CA1260923A

CA1260923A - Revolving cutters for rock bits

Info

Publication number: CA1260923A
Application number: CA000531987A
Authority: CA
Inventors: George Fyfe; Kenneth W. Jones
Original assignee: Smith International Inc
Current assignee: Smith International Inc
Priority date: 1986-03-13
Filing date: 1987-03-13
Publication date: 1989-09-26
Also published as: NO871037L; EP0237359A3; BR8701601A; AU590826B2; NO871037D0; EP0237359A2; MX161103A; AU6998587A

Abstract

REVOLVING CUTTERS FOR ROCK BITS
ABSTRACT OF THE DISCLOSURE

A mechanism is disclosed for rock bits whereby cutting elements, rotatably mounted to fixtures with journals, are constantly forced to rotate or precess by the interaction of the earth formation and the cutter. The cutters are fixed in skewed or offset positions on a cutting face of a rotary drill bit head. These cutting elements act as drag or shear cutters when they are operated in an earth forma-tion.

Description

3~

REVOLVING CUTT~RS FOR ROCK BITS

BACKGROUND OF T~E INVENTION

1 Field of the Invention .
This invention relates to drag type rotary drill bits.
More particularly, it relates to drag tvpe rotary drill bits having cutters mounted to a cutting end of the drill bit, each of the cutters being rota~ably secured to fix-tures extending from the cutting end of the rotary drillbit.-

2. Description of the Prior Art There are a number of issued patents that relate to drag type rock bits as well as rock bits that are combina-tion drag bits and rotary cone bits.
All the prior art drill bits have failed to provide a relatively inexpensive drag bit with long lasting cutters that is not susceptible to early failure as the result of overheating or that prevent the balling of the cutters and the consequent reduction in the penetration rate.

.

;~t .

.

~ 3~
SUMMARY OF T~IE I~VENTION
It is an object of this invention to provide a practi-cal and inexpensive means to prolong the life of synthetic diamond and other hard cutting faces by limiting the cutting time of each segment against a borehole bottom.
Another object of this invention is to provide a means to prevent "balling" of the bit (buildup of debris adjacent the cutting face of the cutting segment).
These and other objects of the invention are accom-plished by ske~ing the face of a rotatable cutting discinsert at an offset angle to the radii from the axis of rotation of the rotary drill head. The cutting elements are rotatably mounted to a saddle, or insert base. Rota-tion of the bit will cause the cutting elements to slowly precess as they contact the borehole formation. This limits the exposure of the cutting discs, limiting the heat buildup that is particularl~ damaging.
To improve heat dissipation when using diamond cutting elements, a plurality of diamond inserts or natural diamond particles are embedded in the cutting face of a disc, the disc being rotatably secured within a saddle or support structure. As the bit body is rotated by the rotary table, downhole motor or any other prime mover connected to a drill string and drill bit, the cutter discs are caused to rotate due to the skewed angle of the saddle with respect to the radii from the axis of rotation of the drill string.
Each of the multiplicity of cutter segments, eauidistantly or randomly spaced as required around a disc, are exposed as the cutter disc slowly rotates.

Since fluid nozzles are fixed in the bit body, j(3~
fluid is directed toward the borehole bottom and, as thc cutters rotate, the fluid washes and cools the synthetic or natural diamond segments or particles adjacent the bottom of borehole.
In order to provide a rotating cutter element sturdy enough to withstand downhole conditions yet be capable of slowly precessing the cutter, a cutting disc is rotated on a journal that is supported by a pair of journal blocks.
Such a structure provides for a larger diameter cutting 10 disc causing slower rotation and consequent longer life.
This arrangement also permits selectability of the role of the cutter disc to provide for compressive or shear cutting forces on the formation.

.

~0

- 3 -3q~
BRIEF ~)ESCRIPTION OE THE DRAWINCS
Other objects and many of the attendant advarltages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying draw.ings in which like reference numerals, designate like parts throughout the figures thereof and, wherein:
FIGURE 1 is a perspective of a rock bit having cutters 10 structured to rotate;
FIGURE 2 is a perspective of the rear of one of the cutter elements from the rock bit of FIGURE 1;
FIGURE 3 is a cross section along 3-3 of FIGURE 2;
FIGURE 4 is a top plan view of a cutter and its placement on the head of the rock bit;
FIGURE 5 is a perspective of a rock bit having a preferred embodiment of cutters structured according to the present invention;
FIGURE 6 is a cross section of one of the cutter 20 elements shown in FIGURE 5;
FIGURE 7 is a plan frontal view of an alternate embodiment of a cutting disc according to the present ~`
invention;
FIGURE 8 is a plan frontal view of an alternate cutting aisc according to the present invention;
EIGURE 9 is a perspective of a rock bit showing an alternate preferred embodiment of cutter elements according to the present invention;

