STABILISER FOR BOREHOLE DRILLING APPARATUS

Abstract: A drill string stabiliser (10) for bore hole drilling apparatus, which comprises a plurality of fixed spiral blade arms (11) provided with replaceable wear elements (12).

Description: STABILISERFOR BOREHOLEDRILLINGAPPARATUS This invention relates to stabilisers for borehole drilling apparatus and more particularly to a drill string stabiliser having fixed blade arms provided with replaceable wear elements. Drill string stabilisers, sometimes referred to as drill collar stabilisers, or as drill stem stabilisers, are used in earth boring operations to centralise the drill stem in a borehole during drilling operations, especially in the drill collar section of the drill string, for example, at distances of from 0-300 metres above the drill bit. The drill string stabiliser has a variety of functions as follows: (i) to control the hole angle direction; (ii) to prevent the bit from drifting laterally; and (iii) to improve the cutting performance of the bit by keeping it rotating centrally about its axis so as to provide a substantially equal force loading on all three drill bit cones. In addition, where the surrounding rock formation is not too hard, the stabiliser may also provide a reaming function for undersized or irregularly shaped boreholes. This invention is particularly concerned with rotatable stabilisers of the kind which rotate together with the drill string. The wall-contacting members of a rotatable stabiliser are subject to the various forces attendant on the entire drill string, which may include thrust forces, fretting forces, and the forces resulting from drill string manipulations, the conditions of the borehole, and the fluid conditions internal and external to the drill string. In the rotary system of drilling, employing a liquid circulating through the drill string and through the annulus between the drill string and the borehole, it is necessary that the stabiliser includes not only fluid passage means therethrough to form part of the drill string flow passage, but also fluid passage means to form part of the annulus fluid passage. The annular fluid passage means are provided at the outer periphery of the stabiliser, with the result that the wall-contacting portion of the stabiliser is not continuous around the circumference thereof, but instead consists of a number of blades azimuthally spaced apart by the fluid passage means. It is known to provide fixed blade arms, incorporating wear elements, which are welded to the stabiliser, or to a sleeve surrounding the stabiliser, and such "welded-blade" stabilisers are disclosed in GB 2096210, US 2288124, and US 3263274, the entire disclosures of which are incorporated herein by reference for all purposes. It is also known to provide rotatable stabilisers with devices for connecting wear elements to fixed blade arms, enabling the wear elements to be detached and replaced. Such mechanisms include various slot and groove connections, cap screw connections, tapering wedging connections and combinations of these. Typical arrangements are shown in US 3680647 and US 3818999, the entire disclosures of which are incorporated herein by reference for all purposes. Whilst all the above patents are concerned with stabilisers in which the blades lie parallel to the axis of the drill string, there is another class of stabilisers, known as spiral blade stabilisers, for which no solution to the problem of providing replaceable wear elements has yet been found. According to the present invention, there is provided a drill string stabiliser for borehole drilling apparatus, which comprises a plurality of fixed spiral blade arms provided with replaceable wear elements. The stabiliser may be provided with any suitable number of spiral blade arms, but usually two or three are sufficient for most purposes. A larger number of blade arms can, however, be used if appropriate. The replaceable wear elements are preferably provided with seating portions on the side opposite to the working or wear face, which seating portions are located in longitudinal grooves or recesses in the external faces of the blade arms. The wear elements can comprise silicon carbide, or similar hard materials. Preferably, each spiral blade arm is provided with a single wear element, curved to form a segment of a spiral or helix, which extends for the full length of the working surface of the blade arm. The wear element preferably has a surface which is proud of the blade arm, and can, for example, extend to a radial distance of from 10 to 500 mm from the blade arm. The wear elements may be retained in the grooves of the external faces of the blade arms by any suitable means, but preferably the shoulders of the blade arms and the seating portions of the wear elements are provided with holes which, when the wear element is located in its groove, are aligned, such that a connecting means such as an elongate pin or similar device can be inserted into the holes to secure the wear element to the blade arm. Examples of spiral blade stabilisers provided with replaceable wear elements in accordance with the invention will now be described with reference to the accompanying Drawings in which: Figure 1 shows a side elevation of a prior art spiral blade stabiliser; Figure 2 shows a side elevation of a first embodiment of a spiral blade stabiliser according to the invention; Figure 3 shows a perspective view from the side and one end of a wear element suitable for use in a stabiliser of the present invention; Figure 4 shows a sectional end elevation of a spiral blade stabiliser according to the invention, illustrating three different types of seating for the wear element; and Figures 5(a) to (e) illustrate various securing devices by which the wear element can be secured to the spiral blade arm. Referring firstly to Figure 1, there is illustrated a prior art spiral blade stabiliser 1 having a body 2 provided with spiral blade arms 3 having wear surfaces 4. Spiral channels 5 are provided between adjacent blade arms to permit drilling fluid, carrying debris from the borehole, to pass therealong. Figure 2 illustrates a first embodiment of a spiral blade stabiliser according to the invention, in which the stabiliser 10 has blade arms 11 having wear elements 12 seated in grooves 13 in the blade