GB2397317A

GB2397317A - A rotary drag bit with cutter posts of particulate abrasive material

Info

Publication number: GB2397317A
Application number: GB0405546A
Authority: GB
Inventors: Volker Richert; Van Jordan Brackin; Matthew Ray Isbell
Original assignee: Baker Hughes Inc
Current assignee: Baker Hughes Holdings LLC
Priority date: 1999-11-29
Filing date: 2000-11-29
Publication date: 2004-07-21
Anticipated expiration: 2020-11-29
Also published as: GB0405546D0; GB2397317B; GB2397317A8

Abstract

A rotary drag bit (Fig. 1, 10) for drilling subterranean formations which comprises a bit body (Fig. 1, 12) having a face (Fig. 1, 16) extending from a centreline to a gage, optionally a plurality of blades 18 and a plurality of cutting structures 24 which consist of discrete posts protruding upwardly from the face or blades and comprise a particulate abrasive material and whose outermost end includes a formation engagement surface 26 which is parallel to a portion of the face or blade 30 to which the post is mounted. The particulate abrasive material may be synthetic or natural diamond grit. The bit body may be a matrix bit body. The cutting structures and blades may be integral with the bit body. The blades may extend radially-linearly, spirally or in serpentine-fashion over the bit face.

Description

1 2397317

IMPREGNATED BIT WITH PDC CUTTERS IN A CONE AREA

The present invention relates to fixed cutler or drag type bits for drilling subtena,ean formations. More specifically, the present invention relates to drag bits for drilling hard and/or abrasive rock formations, and especially for drilling such formations interbedded with soft and nonabrasive layers.

So-called "impregnated" drag bits are used conventionally for drilling hard and/or abrasive rock formatioris, such as sandstones. The impregnated drill bits typically employ a cutting face composed of superhard cutting elements, such as natural or synthetic diamond grit, dispersed within a matrix of wear resistant material.

As such a bit driiis, the matrix and diamonds wear, worn cutting elements are lost and new cutting elements are exposed. These diamond elements may either be natural or synthetic, and may be cast integral with the body of the bit, as in low-pressure infiltration, or may be preformed separately, as in hot isostatic pressure infiltration, and attached to said bit by brazing or furnaced to bit during manufacturing.

Conventional impregnated bits generally exhibit poor hydraulics design by employing a crow's foot to distribute drilling fluid across the bit face and providing only minimal flow area. Further, conventional impregnated bits do not drill effectively when the bit encounters softer and less abrasive layers of rock, such as shales. When drilling through shale, or other soft formations, with a conventional impregnated drag bit the cutting structure tends to quickly clog or "ball up" with connation material making the drill bit ineffective. The softer formations can also plug up fluid courses formed in the drill bit causing heat build up and premature wear of the bit. Therefore, when shale type formations are encountered, a more aggressive bit is desired to achieve a higher rate of penetration (ROP). It follows, therefore, that selection of a bit for use in a particular drilling operation becomes more complicated when it is expected that formations of more than one type will be encountered during the operation.

Thus it would be beneficial to design a drill bit which would perform more aggressively in softer less abrasive formations while also providing adequate ROP in harder more abrasive formations without requiring increased WOB during the drilling process.

The present invention comprises a rotary drag bit employing impregnated cutting elements in the fond of discrete, post-like, musically separated cutting structures projecting upwardly from radially extending blades on the bit face, the blades defining fluid passages therebetween extending to junk slots on the bit gage.

The cone portion, or central area of the bit face, is of a relatively shallow configuration and is provided with superabrasivc cutters in the form of polycrystalline diamond compacts (PDCs) having cutting faces facing generally in the direction of bit rotation. The PDC cutters provide superior performance in interbedded and shaley formations. Bit hydraulics is enhanced by the aforementioned fluid passages, which are provided with drilling fluid by a plurality of nozzles located in ports distributed over the bit face for enhanced volume and apportionment of drilling fluid flow.

