NZ240761A - Well drilling bit; cutting discs mounted with rearwardly offset axes relative to direction of rotation of drill shaft - Google Patents

Description

240761 r.":o -i' Dz'.' !r'.: £2^&/o/lS- Pubic..21 AUG,19$ P.?. J ?■:- Patents Form No. 5 NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION DISC DRILL BIT WE, NORVIC S.A., a Swiss company of Me Andrey Notaires, 1 rue Hans Fries, 1700 Fribourg, SWITZERLAND hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: (followed by page 1a) io\ 2407 DISC DRILL BIT The present invention concerns a drilling device comprising a drilling head equipped with a rotating 5 body through which runs a duct for supplying drilling fluid or air to the well bore and at least one cutting disc placed on the outside of the main body.

Existing drilling devices comprising a drilling head 10 equipped with three cutting elements markedly conical or in the shape of a truncated cone have been known and in use since the 1930's. These devices require great pressure to break the rock and subsequently cut it up and flush it away. Because of the great compression 15 needed to break the rock, such devices affect a greater surface than that of the drilling, thus creating an irregular drilling profile and an unstable wall.

The present invention makes it possible to produce a 20 drilling device operating at low power, and reduced down pressure, utilizing at least one cutting element mounted on the outside of the drilling head, its axis of rotation being, according to a preferable embodiment, offset laterally in a backward direction 25 from the centerline of the main drill body in relation to the direction of rotation of the main body, enabling the device to penetrate and evacuate rock more rapidly than with other known methods.

The present invention aims to make it possible to produce a drilling device operating with a light thrust utilizing preferably three cutting elements or discs easily mounted on the drilling head, and enabling it to evacuate large pieces of debris. (followed by page 2) 2 240761 Summary of the invention The drilling bit according to the present invention comprises, a main drill body designed to rotate about a substantially vertically disposed axis of rotation and incorporating a longitudinal duct for either supplying a drill fluid or air under pressure to the 10 well bore or removing a drill fluid or air combined with debris and excavated rock from the well bore, and adapted to be assembled to a drill rod, at least one generally circular, rotatable cutting disc 15 mounted on a lower portion outside said main drill body, allowing the said drill bit to form a well bore having a substantially cylindrical wall portion and a generally concave portion, the said cutting disc having cutting elements disposed in generally ring-shaped 20 formations, with the disc axis of rotation disposed at an acute angle to the axis of rotation of the main body, the lowest cutting point of the said disc being radially remote in relation to the axis of rotation of the drill body the axis of the cutting disc being slightly offset laterally in a rearward direction from the centerline of the main drill body in relation to the direction of rotation of the main body, while leaving all the angles 30 between the axes unchanged, causing the drill bit to be placed in a non-equilibrium position, rotation of the main body enabling the drill bit to seek equilibrium by the cutting elements penetrating the wall and shearing rocks as combined downward ^ forces exceed ' . opposing forces (making the drill bit /JS6 /Q. /w If 10SEP1W/ 240761 self-loading), the downward forces being essentially concentrated on the lowest cutting element causing a destabilization of the well wall making easier the cutting action of the bit.

Preferably the drill bit comprises three cutting discs.

Each cutting element is a disc provided with highly efficient cutting surfaces (teeth).

Because the discs act at the bottom and on the concave portion of the wall to be cut and have a generally ring-shaped surface equipped with cutting means, the action of the discs is primarly to shear the rock and 15 not to compress it in order to obtain its disintegration.

Because the axes of rotation of the discs are offset laterally backwards in relation to the direction of 20 rotation of the main drill body, the cutting action of each disc is performed by the teeth in the lower rear quadrant. Penetration of the rock is easily achieved as the net downward force (thrust) is essentially concentrated around the six o'clock position on each 25 disc, which is an important factor in destabilizing the rock in the lower portion of the hole.

Movement of the earth's crust over many millions of years has subjected almost all rock to immense stresses 30 and strains. These forces have been relieved by the formation of tiny fissures and faults in the rock. Most known drilling devices compress the rock they are about to cut eliminating these faults and fissures, and then grind it with a rotary action. 10SEP1993 1 \.v. 4 240761 Off-setting the axis or axes of rotation of the cutting disc or discs laterally from the longitudinal axis of the main drill body places the entire bit in a non-equilibrium position. The rotation of the main drill body causes 5 the disc or discs to seek equilibrium by penetrating and shearing the rock.

By off-setting the axis of rotation of the cutting disc in a rearward direction, the disc moves towards 10 equilibrium as the cutting elements penetrate and shear the rock as the disc revolves on its axis as a result of the rotation of the main drill body. As the disc approaches equilibrium it is once again prevented from reaching it by the next cutting element entering the rock just 15 before six o'clock position, and the cutting cycle is repeated.

