WO1996024744A1

WO1996024744A1 - Improvements in or relating to drill bits

Info

Publication number: WO1996024744A1
Application number: PCT/GB1996/000255
Authority: WO
Inventors: Neil Simpson; Michael Wardley
Original assignee: Brit Bit Limited
Priority date: 1995-02-07
Filing date: 1996-02-07
Publication date: 1996-08-15
Also published as: GB9502378D0; AU4629496A

Abstract

Improved drill bits for use in the drilling of boreholes or the like, having a plurality of fluid jets (112) whereby fluid is provided to clean and cool the bit and to pump away cuttings, in which the jet nozzles are oriented so as to provide lateral jetting of the fluid (i.e. fluid jets which are directed outwardly from the centre of the bit at a shallow angle with respect to the bottom of the borehole and have a relatively long path length prior to impact with the formation). The nozzles are located and the drill bit is configured to ensure that there is sufficient fluid flow to provide adequate cleaning and cooling of the centre of the bit. In certain embodiments, the location and configuration induce a suction flow of fluid across the bit surface in response to the jet flow from the nozzles. In other embodiments, additional, low pressure, fluid outlets are provided at the centre of the bit to provide additional fluid flow for cleaning and cooling. The use of lateral jetting provides a drill bit with enhanced performance.

Description

"Improvements in or Relating to Drill Bits"

The present invention relates to improvements in or relating to drill bits of the type employed, for example, in the drilling of boreholes for oil wells and the like. More particularly, the invention relates to improvements in drill bits employing fluid jetting nozzles.

Conventional drill bits of the type having roller cone cutter elements or fixed cutter elements (i.e. polycrystalline diamond compact (PDC) cutters or the like) use fluid jetting nozzles to clean and cool the face of the bit and to dislodge cuttings from the hole bottom. Pressurised fluid is pumped down the interior of the drill string to which the bit is attached and exits the jetting nozzles. The nozzle exit velocity is sufficiently high to cause a high degree of turbulence which scours the cuttings away from the cutting face of the formation (i.e. that part of the formation at the borehole bottom being acted upon by the drill bit) and up the borehole annulus surrounding the drill string.

This approach to bit cleaning has been the standard approach for more than thirty years. Although some changes have been made with the nozzle placement and orientation, the path length of the jet stream between the jet nozzle and the cutting face of the formation has always been short and the angle of fluid flow with respect to the cutting face has always been large; i.e. close to perpendicular.

The reason for this has been due to a number of factors:

(i) the success of this approach with roller cone bits; (ϋ) the increase in performance with roller cone bits when maximising hydraulic horsepower or jet impact force, which is thought to reduce chip hold down; (ϋi) the geometry of the roller cone and fixed cutter bits making it difficult to mount nozzles with "shallow" angles of flow relative to the cutting face.

It is far easier from a manufacturing viewpoint to bore nozzle ports from the outside of the bit, with the flow path from the centre of the bit to the exit point being a straight line. This means that, for the majority of bits, the direction of travel of the fluid jet at the point of exiting the nozzle parallel or close to parallel to the direction of travel of the bit; i.e. at or close to 90° to the cutting face at the impact point. Conventional jets of this type will be referred to herein, for convenience, as "perpendicular jets" (it being understood that this term embraces jets which are close to perpendicular) .

The introduction of investment casting techniques for the manufacture of bit bodies for fixed cutter bits has made it considerably easier to form curved fluid conduits within the bit body. This has made possible the incorporation of "lateral jets", of the type illustrated in Fig. 1(a) of the accompanying drawings, which shows a bit 10, formed by investment casting techniques, having a plurality of fixed cutter elements 12 mounted in the blades thereof and having a curved fluid conduit 14 extending from the centre of the drill bit, which is in fluid communication with the interior of the drill string, in use, to a nozzle 16 mounted in the slot between a pair of adjacent blades of the bit and oriented such that the fluid flow from the nozzle is at a "shallow" angle with respect to the cutting face; i.e. at a "large" angle with respect to the direction of travel of the bit. For comparison, Figs. 1(b) and 1(c) show comparable steel and matrix bits formed by conventional means and incorporating linear fluid conduits and perpendicular jets of the type discussed above.

