Hard Rock Rotary Drill Bit and Method of Drilling Using Crowned Cutter Elements
This rotary drill bit provides a plurality of spaced polycrystalline diamond compact cutter elements arranged at spaced 120° concentric rings around the face of the drill bit and a secondary, redundant deeper set polycrystalline diamond compact cutter elements placed to commence scuffing the face of a bore upon wear of the primary cutter element, thereby providing extended continuous service in hard rock drill applications previously unattainable with conventional PDC bits.
Latest Tiger 19 Partners, Ltd. Patents:
The present invention relates to a drill bit for use in drilling a bore in a hard-rock formation; and more specifically, to a rotary drill bit having a plurality of hardened cutting elements providing a polycrystalline diamond compact (PDC) crown coating on each spaced carbide insert button for scuffing a bore hole face and providing a secondary shadowing or redundant hardened PDC crowned cutting element to assume the scuffing action at the same radial groove created by the primary cutter element, after wear removes the PDC crown from the primary button. Button drill bits have long been known to be useable for drilling in formations for percussion-type bits. Some have suggested shaped button drill bits for rotary drill bit applications having cutting edges for cutting into the rock face. Others have provided enlarged buttons for crushing engagement of the well bore face. As an example, U.S. Pat. No. 4,109,731 discloses a drill bit having a plurality of PDC cutter element disposed on a bit shank, but which does not attempt to systematically scour the face of the bore and only seeks to minimize the chipping forces experienced by the brittle PDC element. In the '731 patent, the cutters are angled and mounted on compression fit posts to maximize the support given the cutter element. The PDC elements have long been known to withstand direct engagement with the well bore face but easily chip when minimally stressed on an angle to the cutter body. References herein to PDC cutter elements shall mean polycrystalline diamond compact crowns or coverings on carbide inserts. The present arrangement seeks to maximize the scouring force while aligned with the longitudinal orientation of each PDC cutter element, thereby maximizing wear and minimizing chipping. The spacing of the elements and the generous fluid flow around them prevents chipping forces from prematurely fracturing the PDC elements.
SUMMARY OF INVENTIONThis rotary drill bit comprises a body having a proximal end adapted to connect to a drill string with a longitudinal passage accommodating a fluid flow through a face on a distal end of the drill bit. The rotary drill bit is populated with PDC elements which are ballistic conical buttons providing a minimal radius point to contact a bore face with a scuffing motion, thus removing a minimal amount of hardened rock in concentric tracks around the bore. These PDC elements comprise: a central PDC element with a coating of PDC creating a composite crown on a hardened element connected on the face adjacent a longitudinal axis of the drill bit; a first plurality of evenly spaced PDC crowned elements connected on the face in concentric rings providing a single point of contact on each concentric ring; and, at least three full-gauged PDC elements peripherally and evenly spaced around the face and angled from the longitudinal axis of the drill bit for contacting a bore.
This rotary drill bit can also have a second and redundant plurality of PDC elements, here each spaced about 180° from the first plurality of spaced PDC elements but placed on the same concentric radial ring, save and except for the central cutter element directly adjacent to the longitudinal axis, which has no redundant element. Each of these redundant elements has a surface profile substantially equal to the depth of the surface thickness of the PDC crown on the hardened elements of the first plurality of spaced PDC elements and there may be one or more evenly spaced plurality of PDC elements on each concentric ring. The spacing of each redundant PDC element, from one concentric ring to the next outer concentric ring, is about 120°, in the same manner as the spacing of the first plurality of elements.
At the outer edge of the rotary drill bit, the peripherally spaced full-gauged PDC crowned elements are angled away from the longitudinal axis at about 30°. As each cutter element on a concentric ring scores the wellbore face, the hardened PDC composite crown of the first plurality of spaced elements wears down. Upon full wear of the crown of each primary PDC element, the second plurality of spaced PDC elements assumes the scuffing of the well bore in place of the first on each concentric ring. The outermost elements are placed at an angle of about 30° away from the longitudinal axis to continue scuffing the well bore face as well as to prevent excessive wear on the edge of the drill bit as drilling continues into the bore.
This disclosure also provides a method for rotary drilling of hard rock providing the steps of attaching a rotary bit having radially-spaced, longitudinally-aligned ballistic conical PDC crowned carbide elements arranged in a manner that permits only a single ballistic conical element to engage a borehole face at a radius from the central longitudinal axis of the drill bit; turning the rotary bit to engage the borehole face at a central location scouring a central groove in the borehole face; increasing the forward movement of the rotary drill bit to progressively advance the crowned carbide elements against the borehole face; and, clearing borehole cuttings from the face of the borehole utilizing the hydraulic pressure from a plurality of jetting nozzles in the face of the rotary bit. The velocity of the longitudinal movement of the drill string and bit can be increased after a desired borehole width is achieved, by increasing both the speed of rotation and increasing the weight on the bit, all in a manner well known in the drilling industry. Since each radial groove is being cut in the borehole face by a single cutter, the borehole face erodes quickly from both the deepening of the grooves formed by the PDC cutter elements and the collapse of the intervening peaks from one groove to the next outer groove.
