WO1999005391A1

WO1999005391A1 - Drill string stabilizer

Info

Publication number: WO1999005391A1
Application number: PCT/US1997/018760
Authority: WO
Inventors: Robert A. Weiss; Jerry W. Welch
Original assignee: Weiss Robert A; Welch Jerry W
Priority date: 1997-07-25
Filing date: 1997-10-14
Publication date: 1999-02-04

Abstract

A stabilizer (10) for use in the rotary drilling of an earth borehole, including an elongate tubular body (12), at least three circumferentially disposed stabilizing blades (24) integrally formed on the body (12), each blade (24) having a first lateral wall (28) and a borehole-engaging surface (26), the intersection of said lateral wall (28) and borehole-engaging surface (26) forming a leading edge (34), each pair of adjacent blades defining a groove therebetween (32), a wear-resistant formation (38) positioned axially along each first lateral wall (28) at least along the lower end of each blade (24), said wear-resistant formation (38) having an exposed wear-resistant edge that is closely adjacent said leading edge (34), said wear-resistant formation (38) being formed of a material harder than that of said blade (24) and being free of any surface that projects radially outwardly of said borehole-engaging surface (26).

Description

DRILL STRING STABILIZER

Related Applications

This application is a continuation-in-part of Application Serial No. 08/900,169, filed July 25, 1997.

Background of the Invention

Field of the Invention

The present invention relates to rotary borehole drilling devices. More particularly, the present invention relates to a stabilizer for incorporation into a rotary drill string used in the rotary drilling of a borehole, such as an oil and gas well.

Description of the Prior Art

In the drilling of earth boreholes such as are required for oil and gas wells, it is common practice to use a rotating drilling bit driven by a long assembly known as a drill string. The drill string can consist of numerous elements, depending upon the type of well being drilled, interengaged by means of screwed connections. All of the drill string components contain a throughbore to transmit drilling fluid or mud under pressure to cool the bit, carry the cuttings, and/or operate a downhole mud turbine or hydraulic motor.

Almost invariably, one of the drill string components is a stabilizer that consists of a tubular body having screwed or other connections top and/or bottom for engagement with other drill string components, the stabilizer further including a plurality of ribs or blades that engage the wall of the borehole and that define radially opening grooves through which the return drilling fluid can pass upwardly through the borehole. Such a stabilizer may be used in the string located near the bit and/or in any other location intermediate of the length of the drill string. As is well known, virtually all of the drill string components, except for the bit and the stabilizer, have an outside diameter that is smaller than that of the hole being drilled.

One function of a stabilizer is to centralize the neighboring drill string components in the whole, thus preventing or reducing whip, vibration, and wear of other components. Particularly in recent years, an important function of stabilizers is to control the direction of drilling or change in direction in both elevation and azimuth. The latter function has become particularly important in drilling a number of directional wells from one site, e.g., an offshore platform, especially in so-called horizontal wells.

The outer surfaces of the stabilizer blades or ribs that contact the wall of the borehole form an interrupted cylinder. These surfaces (contact surfaces), which rub on the formation, are subject to wear, which can become particularly severe when the stabilizer is rotated at very high speed in hard and abrasive formations, such as occurs with a "near-bit stabilizer" used immediately above a bit driven by a downhole motor. As disclosed in U.S. Patent No. 4,081,203, one method of reducing wear on the contact surfaces of the blades is to insert plugs of hard material, such as diamond, into blind holes formed in the contact surfaces of the ribs such that the outer surface of each plug is substantially flush with the contact surface of the rib.

While this technique minimizes wear of the outer surface of the ribs of the stabilizer, it does not totally solve the problem of accelerated wear of the stabilizer blades caused by contact of the leading edges of the blades with the borehole walls. U.S. Patent No. 5,474,143 discloses a drill bit ream stabilizer wherein a stabilizer having spiral flutes and lands is provided with polycrystalline diamond layer inserts at a leading edge to provide a reamer, the inserts projecting radially outwardly from the spiral lands and adapted to ream a hole substantially the same size as the nominal size of the drill bit. The structures disclosed in U.S. Patent No. 5,474,143, as that disclosed in U.S. Patent No. 4,081,203, do not solve the problem of preventing wearing of the leading edges of the ribs or flutes, which invariably leads to wearing away of the metal that protects the hard surfacing on the contact surfaces of the blades, ultimately reducing the useful life of the stabilizer.