As used herein, the term "lateral jet" means a jet in which the jet nozzle is oriented on the drill bit such that the angle of the jet stream axis with respect to the cutting face of the formation is small or "shallow"; i.e. substantially less than perpendicular. This means that the jet stream from the nozzle has a relatively long path length prior to striking the formation.

The "cutting face" is the surface of the formation at the bottom of the hole, and can be regarded as nominally planar and perpendicular to the direction of travel of the bit. The angle at which the fluid from a lateral jet actually strikes the formation may vary, and may be quite large, depending upon the actual geometry of the cutting face and the location of the nozzles on the bit. A lateral jet provides a jet stream directed at a shallow angle relative to the nominal plane of the cutting face and, therefore, having a long path length compared with a "perpendicular" jet.

For practical purposes, a "lateral jet" may be considered to be a jet oriented at a "shallow" angle relative to the cutting face, and a "shallow angle" may be considered to be an angle less than or equal to 45°, and preferably close to parallel, with respect to the cutting face.

It is well known that the venturi effect creates a zone of low pressure surrounding a fast-moving jet of liquid at and close to its exit point. This effect can be used to entrain other fluids or particulate material into the jet stream. This basic principle is used in a variety of applications such as:

- spray guns and automotive carburettors where air is the driving fluid and paint or fuel is the entrained fluid; - jet-type dredge pumps where water or other liquid is the driving fluid and particulate material is entrained and pumped away.

In the case of drill bit nozzles, such a zone of low pressure also exists at and close to the exit point of the nozzle. In the majority of bit nozzle configurations, where the jet is fired at or close to 90° to its impact point, this low pressure zone causes a recirculation of fluid which enhances the turbulence caused by the jet, but also recirculates the particulate material in the vicinity of the nozzle. This effect is illustrated in Fig.2, which shows a matrix bit 20 similar to that of Fig. 1(c), having linear fluid conduits 22 and perpendicular nozzles 24, where the arrows 26 indicate the recirculating motion of the fluid exiting the nozzles 24.

It can be seen that the effect of the fluid jets could be enhanced by utilizing the low pressure zone surrounding the jet to greater advantage. This can be done by directing the jet nozzle in such a way that the area of the jet which creates the low pressure effect is increased. One way in which this can be achieved is by directing the nozzle at a shallow angle, so as to create a lateral jet. This effect is maximised when the jet stream axis is parallel or close to parallel (i.e. "substantially parallel") to the nominal plane of the cutting face, with the nozzle exit points being located as close as possible to the cutting face in the direction of travel of the drill bit.

This is illustrated in Fig. 3 which shows a drill bit 30, similar to that of Fig. 1(a), having a curved fluid conduit 32 and a lateral nozzle 34, where the arrows 36 indicate the recirculating motion of the fluid exiting the nozzle 34.

Lateral jets have been used to a limited extent in "hybrid" bits in which the main fluid flow through the bit is provided by conventional, perpendicular jets, augmented by additional flow through lateral jets. One such hybrid bit included four perpendicular jets and two lateral jets. The present inventors' experience showed that such hybrid bits exhibited improved performance in comparison with conventional bits in which the entire fluid flow through the bit is provided by perpendicular jets.

This experience suggested that further performance enhancement could be obtained with a drill bit in which all, or substantially all, or at least a majority of the fluid flow through the bit is provided by means of lateral jets. However, this raises difficulties in the design of the bit to accommodate the required lateral jets. Also, existing lateral jets are directed outwardly from the bit from locations which are themselves spaced outwardly from the centre of the bit. This creates a problem as regards adequate cleaning and cooling of the central portion of the bit, since little fluid flow is generated in the central portion of the bit. In use, inadequate cleaning and cooling would result in failure of the bit.

In accordance with the present invention, there is provided a drill bit adapted for connection to a drill string including a plurality of cutting elements and a plurality of fluid passages, at least some of which include jet nozzles, adapted for fluid communication with the interior of said drill string in use of the drill bit, wherein the fluid passages are located and oriented such that at least a majority of the fluid flow through the drill bit is provided, in use, by means of lateral jets.