In one embodiment, the blades extend generally radially outwardly in a linear fashion from locations within the cone at the centerline of the bit (in the case of blades carrying the PDC cutters in the cone), within the cone but not at the centerline, or at the edge of the cone, to the gage of the bit, where contiguous gage pads extend longitudinally and define junk slots therebetween. In another embodiment, the blades are curved and extend generally radially outwardly in a spiral fashion from the centerline (again, in the case of the blades carrying PDC cutters)' within the cone, or at the edge of the cone, to the gage of the bit and contiguous with longitudinally extending gage pads defining junk slots therebetween. The elongated nature of the spiraled blades provides additional length for carrying the discrete cutting structures so as to enhance redundancy thereof at any given radius.

FIG. 1 comprises an inverted perspective view of a first embodiment of a bit of the present invention; FIG. 2A is a schematic top elevation of portions of a plurality of blades of the bit of FIG. 1 carrying discrete cutting structure and FIG. 2B is a side sectional elevation taken across line B--B of FIG. 2A; FIG. 3 is an enlarged, inverted perspective view of part of the cone portion of the face of the bit of FIG. 1, showing wear of discrete, diamond grit-impregnated cutting structures and PDC cutters; FIG. 4 is a top elevation of the bit of FIG. 1 after testing, showing wear of the discrete cutting structures and PDC cutters; FIG. 5 is a top elevation of a second embodiment of the bit of the present im.enfior.; and FIG. 6 is an ir.vecd perspective view c,f the bit of Fi G. 5.

Referring now to FIGS. 1-3 of the drawings, a first embodiment lO the bit of t he present invention is depicted in perspective, bit 10 being inverted from its normal face-down operating orientation for clarity. Bit lO is, by way of example only, of 2159mm (81/2") diameter and includes a matrix-type bit body 12 having a shank 14 for connection to a drill string (not shown) extending therefrom opposite bit face 16.

A plurality of (in this instance, twelve (12)) blades 18 extend generally radially outwardly in linear fashion to gage pads 20 defining junk slots 22 therebetween.

Unlike conventional impregnated bit cutting structures, the discrete, impregnated cutting structures 24 comprise posts extending upwardly (as shown in FIG. l) on blades 18 from the bit face 16. The cutting structures are formed as an integral part of the matrix-type blades 18 projecting from a matrix-type bit body 12 by hand-packing diamond-grit impregnated matrix material in mold cavities on the interior of the bit mold defining the locations of the cutting structures 24 and blades 18. It is noted that the cutting structures 24 could be placed directly on the bit face 16, dispensing with the blades. However, as discussed in more detail belovv, it is preferable to have the cutting structures 24 located on the blades 18. It is also noted that, while discussed in terms of being integrally formed with the bit 10, the cutting structures 24 may be formed as discrete individual segments, such as by hot isostatic pressure, which are subsequently brazed or furnaced onto the bit 10.

Discrete cutting structures 24 are mutually separate from each other, to promote drilling fluid flow therearound for enhanced cooling and clearing of Connation material removed by the diamond grit. Discrete cutting structures 24, as shown in FIG. 1, are generally of a round or circular transverse cross-section at their substantially flat, outermost ends 26, but become more oval with decreasing distance from the face of the blades 16 and thus provide wider or more elongated (in the direction of bit rotation) bases 28 (see FIGS. 2A and 2B) for greater strength and durability. As the discrete cutting structures 24 wear (see FIG. 3), the exposed cross- section of the posts increases, providing progressively increasing contact area for the diamond grit with the formation material. As the cutting structures wear down, the bit takes on the configuration of a heavier set bit more adept at penetrating harder, more ab;^as.-vc fol. llations. Even if discrete cutting s+."c+urcs o4 wear completely away, the diai^llond-ii^l^lpre.ated blades 1 wi]' provide sortie cutting action, reducing any possibility of ring-out and having to pull the bit 10.