How this is achieved is explained by Fig 1 and Fig 2. Fl (downward load) is generated from the basic weight 20 of the drill bit, drill pipe and drill rig loading. The downward load is essentially exerted on the lowest point or points in the six o'clock position, which maximises penetration and destabilizating the rock.

In Figure 1, the clockwise rotation of the main drill body (viewed from above said body) causes the cutting disc or discs to rotate in an anti-clockwise direction (viewed from the outer face of said disc or discs), so that once the cutting elements have penetrated the rock 30 they move upward through it, resulting in a downward thrust greater that the opposing force (FL + Fs > F0, where Fs = I Fs s the combined downward forces of the cutting elements in the cutting quadrant), thereby making the system self loading. The disc will therefore tend to 35 screw itself into the rock, which has been r o\ 4 240761 destabilized, shearing it in an ascending spiral, making it self cleaning and allowing FL to become negligible. This is essentially carried out by the center ring of cutting elements or teeth (601, Figure 5 10).

It is believed that during operation the following takes place. Penetration into and destabilization of the rock is achieved during the rapid transition of the 10 cutting action from compressive to up-cut shearing. From the point at which it enters the rock, as it approaches the 6 o'clock position, the lowest tooth on the disc exerts into the rock a combination of downward thrust and rotational energy (or torque), originating 15 from the pull-down on and rotation of the main drill body. This energy increases rapidly until it reaches a maximum when the tooth reaches the 6 o'clock position, after which it moves into an up-cut shearing action. Preferably, this phase is completed by each tooth 20 before another enters the rock, but in another version one or more other teeth may enter the rock before the first tooth has reached full penetration.

Once the teeth have fully penetrated the rock and 25 passed the 6 o'clock position, they have to overcome the resistance of the rock if the up-cut shearing or excavating action is to take place. As the teeth move upwards in the rock through the lower rear quadrant of the cutting disc the downward energy they exert on the 30 rock progressively diminishes from its high point at 6 o'clock, becoming negligible as the teeth approach the 3 o'clock position. The lateral rearward offset of the axis of rotation of the disc in relation to the axis of rotation of the drill bit means that the teeth on the 35 disc move farther away from the center line of the 6 24 076 1 § drill bit as they move upwards from the 6 o'clock position, until they reach a maximum distance from the centerline on, or sometime after if the disc has been tilted down, they have passed the 3 o'clock position.

The result of this outward movement is that the teeth exert a force on the rock in a direction parallel to the axis of rotation of the disc. This lateral force progressively increases as the teeth move away from the 10 6 o'clock position, reaching a maximum as the teeth reach the point that is the farthest perpendicular distance from the centerline of the hole. Thereafter the force diminishes rapidly as the teeth withdraw from the rock, ceasing altogether at the point at which they 15 lose contact with the rock. Therefore, it is believed that the lateral force, combined with the acute angle of the disc to the centerline of the main drill body and the convex shape of the outer face of the disc, brings the teeth on the outer cutting ring into play, 20 forcing them to enter the rock and excavate it with an up-cut shearing action.

An element of the outward lateral force exerted by the teeth on the outer face of the disc is counter-balanced 25 by an inward lateral force exerted by teeth on an inner cutting ring Fig. 10, 603. This inward force causes the teeth to enter, shear and excavate the rock in a center column at the base of the hole fig. 10, 611, said column being left because, at their lowest 30 point, the teeth on the periphery of the cutting discs are radially remote from the centerline of the main body.

The teeth on the inner cutting ring excavate the 35 central column and cease to be in contact with the rock 240761 face sometime before the teeth on the outer ring cease to be in contact with the well wall. This means that there is a sudden falling off of the inward lateral pressure at the same time as the outward lateral 5 pressure is increasing. The result is a torsional inward force on the cutting disc in the lower rear quadrant.

The torsional energy required to overcome the 10 resistance of the rock to the combined effects of these interacting downward and the lateral forces increases rapidly as the teeth first penetrate the rock, reaching a peak at the 6 o'clock position, it then reduces slowly as the increasing (but secondary) lateral force 15 offsets the reducing (primary) downward force, only to reduce rapidly once the downward force has become negligible and the teeth begin to withdraw from the rock.

Because the cutting disc rotating around its axis as well as being rotated around the centerline of the main body, the speed with which the cutting teeth rotate around the centerline fluctuates compared to the rate of rotation of the main drill body. The magnitude of 25 this fluctuation is affected by the extent to which the highest point on the periphery of the disc is radially remote from the lowest point - the amount of vertical ' tilt on the disc.

