OA11327A

OA11327A - Drill bit.

Info

Publication number: OA11327A
Application number: OA1200000056A
Authority: OA
Inventors: Djurre Hans Zijsling
Original assignee: Shell Int Research
Priority date: 1997-08-28
Filing date: 2000-02-28
Publication date: 2003-12-09
Also published as: BR9811389A; WO1999011900A1; ID24483A; RU2206701C2; AU727657B2; EG21701A; GB2344842A; AU9537898A; CN1098400C; GB0003248D0; AR016883A1; GB2344842B; NO20000938L; CN1268991A; NO318151B1; NO20000938D0; CA2300158A1

Abstract

A rotary drill bit for drilling a borehole in an earth formation is provided. The drill bit comprises a plurality of cutting elements (7, 9) arranged to cut a plurality of substantially circular, radially spaced cuts (22, 24, 26) into the bottom of the borehole, the cutting elements including at least one cutting/shearing element (7), each cutting/shearing element being arranged so as to cut into the bottom of the borehole at an angular interval behind another one of said cutting elements (9). A body of rock material (28) is defined between the trajectories of the cuts created by the cutting/shearing element and said other cutting element. The cutting/shearing element is provided with means for shearing-off said body of rock material in the direction of the cut created by said other cutting element.

Description

011327

DRILL BIT

The présent invention relates to a rotary drill bit for drilling a borehole in an earth formation. In the prior art various types of drill bits are applied, for example roller cône bits or jet cutting bits. These drill 5 bits are generally provided with abrasive cutting éléments which are made of a material having a high wearrésistance, diamond or tungsten Carbide being for examplecommonly applied. The cutting action of these cuttingéléments mainly results from scraping of the éléments10 along the borehole bottom. The progress of the drill bit in the borehole (i.e. the speed of drilling) dépends onmany factors such as the amount of wear of the cuttingéléments, the hardness of the rock and the weight on bit.As the costs of drilling of a wellbore form a substantial15 part of the overall wellbore costs there is a continuous need to reduce the drilling time, viz. to increase thedrilling speed.

Accordingly it is an object of the invention toprovide a drill bit which allows an increased speed of20 drilling of a borehole in an earth formation.

In accordance with the invention there is provided arotary drill bit for drilling a borehole in an earthformation, the drill bit comprising a plurality ofcutting éléments arranged to eut a plurality of25 substantially circular, radiallyspaced cuts into the bottom of the borehole, the cutting éléments including atleast one cutting/shearing element, each cutting/shearingelement being arranged so as to eut into the bottom ofthe borehole at an angular interval behind another one of30 said cutting éléments, whereby a body of rock material is defined between the trajectories of the cuts created by 011327 the cutting/shearing element and said another cuttinci element, the cutting/shearing element being provided with means for shearing-off said body of rock material in the direction of the eut created by said another cutting 5 element.

The body of rock material can be sheared-off by thecutting/shearing element because 1) the other cuttingelement créâtes a first eut which forms a boundary forthe body of rock material to be sheared-off and 2) 10 because the first eut provides a space into which the body of rock material is moved by the action of thecutting/shearing element. Thus, the drill bit accordingto the invention performs both a cutting action and ashearing action, allowing the drill bit to remove15 significantly larger pièces of rock material from the borehole bottom than conventional drill bits. The speedof drilling is therefore significantly larger than forconventional drill bits.

Suitably the rotary drill bit further comprises a bit20 body and a plurality of roller cônes rotatably connected to the bit body so as to substantially roll along theborehole bottom, the axes of rotation of the roller cônesextending in different radial orientations, each rollercône being provided with at least one of said 25 cutting/shearing éléments.

Effective cutting and shearing-off of the body ofrock material is achieved if each cutting/shearingelement forms a dise cutter extending around the axis ofrotation of the roller cône to which the cutting element30 is provided.

Preferably each roller cône is provided with a set ofsaid dise cutters spaced along the axis of rotation ofthe roller cône, the sets of dise cutters of thedifferent roller cônes being displaced relative to each35 other in radial direction of the drill bit. 011327

The invention will now be described by way of example with reference to the accompanying drawings in which

Fig. 1 schematically shows a side view of a first embodiment of the drill bit; 5 Fig. 2 shows the right half of the first embodiment shown in Fig. 1;

Fig. 3 schematically shows a side view of a secondembodiment of the drill bit; and

Fig. 4 schematically shows a side view of a third10 embodiment of the drill bit.