working surfaces 14. Figure 3 shows a novel wear element for use in a stabiliser according to the invention. The wear element 20, which is curved in two directions in order to conform to the external surface of a spiral blade, has a working surface 21, and a wedge-shaped seating portion 22. The location of the wear element 20 on a spiral blade arm is shown in figure 4, top right hand side. The spiral blade arm 30 is provided with shoulders 31 defining a wedge-shaped groove 32 in the external surface of the blade arm 30. The wear element 20 is seated on the blade arm 30 such that the wedge-shaped seating portion 22 of the wear element fits tightly into the groove 32. Although the seating faces 33, 34 are shown as straight, they need not be straight, or symmetrical, and any suitable curved shape can be used as appropriate. The wear element 20 is seated proud of the blade arm 30 as shown. Figure 4 also illustrates an alternative seating arrangement. At the bottom right hand side there is shown blade arm 40 having shoulders 41 defining a wedge- shaped groove 42 with rounded bottom corners 43. The wear element 44 is seated with its wedge-shaped seating portion 45 in the groove 42, and is held tightly by the sides thereof such that it extends proud of the blade 40. Again, the sides do not have to be straight or symmetrical. Figure 5 shows various alternative arrangements for mounting and securing the wear elements to the blade arms of a stabiliser. In figure 5(a), the stabiliser blade arm 50 has shoulders 51 having aligned, transversely directed holes 52 therein. The flanged wear element 53 has a seating portion 54 in which there is a transverse hole 55 which is aligned with the holes 52 to provide a through passage. A tapered pin 56, which is a tight fit in the passage formed by the holes 52 and 54, is inserted therein to secure the wear element 53 in place. Figure 5(b) shows a second arrangement in which the blade arm 60 is provided with shoulders 61 having a passage 62 drilled transversely therethrough. The wear element 63 has a corresponding recess 64 drilled therein so as not to provide an obstruction to the passage 62 when the wear element is seated on the blade arm 60. A barrel nut 65 is positioned in the passage 62 and aligned such that its central threaded hole 66 is immediately beneath a bolt hole 67 in the wear element 63. The bolthole 67 is countersunk to accept a bolt 68 such that the head of the bolt 69 is below the working surface of the wear element 63. In Figure 5(c) there is shown a further mounting arrangement which is similar to that of Figure 5(a) except that the tapered pin 56 is replaced by a roll pin 70 and the shoulders 71 of the blade arm 72 have straight sides and curved corners to accommodate a similarly shaped seating portion 73 of wear element 74. Figure 5(d) shows a similar arrangement to that of Figure 5(c) except that in this case the groove 80 in the blade arm 81 is wedge-shaped to accommodate a wedge- shaped seating portion 82 of the wear element. Finally, Figure 5(e) shows a still further arrangement which is similar to that of Figure 5(c) except that the roll pin is replaced by a bent or cranked pin 90 fixed at one end to a locking plate 91 carrying a locking screw 92. Locking plate 91 and screw 92 fit within a recess 93 of the blade arm 94 and the locking screw is secured to the blade arm 94 via a screw threaded hole 95. The bent or cranked pin provides a radial force to maintain the flanged wear element 96 firmly secured to the blade arm 94 and its orientation is maintained by the locking plate and screw arrangement 91, 92. The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. The invention is not restricted to the details of the foregoing embodiment(s). This invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims: CLAIMS. 1. A drill string stabiliser for bore hole drilling apparatus, which comprises a plurality of fixed spiral blade arms provided with replaceable wear elements. 2. A stabiliser according to Claim 1, wherein the replaceable wear elements are provided with seating portions which are located in longitudinal grooves or recesses in the external faces of the blade arms. 3. A stabiliser according to Claim 1 or 2, in which the wear elements comprise silicon carbide. 4. A stabiliser according to any of the preceding claims, in which each spiral blade arm is provided with a single wear element which extends for the full length of the working surface of the blade arm. 5. A stabiliser according to any of the preceding claims, in which the wear elements extend to a radial distance of from 10 to 500mm from the blade arm. 6. A stabiliser according to any of the preceding claims, in which the blade arms are provided with shoulders defining longitudinal grooves or recesses in the external faces of the blade arms, and the shoulders and the seating portions of the wear elements are provided with holes which, when a wear element is located in its groove or recess, are aligned, such that a connecting means can be inserted into the holes to secure the wear element to the blade arm. 7. A stabiliser according to Claim 6, in which the connecting means is an elongate pin. 8. A stabiliser according to any of the preceding claims substantially as hereinbefore described with reference to and as illustrated in the accompanying Drawings. 9. A spiral blade stabiliser provided with replaceable wear elements substantially as hereinbefore described. 10. A wear element for a spiral blade stabiliser which comprises a working face, and a seating portion on the side opposite thereto, the wear element being of generally elongate shape and curved transversely to its longitudinal axis to form a segment of a spiral or helix. 11. A wear element according to Claim 10 substantially as hereinbefore described with reference to and as illustrated in the accompanying Drawings. 12. A wear element for a drill string stabiliser substantially as hereinbefore described.

Inventors: RUSSELL FREDERICK BRIAN, RUSSELL MARK ALEXANDER, RUSSELL, FREDERICK, BRIAN, RUSSELL, MARK, ALEXANDER
Applicants: CUTTING & WEAR RESISTANT DEV, RUSSELL FREDERICK BRIAN, RUSSELL MARK ALEXANDER, CUTTING & WEAR RESISTANT DEVELOPMENTS LIMITED, RUSSELL, FREDERICK, BRIAN, RUSSELL, MARK, ALEXANDER
Application year: 1997
Main classification: E21B17
IPC codes: E21B17