When a tooth is at 9 o'clock on the disc it is rotating at the same speed as the drill body. As it moves backwards, relative to the direction of rotation of the drill body, its own rotational speed drops, reaching its lowest speed at 6 o'clock - the point at which its 35 downward movement becomes an upward movement - it then 8 240 7 6 1> speeds up as it moves through the lower rear quadrant until, at 3 o'clock, it is once again moving at the same speed as the main body. As the tooth moves past 3 o'clock it continues to increase rotational speed 5 relative to that of the main body, reaching its highest speed at twelve o'clock before slowing down until both speeds match again at 9 o'clock.

Thus it is believed the combination of increasing tooth 10 speed and reducing outward lateral pressure as the teeth withdraw from the rock that cause the teeth in the upper rearward quadrant to stop shearing and excavating the rock and to burnish the wall of the hole. Whilst there is still an outward lateral force in 15 this quadrant its effect is believed to be a compressive one which compacts any loose rock and smooths the wall of the hole.

If the said cutting disc is then tilted in the 20 direction of rotation of the said main drill body, the outer excavating teeth are pressed further into the rock increasing the work of the said outer excavating teeth and reducing the work done by the penetrating destabilizing teeth which increases the life of the 25 said penetrating destabilizing teeth. The life of the outer excavating teeth can be extended by using highly wear resistant inserts such as diamond carbide inserts, thereby extending the life of the bit. This is particularly valuable when the well bore being cut is 30 very deep as it reduces the down-time caused by raising the bit to the surface to replace it when it is worn.

Because the net downward force on the bit is essentially concentrated on a single point, the tooth 35 at six o'clock on the cutting disc, penetration into 9 240761 the rock is easily achieved in almost any known rock. The bit will therefore drill with little downward thrust and only a small increase is required to achieve full penetration if the teeth are lengthened. Most of 5 the force needed to overcome the resistance in the rock is rotary and any increase in resistance is largely overcome by increasing the torque on the main drill body which is transferred to the cutting disc or discs.

In any bit using more than one disc it is necessary to have a different number of teeth on each disc to ensure that the cutting paths of the lowest teeth lie side by side. With the same number of teeth on each disc the cutting paths overlap in a regular repeating pattern 15 that creates tracking and inhibits the destabilizing action of the lowest teeth and therefore the drilling process. The characteristics of the cutting path are partly determined by the configuration of the disc and its teeth.

If the lateral displacement of the axis of rotation were to be in a forward direction relative to the direction of rotation of the main drill body, the cutting action would be performed by the lower forward 25 quadrant of the disc. Penetration of the rock would start just before the nine o'clock position, and move in a descending spiral with the penetration increasing until the teeth were fully embedded in the rock at the six o'clock position, (see fig 2).

The effect of this forward displacement would be to generate a force opposed to that needed to reach equilibrium, and to compress rather than destabilize the rock, making it harder to cut and putting undue 35 stress on the cutting teeth and the bearing. The debris 240761 is also directed downwards towards the bottom of the hole which in certain rock conditions could cause the bit to jam in the hole.

The principle of this invention applies to a bit containing one or more cutting discs. According to another embodiment of the invention the upper portion of the said main drill body has a number of burnishing or cutting elements disposed at regular intervals 10 around the periphery of the main drill body and situated no lower than the point at which the concave bottom portion of the well bore joins the cylindrical portion.

This invention facilitates faster straight line rock penetration with constant hole diameter, using less downward pressure and power, thereby substantially lowering the cost per foot of drilling.

In soft rock the volume of chippings or debris is considerably greater, so at small hole diameter the device is more effective with one or two rotating cutting discs leaving more space at the bottom of the hole to evacuate the debris. Normally the drill 25 comprises three cutting discs.

The invention has an additional advantage of providing directionally stable drilling because the vector of the cutting force combined with the rotation of the main 30 drill body creates a core of destabilization the apex of which lies below the bottom of the hole on the centerline of the main body. This directional stability is reinforced by the action of the burnishing or cutting elements in the upper portion of the main drill 35 body which holds the bit in the center of the hole. 11 2407 61 Another advantage of the burnishing elements is to ensure that the withdrawal movement of bit in the hole is operated in a straight line so avoiding the drill body to be deviated. If the drill body during the 5 upwards or backward movement is deviated from the straight line a disc or more discs may be engaged in the wall of the hole causing either a failure or breakage of the disc or its bearing whereupon it will fall down the hole or remain in the wall of the hole, 10 or cause the entire bit to become stuck in the wall of the hole thereby preventing successful withdrawal.