Preferably, the location and orientation of said fluid passages and the configuration of the drill bit are selected such that the fluid flow generated externally of the drill bit by said fluid flow through the drill bit is adequate to cool and to clean the drill bit in use thereof.

In accordance with certain embodiments of the invention, the entire fluid flow through the drill bit is provided by means of lateral jets, the drill bit being configured and the jet nozzles being located and oriented such that the jet flow from said lateral jets, in use, generates a suction flow of fluid external of the drill bit, which suction flow serves to clean and cool a central portion of the drill bit.

Preferably, the drill bit includes a plurality of blades upon which said cutting elements are mounted, and a plurality of junk slots disposed between said blades, each of said jet nozzles being located in one of said junk slots adjacent the centre of the drill bit and oriented so as to direct a jet flow outwardly from the centre of the drill bit, and each of the junk slots in which one of said nozzles is located being in communication with a further junk slot, such that low pressure zones generated by said outward jet flow in said junk slots in which the jet nozzles are located results in inward suction flow toward the centre of the drill bit in said further junk slots.

In accordance with a first preferred embodiment, said jet nozzles comprise discrete nozzle elements mounted in a drill bit body and communicating with a chamber in the centre of said drill bit body.

In a second preferred embodiment, said jet nozzles are provided in a unitary nozzle assembly mounted in a drill bit body, the individual nozzles of said nozzle assembly communicating with a chamber in the centre of said nozzle assembly, and said chamber in the centre of said nozzle assembly communicating with a chamber in the centre of said drill bit body.

In accordance with other embodiments of the invention, the entire fluid flow through the drill bit is provided by means of lateral jets, the drill bit being configured and the jet nozzles being located and oriented such that the jet flow from said lateral jets. in use, originates sufficiently closely to the centre of the bit as to clean and cool a central portion of the drill bit.

In a preferred embodiment, said jet nozzles are integrally formed in a unitary nozzle assembly mounted in a drill bit body, the individual nozzles of said nozzle assembly communicating with a chamber in the centre of said nozzle assembly, and said chamber in the centre of said nozzle assembly communicating with a chamber in the centre of said drill bit body.

In accordance with other embodiments of the invention, at least a majority of the fluid flow through the drill bit is provided by means of lateral jets spaced from the centre of the drill bit, and the remainder of the fluid flow through the drill bit is provided by at least one additional fluid passage located at or adjacent to the centre of the drill bit.

Preferably, said at least one additional fluid passage communicates with a central fluid conduit extending along a central longitudinal axis of the drill bit and said jet nozzles communicate with an annular fluid conduit surrounding said central fluid conduit, and said central and annular fluid conduits communicate, in use with the interior of the drill string to which the drill bit is attached.

Preferably also, said jet nozzles communicate with said annular fluid conduit via curved passages formed in the drill bit body.

Optionally, said central fluid conduit may include a restrictor nozzle at an upstream end thereof so as to reduce the pressure of fluid passing through said central fluid conduit relative to the pressure of fluid passing through said annular fluid conduit.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Fig. 1(a) is a sectional side view of a drill bit formed by investment casting to include a curved fluid passage providing a lateral jet;

Fig. 1(b) is a sectional side view of a conventional steel drill bit including linear fluid passages providing perpendicular jets;

Fig. 1(c) is a sectional side view of a conventional matrix drill bit including linear fluid passages providing perpendicular jets;

Fig. 2 is a sectional side view of a drill bit similar to that of Fig. 1(c) illustrating the flow pattern of fluid exiting its jet nozzles;

Fig. 3 is a sectional side view of a drill bit similar to that of Fig. 1(a) illustrating the flow pattern of fluid exiting its jet nozzles;

Fig. 4 is a perspective view of one embodiment of a drill bit in accordance with the present invention;

Fig. 5 is a sectional side view of a drill bit body of the drill bit of Fig. 4 showing the mounting of a jet nozzle therein;

Fig. 6 is a bottom end view of the drill bit body of Fig. 5; Figs. 7(a) and 7(b) are detail views of portions of the drill bit body of Fig. 5 in which the jet nozzle is mounted;

Figs. 8(a), 8(b) and 8(c) are, respectively, front, top and sectional side views of the jet nozzle of Fig. 5;

Figs. 9(a), 9(b) and 9(c) are sectional side views of an alternative embodiment of a drill bit body of the drill bit of Fig. 4, in which the jet nozzles are provided by a unitary nozzle assembly mounted within the drill bit body;

Figs. 10(a) and 10(b) are, respectively, sectional plan and side views of a main body of the nozzle assembly of Fig. 9 and Fig. 10(c) is a sectional detail view of a portion thereof;

Fig. 11 is a plan view of a further embodiment of a drill bit embodying the invention; and

Fig. 12 is a sectional side view of the drill bit of Fig. 11.

