Diamond drilling bit for soft and medium hard formations

The invention relates to bore hole drills employing spaced shaped cutters in arrays separated by fluid channels in which there are positioned arrays of nozzles suitable for bit cleaning and detritus removal action.

BACKGROUND OF THE INVENTION 
The invention relates to bore hole drills in which shaped cutters are 
included as preforms of bonded abrasive particles or as relatively large 
bodies of ceramics such as boron carbide, silicon carbide, titanium 
carbide and natural abrasives such as carbonados. The shaped cutters are 
of a size and shape of a different order of magnitude than diamonds, 
employed in prior art diamond drills. This difference creates a problem 
arising from the geometry of the drill and space consideration. 
The problems of a suitable distribution of the shaped cutters in order that 
the cutters traverse the entire face of the bore hole which is being cut 
by the bit is aggravated by the requirements of the bit hydraulics. 
As is well known in this art, the drilling fluid which is introduced 
through passageways in the bit is designed to cool the bit, wash the 
cutting elements so that they present a clean cutting face, move the 
cutting to the gage of the bit and lift them up the annulus between the 
drill string and the wall of the hole. 
In order that the drilling fluid have this function, it must have a 
desirably high mass velocity through the drill bit nozzles without 
requiring an undesirable high back pressure. 
These various requirements have been particularly difficult to meet where 
the bit is destined for operation in relatively soft formations where 
clogging of the bit is appreciable. It is also a problem in harder 
formations. 
STATEMENT OF THE INVENTION 
It is an object of our invention to employ discrete shaped cutters 
positioned at spaced locations across the face of the bit and to provide 
for bit hydraulics to insure cleaning of the cutters and to provide the 
required flushing and detritus lifting action. We accomplish this 
objective by the following expedients: 
By employing shaped cutters such as preforms or carbonados, diamonds, and 
other shaped abrasive members in suitable arrays so that their paths on 
rotation of the bit cover substantially the entire surface to be cut. 
By an arrangement of the nozzles so that the emitted fluid jets sweep 
across the array of cutters and on rotation cover the entire surface of 
the cut. 
The shaped cutters are positioned on the face of the bit in spaced 
longitudinal arrays about the face of the bit from adjacent the center of 
the face to adjacent the gage of the bit with the cutting faces of the 
cutters in the same angular direction as the rotation of the bit. The 
cutters are arranged in each array in close relation so that on rotation 
of the bit the cutters traverse substantially the entire face of the bore 
hole end surface to be cut by the bit. 
The longitudinal array of cutters are separated by junk slots which are 
also water courses. The junk slots separate the face of the bit into 
blades of wedge shape. 
The drilling fluid is introduced through an axial bore of the bit and is 
discharged into fluid channels which may be but need not act as junk 
slots. 
In our preferred embodiment, the discharge of drilling fluid passes through 
passageways which in our preferred embodiment terminate in nozzles which 
are positioned in the junk slots so that the fluid velocity along the 
slots is sufficient to cause a scouring of the cutters and is sufficient 
to carry the cuttings to the gage of the bit and up the annulus. 
The nozzles are positioned in the junk slots in the face of the bit with 
their axis oriented and so distributed across the face of the bit that the 
ejected streams wash over the cutters and cover substantially the entire 
surface of the formation being cut by the bit when the bit is rotated. 
These functions are accomplished in our preferred embodiment by positioning 
the nozzles in a spiral array so that they are in a plurality of 
substantially longitudinal arrays in each junk slot. In each junk slot the 
array is more closely positioned to the leading edge of the junk slot 
where the cutters are positioned than to the trailing edge of the next 
preceding blade portion. The several nozzles in our preferred embodiment 
are arranged in each longitudinal array so that the nozzle in each junk 
slot are spaced substantially equally from the leading edge of the junk 
slot where the cutters are positioned.

The bit shown in the figures may be formed as described in the copending 
applications, Ser. No. 704,424 and Ser. No. 745,087 and the patents 
therein referred to, all assigned to the same assignee as the assignee of 
this application. We may employ the preforms and other cutter elements as 
described in said applications and patents. Said applications and patents 
are herein incorporated by this reference. 
Instead of employing the spirally arranged stepped configuration as shown 
in the above applications, we may employ ridges and arrange them spirally 
as described in said applications or concentrically with suitable 
arrangement of cutters as described herein. 
As described in said referenced applications and patents, the bit may be 
formed by the techniques usually employed in producing diamond bits 
whereby a hollow tubular steel mandrel, suitably formed, is coated in a 
carbon mold with metal bonded hard material such as tungsten carbide. The 
carbon mold is of a configuration such as to give a bit of the desired 
form. These procedures are well known to those skilled in the art. 
As shown in FIGS. 1 and 2, the face of the bit is formed on the closed end 
of a hollow steel mandrel 1. The face of the bit is formed with spaced 
ribs 2 which may extend either concentrically or spirally from adjacent 
the central portion of the bit 3 to adjacent the gage of the bit 4. In the 
forms of FIGS. 1 and 2, the ribs are in the form of steps 5 each composed 
of the land 6 and the rise 7. The central portion of the bit is formed 
(See FIG. 6) by an end surface 8 and a conical surface 9 with its apex at 
10 at the central axis 11 of the bit. The end surface 8 is substantially 
flat and substantially perpendicular to the central axis 11 and connects 
to the stepped portion 5 and to a conical portion 9 at the center of the 
bit. 