The device is designed to provide an agressive cutting disc by off setting laterally in a backward direction 15 the axis of rotation of each disc from the centerline of the main body relative to the direction of rotation of the main drill body. The amount of offset will vary according to the diameter of the bit and the configuration and design of the discs.

The ducts through which water, drilling muds or air pass out of the main body are designed to provide adequate flow to flush out the brocken rock and to cool the discs during drilling. The burnishing or 25 cutting elements on the upper portion of the main drill body are disposed in a polygonal and preferably hexagonal formation. We may call this formation a gauge ring. This gauge ring should preferably be equipped with highly wear resistant inserts which touch the wall 30 of the well at the specified distance from the center of the hole at specified points around the diameter of the gauge ring. Therefore, even if the cutting elements on the discs should wear after extensive drilling, the gauge ring ensures a constant diameter of Zk 07 the hole, by removing the residual rock not reached by the worn cutting surface of the discs. The inserts of the gauge ring will eventually be subject to wear as well, but in practice this system ensures hole diameter 5 stability in most drilling applications beyond the point at which other traditional systems would have already failed.

Although the inserts on the gauge ring will remove any 10 residual rock left by worn cutting discs, they do not perform the removal as rapidly as the discs and a marked and progressive reduction in the rate at which drilling proceeds would be indicative or excessive wear on the discs.

The bottom central portion of the main drill body can be provided with cutting elements to remove residual "chimneys" of rock not directly reached by the cutting surfaces of the discs.

The cutting discs are provided with supplementary cutting elements disposed in a ring formation spaced out around the disc and disposed behind the main cutting elements at an angle making them point towards 25 the center of the hole in such a way that they will not impinge on the well wall when the main cutting elements are at work. The purpose of these subsidiary cutting elements is to jolt and cause to disintegrate any central chimney of rock forming in the center of the 30 hole as the cutting discs rotate.

As should now be clear, the invention provides a self-aligning bit well suited to directionally stable drilling of constant diameter holes, using lighter and 35 less costly equipment. Penetration rates are 20-400 13 240761 percent faster than those achieved by traditional methods. The drill device has been engineered to withstand easily all the shocks, pressures and wear normally encountered in commercial drilling operations.

It is therefore apparent that a drill bit for use in drilling a well bore in accordance with this invention comprises a main body designed to rotate about a substantially vertically disposed axis of rotation and 10 incorporating a longitudinal duct for supplying a drill fluid or air under pressure to the well bore.

In a further embodiment the bit will incorporate a central duct either passing through the center of bit 15 or splitting into a number of directed ducts. Drill fluid or air combined with debris and excavated rock from the well bore will pass through this duct or ducts to remove said debris and excavated rock.

The drill bit may have multiple cutting discs mounted at spaced intervals. For example, there may be three cutting discs at spaced intervals. Multiple cutting elements may be mounted at specified locations to create a large combination bit capable of drilling wide diameter holes, the discs and cutting elements 25 being arranged at varying heights in relation to each other to create a stepped cutting profile at the base of the well bore.

Three rotatable cutting discs are preferably mounted on the outside of the main drill body at equally spaced 30 intervals, with these cutting discs having multiple cutting elements. Nevertheless, it is possible to have a drill provided with less or more discs. Each of the cutting discs has an axis of rotation disposed at an acute angle to the vertical axis about which the main 35 drill body rotates, thus causing the cutting elements ■ - J SEP 1993 > V Ji A 14 240761 to be positioned in such a way as to achieve efficient agressive cutting in the direction of rotation of the main drill body, and ensures that the first cutting element is the one approaching the lowest one of each disc.

The angle at which the axes of rotation of the cutting discs are disposed is typically 40 to 80 degrees to the axis of rotation of the main drill body.

The amount of lateral offset of the axis of rotation of each cutting disc from the centerline of the main drill body is about 1/32 inch to i inch, or { inch to 1 inch or more. The cutting disc may be dynamically balanced and placed so as to effectively counter-react another disc. The drill bit may be self-aligning.

The cutting disc or discs may be substantially flat, or may be substantially concave in the outer surface. in use the cutting elements may form a cylindrical wall portion, of a maximum diameter greater than the diameter formed by the cutting discs.

The main drill body may be provided with means adapted to drive it in rotation even if the drill rod is not in rotation, as when the bit has been deviated to alter the direction of penetration. The means of rotation may comprise at least one driven turbine.