3q~t~
FIGURE 10 is a top view of the drag bit head showing placement of cutter elements according to the present invention;
FIGURE 11 is a side perspective of the drag bit and cutter elements shown in FIGURE 10;
FIGURE 12 is a side plan view of a cutter element that could be used in FIGURES 9, 10 and 11;
FIGURE 13 i5 an end view of the cutter element shown in FIGURE 12;
FIGURE 14 lS a side plan view o~ an alternate pre-ferred embodiment showing an alternate mounting for a disc cutter element according to the present invention;
FIGURE 15 is a perspective of a rock bit showing an alternate preferred embodiment of cutter elements according to the present invention;
FIGURE 16 is a side plan view of a cutter element used in the rock bit of FIGURE 15;
FIGURE 17 is an end view of the cutter element of FIGURE 16;
FIGURE 18 is a side plan view, partially broken away, of another embodiment of a cutter element;
FIGURE 19 is an end view of the cutter element of FIGURE 18; and FIGURE 20 is a front view of the cutter element of FIGURE 18.

-- 5~-DESCRTPTION OF THE PREFERRED ~A.BODIMEMTS ANr) BEST MODE FOR C~.RYING OUT THE :~NVENTION
.
Referring first to FIGURE 1, a drag bit, generally designated as l1, is rnodified to accommodate ~he cutter elements of the present invention. Drag bit 11 consists essentially of body 15 having a cukter face end 17 and a pin end 13. The pin end 13 is the shank of the bit tha-t connects to a drill string for rotation (not shown).
Although FIGURE 1 illustrates cutter face end 17 in an 10 upward direction from the pin end 13, it will be understood by all those skilled in the art that the face end, when in the hole will be in a downward direction from pin end 13.
The reader should bear this in mind as he follows through the descriptive portion of this patent specification.
Mounted on the cutter face 17 of bit 15 is a plurality of cutter elements, generally designated as 19, which generally lie on radial lines eY.tending from the center of the face 17 of the drag bit 15. Each of the cutter ele-ments 19 are comprised of an insert base or saddle 21 and a 2Q cutter segment 22.
The insert base 21 is preferably a tungsten carbide b]ock having an aperture 24 therethrough (FIG~RE 3). The base of the saddle 21 is preferably keyed with a slot 27 ~hich fits into an aperture and mating key formed in the face 17 of the drill bit. The saddle ~1 may be press or interference fitted into an aperture formed in the face or may be fastened by brazing or some other convenient fasten-ing means.
The cutter segment 22 is rotatably mounted within the 30 aperture 24 of the saddle 21. The structure of the cutter ~ 3~ ~
element 19 preferably comprises a suppor~ crclnk 25, which rotates within the journal aperture 24, bearing prirnarily against conical surface 24', formed on the end of the crank 25. The end of the crank 25 supports cutter elernent 22 mounted ~hereon. The crank 25 is contained within saddle block 21 by a keeper sleeve 23 tapered as sho~m in YIGURE
3. The keeper is, for example, brazed onto the shaft of crank 25 to maintain the crank and cutter in place within the saddle.
As shown in FIGURE 3, which is cross section along 3-3 of FIGURE 2, the saddle 21 has an aperture 24 therethrough which is a journaled bearing for the crank 25. The aper-ture 24 is tapered at both ends (12 and 14) in a manner which provides for both a rotary bearing and a thrust bearing surface. Tapered end 14 may support, for example, a conically shaped bearing sleeve 30O The sleeve may be fabricated from, for example, aluminum bronze, copper alloys or a spinodal alloy, all of which are suitable bearing materials.
Moreover, all of the bearing surfaces 12, 14 and 24 may be lined with a sleeve of bearing material as set forth above (not shown).
In a preferred embodiment, the cutter element 22 consists of a wafer of synthetic diamonds such as described in U. S. Patent No. 4,253,533, for example. As shown in FIGURE 3, the cutting wafer 22 is at a negative rake angle "A" which is the result of the face 28 of saddle 21 being slanted as shown. This negative rate angle creates a compressive cutting force against the bottom 16 of the - horehole which ten~s to crush more than slide away the earth formation.
The saddle 21 of each of the cutter elements 19 is mounted on face 17 of bit 11 along a radial line 32 (FIGURE