While the cutting structures 24 are illustrated as exhibiting posts of circular outer ends and oval shaped bases, other geometries are also contemplated. For example, while not depicted in the drawings, the outermost ends 26 of the cutting structures may be configured as ovals having a major diameter and a minor diameter.

The base portion adjacent the blade 18 might also be oval having a major and a minor diameter wherein the base has a larger minor diameter than the outermost end 26 of the cutting structure 24. As the cutting structure 24 wears towards the blade 18 the minor diameter increases resulting in a larger surface area. Furthermore, the ends of the cutting structures 24 need not be flat, but may employ sloped geometries. In other words, the cutting structures 24 may change cross sections at multiple intervals, and tip geometry may be separate from the general cross section of the cutting structure.

Other shapes or geometries may be configured similarly. It is also noted that the spacing between individual cutting structures 24, as well as the magnitude of the taper from the outermost ends 26 to the blades 18, may be varied to change the overall aggressiveness of the bit 10 or to change the rate at which the bit is transformed from a light set bit to a heavy set bit during operation. It is further contemplated that one or more of such cutting structures 24 may be formed to have a substantially constant cross-sections if so desired depending on the anticipated application of the bit 10.

Discrete cutting structures 24 may comprise a synthetic diamond grit, such as DSN-47 (RTM) Synthetic diamond grit, commercially available from DeBeers of Shannon, Ireland, which has demonstrated superior toughness to natural diamond grit.

The tungsten carbide matrix material with which the diamond grit is mixed to form discrete cutting structures 24 and supporting blades 18 is preferably a fine grain carbide, such as, for example, DM2001 powder commercially available from Kennametal Inc., of Latrobe, Pa. Such a carbide powder, when infiltrated, provides increased exposure of the diamond grit particles in comparison to conventional matrix materials due to its relatively soft, abradable nature. The base 30 of each blade is preferably formed of a more durable 121 matrix material, obtained from Firth MPD of Houston, Tex. Use of the more durable material in this region helps to prevent ring- out even if all of the discrete cutting structures 24 and t'ie major+; of each blade ' 8 It is noted, however, that alternative particulate abrasive materials may be suitably substituted for those discussed above. For example, the discrete cutting structures 24 may include natural diamond grit, a combination of synthetic and natural diamond grit. Alternatively, the cutting structures may include synthetic diamond pins.

Referring now to FIG. 4, the radially innermost ends of two blades 18 extend to the centerline of bit 10 and carry PDC cutters 32 in conventional orientations, with cutting faces oriented generally facing the direction of bit rotation. PDC cutters 32 are located within the cone portion 34 of the bit face 16. The cone 34, best viewed with reference to FIG. 1, is the portion of the bit face 16 wherein the profile is defined as a generally cone shaped section about the centerline of intended rotation of the drill bit 10. While both discrete cutting structures 24 and PDC cutters 32 are carried by the bit, as is apparent in FIGS. ] and 4, there is desirably a greater quantity of the discrete cutting structures 24 than there are PDC cutters 32.

The PDC cutters may comprise cutters having a PDC jacket or sheath extending contiguously with, and to the rear of, the PDC cutting face and over the supporting substrate. For example, a cutter of this type is offered by Hughes Christensen Company, a wholly-owned subsidiary of the assignee of the present invention, as Niagara.TM. cutters. Such cutters are further described in U.S. patent application Ser. No. 09/205,138, now U.S. Pat. No. 6,401,844 entitled CUTTER

WITH COMPLEX SUPERABRASIVE GEOMETRY AND DRILL BITS SO

EQUIPPED. This cutter design provides enhanced abrasion-resistance to the hard and/or abrasive formations typically drilled by impregnated bits, in combination with enhanced performance (ROP) in softer, non-abrasive founation layers interbedded with such hard formations. It is noted, however, that alternative PDC cutter designs may be implemented. Rather, PDC cutters 32 may be configured of various shapes, sizes, or materials as known by those of skill in the art.