Summary of the Invention It is therefore an object of the present invention to provide an improved rotary drill string stabilizer.

Another object of the present invention is to provide a rotary drill string stabilizer that minimizes wearing of the leading edge of the stabilizer blades or ribs. Yet a further object of the present invention is to provide a rotary drill string stabilizer, particularly for use in highly deviated boreholes, e.g., horizontal boreholes, exhibiting enhanced wear resistance.

The above and other objects of the present invention will become apparent from the drawings, the description given herein, and the appended claims.

The rotary drill string stabilizer of the present invention includes an elongate, tubular body having a first end and a second end, typically the first end and the second end providing threaded connections whereby the stabilizer can be connected in the drill string. At least three, circumferentially spaced stabilizing blades or ribs are integrally formed on the body of the stabilizer, each blade having a first, lateral wall and a borehole-engaging surface, the intersection of which form a leading edge. Each blade also has a lower end adjacent the first end of the tubular member and an upper end adjacent the second end of the tubular member, each pair of adjacent blades defining a groove therebetween. A wear- resistant formation is positioned in each first lateral wall along the lower edge of each blade, the wear-resistant formation extruding axially along each of the first lateral walls such that an exposed wear-resistant edge is formed closely adjacent the leading edge of each blade. The wear-resistant formation is formed of a material that is harder than the material of said blade and is free of any surface that projects radially outwardly of the borehole-engaging surface.

Brief Description of the Drawings

The invention can be best understood with reference to the accompanying drawings in which:

Fig. 1 is a side, elevational view showing one embodiment of the stabilizer of the present invention; Fig. 2 is an end view taken along the lines 2-2 of Fig. 1;

Fig. 3 is a side, elevational view showing another embodiment of the stabilizer of the present invention;

Fig. 4 is an end view taken along the lines 4-4 of Fig. 3;

Fig. 5 is an enlarged, cross-sectional view taken along the lines 5-5 of Fig. 3; Fig. 6 is a fragmentary, side elevational view of another embodiment of the present invention;

Fig. 7 is a fragmentary, side elevational view of another embodiment of the present invention; Fig. 8 is a partial, side elevational view of a three-ribbed stabilizer of the present invention showing the staggering of three sets of wear-resistant inserts on the three ribs, respectively, and showing how in rotated elevation such staggering presents an essentially continuous wear-resistant edge formed by said inserts; and

Fig. 9 is a fragmentary, side elevational view of another embodiment of the present invention.

Fig. 10 is a cross-sectional view taken along the lines 10-10 of Fig. 9.

