Failure indicator for rolling cutter drill bit

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. Provisional Patent Application No. 60/227,336 filed Aug. 23, 2000.

BACKGROUND OF INVENTION

1. Field of the Invention

The invention relates generally to rolling cutter earth boring drill bits used for the exploration and retrieval of petroleum and other minerals from the earth. In particular, the invention is a new form of bearing failure indicator for a rolling cutter earth boring drill bit.

2. Description of the Related Art

It is commonplace during drilling into the Earth for minerals such as oil and natural gas to drill boreholes thousands of feet deep. A rolling cutter drill bit used to drill these wells is so remote from the surface that even high quality instrumentation located near the bit while drilling is not able to accurately indicate the impending failure of the bearing in the drill bit. Oftentimes the drill bit fails suddenly and causes the drilling operation to be halted while the “junk” left behind by the failed bit is removed from the bottom of the borehole. The time lost in recovering this junk may cost the drilling company many thousands of dollars, and unless all the junk left by the failed bit is recovered, the replacement drill bit may also fail prematurely from damage by the junk.

Detecting impending bit failure is particularly difficult with rolling cutter type drill bits that utilize sealed and lubricated friction bearing systems. The reason for this is that when these bits first experience bearing failure, only relatively minor changes in drilling torque and drilling rate of penetration occur. Since these changes are usually within the range of normal torque and ROP variations, the bearing failure is usually not detected at the surface.

Often, the only indication of failure is the sudden decrease in drilling rate of penetration that occurs when bearing failure is total and junk is left in the hole. Although instrumentation packages built into measuring while drilling tools may at times be able to accurately detect impending bit failure, they are not able to detect it reliably. Furthermore, these MWD packages often add considerable expense to the drilling operation, and are therefore used sparingly. Consequently, it is highly desirable that any bearing failure mechanism be made into the drill bit.

Bearing failure indicator schemes are disclosed in numerous different rolling cutter drill bit designs, including U.S. Pat. Nos. 3,058,532, 3,011,566, 3,062,302, 3,363,702, 3,678,883, 3,853,184, 4,346,591, 4,436,164, 4,548,280, 4,655,300, 4,785,894, 4,785,895 and 5,183,123, all incorporated by reference herein for all they disclose. The complexity of these designs, and/or their tendency to falsely indicate a bearing failure have limited their utility. In fact, these designs have had only limited commercial success.

SUMMARY OF INVENTION

A new type of bearing failure indicator for sealed and lubricated rolling cutter drill bits is disclosed. The rolling cutter drill bit comprises a bit body adapted for rotation about a longitudinal axis, a plurality of extending legs, and a cantilevered bearing spindle formed on each leg. A plurality of rolling cone cutters are rotatably mounted upon the bearing spindles with the cone apices adjacent to the longitudinal axis of the bit. A plurality of cutting inserts are secured in the rolling cone cutters, and arranged in a plurality of rows. At least two of the rolling cone cutters are intermeshing cutters, arranged such that they have intermeshing rows of cutting inserts. At least one of the intermeshing cutters has at least two rows of cutting inserts arranged as two inner rows. A groove is formed intermediate the two inner rows. Within the groove is a row containing a plurality of generally flat top bearing inserts.

In the normal operation of the drill bit, the rows of generally flat top bearing inserts do not contribute to the drilling action of the drill bit. However, when a bearing assembly fails in operation, the generally flat top bearing inserts engage the intermeshing rows of inserts in the adjacent intermeshing cutter.

This engagement causes a sudden, relatively large increase in the drilling torque of the drill bit. This torque increase is readily discernable at the drill rig by the drilling crew, providing a reliable indication of a failed bearing. The disclosed arrangement provides an extremely reliable means of indicating a failed bearing in a rolling cutter drill bit.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1

is a perspective view of a rolling cutter drill bit of the present invention.

FIG. 2

is a cross section view of a rolling cutter mounted on one of the legs of a rolling cutter drill bit of the present invention.