A supplementary cutting disc may be mounted on the vertical axis, at the lowest point of the main drill body and comprising a means adapted to drive the supplementary cutting disc in rotation independent of the rotation or lack of rotati£3n\of the main drill body. 0""" ■ • LN 2 to SEP 1993 (followed by page «3^fr" v l ^ 240761 A principal advantage of the invention is to provide a drill bit of inexpensive and highly effective 5 construction, which drill bit is further characterized by being self-aligning, thus having the ability to drill in a directionally stable manner.

Brief description of drawings Fig 1 is a lateral schematic view of a drill bit provided with a rearward offset cutting disc; Fig 2 is a lateral schematic view of a drill bit 15 provided with a forward offset cutting disc; Fig 3 is a perspective view of a drill bit provided with three cutting discs; Fig 4 is a perspective view of a drill bit as in fig 3 provided with a gauge ring; Fig 5 is a bottom view of a drill bit in a drilled hole, the axes of rotation of the cutting disc being 25 offset in a rearward direction in relation to direction of rotation of the main body; Fig 6 is a bottom view of a drill bit similar to the drill bit of fig 5 the axes of rotation of the cutting 30 discs being offset in a forward direction; Fig 7 is a perspective view of a drill bit provided with rearward offset and forward tilted cutting discs; t »'• f > a Fig 8 is the bottom view of the drill bit shown (followed by: page 15) 240761 Fig 9 is a perspective view as in fig 7 of a drill bit designed to have the drill rod attached at the base of the bit for drilling upwards.

Fig 10 is a lateral view of a drill bit provided with a single cutting disc.

Fig. 11 is a lateral schematic view of a multiple layered disc assembly for drilling wide diameter holes.

Detailed description Although the description is limited to a drill bit equipped with three cutting discs, drill bits with one, 15 two or more cutting discs correspond to the present invention.

With reference to Fig 3 a rotary drilling device 10 in accordance with this invention may be seen to comprise 20 a body member or housing 12 fitted with male connector 14 at its uppermost portion, enabling it to be connected to a rotary drive system, in this instance a rotary drive shaft, called drill rod equipped with corresponding female connector at its lowermost end. By 25 engagement of the male and female part, the body member or housing 12 is enabled to be attached very tightly to the lowermost end of a drive shaft not shown, yet readily removed therefrom for replacement should such become necessary from time to time.

The power-applying shaft has a centrally disposed longitudinal hole to permit the flow of coolant therethrough, and the shaft is rotatable about a . . '/ ' ' ^ 1 ^ 4 C 16 240761 centerline or axis of rotation 20. The centerline may be regarded as also extending through the body member 12.

The body member 12 has a centrally located coolant duct located in alignment with the central hole of the shaft, with the duct of body member 12 opening into orifices provided for the circulation of drilling fluid or air under pressure to the area of the rotating discs 10 or wheels 34, 36 and 38 mounted on the body member 12.

Each disc 34, 36, 38 is provided with cutting elements disposed in a ring shape formation, their length, shape, and disposition pattern depending on the 15 condition of the rock to be cut.

In fig 4 a drill bit similar to this of fig 3 is shown the only difference being the gauge ring 40 which is preferably of polygonal configuration. In accordance 20 with this invention, burnishing inserts or teeth 42 are mounted at the intersection of each of the sides of the gauge ring, which may be regarded as forming the maximum diameter of the drill bit.

It will be noted with regard to the sides of the gauge ring, that each of the sides is concave, extending in towards the center of rotation of the bit from the intersection points on the outer diameter of the gauge ring at which the burnishing inserts or teeth are 30 mounted. This construction maximizes the space available for pieces of rock and other cuttings to pass between the well wall and the concave faces of the gauge ring 40 and facilitates their removal from the disc area by means of the fluid used during operation 35 of the drill bit. This detail is made quite clear in 17 240761 figure 5. The gauge ring 40 may be referred to as being in the shape of a modified polygon.

During extended drilling, the gauge ring 40 will insure 5 a constant diameter of the hole being created in the rock, in spite of the possibility that the cutting surface of the discs should wear, and thereby reduce the effective cutting diameter of the wheels or discs 34, 36 and 38. This reduction in cutting diameter is 10 compensated for in accordance with this invention by the inserts 42 of the gauge ring 40 utilized at the maximum diameter, upper portion of the drill bit. These are of course highly wear resistant inserts located at each point that touches the hole 11 created in the 15 rock, as previously mentioned. Theoretically, the inserts or teeth 42 of the gauge ring 40 would eventually be subject to wear as well, but in practice this novel system will insure a hole diameter stability in most drilling applications beyond the distance at 20 which other conventional systems would already have failed, by removing the residual rock not reached by the worn teeth of the wheels or discs.