Description of the Preferred Embodiments

In the description given herein, like parts of different embodiments will be described with like numbers. With reference first to Fig. 1, the stabilizer shown generally as 10 is a generally cylindrical, tubular body 12, elongate in nature, and having an axial bore 14 extending generally centrally therethrough. For purposes of the description given herein, upper and lower will have reference to how the stabilizer would be positioned in the borehole; i.e., the upper portion or end of the stabilizer would be uphole while the lower portion of the stabilizer would be nearer the drill bit. Body 12 has an upper cylindrical shank 16 with a threaded box 18 formed therein and a lower cylindrical shank 20 on which is formed a threaded pin 22. It will be appreciated that in certain environments, e.g., in near bit usage, box 18 may be formed at the lower end of stabilizer 10 with the pin 22 formed at the upper end of stabilizer 10. Alternately, both ends of stabilizer 10 could use threaded box connections, such as box 18. Integrally formed, e.g., by machining, casting, or some other suitable technique, on body 12 are three circumferentially disposed and equally spaced blades or ribs, shown generally as 24, blades 24 projecting radially outwardly from body 12. Each of blades 24 has a borehole-engaging radially outermost surface 26 (contact surface), a first, lateral side wall 28, and a second, lateral side wall 30. In the embodiment of Fig. 1, the blades 24 are spiral in nature, each adjacent pair of blades 24 forming a spiral groove 32 therebetween. Lateral side wall 28 can be considered a leading side of blade 24 in the sense that in normal usage in a borehole, stabilizer 10 and the remainder of the drill string would be rotated in a clockwise direction when viewed from the top, i.e., looking down the borehole, or counterclockwise when viewed from the bottom, as shown in Fig. 21 by arrow A. Each of lateral side walls 28 and contact surface 26 on each blade 24 intersect to form a leading edge 34. As can be seen, blades 24 also include lower and upper and lower chamfered surfaces 27 and 29, respectively, that taper from the diameter of contact surface 26 to the diameter of lower shank portion 20 and upper shank portion 16, respectively. As can be seen, the contact surfaces 26 of blades 24 are essentially formed by hard surfacing material 36 in the form of rectangular tiles that are affixed to the hard blades 24 in the well-known fashion. It will be appreciated that the hard surfacing material 36 can be made of numerous different materials, such as, for example, tungsten carbide, diamond, cubic boron nitride, etc. Additionally, as taught in U.S. Patent No. 4,081,203, hard surfacing on the outer borehole-engaging surfaces of the ribs 24 may be accomplished by means of plugs of a hard metallic matrix having a plurality of diamonds held within the matrix, the plugs being located in blind bores in the outer surface of the blades, the outer surface of the plugs being generally flush with the outer borehole- engaging surface of the blades. Stabilizer 10 is also provided with a plurality of wear- resistant inserts 38, which are positioned in lateral wall 28 adjacent the leading edge 34 in a manner and for a purpose to be described more fully hereinafter.

With reference now to Fig. 3, there is shown another embodiment of the stabilizer, designated as 10a, which differs from stabilizer 10 in that the blades 24a are substantially straight, i.e., parallel with the axis passing through bore 14a. As can be seen, ribs 24a have lateral side walls 28a and 30a and outer borehole-engaging surfaces 26a carrying hard surfacing 36a (see Fig. 5). Hard surfacing tiles 36a are received into the outer borehole-engaging surfaces 26a of blades 24a such that the radially outermost surface of hard surfacing tiles 36 is substantially flush with the surface 26a of rib 24a. The hard surfacing tiles are likewise disposed in the contact surface of the blades 24 of stabilizer 10. Thus, the exposed portion, if any, of blades 24a and tiles 36 cooperate to form the contact surface. In general, stabilizer 10a, with the exception of the configuration of blades 24a forming straight grooves 32a, is, in all respects, the same as stabilizer 10. Accordingly, as noted, like parts have been numbered the same as the numbering used with respect to stabilizer 10.

As best seen with respect to either Figs. 2 or 4, the contact surfaces 26 and 26a of blades 24, 24a of stabilizers 10, 10a, respectively, form interrupted cylinders, i.e., interrupted by the grooves 32, 32a, respectively, formed between each adjacent pair of blades 24, 24a. It will be apparent that as the stabilizers rotate in the direction shown by arrows A, i.e., as viewed from looking at the bottom of the stabilizers, the contact surfaces 26 and 26a lie on a cylindrical surface having a diameter essentially the same as that of the borehole and, accordingly, will engage the borehole as the drill string is rotated. As a consequence, the leading edges 34 and 34a will be the first portion of the blades to contact the borehole for a given rotation of the stabilizers 10, 10a.