FIG. 3A

is a perspective view of one of the rolling cutters of a rolling cutter drill bit of the present invention.

FIG. 3B

is a partial cross section view of one of the cutters of a rolling cutter drill bit of the present invention showing the mounting and orientation of the cutting inserts.

FIG. 4

is a layout view of the three rolling cutters showing the operating arrangement and intermeshing of the cutting inserts.

FIG. 5

is a layout view of the three rolling cutters showing the arrangement and intermeshing of the cutting inserts after one of the bearings has failed.

DETAILED DESCRIPTION

Referring now to the drawings in more detail, and particularly to

FIGS. 1 and 2

, a rolling cutter earth boring drill bit

10

includes a body member

12

adapted for rotation about a longitudinal axis

8

. A plurality of extending legs

14

depend from the bit body

10

. Formed on each leg

14

is a cantilevered bearing spindle

16

which extends inwardly, toward the longitudinal axis

8

of the drill bit

10

. Rotatably mounted on each bearing spindle

16

are rolling cone cutters

17

,

18

, and

19

. The rolling cone cutters

17

,

18

, and

19

have cone apices

15

oriented so they are adjacent to the longitudinal axis

8

of the bit. Secured to a typical rolling cone cutter

18

are cutting inserts

20

, which in operation engage the earth while the bit

10

is rotated about its longitudinal axis

8

. The rotation of the drill bit

10

causes rotation of the rolling cone cutters

17

,

18

,

19

as they engage the earth to effect a drilling action.

Internal passageways

22

,

24

, and

26

, as well as a reservoir

28

and bearing area

30

of the leg

14

, are filled with lubricant (not shown) during bit assembly. The lubricant helps reduce bearing friction and wear during bit operation and is retained within the cutter

18

by a seal assembly

32

. Pressure differentials between the lubricant and the external environment of the drill bit

10

are equalized by the movement of a pressure balancing diaphragm

34

.

A sliding bearing member

36

is mounted between the spindle

16

and a mating bearing cavity

38

formed in the cutter

18

. This bearing

36

is designed to carry the radial loads imposed upon the cutter

18

during drilling. A second bearing member

42

is configured as a split threaded ring which engages internal threads

40

in the bearing cavity

38

of the cutter and a groove

44

formed in the bearing spindle

16

. This second bearing member

42

serves to retain the cutter

18

upon the bearing spindle

16

by resisting the forces which tend to push the cutter

18

inward, toward the longitudinal axis

8

of the bit, during drilling. A thrust bearing member

46

is disposed between the bearing spindle

16

and the cutter

18

. This bearing member

46

carries the onward thrust forces imposed upon the cutter

18

during drilling.

Although the particular configuration of the rolling cone cutter

18

on the leg

14

shown in

FIGS. 1 and 2

is typical for many rolling cutter drill bits, many other variants are possible without departing from the scope and spirit of the present invention. For example the second bearing member

42

may comprise a plurality of steel ball bearings. The sliding bearing member

36

could be the direct contact of the rolling cone cutter

18

on the bearing spindle

16

. The seal assembly

32

could be a rigid face seal, an elastomer coated elastic sealing element, or any other suitable seal design. Finally, numerous configurations for the lubricant system may be possible, including the absence of the lubricant system including the internal passageways

22

,

24

, and

26

, and the reservoir

28

, as well as the seal assembly

32

. The particular configuration shown and described is provided only to aid in the understanding of the present invention.

The cutting inserts

20

are fitted into sockets formed into the surfaces of the cutters

17

,

18

,

19

. Cutting inserts

20

will preferably be formed of a hard, wear resistant material such as cemented tungsten carbide or other ceramics adapted to cut an earthen formation. Cutting inserts

20

may also be formed or coated with other materials including superhard materials such as polycrystalline diamond, CBN and diamond like carbon.