Referring now to the drawings, Fig. 4 shows a first embodiment of a drill bit 100 in accordance with the invention. The drill bit has a plurality of blades 102, 104 with junk slots 106, 108 separating adjacent blades. Cutting elements (such as PDC's) 110 are mounted on the leading edges of the blades 104, 106 as is well known in the art. Additional cutting elements (not shown) would also be mounted on the lower flanks of the blades.

In this example, there are a total of six blades. Three of the six blades 102 are joined at the centre of the top of the generally dome-shaped bit and the remaining three blades 104 are located therebetween, terminating short of the centre where the first three bits 102 are joined. Accordingly, the junk slots 106 communicate with the junk slots 108 at their uppermost ends adjacent the centre of the bit.

Fluid jet nozzles 112 (three in this case, of which one is visible in Fig. 4) are located in each of the junk slots 106. The nozzles are each oriented to provide lateral jetting of fluid exiting therefrom (as discussed and defined above) . An example of the mounting and orientation of the nozzle in the bit body is best seen in the sectional view of Fig. 5. As is also seen in Fig. 5, the nozzle exit is located in an outwardly facing step surface of the junk slot 106 in which it is located, the bottom surface of the junk slot 106 inwards of the nozzle exit being essentially contiguous with the bottom surface of the junk slot 108, with which it communicates, at the centre of the top of the bit.

In this example, the nozzles 112 comprise individual nozzle units 114 (typically of tungsten carbide), which are located in holes 116 formed in the bit body. The arrangement of the holes 116 relative to the blades 102, 104 and junk slots 106, 108 can be seen in the bottom view of the bit body in Fig. 6, and the detailed configuration of the holes 116 can be seen in the detail views of Figs. 7(a) and 7(b). Details of the nozzle unit are shown in Figs. 8(a), 8(b) and 8(c).

The bit body is hollow, having a central chamber 118 which, in use, is in fluid communication with the interior of the drill string (not shown) to which the drill bit is attached. The nozzle units are mounted in --

12 the holes 116, being sealed by O-rings and retained by circlips, as is well known in the art, and thus provide fluid passages between the interior chamber 118 and the exterior of the drill bit.

As has been discussed above, the fluid jets exiting the nozzles 112 create zones of low pressure at and close to the nozzle exits. In this embodiment, the fact that the respective junk slots 106, 108 communicate with one another allows the outward jet flow from the nozzles 112 to induce an inward suction flow in the corresponding junk slots 108. The jet flows from each of the nozzles are indicated in Fig. 4 by arrows 120 and the suction flows by arrows 122.

This arrangement provides an external fluid flow at and around the central portion of the drill bit, such that this central portion is cleaned and cooled, in use, in a manner which would not otherwise be effected by the lateral jets of the drill bit. Accordingly, the benefits of lateral fluid jetting can be obtained while still maintaining adequate cooling and cleaning of the entire drill bit.

Figs. 9(a), 9(b) and 9(c) illustrate a variant of the embodiment of Fig. 4, in which the nozzles 112 are provided in a unitary nozzle assembly 124 which is mounted at the top of the chamber 118 of the drill bit body. The nozzle assembly 124 comprises a nozzle assembly body 126 and a plurality of nozzle units 128 mounted therein, which are aligned with holes 130 formed in the drill bit body. Figs. 10(a), 10(b) and 10(c) show the configuration of the nozzle assembly body 126, which comprises a generally cylindrical block having a central chamber 132, which is open at the bottom of the body 126 to communicate with the chamber 118 of the drill bit body, and a plurality of bores 134 extending from the peripheral surface of the block to the central chamber 132. The nozzle units 128 are located in the bores 134, which are profiled to receive O-rings and circlips (not shown) to seal and locate the nozzle units 128.