With reference now to Fig. 5, there is shown the positioning of the wear-resistant inserts 38a in stabilizer 10a, it being understood that inserts 38 with respect to stabilizer 10 are likewise positioned. Each insert 38 is received in a bore 50 formed in lateral wall 28a adjacent the leading edge 34a. The wear-resistant inserts 38 are positioned in the lateral side wall 28a adjacent the leading edge 34a, the inserts being disposed along each of the lateral walls 28a in axial juxtaposition to one another. As can be seen, inserts 38a have an exposed wear-resistant edge 52 that lies closely adjacent leading edge 34a. However, as can also be seen, no surface of insert 38 projects radially outwardly of contact surface 26a. More specifically, no surface of the wear-resistant formation, e.g., inserts 38, extends radially outwardly of an imaginary cylindrical surface formed by contact surfaces 26 rotated. This is an important feature of the present invention inasmuch as if the wear-resistant inserts had any portion that extended radially outwardly of the contact surfaces of the blades, the stabilizer would become a reamer and would enlarge the hole to above the desired gauge. As noted above, in the usual case the stabilizer and the bit gauge are the same. Allowing the stabilizer to ream a larger hole than is being drilled by the bit would, in many cases, permit the drill string to wobble with all of the undesirable side effects discussed above. It will be appreciated that the unique positioning of inserts 38 in the manner described prevents the metal 54 (broken away in further cross-section) of the blade 24a, which defines leading edge 34a, from wearing and hence ultimately prevents the hard surfacing tiles 38 from being dislodged or broken off. In this regard, since lateral wall 28a forms a leading wall, it will be appreciated that leading edge 34a lying on the interrupted cylindrical surface will be in greatest interference contact with the wall of the borehole and hence is subject to accelerated wearing. Without wear-resistant inserts 38a, the metal 54 forming leading edge 34a of blade 24a will eventually wear away, causing the hard surfacing tiles 38 to break away from surface 26a such that eventually the blades 24a will wear away to the point where the centralizing function of the stabilizer 10a will be effectively lost. Once the contact surface 26a of the blades begins to wear away, the cylindrical diameter of stabilizer 10a is reduced so that it is under gauge, i.e., smaller than the gauge of the drill bit and, accordingly, smaller than the gauge of the hole being drilled. This will allow wobbling of the drill string, resulting in erratic drilling direction, as well as increased fatigue failure of the drill string components.

As can be seen with reference to Figs. 1 and 3, the wear-resistant inserts 38 are disposed along the leading or lower end of the ribs 24, 24a, since it is these portions of the blades that are the most subject to wear as they encounter the walls of the borehole first during the drilling operation. Accordingly, it is this portion of the blades that is the most susceptible to rapid wearing, leading to premature failure of the stabilizers. However, if desired, wear-resistant inserts can be placed in the lateral walls along the full length thereof in the manner described above, i.e., positioned such that they are in axial juxtaposition and have an exposed wear-resistant edge that is closely adjacent and parallel to the leading edge. Such a stabilizer is shown in Fig. 7 as 10b, which structurally is essentially the same as stabilizer 10a, wear-resistant inserts 38 being positioned along the full length of wall 26a, including along the upper and lower chamfered surfaces 27a, 29a of the blades 24a. Fig. 6 shows another embodiment of the present invention wherein the stabilizer, shown generally as 10c, which structurally is essentially the same as stabilizer 10a, incorporates wear-resistant inserts 38 at the upper and lower ends of the blades 24; i.e., the wear-resistant inserts do not extend along the full length of the blades, as shown in Fig. 7. Positioning the wear-resistant inserts 38c at both the upper and lower ends of the stabilizer 10c protects the stabilizer contact surfaces from wear whenever the borehole is being back-reamed or when the drill string is being pulled out of the hole. It will be appreciated, for example, that if the drill string is pulled out of the hole, i.e., in the direction of arrow B, as the string is rotated, the upper end of the stabilizer 10c, i.e., adjacent chamfered surfaces 29, 29a and hence the upper ends of the blades 24a, will initially engage the borehole walls, with the result that wearing will be concentrated at the upper end of the blades 24a.

In a preferred embodiment of the stabilizer of the present invention, when wear- resistant inserts are used, the wear-resistant inserts on each of the blades are in a staggered relationship to one another, i.e, in the axially juxtaposed position such that when viewed in side elevation, rotated profile, the exposed wear-resistant edges of the inserts that lie closely adjacent the leading edges of the blades present an essentially continuous wear- resistant edge adjacent the leading edge of the blade. With reference then to Fig. 8, there are shown the three separate blades of a stabilizer, such as stabilizer 10a, in Fig. 3, the blades being indicated generally as 50, 60, and 70. As can be seen first with respect to blade 50, wear-resistant inserts 52 are positioned in the side wall 54. The inserts 52 are, as described above, in axial juxtaposition to one another and have an exposed wear- resistant edge 56 that lies closely adjacent leading edge 58. With reference now to blade 60, the wear-resistant inserts 62 are likewise positioned in the lateral wall 64, an exposed wear-resistant edge 66 lying closely adjacent the leading edge 68. Note, however, that inserts 62 are axially displaced relative to inserts 52. In like manner, with reference to blade 70, inserts 72 are positioned in lateral side wall 74 such that an exposed wear- resistant edge 76 of inserts 72 lies closely adjacent leading edge 78. Again, it will be noted that inserts 72 are axially displaced both with respect to inserts 62 on rib 60 and inserts 52 on rib 50. It will thus be appreciated that as the stabilizer is rotated, because of the staggering of the inserts on the individual ribs each with respect to one another, when the stabilizer is viewed in rotated profile, as shown at the far right of Fig. 8, a substantially continuous, almost straight wear-resistant edge 80 of wear-resistant material is presented. The "rotated overlapping" that occurs with inserts 52, 62, and 72 is clearly depicted on the right-hand side of Fig. 8.

