DRILL BIT WITH STAGED DURABILITY, STABILITY AND ROP CHARACTERISTICS
Drill bit with multiple stages of durability and ROP characteristics is disclosed. The drill bit has multiple layers of cutters established by deploying the cutters on blades of different heights or maintaining the blades at the same height and deploying the cutters to have different heights on one or more blades. Each layer provides independent bottom hole coverage and has independent stabilization, ROP, and durability characteristics so as to effectively drill through different subsurface formations. Cutters deployed on the different layers have their respective centers at substantially different radial positions. Due to the different radial positions, cutters in different layers cut different swaths in the subsurface formation. Cutters in different layers may also have different initial peripheral portions or shear lengths, resulting in different impact resistance characteristics for the different layers. This changes the wear and/or cutter deterioration processes for the different layers, resulting in different and/or improved toughness characteristics.
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This application for patent claims priority to, and hereby incorporates by reference, U.S. Provisional Application Ser. No. 60/746767, entitled “Drill Bit with Staged Durability and ROP Characteristics,” filed May 8, 2006 with the United States Patent and Trademark Office.
FIELD OF THE INVENTIONThe present invention relates to rotary drill bits for rotary drilling of subterranean formations and, more specifically, to a rotary drill bit having multiple stages of durability and ROP (rate of penetration) characteristics.
BACKGROUND OF THE INVENTIONSubsurface formation drilling to recover hydrocarbons is well known in the art. The equipment for such subsurface formation drilling typically comprises a drill string having a rotary drill bit attached thereto that is lowered into a borehole. A rotary table or similar device rotates the drill string, resulting in a corresponding rotation of the drill bit. The rotation advances the drill bit downwardly, causing it to cut through the subsurface formation (e.g., by abrasion, fracturing, and/or shearing action). Drilling fluid is pumped down a channel in the drill string and out the drill bit to cool the bit and flush away any debris that may have accumulated. The drilling fluid travels back up the borehole through an annulus formed between the drill string and the borehole.
Many types of drill bits have been developed, including roller cone bits, fixed cutter bits (“drag bits”), and the like. For each type of drill bit, several patterns or layouts of cutting elements (“cutters”) are possible, including spiral patterns, straight radial patterns, and the like. Different types of cutting elements have also been developed, including milled cutting elements, tungsten carbide inserts (“TCI”), polycrystalline-diamond compacts (“PDC”), and natural diamond cutting elements. The selection of which particular drill bit, cutting element type, and cutting element pattern (i.e., cutting structure) to use for a given subsurface formation can depend on a number of factors. For example, certain combinations of drill bit, cutting element type, and cutting element pattern drill more efficiently and effectively in hard formations than others. Another factor is the range of hardness encountered when drilling through the different formation layers.
One common pattern for drill bit cutting elements in a fixed cutter drill bit is a spiral configuration an example of which is shown in
With existing drill bit configurations, it is known to have blades 110a-f and/or cutting elements 112 that are offset (i.e., have different heights) relative to other blades and/or cutting elements on the drill bit 100. The height of the blades 110a-f and/or cutting elements 112 is measured herein relative to the drill bit body 102. For blades 110a-f that are offset, the cutting element tips are set at the same height relative to each other, but one or more of the blades 110a-f have a height that is greater than one or more other blades 110a-f. Where the cutting elements 112 are offset, the blades 110a-f have the same height, but the tips of certain cutting elements are set at different heights relative to other cutting elements. In either case, the end result is a primary layer of cutting elements that performs the initial drilling, followed by a secondary layer of cutting elements, and in some applications, a tertiary layer and so forth as needed.
Because of the difference in height, the primary layer of cutting elements wears away or deteriorates faster than the secondary layer of cutting elements. As the primary cutting elements progressively wear away, however, the secondary cutting elements compensate increasingly more for the decreased effectiveness of the primary cutting elements in terms of bit durability and ROP. This allows the drill bit 100 to be able to drill at an acceptable ROP for longer durations before having to be replaced, in essence performing the work of multiple (e.g., two in this instance) drill bits 100.
The above arrangements are illustrated in
In existing drill bits, the cutting elements are essentially uniform in size and shape (typically a round shape). In addition, the cutting elements 206a-n of the primary layer 202 and the cutting elements 208a-n of the secondary layer 204 share substantially the same radial positions on their respective blades, or share a common reference axis.
