EP2038505A1

EP2038505A1 - A pdc drag bit

Info

Publication number: EP2038505A1
Application number: EP07784643A
Authority: EP
Inventors: Adel A. Bassal; Magdr M. Zaki; Hossam Gharib
Original assignee: Omni Oil Technologies
Current assignee: Omni Oil Technologies
Priority date: 2006-07-12
Filing date: 2007-07-12
Publication date: 2009-03-25
Also published as: WO2008006170A1

Abstract

A drilling apparatus characterized in that it includes a drill bit adapted to be attached to a drilling string, the drilling string serving to rotate said drill bit and to provide gravitational force, so that the drill bit engages a rock face with rotational and gravitational forces, said drill bit adapted to include a means of receiving drilling fluid, said drill bit adapted to include a means of mounting cutting elements onto the outer surface of said drill bit, and whereby said drill bit comprises an ellipsoidal shape, whereby said ellipsoidal shape comprises a half elliptic portion at the forward end of said drill bit and a cylindrical gauging portion.

Description

A PDC Drag Bit

FIELD OF THE INVENTION

The present invention relates to a polycrystalline diamond compact (PDC) drag bit. In particular, a PDC drag bit or drill bit, with a plurality of cutting elements, used to form a bore hole through the action of rotating the drag bit.

BACKGROUND OF THE INVENTION

A drag bit is a drill bit used to shear a rock formation through a combination of continuous downwards pressure and a rotary action. The drag bit is shaped so that its raised ridges, extending radially across the bit face, engage and penetrate the rock formation and effectively gouge out the rock face. The shape of the drag bit therefore defines the amount of surface area that can engage the rock formation. The greater the surface area of the bit face, engaging the rock formation, the more rock that can be cut and cleared away from the bit face. However, other factors such as the hardness of the rock and the ability to clear away rock cuttings also affect the penetrating efficiency.

In order to improve the penetrating ability of a drag bit, especially for harder rock formations, abrasive cutting elements are placed on the drill bit's raised ridges. These abrasive cutting elements are generally man made polycrystalline diamond compact (PDC) cutting elements and are bonded and mounted on the drill bit face so as to withstand the high operating pressures and provide greater cutting ability.

The cutting element type, size and arrangement of the cutting elements on the surface of the drill bit are dependent on the surface to be drilled. The PDC cutting element is made by bonding a carbide plate to a man made polycrystalline diamond. PDC cutting elements allow for the drilling of a wider range of surfaces than a bit with natural diamond cutting elements. Despite these advancements, cutting elements still experience rapid degradation due to the high pressures and rotation speed needed to shear rock. Cutting elements therefore need to be arranged and secured so as to ensure redundancy and maintain penetration into the rock formation. Total degradation of sufficient cutting elements will render the drag bit useless at penetrating certain rock formations and will require the total replacement of the drill bit, causing considerable loss of time and expense. The operation of PDC drag bits is further enhanced by the addition of drilling fluid. Drilling fluid is directed by fluid discharge nozzles in the drag bit used to supply the drilling face with a drilling mud so as to scrub the surface being drilling, remove any cuttings produced and reduce heat build up. Cuttings from the drag bit, if not cleared from the bit face, will constrict the action of the drill bit and reduce the rate of drilling penetration. Also, as cutting element technology increases, a drag bit equipped with these improved cutting elements can shear rock at a much quicker rate than cuttings can be removed from a bit face. Therefore, it is becoming increasingly important to remove the cuttings from the bit face to ensure a higher drilling efficiency and rate of penetration.

The size and geometry of the nozzles, as well as the volume and pressure of drilling fluid released, are important factors in improving drilling efficiency. Drilling fluid directed towards the bit face assists in reducing heat build up and provides lubrication. The drilling action will cause cuttings to gather in the drilling fluid and further drilling fluid needs to be directed and adapted to guide the fluid containing the cuttings away from the bit face.

The fluid discharge nozzles in the drag bit also need to be adapted to reduce the instances of clogging of fluid flow or "balling". Balling occurs, whilst drilling in softer rock formations, when the cuttings and the drilling mud stick to the drill bit face and reduce the cutting ability of the drill bit. The situation generally occurs in shale or clay based formations and with the use of water based drilling mud. The fluid discharge nozzles are arranged so as to direct drilling mud in order to reduce the effects of balling by scrubbing or cleaning both the rock face and the cutting elements so as to provide for a more efficient penetration and removal of cuttings. This arrangement allows the PDC drag bit to be used on a greater range of surfaces and with a greater rate of penetration.

It is an object of the present to provide the public with a useful alternative to exiting PDC drag bit arrangements.

