according to any preceding claim, wherein the tightening means (9, 15) comprises externally threaded bolt means (15) through one (10) of the end portions (4, 10) co-operating with internally threaded bore means (9) in the other (4) of the end portions (4, 10). A stabilizer according to any preceding claim, wherein the positioning and orientation of the tightening means (9, 15) are selected to minimize friction between the camming surface (7) and the second end portion (10). A stabilizer according to any preceding claim, and further comprising loop-opening means (13, 15) operable to open out the loop (1), the loop-opening means (13, 15) comprises internally threaded bore means (13) through one (10) of the end portions (4, 10) and externally threaded bolt means (15) through that one (10) of the end portions (4, 10) and co-operating with the internally threaded bore means (13) for bearing against the other (4) of the end portions (4, 10).

Inventors: SWIETLIK, GEORGE
Applicants: SWIETLIK, GEORGE
Application year: 1987
Main classification: E21B17
IPC codes: F16B2, F16L7, E21B17