The central cutter element 16 is affixed to the drill bit adjacent the central longitudinal axis 11 of the drill bit. Central cutter element 16 is the first to engage the face of the bore and scuffs and scores the face. Since the angle of incidence of the central cutter element 16 is virtually at 90° to the rock face, no or little chipping force is experienced by this cutter element. Upon sufficient penetration of the central cutter 16, a second cutter element 18 begins to engage the bore face. The outer diameter of this second primary cutter element 18 is located a radial distance from the longitudinal center axis 11 of the drill bit equivalent to the central cutter 16 diameter, and rotated about 120° from the radius on which the central cutter is located. In
Except for the central cutter element 16, each subsequent primary cutter element, beginning with the second, has a secondary or twin, redundant or shadow cutter element shown as broken-lined elements. Accordingly, the redundant cutter 18′ is located on a concentric radial ring (not shown) occupied by the primary cutter 18 and is located 180° from the primary cutter 18 at the same radial distance from the longitudinal central axis 11 of the drill bit. Each redundant cutter is attached at a distance of about 0.050″ (0.13 cm) deeper into the face of the drill bit equivalent to the depth of the PDC crown on the primary cutter, thus allowing the secondary or redundant cutter to assume and continue the scuffing action commenced by the action of the primary cutter as wear erodes the PDC crown of the prior cutter.
Accordingly, PDC element 20 is located on a radius outside element 18 and rotated as described 120°. Shadow or redundant cutter element 20′ is on the same radius as its primary 20, and is placed on the same radius at 180° from the primary 20. Similarly, PDC element 22 is located on the next radial ring further from the axis and is 120° from element 20. Its redundant cutter element 22′ is on the same radius at 180° from the primary cutter element 22. Similarly, in this embodiment, primary cutter elements 24, 26 and 28 are placed at 120° from each other and their respective secondary shadow cutter elements 24′, 26′ and 28′ are placed 180° on the same radius from their respective primary cutter elements.
The concentric lines shown of
Located around the periphery of the drill bit, as more fully shown in
Fabricators can immediately note that as the size of the drill bit made larger, exposing a greater area cut by the drill bit, the number of PDC elements increases only linearly and not in proportion to the total area of the drill bit face. This feature makes this drill bit less expensive to scale up for use in larger diameter holes; distinguishing it from other PDC drill bit products, which require additional coverage area of the PDC cutter elements to increase the size of the drill bit. The amount of space between adjacent cutter elements is believed to minimize the chipping occurring from the swarf cut from the bore face since large pathways are provided to move the cuttings into the junk slots and up the annulus. The redundant cutter elements are believed to extend the cutting life of this bit in hard rock. Testing performed in 35 Ksi granite suggests exceptional wear characteristics might be expected in drilling hard-rock formations.
Each of the foregoing aspects of the invention may be used alone or in combination with other such aspects. The embodiments described herein are exemplary only and are not limiting of the invention, and modifications thereof can be made by one skilled in the art without departing from the spirit or teachings of this invention. Many variations and modifications of the embodiments described herein are thus possible and within the scope of the invention. Accordingly, the scope of protection is not limited to the embodiments described herein.
Claims
1. A rotary drill bit comprising:
- a body having a proximal end adapted to connect to a drill string with a longitudinal passage accommodating a fluid flow through a face on a distal end of the drill bit;
- a central PDC element providing a coating of PDC creating a composite crown on a hardened element connected on the face adjacent a longitudinal axis of the drill bit;
- a first plurality of spaced PDC crowned elements connected on the face in concentric rings providing a single point of contact on each concentric ring; and,
- at least three full-gauged PDC elements peripherally spaced around the face angled from the longitudinal axis of the drill bit for contacting a bore.
2. The rotary drill bit of claim 1 further comprising:
- a second redundant plurality of PDC elements spaced 180° from the first plurality of spaced PDC elements, and having a surface profile substantially equal to the depth of the surface thickness of the PDC crown on the hardened elements of the first plurality of spaced PDC elements.
3. The rotary drill bit of claim 1 wherein the spacing of each PDC element, from one concentric ring to the next outer concentric ring, is about 120°.
4. The rotary drill bit of claim 1 wherein the peripherally spaced full-gauged PDC crowned elements are angled at about 30°.
5. The rotary drill bit of claim 1 wherein the PDC elements are ballistic conical buttons providing a minimal radius point to contact a bore face with a scuffing motion.
6. A method for rotary drilling of hard rock comprising:
- attaching a rotary bit having radially-spaced, longitudinally-aligned ballistic conical PDC crowned carbide elements arranged in a manner that permits only a single ballistic conical element to engage a borehole face at a radius from the central longitudinal axis of the drill bit;
- turning the rotary bit to engage the borehole face at a central location scouring a central groove in the borehole face;
- increasing the forward movement of the rotary drill bit to progressively advance the crowned carbide elements against the borehole face; and,
- clearing borehole cuttings from the face of the borehole utilizing the hydraulic pressure from a plurality of jetting nozzles in the face of the rotary bit.
7. The method of claim 6 wherein the velocity of the longitudinal movement is increased after a desired borehole width is achieved.
Type: Application
Filed: Nov 24, 2010
Publication Date: May 24, 2012
Applicant: Tiger 19 Partners, Ltd. (Cypress, TX)
Inventor: Allen Kent Rives (Cypress, TX)
Application Number: 12/953,798
International Classification: E21B 7/00 (20060101); E21B 10/36 (20060101);