In the Figures like reference numerals relate to likeéléments.

The first embodiment shown in Figs.1 and 2 of a drillbit 1 includes a bit body 3, a screw connector 5 for15 connecting the bit 1 to a drill string, and two opposite roller cônes Ί, 9 rotatably connected to the bit body 3whereby the axes of rotation 10, 11 of the roller cônes7, 9 are inclined in downward direction and intersectwith axis of rotation 12 of the bit 1 at intersection20 point 14. Alternatively, the roller cônes can be offset in the sense that the axes of rotation of the rollercônes do not intersect the axis of rotation of the drillbit 1. Roller cône 7 is provided with a set ofcutting/shearing éléments in the form of dise cutters 7a,25 7b, 7c, 7d, 7e and roller cône 9 is provided with a set of cutting/shearing éléments in the form of dise cutters9a, 9b, 9c, 9d, 9e. Each dise cutter has a cutting edgeextending perpendicular to the akis of rotation of rollercône 7, 9 to which the dise cutter pertains. The dise30 cutters 7a-d and 9a-d are arranged so that the envelope of contact points of the dise cutters with the boreholebottom has a convex shape.

The set of dise cutters 7b-e and the set of disecutters 9b-e are arranged staggered relative each other35 in radial direction of the borehole. Thus, when seen in C11327 radial direction,, the dise cutters 7b-e and the dise cutters 9b-e alternately contact the borehole bottom. To illustrate the staggered arrangement of the sets of dise cutters, the lower portions of the dise cutters 7b-e are 5 indicated in phantom between the lower portions of the dise cutters 9b-e. Thus, the dise cutters 7b-e assume thepositions shown in phantom when the drill bit 1 hasrotated 180° from the orientation shown in Fig. 1.

The radially outermost dise cutters 7a, 9a are10 arranged at substantially equal radial positions of the drill bit and are provided with (outer) insert cuttingéléments 16 at the side facing the borehole wall so as toeut a radially outer portion of the borehole. Similar(inner) insert cutting éléments 16 are provided at the15 inner end part of each roller cône so as to drill out the rock material located near the axis of rotation 12 of thedrill bit 1.

Each dise cutter has two side surfaces 18, 20defining a wedge-shaped cutting edge 17, as shown in20 Fig. 1 only, the other dise cutters having similar side surfaces and cutting edge. Each side surface 18 extendsperpendicular to the axis of rotation 10, 11 of theroller cône 7, 9 to which the dise cutter pertains.Thereby during drilling side surface 18 pushes against25 the rock in the direction of the point of intersection 14. Side surface 20 extends parallel to the axis ofrotation 12 of the drill bit 1 at the point of contactwith the borehole bottom.

In Fig. 3 is shown a second embodiment of a drill bit30 31 according to the invention which is largely similar to the first embodiment, the différence being that the drillbit 31 has three roller cônes 35, 37, 39, of which onlyroller cône 39 is shown here. The three roller cônes areoriented at 120° intervals and are similar to those of 011327 the first embodiment described with reference to Figs. 1 and 2. For ease of understanding only three dise cutters and no stabilisation cutters are assumed for each of the three roller cônes. It will be understood that in 5 practice any suitable number of dise cutters and stabilisation cutters can be provided at each rollercône. In the embodiment of Fig. 3, roller cône 35 has setof dise cutters 35a, 35b, 35c, roller cône 37 has set ofdise cutters 37a, 37b, 37c, and roller cône 39 has set of10 dise cutters 39a, 39b, 39c. The three sets of dise cutters are arranged staggered in radial direction of theborehole. Thus, when seen in radial direction, the disecutters 35a-c, 37a-c and '9a-c alternately contact theborehole bottom. To illustrate the staggered arrangement15 of the sets of dise cutters, the lower portions of the dise cutters 35a-c and 37a-c are indicated in phantombetween the dise cutters 39a-c. The dise cutters 37a-cassume the positions shown in phantom when the drill bit1 has rotated 120° from the orientation shown in Fig. 1,20 and the dise cutters 39a-c assume the positions shown in phantom when the drill bit 1 has rotated 240° from theorientation shown in Fig. 1.