The face of the bit is interrupted by fluid channels 12 which also act as 
junk slots and which separate the face of the bit into blades 13. At the 
leading edge 14 of the blades cutters 15 are positioned in an arrays so 
that the cutters in one longitudinal array overlaps the cutters in the 
trailing blade so that the cutters will traverse the portion of the cut 
not covered by the cutters of a preceding leading blade, to assure that 
all portions of the surface to be cut are traversed by the cutters. 
The junk slots in both the forms shown in FIGS. 1 and 3 extend from the 
center of the bit to the gage 4 of the bit. The junk slots at the gage 
connect with passageways 16 positioned in the stabilizer section 18 of the 
bit. Referring to FIGS. 1 and 2, the blades are formed with steps spaced 
from each other from a position at an area adjacent to the gage of the bit 
to the flat portion 8. The steps extend from the leading edge 14 of the 
blades to the trailing end 19 of the blades. 
While the ribs may be arranged on concentric circles about the axis of the 
bit, we prefer to arrange them in a spiral formation starting adjacent the 
flat portion 8 of the bit to adjacent the gage of the bit as shown on 
FIGS. 1 and 2. 
An alternative and preferred form of the bit of our invention is shown in 
FIGS. 3 and 4. This bit is formed as is described for the form shown in 
FIGS. 1 and 2. 
The difference is in the form of the ribs and the shape of the face. 
Instead of lands and rises, the ribs are in the form of arcuate ribs 102 
of cross section which may be semi-circular or segmental. The face of the 
bit extending from the rib is convex of an egg shaped form curving to a 
cuspidal central portion. The ribs extend from adjacent the gage to the 
central portion 136. All other parts are constructed similarly to those of 
FIGS. 1 and 2 and are similarly numbered. 
The ribs, as in the case of steps of FIGS. 1 and 2, may be concentric 
circles or form a spiral which extends from adjacent the central portion 
of the face to adjacent the gage of the bit as shown on FIGS. 3 and 4. 
The ribs are interrupted by junk slots which form wedge shaped blades 
similar to those shown in FIGS. 1 and 2 and which extend beyond the ribs 
into the central portion. 
The ribs in the blades are spaced so as to form channels 20 which extend 
across the blades and interconnect the junk slots at the leading and 
trailing edges of the blades. 
In the forms shown in FIGS. 1 and 4, the shaped cutters are mounted in the 
leading end of the ribs of the blades in sockets provided in the face of 
the bit at the appropriate location as described below. 
The cutter elements to be more fully described below are positioned in 
sockets formed in the face of the bit at the leading edge of the blades. 
They are positioned in the leading edges of the ribs of the blades in 
longitudinal arrays. They are also held in like manner in equally spaced 
array in the flat portion 8 and the conical portion 9 of FIGS. 1 and 2. As 
stated previously, the spacing of the cutters in each of the longitudinal 
arrays is such that they traverse the entire surface of the cut when the 
bit is rotated. The cutters are each of suitable shape and size to 
accomplish this purpose as will be more fully described below. 
The hydraulics, that is the distribution of the drilling fluid across the 
face of the bit, is provided by suitably arranged nozzles 21 positioned in 
passageways 22 in the face of the bit which passageways commence at the 
central bore 23 of the bit and terminate at the junk slots. 
The individual nozzles, see FIG. 6, are positioned, in the form of FIGS. 1 
and 3, in each junk slot in a longitudinal array but not necessarily a 
linear array with the nozzles in the array spaced more closely to the 
leading edge of the blades where the cutters are positioned than they are 
to the trailing edge of the next leading blade. 
Due the wedge shape of the blade which provides that the edges of the blade 
are not radially positioned, and the conical shape of the envelope of the 
face, see FIG. 2 or the egg-shaped form of the face of FIG. 4, the nozzles 
in each longitudinal array may be displaced from a linear array in order 
to provide for substantially equal distances between the axis of each of 
the nozzles and the adjacing leading edge of the adjacent blade in each 
nozzle array. 
The nozzles are arranged in our preferred embodiment in longitudinal arrays 
which are separated from each other at substantially equi-angular 
distances. A preferred embodiment is, as illustrated in FIG. 5 where the 
longitudinal arrays of nozzle are as shown separated by approximately 
60.degree. and the nozzles are positioned in longitudinal arrays extending 
from adjacent the center to adjacent the gage of the bit. The several 
nozzles are positioned in a spiral arrangement extending from adjacent the 
center of the bit to the gage of the bit as appears from FIG. 5. 
In the forms of FIGS. 1 and 3, the separation of the ribs from each other 
in each blade forms a communication between the adjacent junk slot across 
the blades. The force of the fluid ejected from the nozzles and the 
rotation of the bit will cause fluid to wash across the face of the blades 
between the ribs and over the ribs to remove detritus which forms between 
the ribs. 