While the invention has been described with respect to the use of three circumferentially and equally space stabilizing blades or ribs, it will be appreciated that more blades may be employed if desired, and indeed four-blade stabilizers are well known to those skilled in the art.

As used herein, the expression "closely adjacent said leading edge" and similar terms referring to the positioning of the wear-resistant edge of the wear-resistant formation relative to the leading edge is intended to mean that, depending upon the nature of the wear-resistant formation, the wear-resistant edge thereof is as close as possible to the leading edge such that the relatively soft metal forming the leading edge will be protected from any abrasion or wearing. Thus, while in the case of the individual inserts the wear-resistant edges thereof may not lie exactly adjacent the leading edge, they will be positioned as closely thereto as practicable, consistent with maintaining the structural integrity of the stabilizer blades and the inserts.

The wear-resistant inserts that are used in the present invention, although shown as cylindrical in shape, can be virtually any shape provided that no surface of the insert projects radially outwardly of the contact surface formed on the blade. However, for ease of installation, it is preferred that the inserts have a cylindrical shank that can be received in a cylindrical blind bore drilled in the lateral walls of the stabilizer blades. The portion of the wear-resistant inserts that forms the wear-resistant edge can be made of numerous materials that are harder than the material of the ribs to which it is attached. Preferably, the wear-resistant material will have a hardness of at least 60 Rockwell or greater. Suitable wear-resistant materials include tungsten carbide, polycrystalline diamond, cobalt boron nitride, etc. Wear-resistant materials that can withstand abrasion in hard formations and that can be bonded or otherwise affixed to mild steel, stainless steel, or the like are well known to those skilled in the art. The wear-resistant inserts can be made, for example, with a cemented carbide body or shank that is received in a bore in the stabilizer blade to which is bonded, directly or through an intermediate transition layer, a polycrystalline diamond layer. When used, the transition layer will generally comprise a composite material containing diamond crystal, cobalt, and pre-cemented tungsten carbide particles. In any event, in the usual case, the diamond crystal content of the composite material is greatest adjacent the wear-resistant or outermost surface and lowest adjacent the cemented tungsten carbide body or shank. While the invention has been described above with respect to the wear-resistant formation's being comprised of individual inserts, it is not so limited. With reference now to Fig. 9, there is shown another embodiment of the present invention wherein the wear-resistant formation comprises a continuous insert of wear-resistant material that is deposited, or somehow affixed, to the lateral walls adjacent the leading edge of the blades. With reference then to Figs. 9 and 10, there is shown a stabilizer 90 that structurally is in all respects essentially the same as stabilizer 10a and that includes a continuous wear-resistant formation 92 denning a wear-resistant edge 94 that lies closely adjacent the leading edge 34a of blade 24a. As shown, wear-resistant formation 92 is received in a groove 96 in wall 28a and extends the full length of blade 24a, much in the manner of the inserts 38 shown in Fig. 7. However, it will be appreciated that in the usual case, wear-resistant formation 92 would be positioned adjacent the lower end, i.e., adjacent shank 20 of stabilizer 90. It will be appreciated that while the wear-resistant formation 92 is essentially shown as having a rectangular configuration and cross-section and extending relatively deeply into side wall 28a, it will be appreciated that wear-resistant formation 92 could be formed using hard surfacing tiles 36 abutted in end-to-end relationship so as to lie along and parallel to the leading edge 34a. It will also be apparent that wear-resistant formation 92 can be formed of numerous materials, as described above with respect to wear-resistant inserts 38.