The modified polygon configuration has the further 25 advantage of preventing the discs becoming engaged in the wall of the hole when the bit is being raised in the hole.

Fig 5 is a bottom view of a drill bit similar to that 30 in Fig 4. The only difference is the shape of the cutting discs and the teeth disposition pattern.

Apart from the way in which differences in the discs are indicated by the use of different identifying 35 numerals, the same numerals indicate the same elements 18 240761 of the drill bit, from Figure 3 onwards.

The cutting discs 134, 136, 138 of the drill bit shown in fig 5 are of frustoconical shape and the cutting 5 teeth 135a, 135b, 137a, 137b, 139a, 139b are disposed according two circular lines in a staggered disposition. The axes of rotation a of the discs are laterally offset in a backward direction in relation to the drill bit direction of rotation indicated by the 10 arrow Rl. The magnitude of this backward offset is Ab which may vary with the diameter of the bit. The direction of rotation of the cutting discs is indicated by the arrow R2. The advantage of the laterally backward offset of the discs has been explained earlier 15 with reference to the fig l and 2.

In Fig 5 is also shown three gauge ring 40 with its teeth 42 displaced so as to insure a constant hole diameter 11.

The rearward offset disposition of the disc allows a loose/void media area A1 in front upper quadrant of each disc, and a restabilizing area Ar at the rear upper quadrant of the disc 136, these areas are shown in Fig 25 5 only in relation to the disc 136 but the same is true with any of the three discs.

Teeth 42 of the gauge ring 40 constitute sizing burnisher tools insuring a constant diameter of the 30 well. The teeth of the lower rear quadrant of each disc destabilize and cut the well wall, while the teeth of the upper rear quadrant compact the rock in the well wall after cutting.

In fig 6 is shown a drill bit with three cutting discs 19 240761 234, 236 , 238, whose axes of rotation are laterally forwardly offset in relation to the drill bit direction of rotation. The magnitude of lateral offset is Af.

The disadvantages of this device are already presented in relation to fig 2. For each disc the axis of rotation is offset forward, a loose/void media area A1 is situated at the rear upper of the disc while a cutting area Ad is created in front of the disc. So the 10 cutting is carried out by the front lower quadrant of each disc the teeth of which cut the wall by compressing as the disc rotates anticlockwise as opposed to the drill bit in fig 5 in which the teeth of lower rear quadrant destabilize and cut the well wall.

In fig 7 and 8 is shown a drill bit the axis of rotation of each disc being rearwardly offset in a lateral direction, the magnitude of the offset is Ar, and the disc is forward tilted, in relation to the direction of rotation of the drill bit, according to an angle 6. This disposition of discs 434, 436, 438, presses the lower rear quadrant of each disc closer to the well wall.

In fig 9 is shown a perspective view of another embodiment according to claim 23. The drilling rod is attached to the bottom portion of the main drill body provided with a male connector 500 in order to make possible to drill upwards. Such a bit may be drilled 30 upward from a tunnel gallery or other space located below the rock into which a small diameter hole has been drilled from the surface for the said drill rod to be lowered to the said tunnel or gallery, so that when the bit is drilled upwards it enlarges the diameter of 35 the hole. In fact the bit shown in fig 9 is similar to 0|\ SEP 1993 \ « Ox 24 0 ".! the bit shown in fig 7. It is provided with three cutting discs 534, 536, 538, and a gauge ring 40 with burnishing elements 42. The main difference is that the male connector is situated at the lower part of the 5 bit and its shape and dimensions are different. The bit in fig 9 is not provided with ducts for supplying drill fluid.

Fig 10 is a lateral schematic drawing of a drill bit 10 provided with a single disc 600. The cutting elements of the disc are disposed in three ring shaped formations. The teeth 601 disposed close to the outer periphery of the disc and notably the teeth of the lower rear quadrant penetrate and destabilize the rock 15 610 radially and then with the teeth 602 located on the outer face of the disc excavate the rock. The teeth 603 situated in the inner face of the disc break the chimney rock formation 611 left on the bottom of the hole by the cutting disc. Additional cutting or 20 burnishing element 604 at the lower part of the main drill body allows the cutting or burnishing of the chimney 611. The teeth 602 situated on the rear upper quadrant, in relation with the direction of the rotation of the drill body, compact the well wall. So 25 the cutting elements situated on the disc between 6 o'clock to 9 o'clock have to destabilize, evacuate, break and cut the rock, while the teeth situated on the front of the disc between 9 o'clock to 12 o'clock have a compacting action.