Furthermore, the cutting elements 206a-n of the primary layer 202 and the cutting elements 208a-n of the secondary layer 204 have substantially the same shear length (SL), shown in
The shear length affects the ability of the drill bit to penetrate various types of formation material. For example, hard and abrasive formations requiring a high level of bit stabilization are more effectively drilled with drill bits having longer shear lengths. Soft formation materials, on the other hand, cause minimal impact damage and may therefore be effectively drilled with either longer or shorter shear lengths. Shear length also affects the level of stabilization needed to minimize impact damage, thus reducing the amount of cutting element deterioration For existing drill bits with the type of dual-layer profile shown in
Because of the identical shear lengths, and also because of the shared radial positions, the cutting elements 206a-n and 208a-n in the primary and secondary layers 202 and 204 cut identical swaths through the subsurface formation. This is illustrated in
Referring first to
Turning now to
Because of the same shear lengths and common radial positions, primary layer and secondary layer cutting elements at a given radial position necessarily cut the same swath (see dashed lines) in the subsurface formation This is the case regardless of the specific deployment of cutting elements used to achieve the primary layer and secondary layers. The width of the swath or “cutting zone” created by cutting elements on different blades sharing a common radial position is indicated here by the letter Z and is equal to the diameter D of the cutting elements. Because they cut the same swath the primary layer and secondary layer do not establish independent coverage of the bottom hole. In addition, and from a geometry standpoint and also based on their shear lengths, the wear and/or deterioration process on the cutting element typically starts from the same peripheral locations on the cutting elements for cutting elements in the different layers. This arrangement has a negative effect on overall bit performance, especially durability or longevity.
Thus, despite certain advances made in the industry, there remains a need for a drill bit having an improved cutting element arrangement that enhances stabilization as well as durability and ROP characteristics, and permits the drill bit to drill at economical ROPs for longer durations and through a wider range of formation materials without having to replace the drill bit, thereby reducing costly and time-consuming bit trips.
SUMMARY OF THE INVENTIONEmbodiments of the invention are directed to a drill bit, and method of assembling same, that can drill at economical ROPs for longer durations and in a wider range of formation materials. The drill bit has multiple layers of cutting elements established by deploying the cutting elements on blades of different heights or maintaining the blades at the same height and deploying the cutting elements to have different heights on one or more blades. Each layer provides independent bottom hole coverage and has independent stabilization, ROP, and durability characteristics so as to effectively drill through different subsurface formations. Cutting elements deployed in different layers have their respective centers at substantially different radial positions. Due to the different radial positions, cutting elements in different layers cut different respective swaths in the subsurface formation, and are thus loaded and deteriorate differently and independently of the other layers. Cutting elements in different layers may also have different initial peripheral portions or shear lengths, resulting in different impact resistance characteristics for the different layers. This drastically changes the wear and/or cutting element deterioration processes for the different layers, which results in different and improved toughness characteristics. In some embodiments, cutting elements deployed on different layers have different sizes, shapes, and/or back rake angles, respectively. In other embodiments, cutting elements deployed on different layers have different thermal stability, impact resistance, and/or abrasion resistance, respectively.
In general, in one aspect, the invention is directed to a drill bit. The drill bit comprises a drill bit body, blades formed on said drill bit body, said blades having a plurality of cutting element positions radially located thereon. The drill bit further comprises cutting elements deployed on said blades, said cutting elements forming a primary layer of cutting elements and a secondary layer of cutting elements, said primary layer of cutting elements having a different height relative to said drill bit body from said secondary layer of cutting elements. At least one primary layer cutting element and a corresponding secondary layer cutting element occupy substantially different radial cutting element positions on said blades such that their cutting element profiles overlap, said at least one primary layer cutting element and said corresponding secondary layer cutting element together defining a cutting zone equal to a diameter of one of said at least one primary layer cutting element and said corresponding secondary layer cutting element plus a predetermined percentage or fraction of said diameter.
In general, in another aspect, the invention is directed to a method of assembling a drill bit. The method comprises providing a drill bit body having blades formed thereon, said blades having a plurality of cutting element positions radially located thereon. The method further comprises deploying cutting elements on said blades, said cutting elements forming a primary layer of cutting elements and a secondary layer of cutting elements, said primary layer of cutting elements having a different height relative to said drill bit body from said secondary layer of cutting elements. At least one primary layer cutting element and a corresponding secondary layer cutting element occupy substantially different cutting element positions on said blades such that their cutting element profiles overlap, said at least one primary layer cutting element and said corresponding secondary layer cutting element together defining a cutting zone equal to a diameter of one of said at least one primary layer cutting element and said corresponding secondary layer cutting element plus a predetermined percentage or fraction of said diameter.