4). The vertical center 20 of cutting face 22 intersects the circumferential movement arc 31 and the perpendicular plane 29. However, the cuttiny face 22 does not lie on a plane that is parallel to the radius 32. It is, instead, skewed at an offset angle 33 from the radius 32. This skew angle preferably is at a significant angle~ The amount of s~ew is chosen on the basis of the speed at which the cutting ~ace is to rotate. The smaller the angle of skew, the slower the rotation of cutting element 22. Whether the cutting element 22 turns clockwise or counterclockwise is a matter of choice. The important limit is tha~ it is skewed from the radius of plane 32, causing forces to be exexted on the cutting element 22 as a result of the rotation of the drill face 17 which rotates the crank or body 25 of the cutter to rotate within the journal 24 in the saddle 21 IFIGURE 3) As a result of this rotation, a continually new diametrical portion of cutting element 22 is exposed to the earth formation being scraped away thereby helping to keep the cutting element 22, which is preferably synthetic diamond, cool and relatively clear of debris. Keeping this cutting element 22 cool prolongs the life of the cutting wafer a substantial amount, thereby creating a more effec-tive drag bit with a considerably extended life span. As is well ~nown, diamond subjected to extended periods of 30 high heat concentration will cause the diamond to ~ 3~
disintegra~,e -thus conti,nual movemen~, minimiY,es heat concen~
tration on the cutting edge of elernent 22.
Referxing now to FIGURE 5 which illus-trates a pre-ferred embodiment for the cutter elements according to the present invention, a drag bit 35 is shown having a bit face 39 at the end opposite threaded pin end 37. The cutting elements, generally designated as 41, are as effective as the cutting elements 19 shown in FIGURE 1. They have cutting face 43 at one end of the journal, a saddle 42 and a keeper 45 at the other end of the journal. Each of the elements are mounted along a radial 1ine which extends from the center of the face 39 of the drag bit 35 (not shown).
The face 43 is not covered with a cutting material. Only the circumference of the face 43 has a cutting material 51 equidistantly spaced and inserted thèrein (FIGURE 6).
As can be seen in FIGURE 6, a saddle 42 has a slanting face 47 with a journal 24 therethrough which is slanted (44 and 46) at the face and backsides to provide both thrust and rotary bearing surfaces. The crank 49 is constructed differently than the crank 25 of FIGURE 3 in that it is composed of a series of parts. The first part is a shaft 50 which provides a rotary bearing surface 26, preferably '~-of tungsten carbide material which is cast at end 48 of shaft 50 into cutting face 43, also preferably of tungsten carbide material. The face 43 has attached around its perimeter a plurality of equidistantly spaced cutter segments 51 of polvcrystalline diamond cutting elements, for example, which are fastened directly into the matri~ of the cutting end 43. The other end of the shaft 50 has brazed thereon a shaft keeper element 45. The cutting _ g 3 a~J~.~
element, as shown in FIGURE 6, provi~es for (ornp~ssiJe cutting forces primarily due to the negative r~ke angle ~s shown with respect to FIGURE 3.
Referring now to FIGURES 7 and 8, alternate configura-tions for the cutting face 43 are illustrated. Primaril~
what is shown is that the particular structure for the individual cutting segments 51, mounted along the circum-ference of the cutting face 43, need not be cylindrical.
FIGURE 7 shows cylindrical inserts 51. PIGURE 8 shows ~0 tri~ngular prisms 52 inserted into the circumference of the cutting face 43. Other shapes could also be used as desired. In addition, for example, these cutting sesments are spaced so that the entire circumference of the cutting face is covered by the cutting segment material.
Referring now to FIGURES 9, 10 and 11, other alternate preferred embodiments of the cutters built according to the present invention for use in a drag bit 57 are illustrated.
Drag bit 57 has a face 61 opposite to pin end 59~ Mounted on face 61 is a plurality of cutter elements 67 mounted for rotation about a shaft rotatively secured to journal blocks 63 and 65. The cutting face 73 of the cutter 67 is oriented relative to a radius extending from the center of the face 61 of the drag bit 57, as more clearly shown in FIGURE 10. The desired skew angle of cutting face 73 on each of the cutters 67 is skewed in the same manner as the cutting face 22 of cutting element 19 (FIGURE 4).
FIGURE 10 also illustrates fluid nozzles 77 located in the face 61 of drill bit 57 which causes drilling fluid to be washed across the cutting elements 73 to cool and clean ~ 3~
them as they precess during opera~ion of -the hit in a borehole.
Referring now to FIG~RES 12 and 13, an alternate structure for cutting elements 67 is illustrated. FIGURE
12 illustra~es the cutting face 73 of the cutter 67 which has a plurality of circular shaped cylinders 75 embedded around its perimeter in the manner shown. En~ 74 of cylinders 75 serves as the cutting face for cutter 67. The cutter 67 is mounted to a pair of bearing blocks 69 and 71 which provide both a thrust and a rotary bearing surface Inot shown). The cutter 67 rotates around the shaft which is held by bearing blocks 69 and 72. The shaft may either be journaled into bearing block 69 and 71 or may be fixedly attached into bearing block 69 and 71 with the cutter elements 67 rotating around the fixed shaft. The latter arrangement is preferred.
The cutter 67 comes to an apex 78 which is on the plane passing through the geometric center of the cutter 67. The sloped surfaces 73 and 74 are part of a truncated conical section that slopes awav from the apex 78. One end 74 of the cylinder cutting members 75 are mounted into and exposed at the cutting face side 73 while a small portion of the side of the cylinders 75 are exposed at the opposite side 79. Rotation of the cutter 67 causes different cutting cylinders 75 to come into contact with the formation being gouged away as the drill bit head rotates.
The cutter 67 is preferably of tungsten carbide. The cvlindrical shaped cutter elements 75 are preferably of synthetic diamond which are held fast in the matrix of the tungsten carbide cutter structure 67. The mounting or .