SUMMARY OF THE INVENTION

Therefore in one form of the invention there is proposed a drilling apparatus including: a drill bit adapted to be attached to a drilling string, the drilling string serving to rotate said drill bit and to provide gravitational force, so that the drill bit engages a rock face with rotational and gravitational forces; said drill bit adapted to include a means of receiving drilling fluid; said drill bit adapted to include a means of mounting cutting elements onto the outer surface of said drill bit; and whereby said drill bit comprises an ellipsoidal shape, whereby said ellipsoidal shape comprises a half elliptic portion at the forward end of said drill bit and a cylindrical gauging portion. Preferably said drill bit is adapted to include a means of ejecting said drilling fluid from the outer surface of said drill bit;

Preferably said half elliptical portion has a curve profile to suit the characteristics of said rock face, said curve profile is adapted to withstand and transmit the gravitational and rotational force applied from said drilling sting. Preferably said half elliptical portion and gauging portions of said drill bit adapted to receive said cutting elements on said outer surface, said cutting elements mounted so as to present maximum cutting elements to the rock face and provide for redundancy should any of said cutting elements fail.

Preferably said cutting elements are mounted on said drill bit so that laterally opposed concentric cutting elements are uniform and balanced.

Preferably said cutting elements are polycrystalline diamond compact (PDC) elements.

Preferably said drill bit is adapted to include a plurality of raised ridges extending radially from said half elliptical portion and extending longitudinally along said gauging portion, adjacent to said plurality of raised ridges are a plurality of channels extending radially from said half elliptical portion and extending longitudinally along said gauging portion.

Preferably said cutting elements are mounted and arranged on said raised ridges so as to engage the rock face and form a concave penetration in said rock face, through the action of said gravitational and rotational forces. Preferably said means of ejecting said drilling fluid includes a plurality of forward circulating drilling fluid nozzles, adapted to direct a stream of drilling fluid against the concave penetration in said rock face.

Preferably said plurality of channels are adapted to channel rock cuttings formed by the engagement of said drill bit with said rock face and channel said drilling fluid after impacting said rock face.

Preferably said means of ejecting said drilling fluid includes a plurality of reverse circulating drilling fluid nozzles, adapted to direct a stream of drilling fluid away from said rock face, through said plurality of channels, to remove and force said rock cuttings and said drilling fluid up a bore hole, formed in the penetrated rock face, extending longitudinally along said drilling string.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an embodiment of the invention and, together with the description, serve to explain the advantages and principles of the invention. In the drawings:

Figure 1 illustrates a perspective view of a poly crystalline diamond compact (PDC) drag bit in accordance with the present invention;

Figure 2 illustrates a front perspective view of the poly crystalline diamond compact (PDC) drag bit;

Figure 3 illustrates a perspective view of the poly crystalline diamond compact (PDC) drag bit, including a cut away section exposing the path of travel for the drilling fluid.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following detailed description of the invention refers to the accompanying drawings. Although the description includes exemplary embodiments, other embodiments are possible, and changes may be made to the embodiments described without departing from the spirit and scope of the invention. The present invention refers to a rotary drill bit, in particular a polycrystalline diamond compact (PDC) drag bit. Figure 1 shows a PDC drag or drill bit 10 consisting of a drill bit segment 12, with an ellipsoidal shape, with a plurality of raised ridges 14 raised above the bit body and extending longitudinally, and an attachment means 16, adapted to attach the drill bit 10 bit to a drilling rig. The bit 10 is suspended, by a drilling string which is in turn attached to a drilling rig mounted on the surface (both are not shown). The drilling rig is adapted to rotate the drilling string and thus rotate the drill bit 10. The drill bit 10 engages the rock formation and shears the rock by both rotating and applying pressure to the rock formation via the weight of the drilling string. The attachment means 16 is adapted to include a means of attaching a drilling fluid supply and contains a drilling fluid chamber, extending longitudinally from opening 18 through the drill bit segment 12.

Drill bit segment 12 extends from the base of the raised ridges 14 to the tip of the ellipsoidal bit structure and consists of two distinctly shaped portions. At the forward end or rock face end, the bit segment is a half ellipsoid, with the degree of curvature dependent on the surface being drilled. A harder rock formation would require a narrower ellipsoidal shape, with a more acute conical angle, to more efficiently penetrate the rock. Whist a softer surface, for example clay, is easier to penetrate and a flatter drill bit shape would be more efficient in removing material from the rock face.