In general, in yet another aspect, the invention is directed to a drill bit body. The drill bit body comprises blades formed on said drill bit body and cutting element positions formed on said blades. The cutting element positions are radially located such that when cutting elements are deployed on said blades, said cutting elements form a primary layer of cutting elements and a secondary layer of cutting elements, said primary layer of cutting elements having a different height relative to said drill bit body from said secondary layer of cutting elements. At least one primary layer cutting element and a corresponding secondary layer cutting element occupy substantially different cutting element positions on said blades such that their cutting element profiles overlap when said cutting elements are deployed on said blades, said at least one primary layer cutting element and said corresponding secondary layer cutting element together defining a cutting zone equal to a diameter of one of said at least one primary layer cutting element and said corresponding secondary layer cutting element plus a predetermined percentage or fraction of said diameter.
In general, in another aspect, the invention is directed to a drill bit capable of drilling effectively in long intervals of formation material or sections having grossly different mechanical and/or geologic properties (i.e. sandstone, carbonates and chert or pyrite).
In general, in still another aspect, the invention is directed to a drill bit capable of effectively drilling in formations infested with chert, pyrite or nodules, where these specific materials are located at the top, middle or bottom sections of the formation interval, and where conventional drilling practices typically require the use of multiple drill bits, which may have drastic effects on drilling and operational costs.
Additional aspects of the invention will be apparent to those of ordinary skill in the art in view of the detailed description of various embodiments, which is made with reference to the drawings, a brief description of which is provided below.
BRIEF DESCRIPTION OF THE DRAWINGSThe foregoing and other advantages of the invention will become apparent from the following detailed description and upon reference to the drawings, wherein:
Following is a detailed description of the invention with reference to the drawings. It should be noted that the drawings are provided for illustrative purposes only and are not intended to be a blueprint or manufacturing drawings, nor are they drawn to any particular scale.
As mentioned above, existing drill bits have primary layer and secondary layer cutting elements that are uniform in size and shape and share the same radial positions. This results in the cutting elements of the secondary layers following an identical swath through the subsurface formation as the cutting elements of the primary layers. Consequently, the primary layer and secondary layer cutting elements do not establish independent coverage of the bottom hole. In this regard, the tips of the cutting elements in the different layers, which are the first points of contact with the formation being drilled, begin to fail or deteriorate along a common line. Such failure initiation at the tips of the cutting elements in the primary layer immediately exposes the cutting elements in the secondary or other layers to failure also because the mentioned tips are in a straight line. As such, the secondary or other layer's failure is dependent on the initiation and rate of failure of the secondary or other layer. This arrangement or deployment in existing drill bits has a negative effect on bit performance. In addition, the cutting elements of the primary layers and the cutting elements of the secondary layers have substantially the same shear lengths. This decreases the effectiveness of existing drill bits, in terms of their durability, stabilization and ROP, thus narrowing the range of formation materials with which they can be used.
Embodiments of the invention provide a drill bit where at least one cutting element of the primary layer occupies a substantially different radial position from a corresponding cutting element of the secondary layer. Specifically, the at least one primary layer cutting element and the corresponding secondary layer cutting element together define a cutting zone that spans a predetermined distance. In some embodiments, the predetermined distance may be the diameter of one of the cutting elements plus a certain percentage or fraction of that diameter. The diameter may be that of the primary layer cutting element or it may be that of the secondary layer cutting element, and the fraction may be about 1/10 to about ⅓ of that diameter. As a result, the different layers establish bottom hole coverages that are independent of each other. In one embodiment, the primary layer establishes nearly 100% coverage of the bottom hole and the secondary layer establishes at least 80% coverage. This determination is typically based on the intended application and may be influenced by bit size, blade count, bit profile, as well as the lengths of the secondary and tertiary blades used in the bit design.
The cutting elements of the different layers having different cutting element tip heights are deployed so as to define different layouts or cutting structures. In one embodiment, the different layers are adapted for specific applications based on the ROP, durability, and stabilization requirements of different drilling environments. The cutting elements may be any suitable type of cutting element known to those having ordinary skill in the art, including TCI cutting elements, PDC cutting elements, natural diamond cutting elements, and combinations thereof. Furthermore, cutting elements deployed on the primary layer and cutting elements deployed on the secondary layer may have substantially different shear lengths, sizes, shapes, back rake angles, thermal stability, abrasion resistance and/or impact resistance. Based on the blade count and cutting element type and deployment, the drill bit of the invention may be customized for specific subsurface formations, including formations infested with chert, nodules, and/or pyrite. The drill bit of the invention is capable of drilling through formations with such infestations at acceptable ROPs regardless of the location of the chert, nodules, and/or pyrite in a given formation interval or hole section Such an arrangement results in a drill bit that can drill at economical ROPs for longer durations and with a wider formation bandwidth, thus reducing costly and time-consuming bit trips. Note that while embodiments of the invention are described herein mainly with respect to drill bits having a primary layer and a secondary layer of cutting elements, the teachings and principles discussed are fully applicable to drill bits having one or more additional layers of cutting elements (e.g., a tertiary layer, etc.).