3~
bearing block 69, 71 are also pre~erably of tunqsten carbide or similar high streng~h material held fas~ ~co the face 61 of drill bit 57, either by press fi-t or some other well known technique, such as brazing for example.
Refer now to FIGURE 14. Another alternate preferred embocliment of a cutter element according to the present invention is illustrated. This embodiment is constructed - to provide a positive rake angle "B" thereby providing true shear forces for slicing away the earth formation 88. A
10 pair of bearing blocks 85 and 83 are utilized and are fastened-to the bit face 90. Mounted for rotation with these bearing blocks is a truncated cone shaped cutter 92 having a cutting face 94 which is the base of the cone~
The sides of the cone 91 are sloped at an angle 93 that is less than ninety degrees. The axis of rotation 89 of the cone cutter 92 is at an angle to the face 90 of the drill bit, creating a positive rake angle "B" with respect to the earth formation 88. The cone cutter 92 rota-tes about the axis of rotation as explained above. The journal blocks 85 and 83 are shaped to provide for both thrust and rotary bearing surfaces. The cone cutter 92 is preferahly con-structed of a hard material such as tungsten carbide. In the alternative, cutter elements may be located along its circumference in the manner illustrated for the embodiments of FIGURES 7-13.
Referring now to FIGURES 15, 16 and 17, an alternate preferred embodiment of a drag bit with cutter elements according to the present invention is illustrated. Drag bit 103 has a face 101 opposite pin end 105. Mounted on the face 101 is a plurality of disc shaped cutters, q~
generally designated as 107, each mounted to ,I pair of journal blocks 109 and 111. ~}le orientation of the cutt:in~
faces 112 of cutter elements 113 of cutters 107 is the sc~rne as the orientation of the cut-ters shown in FT~,UR~S 9, ]0 and ll.
The cutter elements 113 mounted in the cylindrical cutter 115 is an arcuate segment that is, for example, three-quarters of an inch between radial sides 117 and 119.
The inlaid segments 113 are approximately five-eighths of an inch thick. The diameter of the cylinder 115 for this size cf cutting segment is preferably four inches. The material variations of the cutter elements 113, the cylin-drical cutter 115 and the mounting blocks 109 and 111 are e~plained above. The cutting face 113 of the disc shaped cutter 107 is preferablv mounted at a negative rake ang]e "C" of up to forty-five degrees from the perpendicular to the face 101 of the drag bit in certain situations.
Referring now to FIGURES 18, 19 and 20, which illus-trate another emhodiment for the cutter elements according to the present invention. The cutting elements, generally designated as 241, are effective in particularly hard formations. This particulax embodiment has a toroidally `
shaped cutting face 243 at one end of the journal generally designated as 249. A saddle 242 is provided for journal 249 which provides a bearing surface 240 thereby. A
journal keeper 245 is provided at end 250 of journal 249.
At the opposite end of journal 249 is cutter end 243, the peripheral ed~e of which is rounded or toroidally shaped at periphery 252. The back side 260 of cutter end 243 is conically shaped and provides a bearing surface which mates .