The drag bit 10 requires pressure to be exerted onto the rock face to operate effectively. As a result, the shape of the bit segment 12 needs to be adapted to withstand and transmit these forces to the rock face. An ellipsoidal shape is known for its integral strength and is most efficient in withstanding the forces and presenting a large cutting surface area to the rock formation. Hence, the ellipsoidal shape will wear better and be less prone to catastrophic failure, prolonging the life span of the bit 10, and increasing the efficiency of the drilling process. At the rearward end of the drill bit segment 12, the shape is essentially cylindrical. The raised ridges in this cylindrical portion engage the walls of the already penetrated rock formation and effectively gauge and clean the bore hole being drilled.

At the forward end of the drill bit, the half elliptical portion 24 of the bit segment 12 is defined between the rearward ellipsoidal section 20 and the outermost tip of the ellipse (shown in figure 2). The raised ridges 14 only extend part of the half elliptical portion 24 as the plurality of raised ridges 14 converge radially to the focus or pole of the ellipse. The focus or pole of the half elliptical portion is more clearly shown in figure 2. The half elliptical portion 24 is defined by a circle with a diameter formed at the forward end of the raised ridge 22 and converges in an ellipsoidal manner to a point. The rearward or gauging portion 28 of the bit segment 12 is defined between the rearward ellipsoidal section 20 and the rearward bit segment 26. At the rearward bit segment 26, the raised ridges 14 return to the bit body and the bit segment 12 joins the attachment means 16.

The plurality of raised ridges 14, extending radially from the half ellipse focus point and longitudinally along the body of the drill bit segment 12, are raised above the bit body 30 forming a plurality of channels 31 between the adjacent raised ridges 14. These channels 31 allow for the cuttings of rock to be removed from the area near the bit face and for drilling fluid to be channelled away. Drilling fluid or drilling mud is used to assist the drilling process by impacting the rock surface at high speed. The drilling fluid is ejected, at a high flow rate, from nozzles in the bit body 30 and is used to reduce the temperature of the drill bit 10, clear and scrub the rock face and remove cuttings.

Figure 1 shows a reverse circulating nozzle 32, directed at ejecting drilling fluid back up the bore hole in order to remove any cuttings embedded in the drilling fluid from the face of the drill bit 10. The bit body 30 contains a plurality of reverse circulating nozzles 32 and each are directed at removing cuttings and drilling fluid in order to increase the efficiency of the drilling process and ensure that the maximum amount of drill bit 10 is engaged with the rock formation. The addition of these reverse directed nozzles allows for the fluid to be ejected, from the bit body 30, at lower pressures than prior art solutions. High drilling fluid pressures can reduce the effectiveness of the drilling process by reducing the force exerted by the drill bit 10 on the rock formation.

Figure 2 illustrates a front perspective view of the PDC drag bit 10 and shows the geometry of the number and shape of raised ridges 14, the number and positioning of drilling fluid ejecting nozzles and the arrangement of the plurality of cutting elements 38. From figure 2, it can be seen in this embodiment that there are eight raised ridges 14, equally spaced and 45 degrees apart, extending radially from the bit body conical portion 36. The cutting elements 38 are arranged and mounted on the half ellipse pole 36 of the bit body 30 and on the raised ridges 14. Cutting elements 38 include a stud portion 40, for mounting into the bit body 30 and a poly crystalline diamond portion 42 for cutting into the rock surface.

The cutting elements 38 are closely spaced over the surface of the half ellipse pole 36 and the raised ridges 14, so as to ensure the maximum cutting ability and drilling efficiency. The cutting elements 38 are mounted in such a fashion that the cutting edge 42 of the cutting elements 38 will engage the rock face in an anti- clockwise direction of rotation. The closely spaced arrangement of cutting elements 38 allows for redundancy should any of the cutting elements fail. Cutting elements 38 are also mounted on the raised ridges 14 of the gauging portion, to assist with the cutting, gauging and smoothing of the bore hold being drilled. The gauging portion is also used to stabilise the drill bit and provide for more accurate drilling. The size of the gauging portion 28 relative to total size of the drill bit 10 is dependent on the angle of hole being drilled. A vertical bore hole requires a longer gauging portion, whereas a curved borehole requires the use of a shorter gauging portion.

The cutting elements 38 are mounted around the forward fluid circulating nozzles 34 and 44. In this embodiment, the half ellipse pole 36 contains four forward circulating drilling fluid nozzles 44, each equally spaced and 90 degrees apart. These nozzles 44 are directed at ejecting drilling fluid at the rock face, assisting the action of the cutting elements 38 mounted on the half ellipse pole 36. Located on the forward portion of the channels 31, adjacent to the forward end of the raised ridges 22, are four equally spaced forward circulating nozzles 34. These four nozzles are spaced at 90 degrees from each other and are directed to eject drilling fluid towards the rock face, assisting the action of the cutting elements 38 mounted on the raised ridges 14. The cutting elements 38 are arranged and mounted on the drill bit so that concentric laterally opposed cutting elements are uniform and balanced so as to ensure less wear on the drill bit and a longer bit life.