In a further variant (not illustrated), the nozzle assembly might be formed as an integral unit, the jet nozzles being formed in the body of the assembly rather than being provided as separate nozzle units mounted in the body. In this case, the nozzle assembly might be made sufficiently small that the nozzle exits could be close enough to the centre and top of the drill bit that the fluid flow generated by the fluid jets would be sufficient to clean and cool the centre of the drill bit without the need for the arrangement of stepped, interconnecting junk slots included in the embodiments of Figs. 4 to 10.

As previously discussed, "lateral jetting" means that the fluid flow is directed at a shallow angle to the cutting face of the formation, providing a relatively long path length before impact. Generally, where the nozzle exits are close to the top of the drill bit, this means that the jet axis is preferably at or close to right angles to the central, longitudinal axis of the drill bit in order to maximise the beneficial effects of lateral jetting. In the illustrated examples, the jets are inclined slightly towards the top of the bit. It has been found also that the low pressure effect previously discussed is effective when the nozzle exit points are arranged such that the distance between the nozzle exits and the bottom of the hole is no more than about seven nozzle exit diameters. The effect is increased as this distance is reduced. Accordingly, it is desirable that distance between the nozzle exit and the bottom of the hole be made as small as practicable.

(It is noted here that the "top" of the bit as shown in the drawings and as described herein will normally be the "bottom" of the bit as oriented in use) .

Figs. 11 and 12 illustrate a further embodiment of the invention. In this case, the drill bit 200 again includes a plurality of blades 202 (six in this example) having cutting elements 204 such as PDC's mounted thereon. The blades 202 are separated by junk slots 206, and the bit further includes a plurality of fluid jet nozzles 208 (one for each blade -i.e. six - in this example) arranged to provide lateral jetting. In this embodiment, fluid flow for cleaning and cooling the central portion of the bit is provided by additional fluid passages 210 exiting at or adjacent to the centre of the drill bit. The lateral jet flow from the nozzles 208 is indicated in Figs. 11 and 12 by arrows 212, and the additional "feeder" flow from the passages 210 at the bit centre into the junk slots 206 by arrows 214.

As is seen in Fig. 12, the drill bit includes a central, longitudinal bore 218 which, in use, is in fluid communication with the interior of the drill string (not shown) and which communicates with a chamber 220 in the bit body. A central fluid conduit 222 extends along the length of the bore 218, having an inlet end 224 which communicates with the interior of the drill string, in use, and having an outlet end 226 which communicates with the additional fluid passages 210. The space between the exterior of the central conduit 222 and the wall of the bore 218 provides an annular fluid conduit 227 which connects the interior of the drill string to the chamber 220. Curved fluid passages 228, of which one is shown in Fig. 12, provide fluid communication between the various nozzles 212 and the chamber 220.

In the example illustrated, the central conduit 222 has a restrictor nozzle 230 fitted at its inlet end. This has the effect of dividing the total fluid flow from the drill string into a restricted, low pressure flow through the central conduit 222 to the additional fluid passages 210 and a high pressure flow through the annular conduit 227 to the nozzles 208. Alternatively, if no pressure differential is required between the fluid supplied to the passages 210 and the nozzles 208, then the restrictor nozzle 230 can be dispensed with, as can the central conduit 222 itself.

The advantages provided by lateral jetting include:

(a) Increased rate of penetration (ROP) due to the low pressure surrounding the fluid jets creating a localised reduction in bottom hole pressure (a locally produced overbalance) which recovers beyond the bit face; i.e. normal or slightly elevated pressures in the bit junk slot areas and hole annulus. (b) Enhanced cutting efficiency due to the entrainment effect of the jet causing bottom hole scavenging of any loose material or cuttings from the bit face. (c) Erosion damage reduction due to the rapid evacuation of loose material and cuttings by directed lateral jets towards exit points (junk slots) with minimum turbulent erosion to the bit body. (d) Enhanced cutter cleaning and cooling due to the creation of desirable cross flow caused by the low pressure zones behind the lateral jets. (e) The ability to recirculate additional fluid across the bit face for cooling and cleaning by using the cross flow induced by the lateral jets to draw a proportion of the pumped flow exiting from the bit junk slots back across the bit face; i.e. for 600 gallons per minute (GPM) pumped through the bit having (for example) 800 GPM circulated across the bit face. This provides improved cleaning and cooling, especially in areas of restricted flow, such as small diameter and deep hole applications.