In Fig. 4 is shown a third embodiment of a drill bit41 according to the invention which is largely similar to25 the second embodiment, the main différence being that the dise cutters are arranged so that the envelope of pointsof contact of the dise cutters with the borehole bottomhas a concave shape as opposed to the convex shape of thefirst and second embodiment. Furthermore, the side30 surface 18 of each dise cutter is oriented so as to push against the rock material in radially outward direction.Side surface 20 of each cutter (indicated by dottedUnes) extends parallel to the axis of rotation 412 ofthe drill bit 41. Three roller cônes 45, 47, 49 are 011327 provided, of which only roller cône 49 is shown, Four dise cutters and no stabilisation cutter are assumed for each of the three roller cônes. Again, it will be understood that in practice any suitable number of dise 5 cutters and stabilisation cutters can be provided at each roller cône. Roller cône 45 has set of dise cutters 45a-d, roller cône 47 has set of dise cutters 47a-d androller cône 49 has set of dise cutters 49a-d. Similarlyto the second embodiment, the three sets of dise cutters10 are arranged staggered in radial direction of the borehole.

To explain normal operation of the first embodimentreference is made to Fig. 2 showing the right half ofFig. 1. For the purpose of explaining normal operation of15 the drill bit 1 only three dise cutters 9c, 7c, 9d need to be considered, as the other dise cutters operate in asimilar way. During rotation of the drill bit in theborehole, the cutters 9c, 7c, 9d create adjacent cuts 22,24, 26 in the borehole bottom. In Fig. 2 these cuts are20 indicated as straight Unes, however in practice the cuts will hâve a shape corresponding more or less to thesection of the cutters penetrating the borehole bottom.Lines f-j indicate the envelope of the depth-levels ofthe dise cutters as a function of the rotation angle of25 the drill bit. Thus, when starting from 0° bit rotation at borehole depth level f, line g indicates the level at180° bit rotation, line h the level at 360° bit rotation,line i the level at 540° bit rotation and line j thelevel at 720° bit rotation. 30 When the bit has rotated 180° cutters 9c, 9d create cuts 22, 26 to depth level g (180° bit rotation). Ascutter 9c créâtes eut 22 in the borehole bottom, sidesurface 18 of cutter 9c pushes against a body of rockmaterial 28 in the direction of the bit axis 12, which 011327 body of rock material 28 is located between cuts 22 and 26. However, shearing-off of this body of rock material is hampered by the presence of dise cutter 9d in eut 26.

As the drill bit rotâtes to 360°, dise cutter 7c créâtes 5 eut 24 located between cuts 22 and 24. The dise cutters are now at depth level h, therefore eut 24 extends tolevel h. During cutting of eut 24 side surface 18 of disecutter 7c pushes against a portion 28a of the body ofrock material 28, which portion 28a is located between10 cuts 24 and 26. Now the presence of eut 26 allows the portion 28a of rock material to be sheared-off along linesi extending between eut 24 at level h and eut 26 atlevel g.

As the drill bit 1 rotâtes to 540°, cuts 22, 26 are15 deepened by dise cutters 9c, 9d to depth level i. Side surface 18 of dise cutter 9c thereby shears off portion28b of body of rock material 28 by virtue of the absenceof previously removed rock portion 28a. Shearing-off ofthis portion 28b occurs along line s2 extending between20 eut 22 at level i and eut 24 at level h. It will be clear that the cross-sectional shape of the boreholebottom at an arbitrary point in time during drilling isgoverned by the stepwise shearing-off of rock materialportions along Unes si, s2 etc. Therefore each line f-g25 in Fig. 2 only resembles the envelope of the dise cutters rather than the instantaneous shape of the boreholebottom.

As drilling proceeds rock portions 28c and 28d aresheared-off along respective Unes s3 and s4, in a30 similar manner as described with reference to rock portions 28a and 28b. Cutting and shearing-off of therock material by the other dise cutters of the drill bitproceeds in a similar way. Thus, the rock material at theborehole bottom is removed by a combination of cutting 8 011327 end shearing, âllowing la rge r rock psrticles to be removed from the borehole' bottom than by cutting alone (as is the case for conventional drill bits).