The purpose of this arrangement as described above is to cause the several 
streams ejected through the nozzles in each array to wash over the cutters 
in the adjacent cutter array and to impinge on and cover substantially the 
entire surface of the area to be cut on rotation of the bit. The 
arrangement also provides space in the junk slots for a returning stream 
of drilling fluid carrying the cuttings. Room is thus provided for the 
return stream along the junk slot in the face of the bit and up the water 
passages 16 in the stabilizer. 
The cutters referred to above may be natural diamonds including black 
diamonds known as carbonados. 
Instead, we may use shaped ceramic bodies such as boron nitride, silicon 
carbide, tungsten carbide or alumina. 
We prefer, however, to employ a preform cutter formed under high pressure 
and temperatures shown as Compax sold by General Electric Company. It is a 
shaped cutter of diamonds bonded by a suitable matrix material. It is 
understood that this preform is manufactured by a process described in 
U.S. Pat. No. 3,745,623. 
The cutters which may be employed in our invention may be of various 
designs. Several are illustrated in FIGS. 7, 8 and 9. 
In FIGS. 7, and 7a, the cutter is a parallelepiped 24 of lengths so that 
they will extend substantially the width of the lands and along 
substantially the entire surface of the flat and conical section, in 
suitably spaced sockets 25 formed in the face of the bit as shown in FIGS. 
1 and 2. 
In FIGS. 8 and 8a, the cutter 26 is a quarter sector of a right cylinder 
with the central external face 27 at the radius and a peripheral arc 27 
sitting in suitably formed sockets 28 in the face of the bit at the rise 
in each step. 
An alternative and preferred form of cutter is the cylindrical cutter 29 
shown in FIGS. 9 and 9a. The diameter of the cylinder is substantially 
greater than the height of the cylinder. The cylindrical cutter fits into 
a socket 30 formed in the face of the bit at the leading edge of the ribs. 
In each of the forms of cutters, the cutting faces are all oriented in the 
same angular direction in the direction of rotation of the bit and extend 
from the surface of the face of the bit as is illustrated in FIGS. 7, 8, 
and 9. In the form of FIGS. 1 and 2, the cutters in the conical and flat 
portion may be in the shape of the cutters as above and are of length and 
are spaced from each other so that on rotation of the bit the entire 
surface of the cut is traversed by the cutters. 
We prefer to mount the cutters in sockets so that the thrust imposed by the 
cutting action upon the cutter is transmitted to the body of the bit. As 
shown in FIGS. 3, 4, 9 and 9a, we prefer to mount the cutters in sockets 
so that about less than half, and preferably about 20-40%, e.g. 30% of the 
exterior surface of the cutter is exposed and the cutter is backed by the 
body of the bit. 
We also prefer to mount the cutter so that they have a backward rake for 
example, 15.degree. as is illustrated in FIGS. 7, 8 and 9. 
The use of shaped discrete cutting elements such as employed herein 
presents problems in assuring the presence of cutting elements at the 
center and at the gage of the bit. In the forms of FIGS. 1 and 2, the 
presence of the cutting elements at the center is provided by arranging 
the blades so that they extend to various radial distances from the center 
of the bit. (See FIGS. 2 and 4) The terminal ends of the ribs of FIG. 2 
and the terminal ends of the ribs of FIG. 4 are arranged in a staggered 
formation to assure the presence of cutting elements to cover the entire 
surface of the cut. A reference to FIG. 2, the spiral arrangement will be 
seen by reference to terminal ends 31 which crosses the center and 
spirally, 32, 33, 34, 35 and 36 and in FIG. 4 the terminal ends 131, 132, 
133, 134, 135, and 136. 
The provision of cutters in the blades extending to the terminal ends of 
the blades will insure that the entire surface, including the central 
surface is traversed by cutters. If desired, the area at the center and 
between the terminal ends of the cutters of FIG. 2 may be supplemented by 
including diamonds at the central portion. These may be positioned during 
the casting of the bit in the conventional manner. 
In the form of FIGS. 3 and 4 since the central portion of the bit is not 
covered by preforms, the bit would, unless additional cutters are 
provided, leave an uncut portion at the center. To avoid such a result, we 
position in the return portion of the blades a number of diamonds, 
carbonados or preforms in the face of the bit at the central portion. They 
are illustrated by the carbonados shown in FIGS. 3 and 4 at 135. 
In both of the forms of FIGS. 1 and 3, the spacing of the ribs will provide 
an area adjacent the gage where cutters will not be placed. In both the 
forms of FIGS. 1 and 3, diamonds 37 or other suitable abrasive elements 
may be positioned at and adjacent the gage to supplement and complete the 
cutting action of the bit. These may be inserted by the conventional 
manner. 
Additionally, as is conventional, in this art, the stabilizer section may 
be hard faced as for example, by diamond particles distributed along the 
face of the stabilizer as shown in 37. The above configuration of the bit 
will provide that the entire surface of the cut will be traversed by 
cutting elements and that the drilling fluid passing through from the 
nozzles will wash at high velocity over the cutters and cover the entire 
surface of the cut returning the detritus along the junk slots to the 
passageways in the stabilizer to be returned to the annulus.