Fig. 11 is a lateral schematic view of a multiple layered disc assembly for drilling wide diameter holes. Discs of varying sizes are mounted in concentric rings in a stepped pattern such that the vertical distance of 35 any given disc or discs above the lowest point of the /<r °A fi a/ ± °i v 16 NOV 1993 / * / n 21 240761 main drill body increases and the diameters of said discs dx , d2 , d3 , decrease as the radial distances Cj., C2, C3, from the centerline of the said main drill body increase. By varying the size and number of the said 5 discs and their positions relative to the centerline of the main drill body, the stepped cutting profile at the base of the well bore together with the rate of drilling can be varied to suit differing rock types and formations as can the diameter of the well bore.

Thus, the several aforenoted objects and advantages are most effectively attained. Although several preferred emdodiments have been disclosed and described in detail herein it should be understood that this invention is 15 in no sense limited thereby but its scope is to be determined by that of the appended claims. 22 240761

Claims (28)

WHAT WE CLAIM IS:

1. A drill bit for use in drilling a well bore comprising 5 a main drill body designed to rotate about a substantially vertically disposed axis of rotation and incorporating a longitudinal duct for either supplying a drill fluid or air under pressure to the 10 well bore or removing a drill fluid or air combined with debris and excavated from rock from the well bore and adapted to be assembled to a drill rod, 15 cutting disc mounted on a lower portion outside said main drill body, allowing the said drill bit to form a well bore having a substantially cylindrical wall portion and a generally concave portion, the said cutting disc having cutting elements disposed in 20 generally ring-shaped formations, with the disc axis of rotation disposed at an acute angle to the axis of rotation of the main body, the lowest cutting point of the said disc being radially remote in relation to the axis of rotation of the drill body, slightly offset laterally in a rearward direction from the centerline of the said main drill body in relation to the direction of rotation of the main drill body, 30 while leaving all angles between the axes unchanged, causing the entire bit to be placed in a non-equilibrium position, rotation of the said main body enabling the disc to seek equilibrium by the cutting elements penetrating the well wall and shearing , at least one generally circular, rotatable 25 the axis of rotation of the cutting disc being * ? iri 23 240761 rocks as combined downward forces exceed opposing forces (making the drill bit self-loading), the downward forces being essentially concentrated on the lowest cutting element causing a destabilization of the well wall making easier the cutting action of the bit.

2. A drill bit according to claim 1 in which the cutting elements on the at least one disc are disposed in at least 10 three ring shaped formations, the middle ring being close to the outer periphery of the at least one cutting disc while the other rings are respectively located on the outer and inner faces of the disc; vtfiereby in use, the lowest cutting elements in the lower rearward quadrant of the middle ring 15 penetrate and destabilize the rock while the outer and inner cutting elements excavate the destabilized rock and the outer cutting elements in the rearward quadrant compact and burnish the wall of the hole. 20

3. The drill bit as defined in Claim 2 in which the axis of rotation of each cutting disc is also tilted in the direction of rotation of the main body by changing the angle of the axis of rotation in relation to the centerline of the main drill body. 25 30

4. The drill bit as defined in Claim 1 in which the extent of non-equilibrium of each cutting disc is proportional to the distance by which the axis of rotation of the said cutting disc is offset.

5. The drill bit as defined in Claim 1 in which the rotational force needed for each cutting disc to reach equilibrium is proportional to the combined downward forces on the bit. 35 (lOSEPt59!/ * C 5 *' v.. 24 240761

6. The drill bit as defined in Claim 1 in which the achievement of the rotational force needed for each cutting disc to reach equilibrium is proportional to the length, width and profile of the cutting elements. * 10

7. The drill bit as defined in Claim 2 in which two cutting discs are mounted at spaced intervals.

8. The drill bit as defined in Claim 2 in which three 15 cutting discs are mounted at spaced intervals.

9- The drill bit: as defined in claim 2 in which multiple cutting discs are mounted at spaced intervals. 20

10. The drill bit as defined in claim 2 in which multiple cutting discs are mounted at spaced intervals and multiple cutting elements are mounted to create a large combination bit capable of drilling wide diameter holes, said discs and cutting elements being arranged at 25 varying heights in relation to each other so as to create a stepped cutting profile at the base of the well bore.

11. The drill bit as defined in claim 2 in which 30 multiple cutting discs or multiple cutting elements are mounted to create a large combination bit capable of drilling wide diameter holes, said discs or elements arrranged at varying heights in relation to each other to create a stepped cutting profile at 35 the base of the well bore. "" /A*-1' oV //y i * fa c\ t410 SEP V/93r; - // 25 2

12. The drill bit as defined in Claim 1 in which there is an acute angle between the rotating axis of each cutting disc, and the rotating axis of the said main drill body. 5

13. The drill bit as defined in Claim 1 in which the amount of lateral offset of the axis of rotation of each cutting disc from the centerline of the said main drill body is 1/32 inch to 10 1/4 inch.