The radialiy outer portion of the borehole is drilled 5 out by the outer insert cutting éléments 16 at the radialiy outer dise cutters 7a, 9a and the centre portionof the borehole is drilled out by the inner insertcutting éléments 16 at the inner part of each rollercône. The outer insert cutting éléments 16 are subjected10 to cutting forces from the rock. The resulting cutting force component in a plane perpendicular to thelongitudinal axis of the bit acting on each insertelement 16 is pointing inwards from the bore hole wall,and the magnitude of the resulting force increases with15 the amount of radial pénétration of the insert element 16 into the bore hole wall. The total resulting force insaid plane is the vector sum of the resulting cuttingforces acting on ail outer insert éléments. When the bitis subjected to a displacement in a direction20 perpendicular to the centre line of the borehole, this vector sum will change in magnitude and hâve a componentwhich counteracts the displacement. Thus, if the drillbit pénétrâtes further into the borehole wall in oneradial direction than in any other radial direction, the25 déviation in the vector sum of the cutting force components in said plane counter-acts such pénétrationand thereby radialiy stabilises the drill bit duringdrilling. Similarly, the inner ihsert éléments 16 aresubjected to outwardly directed cutting forces from the30 rock at the centre portion of borehole bottom, and thereby also contribute to the radial stability of thedrill during drilling.

Normal operation of the second embodiment is similarto normal operation of the first embodiment, albeit that35 the rock material is sheared-off each 120° rotational 011327 interval of the drill bit instead of each 180° intervalas in the first embodiment.

Normal operation of the third embodiment is similarto normal operation of the second embodiment, albeit that5 now the rock material us sheared-off in radially outward direction of the borehole as a conséquence of the concaveshape of the envelope of points of contact of the disecutters with the borehole bottom.

Claims

011327 10 NEW CLAIMS J

1. A rotary drill bit for drilling a borehole in anearth formation, the drill bit comprising a plurality ofcutting éléments arranged to eut a plurality of substantially circular, radially spaced cuts into the5 bottom of the borehole, the cutting éléments including at least one cutting/shearing element, each cutting/shearingelement being arranged so as to eut into the bottom ofthe borehole at an angular interval of drill bit rotationbehind another one of said cutting éléments, whereby a 10 body of rock material is defined between the trajectories of the cuts created by the cutting/shearing element andsaid another cutting element, the cutting/shearingelement being provided with a side surface for shearing-off said body of rock material in the direction of the 15 eut created by said another cutting element, further comprising a bit body and a plurality of roller cônesrotatably connected to the bit body so as to sub-stantially roll along the borehole bottom, the axes ofrotation of the roller cônes being oriented in different 20 radial orientations, each roller cône being provided with at least one of said cutting/shearing éléments,characterized in that each roller cône is provided with aplurality of cutting inserts arranged to eut an outerradial section of the borehole.
2. The rotary drill bit of claim 1, wherein each cutting element forms a dise cutter extending around the axis ofrotation of the roller cône to which the cutting elementis provided.
3. The rotary drill bit of claim 2, wherein each dise 30 cutter has a wedge-shaped cross-section defining two side surfaces of the cutter, at least one of the side surfaces 011327 11 being arranged to push against said body of rock materialso as to shear-off said body of rock material therebyforming the means for shearing-off the body of rockmaterial.
4. The rotary drill bit of claim 3, wherein the other of said side surfaces extends parallel to the longitudinalaxis of the drill bit.
5. The rotary drill bit of any one of daims 1-4,wherein each roller cône is provided with a set of said 10 dise cutters spaced along the longitudinal axis of the roller cône, and wherein the different sets of disecutters pertaining to the different roller cônes arearranged staggered relative to each other along thelongitudinal axes of the roller cônes.
6. The rotary drill bit of claim 5, comprising a first roller cône having a first set of dise cutters and asecond roller cône having a second set of dise cutters.
7. The rotary drill bit of claim 6, further comprising athird roller cône having a third set of dise cutters.
8. The rotary drill bit of any one of daims 1-7, wherein each roller is provided with an outer disecutter, the outer dise cutters of the roller cônes beingarranged at substantially equal radial position of thedrill bit, each outer dise cutter having an outer surface 25 facing the borehole wall and being provided with said plurality of cutting inserts.
9. The rotary drill bit of any one of daims 1-8,wherein each roller cône is provided with a plurality ofinner cutting inserts arranged at the inner part of the 30 roller cône so as to eut a central section of the borehole.
10. The rotary drill bit of any one of daims 1-9,wherein the envelope of the cutting/shearing éléments atthe borehole bottom has a convex shape, and wherein each 35 means for shearing-off the body of rock material is I - 12 arranged to shear-off said bodyradially inward direction.
11. The rotary drill bit of anywherein the envelope of the eut 011527 of rock materiai in one of daims 1-10,ing/shearing éléments at the borehole bottom has a concave shape, and wherein eachmeans for shearing-off the body of rock materiai isarranged to shear-off said body of rock materiai inradially outward direction.