Again referring to FIG. 4 of the drawings, bit 10 employs a plurality (in this instance, eight (8)) ports 36 over the bit face 16 to enhance fluid velocity of drilling fluid flow and better apportion the flow over the bit face 16 and among fluid passages 36 between blades is and extending to junk slots 22. lAl-lis enhanced fluid -VCilocity alAld anporionment helps prevent bit balling in shale formations, for example, wl-cl, phenomenon is known to significantly retard ROP. Further, in combination with the enhanced diamond exposure of bit 10, the improved hydraulics substantially enhances drilling through permeable sandstones.

Still referring to FIG. 4, an example of employing a conventional impregnated bit gage design in accordance with the present invention is disclosed. By way of illustration only, the gage pads of the illustrated embodiment may be approximately 3 inches long each comprising approximately 1.5 inches of thermally stable product (TSP) diamond and diamond grit-impregnated matrix, and approximately 1.5 inches of carbide bricks and K-type natural diamonds. Such an arrangement may likewise be applied to bits of differing diameters.

In operation, bit 10 according to the present invention would be run into a well and "broken-in" or "sharpened" by drilling into an abrasive formation at a selected WOB as the bit is rotated. For the first several feet of penetration, the diamond grit on the ends of the posts forming discrete cutting structures 24 becomes more exposed, as no substantial volurre of diamond is usually exposed on an impregnated bit as manufactured. Once the bit has been "sharpened" to expose the diamond grit at the outer ends 26 of discrete cutting structures 24, ROP stabilizes. It has been demonstrated in testing on a full scale laboratory drilling simulator that the inventive bit may exhibit an increased ROP over conventional impregnated bits. It has likewise been shown that the inventive bit may exhibit a substantially similar ROP to that of a conventional impregnated bit but at a reduced WOB.

Referring now to FIGS. 5 and 6 of the drawings, another embodiment 100 of the bit according to the invention is depicted. Features previously described with reference to bit 10 are identified with the same reference numerals on bit]00. It will be noted that there is a larger number of blades 18 on bit 100 than on bit 10, and that the blades 18 spiral outwardly from the cone 34 of bit 100 toward the gage. The use of the curved, spiraled blades 18 provides increased blade length and thus greater redundancy of coverage of discrete cutting structures 24 at each radius. it should also be noted that there are a larger number of ports 36 on bit face 16 for fluid distribution typically through nozzles (not shown) installed in the ports 36. The ports 36 within the cone 34 are preferably of larger diameter than Muse Outside of the cone 3.

Alterllatively, the blades 6 Allay be formed iil other shapes or pa++err. s. For example, the blades may be formed to extend outwardly from the cone 34 in a serpentine fashion, each blade forming an "S" shape as it travels across the bit face 16 toward the gage 20.

While the bit of the present invention has been described with reference to certain preferred embodiments, those of ordinary skill in the art will recognize and appreciate that it is not so limited. Additions, deletions and modifications to the embodiments illustrated and described herein may be made without departing from the scope of the invention as defined by the claims herein. Similarly, features from one embodiment may be combined with those of another.

Claims

1. A rotary drag bit for dollying subter anearl fo,,.,ations, comprising: a bit body having a face extending from a centerline to a gage; a plurality of cutting structures consisting of a plurality of discrete, mutually separated posts protruding upwardly from the face, each of the plurality of posts comprising a particulate abrasive material and having and outermost end which includes a formation engagement surface which faces in a direction which is substantially congruent with an orientation of underlying portion of the face.

2. The rotary drag bit of claim 1, wherein each of the plurality of cutting structures are integrally formed with the bit face.

3. The rotary drag bit of claim 1, further comprising a plurality of blades disposed on the face and wherein the plurality of cutters is disposed on the plurality of blades.

4. The rotary drag bit of claim 3, wherein each of the plurality of cutters are integrally fonned with the blades.

5. The rotary drag bit of claim 4, wherein at least one of the plurality of posts include bases of larger cross-sectional area than the outermost ends thereof.