14* The drill bit as defined in Claim 1 in which the amount of lateral offset of the axis of rotation of each cutting disc from the centerline of 15 the said main drill body is 1/4 inch to 1 inch or more.

15. The drill bit as defined in Claim 1 in which each rotatable cutting disc is dynamically balanced, and 20 is placed so as to effectively counter-react to another disc and wherein the drill bit is self-aligning.

16. The drill bit as defined in Claim 1 in which a supplementary cutting disc is mounted on the vertical 25 axis, at the lowest point of said main drill body, the plane of the disc being perpendicular to the axis of rotation of the said main drill body, in order to disrupt any rock chimney left by the rotatable cutting disc or discs. 30

17. The drill bit as defined in Claim 1 in which each cutting disc is substantially flat*

18. The drill bit as defined in Claim 1 in which each \ 16 NOV 1993 26 240761 cutting disc is substantially concave in its outer surface. 5

19. The drill bit as defined in claim 1 in which each cutting disc is substantially convex in its outer surface.

20. The drill bit as defined in Claim 1 in which an upper portion of the said main drill body is polygonal in 10 shape, with various burnishing elements positioned facing outwards on the said main drill body.

21. The drill bit as defined in Claim 1 in which an upper portion of the said main drill body is 15 hexagonal in shape, and incorporates a number of burnishing elements.

22. The drill bit as defined in Claim 1 in which an upper portion of said main drill body has a number of 20 burnishing or cutting elements disposed at regular intervals around the periphery of the said main drill body, and no lower than the point at which a concave bottom portion of the well bore joins the cylindrical wall portion, the use of the said burnishing or cutting 25 elements around the circumference of the said main drill body being to assure a constant desired size of well bore diameter, even when the cutting elements in the or each cutting disc are worn, and also to assure a subsequent compaction and the burnishing of the remaining well 30 wall after destabilising and excavating by the said cutting

23. The drill bit as defined in Claim 1 in which an upper portion of the said main drill body has a number of 35 burnishing or cutting elements disposed at regular discs. 27 2407 61 intervals around the periphery of the said main drill body, and no lower than the point at which a concave bottom portion of the well bore joins the cylindrical wall portion, the said burnishing or cutting elements 5 being positioned in such a way that in use they form a cylindrical wall portion, of a maximum diameter greater than the diameter formed by the said cutting discs, the said burnishing elements on the upper portion of the said main drill body serving to radially compress the 10 well wall and compact it after the destabilization and excavation caused by the said cutting discs.

24. The drill bit as defined in Claim 1 in which the said main drill body is provided with means adapted to 15 drive it in rotation even if the drill rod is not in rotation, as when the bit has been deviated to alter the direction of penetration.

25. The drill bit as defined in Claim 24 in which the 20 said means of rotation comprises at least one driven turbine.

26. The drill bit as defined in Claim 1 in which there are no longitudinal ducts for supplying a drill fluid, 25 and in which the drill rod is attached longitudinally to the bottom portion of the said main drill body in such a way that the bit may be drilled upwardly from a tunnel, gallery or other space located below the rock into which a hole has been drilled from the surface by 30 a small diameter bit of sufficient diameter for the said drill rod to be lowered down the hole from the surface to the said tunnel, gallery or other space to be attached to the said drill bit, so that as the bit is drilled upwardly it enlarges the diameter of the 35 hole, and the debris falls backwards down the hole^^^ 28 240761 behind the bit into the said tunnel, gallery or other space to be collected and removed, the lateral offset of the axis of rotation of the said 5 cutting disc or discs from the centerline of the said main drill body is rearward relative to the direction of rotation of the said main drill body which rotates in the opposite direction to the direction of rotation of the said main drill body when the bit is drilling normally 10 downwardly since the direction of rotation of the said drill rod remains the same but the said drill rod is now attached to the opposite end of the said main drill body. 15

27. The drill bit as defined in Claim 1 in which a supplementary cutting disc is mounted on the vertical axis, at the lowest point of the said main drill body and comprising a means adapted to drive the said supplementary cutting disc in rotation independent of 20 the rotation or lack of rotation of the said main drill body.

28.. a drill bit, substantially as herein described with reference to any one of Figures 1, 3-5 and 7-11. NORVIC S.A By Their Attorneys BALDWIN SON & CAREY