The drilling fluid ejected from the forward circulating nozzles 34 and 44 is directed by the angle of the nozzle holes 46 and 48. Likewise, the rearward circulating nozzle has its ejected fluid stream directed by the angle of the nozzle hole 50 (shown in figure 1).

Figure 3 illustrates a cut away section of the drag bit 10 illustrating the path the drilling fluid takes in the drilling fluid chamber 51. The chamber 51 extends from the opening 18 to the specifically angled exit chambers. The amount of drilling fluid ejected from the forward and rearward nozzles is governed by the diameter and shape of their respective exit chambers. The four forward ejecting nozzles 44, located on the conical end portion 36, are supplied drilling fluid from four exit orifices 52 (two are displayed in figure 3). The four forward ejecting nozzles 34, located in the channels 31, are supplied drilling fluid from exit orifices 56 (one is displayed in figure 3). The four, equally spaced, reverse ejecting nozzles 32 are supplied drilling fluid by the reverse angled exit orifices 54, (one is displayed in figure 3).

Further advantages and improvements may very well be made to the present invention without deviating from its scope. Although the invention has been shown and described in what is conceived to be the most practical and preferred embodiment, it is recognized that departures may be made therefrom within the scope and spirit of the invention, which is not to be limited to the details disclosed herein but is to be accorded the full scope of the claims so as to embrace any and all equivalent devices and apparatus. In any claims that follow and in the summary of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprising" is used in the sense of "including", i.e. the features specified may be associated with further features in various embodiments of the invention.

Claims

1. A drilling apparatus characterized in that it includes:

a drill bit adapted to be attached to a drilling string, the drilling string serving to rotate said drill bit and to provide gravitational force, so that the drill bit engages a rock face with rotational and gravitational forces;

said drill bit adapted to include a means of receiving drilling fluid;

said drill bit adapted to include a means of mounting cutting elements onto the outer surface of said drill bit; and whereby

said drill bit comprises an ellipsoidal shape, whereby said ellipsoidal shape comprises a half elliptic portion at the forward end of said drill bit and a cylindrical gauging portion.

2. A drilling apparatus according to claim 1, characterized in that said drill bit is adapted to include a means of ejecting said drilling fluid from the outer surface of said drill bit;

3. A drilling apparatus according to claim 1 or claim2, characterized in that said half elliptical portion has a curve profile to suit the characteristics of said rock face, said curve profile is adapted to withstand and transmit the gravitational and rotational force applied from said drilling sting.

4. A drilling apparatus according to any one of the preceding claims, characterized in that said half elliptical portion and cylindrical gauging portions of said drill bit are adapted to receive said cutting elements on said outer surface, said cutting elements mounted so as to present maximum cutting elements to the rock face and provide for redundancy should any of said cutting elements fail.

5. A drilling apparatus according to any one of the preceding claims, characterized in that said cutting elements are mounted on said drill bit so that laterally opposed concentric cutting elements are uniform and balanced.

6. A drilling apparatus according to any one of the preceding claims, characterized in that said cutting elements are polycrystalline diamond compact (PDC) elements.

7. A drilling apparatus according to any claims, characterized in that said drill bit is adapted to include a plurality of raised ridges extending radially from said half elliptical portion and extending longitudinally along said gauging portion, adjacent to said plurality of raised ridges are a plurality of channels extending radially from said half elliptical portion and extending longitudinally along said gauging portion.

8. A drilling apparatus according to claim 7, characterized in that said plurality of channels are adapted to channel rock cuttings formed by the engagement of said drill bit with said rock face and channel said drilling fluid after impacting said rock face.

9. A drilling apparatus according to any one of the preceding claims, characterized in that said cutting elements are mounted and arranged on said raised ridges so as to engage the rock face and form a concave penetration in said rock face, through the action of said gravitational and rotational forces.

10. A drilling apparatus according to claim 2, characterized in that said means of ejecting said drilling fluid includes a plurality of forward circulating drilling fluid nozzles, adapted to direct a stream of drilling fluid against the concave penetration in said rock face.

11. A drilling apparatus according to claim 2, characterized in that said means of ejecting said drilling fluid includes a plurality of reverse circulating drilling fluid nozzles, adapted to direct a stream of drilling fluid away from said rock face, through said plurality of channels, to remove and force said rock cuttings and said drilling fluid up a bore hole, formed in the penetrated rock face, extending longitudinally along said drilling string. >