Referring now to

FIGS. 3A

,

3

B, and

4

, typically the cutting inserts

20

of each cutter

17

,

18

,

19

are arranged in a plurality of rows. The gauge rows

50

of the cutters

17

,

18

, and

19

cut the outer wall, or gauge, of the borehole made by drill bit

10

during operation. The gauge reaming rows

52

ream the borehole to full diameter if the gauge rows

50

experience wear. The inner rows

54

cut the bottom of the borehole.

Shown in

FIG. 4

is a layout of cutters

17

,

18

, and

19

commonly used and well known by those skilled in the rolling cutter drill bit industry. The layout shows how the rows

50

,

52

,

54

of inserts

20

are arranged on the cutters

17

,

18

, and

19

. The inner rows

54

of adjacent cutters generally intermesh as shown in the areas

56

,

58

,

60

,

62

,

64

,

66

,

68

, and

70

of the assembled cutters

17

,

18

,

19

. These areas

56

,

58

,

60

,

62

,

64

,

66

,

68

, and

70

are formed by grooves

72

and

74

on cutter

17

, groove

76

on cutter

18

, and groove

78

on cutter

19

which register with the inner row

54

inserts

20

of cutters

17

,

18

,

19

so that they mutually intermesh.

The grooves

72

,

74

,

76

, and

78

generally alternate with the inner rows

54

of inserts

20

on cutters

17

,

18

,

19

. Accordingly, each groove

72

,

74

,

76

, and

78

on respective cutters

17

,

18

, and

19

is located between adjacent inner rows

54

of inserts

20

. One or more rows

80

,

82

,

84

,

86

of generally flat top bearing inserts

88

are positioned in respective grooves

72

,

74

,

76

, and

78

.

In the normal operation of the drill bit

10

, the rows

80

,

82

,

84

,

86

of generally flat top bearing inserts

88

do not contribute to the drilling action of the drill bit

10

. However, when a bearing assembly fails in operation, as shown by cutter

18

in

FIG. 5

, the generally flat top bearing inserts

88

in the rows

80

,

82

,

84

engage the intermeshing inner rows

54

of inserts

20

in the adjacent intermeshing cutter. This is indicated by the contact in intermesh areas

58

, and

60

on row

84

of cutter

18

in

FIG. 5

with inner rows

54

of cutters

17

and

19

. Contact is also made between the inner rows

54

of cutter

18

with row

82

of cutter

17

in intermesh area

70

and with row

86

of cutter

19

in intermesh area

56

.

This engagement causes a sudden, relatively large increase in the drilling torque of the drill bit. This torque increase is readily discernable at the drill rig by the drilling crew, providing a reliable indication of a failed bearing.

Similar to cutting inserts

20

, the generally flat top bearing inserts

88

may be formed of cemented tungsten carbide or coated with other materials including superhard materials such as polycrystalline diamond, cubic boron nitride (CBN) and diamond like carbon. However, it is preferred that the generally flat top bearing inserts

88

be formed of a material that is at least as hard, and preferably harder than that of the inserts

20

in the intermeshing inner rows.

The generally flat top bearing inserts

88

may have top edges that are curved slightly to conform with the surface radius of its groove. In addition, it may be desirable to provide the generally flat top bearing inserts

88

with a slightly domed region at the center of its top. These slight curvatures are provided so that when the inserts

20

engage the generally flat top bearing inserts

88

, there is little or no contact between the tops of inserts and the steel surface of the cutters

17

,

18

, and

19

.

It has been found that this relatively simple arrangement of generally flat top bearing inserts

88

in the grooves

72

,

74

,

76

, and

78

provides a reliable means of indicating a failed bearing in a rolling cutter drill bit

10

. During operation, if one bearing fails, the driller has the option to continue drilling for a short distance if necessary. If a second bearing on the bit

10

fails, a second additional increase in drilling torque will normally occur. Even though the bearings have failed, the driller will have the opportunity to retrieve the bit

10

before one or more of the cutters

17

,

18

,

19

wear so much that they come off of the bit body.

Whereas the present invention has been described in particular relation to the drawings attached hereto, it should be understood that other and further modifications apart from those shown or suggested herein, may be made within the scope and spirit of the present invention.