The present invention allows the advantages of lateral jetting to be exploited as fully as possible while ensuring that the central portion of the bit is cooled and cleaned to an adequate extent.

Improvements and modifications may be incorporated without departing from the scope of the invention.

Claims

1. A drill bit adapted for connection to a drill string including a plurality of cutting elements and a plurality of fluid passages, at least some of which include jet nozzles, adapted for fluid communication with the interior of said drill string in use of the drill bit, wherein the fluid passages are located and oriented such that at least a majority of the fluid flow through the drill bit is provided, in use, by means of lateral jets.

2. A drill bit as claimed in Claim 1, wherein the location and orientation of said fluid passages and the configuration of the drill bit are selected such that the fluid flow generated externally of the drill bit by said fluid flow through the drill bit is adequate to cool and to clean the drill bit in use thereof.

3. A drill bit as claimed in Claim 2, wherein the entire fluid flow through the drill bit is provided by means of lateral jets, the drill bit being configured and the jet nozzles being located and oriented such that the jet flow from said lateral jets, in use, generates a suction flow of fluid external of the drill bit, which suction flow serves to clean and cool a central portion of the drill bit.

4. A drill bit as claimed in Claim 3, wherein the drill bit includes a plurality of blades upon which said cutting elements are mounted, and a plurality of junk slots disposed between said blades, each of said jet nozzles being located in one of said junk slots adjacent the centre of the drill bit and oriented so as to direct a jet flow outwardly from the centre of the drill bit, and each of the junk slots in which one of said nozzles is located being in communication with a further junk slot, such that low pressure zones generated by said outward jet flow in said junk slots in which the jet nozzles are located results in inward suction flow toward the centre of the drill bit in said further junk slots.

5. A drill bit as claimed in Claim 3 or Claim 4, wherein said jet nozzles comprise discrete nozzle elements mounted in a drill bit body and communicating with a chamber in the centre of said drill bit body.

6. A drill bit as claimed in Claim 3 or claim 4, wherein, said jet nozzles are provided in a unitary nozzle assembly mounted in a drill bit body, the individual nozzles of said nozzle assembly communicating with a chamber in the centre of said nozzle assembly, and said chamber in the centre of said nozzle assembly communicating with a chamber in the centre of said drill bit body.

7. A drill bit as claimed in Claim 2, wherein the entire fluid flow through the drill bit is provided by means of lateral jets, the drill bit being configured and the jet nozzles being located and oriented such that the jet flow from said lateral jets, in use, originates sufficiently closely to the centre of the bit as to clean and cool a central portion of the drill bit.

8. A drill bit as claimed in Claim 7, wherein said jet nozzles are integrally formed in a unitary nozzle body mounted in a drill bit body, the individual nozzles of said nozzle body communicating with a chamber in the centre of said nozzle body, and said chamber in the centre of said nozzle body communicating with a chamber in the centre of said drill bit body.

9. A drill bit as claimed in Claim 2, wherein at least a majority of the fluid flow through the drill bit is provided by means of lateral jets spaced from the centre of the drill bit, and the remainder of the fluid flow through the drill bit is provided by at least one additional fluid passage located at or adjacent to the centre of the drill bit.

10. A drill bit as claimed in Claim 9, wherein said at least one additional fluid passage communicates with a central fluid conduit extending along a central longitudinal axis of the drill bit and said jet nozzles communicate with an annular fluid conduit surrounding said central fluid conduit, and said central and annular fluid conduits communicate, in use, with the interior of the drill string to which the drill bit is attached.

11. A drill bit as claimed in Claim 10, wherein said jet nozzles communicate with said annular fluid conduit via curved passages formed in the drill bit body.

12. A drill bit as claimed in Claim 10 or Claim 11, wherein said central fluid conduit includes a restrictor nozzle at an upstream end thereof so as to reduce the pressure of fluid passing through said central fluid conduit relative to the pressure of fluid passing through said annular fluid conduit.