In general, whatever its configuration, be it individual inserts such as inserts 38 or a generally continuous formation such as 92, it is only necessary that the wear-resistant formation present wear-resistant edge(s) lying closely adjacent the leading edge, as defined above, such that any substantial wearing of the metal forming the leading edge of the blade can be eliminated or at least greatly reduced. Thus, with respect to a given blade, the wear-resistant edge can be a discontinuous series of wear-resistant edge segments, such as are provided by the wear-resistant inserts 38, or can be a continuous, uninterrupted wear-resistant edge, such as is provided by the use of wear-resistant formation 92.

The angle at which the inserts are positioned on the blade can be varied such that the wear-resistant inserts serve only to protect the leading edges of the blades or, in certain cases, such that the stabilizer can perform a reaming function. The latter would be desirable when, for example, the borehole has gone undergauge because of wearing of the bit or because of the particular nature of the formation, the borehole has essentially collapsed around the drill string. Accordingly, the angle can vary from about 0° to about 35°, as determined, as shown in Fig. 5, by the angle, α, determined by the intersection of a line x passing through the centerline of the stabilizer and a line y passing across the face 100 of the wear-resistant insert. As shown in Fig. 5, the angle is about 15 to 18°. It will be appreciated that at larger angles of about 20 to 35°, little or no reaming would occur, while at smaller angles, i.e., less than about 20°, the stabilizer would become more aggressive as a reamer in the cases noted above, i.e., when the borehole has gone undergauge because of bit wearing or there has been a collapse of the hole around the drill string. Preferably, the angle will be from about 15 to about 20 ° .

The foregoing description and examples illustrate selected embodiments of the present invention. In light thereof, variations and modifications will be suggested to one skilled in the art, all of which are in the spirit and purview of this invention.

Claims

What is claimed is:

1. A rotary drill string stabilizer for use in rotary drilling of an earth borehole comprising: an elongate, tubular body having a first end and a second end; at least three circumferentially spaced stabilizing blades integrally formed on said body, each blade having a first lateral wall and a borehole-engaging surface, the intersection of which form a leading edge, each blade having a lower end adjacent said first end of said tubular member and an upper end adjacent said second end of said tubular member, each pair of adjacent blades defining a groove therebetween; a wear-resistant formation positioned in each first lateral wall at least along the lower end of each blade, said wear-resistant formation being positioned axially along each of said first lateral walls, said wear-resistant formation having an exposed wear-resistant edge that is closely adjacent said leading edge, said wear-resistant formation being formed of a material that is harder than the material of said blade and being free of any surface that projects radially outwardly of said borehole-engaging surface.

2. The stabilizer of Claim 1 wherein said wear-resistant formation comprises a plurality of wear-resistant inserts, said inserts being positioned along said first lateral walls in axial juxtaposition, said wear-resistant inserts forming a plurality of discontinuous wear-resistant edge segments.

3. The stabilizer of Claim 1 wherein said wear-resistant formation forms a continuous wear-resistant edge.

4. The stabilizer of Claim 1 wherein said borehole-engaging surface comprises abrasion-resistant, hard surfacing material.

5. The stabilizer of Claim 1 wherein said blades are helical.

6. The stabilizer of Claim 1 wherein said blades are substantially straight.

7. The stabilizer of Claim 1 wherein said wear-resistant formation comprises a plurality of wear-resistant inserts, said wear-resistant edge comprising polycrystalline diamond.

8. The stabilizer of Claim 1 wherein said wear-resistant formation extends substantially along the full length of said blade.

9. The stabilizer of Claim 1 wherein said wear-resistant formation has a first portion extending along the lower end of said blade and a second portion extending along the upper portion of said blade.

10. The stabilizer of Claim 2 wherein each plurality of wear-resistant inserts is axially staggered with respect to one another such that a substantially continuous wear- resistant edge appears when said stabilizer is viewed in side elevation, rotated profile.

11. The stabilizer of Claim 10 wherein said wear-resistant edge segments comprise polycrystalline diamond.