6. The rotary drag bit of claim 4, wherein the particulate abrasive material comprises synthetic diamond ant.

7. The rotary drag bit of claim 4, wherein the particulate abrasive material comprises natural diamond grit.

S. The rotary drag bit of claim 4, wherein the bit body comprises a matrix bit body.

9. The rotary drag bit of claim 8, wherein the blades are integral with the bit body.

lO. The rotary drag bit of claim 8, wherein the plurality of discrete, mutually separated posts are comprised of a first meta] matrix material carrying a diamond grit and, wherein at least a portion of each blade is comprised of second matrix material.

11. The rotary drag bit of claim 10, wherein the first matrix material is softer and more abradable than the second matrix material.

12. The rotary drag bit of claim 11, wherein each of the plurality of gage pads is formed of a material comprising a thermally stable product (TSP) diamond.

i A. T he rotary drag b, of claim 12, -w-hc:-cirl each of Me plul ali+y of gage pads further comprises carbide bricks.

12. The rotary drag bit of claim 4, wherein each of the plurality of blades extend radially outwardly over the bit face a substantially linear fashion.

13. The rotary drag bit of claim 4, wherein each of the plurality of blades extend radially outwardly over the bit face in a substantially spiral fashion.

14. The rotary drag bit of claim 4, wherein each of the plurality of blades extend radially outwardly over the bit face in a substantially serpentine fashion.

15. The rotary drag bit of claim 4, further comprising a plurality of gage pads wherein each gage pad extends from an end of an associated blade of the plurality of blades.

16. The rotary drag bit of claim 15, wherein each of the plurality of gage pads is formed of a material comprising a thermally stable product (TSP) diamond.

17. The rotary drag bit of claim 16, wherein each of the plurality of gage pads further comprises carbide bricks. (c'

Amendments to the claims have been filed as follows

] . A rotary drag bit for drilling subterranean formations, comprising: a bit body having a face extending from a centerline to a gage the face including a cone portion surrounding the centerline; a plurality of blades protruding upward from a bit face and extending generally radially outwardly toward the gage to define a plurality of fluid passages between the plurality of blades, the plurality of blades being integrally formed with the bit body; a plurality of primary cutting structures located radially outwardly of the cone portion, the plurality of primary cutting structures consisting of a plurality of discrete, mutually separated posts protruding upwardly from the plurality of blades, each of the plurality of posts being impregnated with a particulate abrasive material and having an outermost end which includes a formation engagement surface which faces in a direction that is substantially congruent with an orientation of an underlying portion of an associated blade on which it is disposed, the plurality of posts being integrally formed with the plurality of blades.

2. The rotary drag bit of claim 1, wherein at least one of the plurality of posts includes a base of larger cross-sectional area than the outermost end thereof.

3. The rotary drag bit of claim 2, wherein the particulate abrasive material comprises synthetic diamond grit.

4. The rotary drag bit of claim lor claim 2, wherein the particulate abrasive material comprises natural diamond grit.

5. The rotary drag bit of any preceding claims, wherein the bit body comprises a matrix bit body.

6. The rotary drag bit of claim 5, wherein the plurality of discrete, mutually separated posts are comprised of a first matrix material carrying a diamond grit and, wherein at least a portion of each blade is comprised of second matrix material.

7 The rotary drag bit of claim 6, wherein the first matrix material is softer and more abradable than the second matrix material.

8. The rotary drag bit of any preceding claim, wherein each of the plurality of blades extend radially outwardly over the bit face a substantially linear fashion.

9. The rotary drag bit of any one of claims 1 to 7, wherein each of the plurality of blades extend radially outwardly over the bit face in a substantially spiral fashion.

l Q. The rotary drag bit of any one of claims 1 to 7, wherein each of the plurality of blades extend radially outwardly over the bit face in a substantially serpentine fashion.

11. The rotary drag bit of any preceding claim, further comprising a plurality of gage pads wherein each gage pad extends from an end of an associated blade of the phrality of blades.