against a complementary rna~ing surface 244 in saddle 242~ Bearing sleeves may b~ provided as set forth relative to FIGURE 3. The conical surfaces 260 and 244 serve to take the brunt of the thrust from the rotating cutter head 243 during operation of the cutter in a borehole. Similar conically shaped bearing surface 246 formed in saddle 242 is provided having complementary surfaces on the keeper 245 which retains the rotating cutter within the saddle 242. The rounded toroid surface 252 of cutter end 248 of the shaft 249 is covered with embedded natural or synthetic diamonds 251, the diamonds being mechanically fixed within a matrix of, for example, tungsten carbide applied to the end 248 of the shaft 249.
This process is well known within the art. The multi-plicity of natural or synthetic diamonds 251 covering the rounded peripheral edge 252 are particularly effective in hard formations as previously indicated. The cutter elements 241 are skewed from the radius of a plane as previously described which causes rotational forces to be 20 exerted on the cutter elements 243.
As stated beore, a continually new diametrical portion of the cutter element 241 is exposed to the earth ' formation being abraded away thereby helping to keep the cutter elements 241 cool and clear of debris. The multi~
plicity of natural or synthetic diamond chips 251 are vulnerable to heat as are the foregoing cutter elements, hence continual rotation of the cutter head 243 within its saddle block 242 is important to maintain the integritv of the diamonds on cutter end 243.

- ~4 -3~t~ .
``` FIGURE 19 illustrates the rear side of the cutter elements 241 showing the multiplicity of natural or syn-thetic diamonds 251 completely covcring the rounded toroid surface 252 of end 243.
FIGURE 20 lllustrates a front face view of the cutter - element 241 showing the outer toroidally shaped .surface 252 covered with natural diamonds 251. The center portion of the cutter end 243 is free of diamond cutter segments since it does not significantly contact any of the formation.
The end 240 of saddle 242 is preferably interference fitted within a hole formed in the face of a drag bit as previously described (not shown).

.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A rotary drag bit for drilling wells comprising:
a bit body rotatable about a central axis and including means for connecting the bit body to a drill string, said bit body having a face opposite to the drill string connection; and a plurality of drag cutters mounted on said face along respective radial lines emanating from said central axis and at different respective distances from the central axis for collectively scraping formation across substantially the entire bottom of a borehole being drilled, each drag cutter comprising:
a mounting block with bearing means at the end remote from the face of the bit body; and a cutter element with journal means mounted for rotation relative to said bearing means, said cutter element having a plurality of cutting segments embedded in a circumferential cutting face, the cutting face being skewed at an angle from a radial line from the central axis to the cutter element so that the cutter element pre-cesses as the cutting face contacts the borehole formation.

2. A rotary drag bit as recited in claim 1 wherein the mounting block comprises a saddle supporting both ends of a shaft and the cutting element is mounted on the shaft between the ends supported by the saddle.

3. A rotary dray bit as recited in claim 2 wherein the shaft is parallel to the face of the bit body.

4. A rotary drag bit as recited in claim 1 wherein the bearing means comprises an aperture in the mounting block and the journal means comprises a shaft extending through the aperture, with the cutting face being at one end of the shaft.

5. A rotary drag bit as recited in claims 1, 2 or 4 wherein the cutting face is skewed so that the side nearest the central axis of rotation extends further forward than the side remote from the central axis.

6. A rotary drag bit as recited in claims 1, 2 or 4 wherein the axis of said bearing means is at an acute angle to the face of the bit body.

7. A rotary drag bit as recited in claim 1 wherein the cutting face is toroidally shaped.

8. A rotary drag bit as recited in claim 7 wherein the cutting face has multiplicity of diamond particles embedded in at least the toroidal surface.

9. A rotary drag bit as recited in claims 1, 2 or 4 wherein the mounting blocks each comprise a tungsten carbide body inserted in the face of the bit body.

10. A rotary drag bit as recited in claims 1, 2 or 4 wherein the cutter element comprises a generally disc shaped tungsten carbide cutter having diamond cutters on its perimeter.

11. A rotary drag bit as recited in claims 1, 2 or 4 wherein the cutting segments comprise a multiplicity of diamond particles embedded in a tungsten carbide matrix.

12. A rotary drag bit as recited in claims 1, 2 or 4 wherein the cutting segments comprise generally cylindrical segments having at least a face of diamond.

13. A rotary drag bit as recited in claims 1, 2 or 4 wherein the cutting segments are generally triangular shaped prisms with at least one exposed end being diamond.