Referring now to
In accordance with embodiments of the invention the primary layer cutting elements and the secondary (and possibly tertiary) cutting elements occupy substantially different radial positions on their respective blades. This is illustrated in
The width of the combined swath or cutting zone for the two corresponding cutting elements, in accordance with embodiments of the invention, spans a predetermined distance that, in some embodiments, is at least equal to the diameter of one of the cutting elements (i.e., where one cutting element has a larger diameter than the other) and at most equal to the diameter of one of the cutting elements plus a predetermined fraction of that diameter. This is illustrated
In
The cutting zone Z′, spanned by a given primary layer cutting element and corresponding secondary layer cutting element, is at least equal to the diameter D of one of these cutting elements and at most equal to the diameter D of one of the cutting elements plus a predetermined fraction of that diameter. That is, Z′=D+0.Y*D, where 0.Y is the predetermined fraction In some embodiments, the diameter D used to define the cutting zone Z′ is the diameter of the primary layer cutting element, while in other embodiments, the diameter D is that of the secondary layer cutting element. In still other embodiments, the diameter D used to define the cutting zone Z′ may be the diameter of whichever cutting element has the larger diameter. And as for the predetermined fraction of the diameter, in some embodiments, this value may be about 1/10 to about ⅓, and preferably about ⅕, of the diameter of whichever cutting element is used.
While the above arrangement has advantages, in some drilling applications, it is desirable to have all the blades be at the same height for stability and durability purposes.
In the drill bit portion shown here, the non-shaded cutting elements 512a-n are deployed so as to have a greater height than the shaded cutting elements 514a-n. These non-shaded cutting elements 512a-n accordingly constitute the primary layer of cutting elements, whereas the shaded cutting elements 514a-n constitute the secondary layer of cutting elements. Both shaded and non-shaded cutting elements 512a-n and 514a-n may be intermixed across different blades 510a and 510b, as depicted here, or cutting elements of different heights may be mounted on their own blades (similar to the implementation of
In the drill bits described thus far, multiple layers of cutting elements have been achieved using a single row of cutting elements on each blade. However, embodiments of the invention may also be implemented using multiple rows of cutting elements on a single blade. Examples of such an arrangement are illustrated in
The implementation of
In both of the above implementations, the primary layer cutting elements 606a-n & 616a-n and the corresponding secondary layer cutting elements 608a-n & 618a-n occupy substantially different radial positions. As a result, they cut substantially different swaths in the subsurface formation. The width of the swath or cutting zone, indicated again as Z′, is at least equal to the diameter D of one of these cutting elements and at most equal to the diameter D of one of the cutting elements (e.g., the primary cutting element) plus a predetermined fraction of that diameter, or Z′=D+0.Y*D.
Referring back to the drill bit profile in
Unlike the drill bit profile segment 400, however, the drill bit profile segment 700 represents a drill bit where the primary layer cutting elements 706a-n have a shear length SL that is different from the shear length SL′ of the secondary layer cutting elements 708a-n. In the specific embodiment of
The width of the swath, or cutting zone, cut by a given primary layer cutting element and a corresponding secondary (or tertiary) layer cutting element in
In some embodiments, the sizes and shapes, and hence the diameters, of the primary and secondary layer cutting elements are substantially the same.
Unlike the embodiments shown in
While the drill bits discussed thus far have primary layer and secondary layer cutting elements that are of substantially the same shape, namely, a round shape, other shapes may also be used. Examples of other shapes that may be used include elliptical shapes, egg shapes, pear shapes, and teardrop shapes (hereinafter, collectively referred to as oval shapes), as well as other common and customized shapes known to those having ordinary skill in the art. In some cases, even non-circular shapes may be used where at least a portion of the shape is flat (e.g., semicircular, diamond, rectangular, etc). Moreover, embodiments of the invention also provide a drill bit where the primary layer or primary cutting element tip profile and the cutting elements, and the secondary layer or secondary cutting element tip profile and the cutting elements, have substantially different shapes and geometries.
Unlike the embodiments shown in the previous figures, the cutting elements 908a-n deployed on the secondary layer 904 in
The substantially different axial volumes affect the durability of the cutting elements in hard and abrasive formations. A larger axial volume increases the ability of the cutting element to withstand higher rotational speeds during the drilling process than a smaller axial volume due to the substantially higher diamond content. For this reason, oval cutting elements are known to be highly effective in abrasive formations or lithologies, such as sandstone and siltstone, from an axial volume perspective. In addition, oval shaped cutting elements are more effective at pre-fracturing of brittle formations, a characteristic that improves ROP in carbonate bearing formations. Round cutting elements, on the other hand, are more effective for shearing non-brittle formations or lithologies, such as shale, sandstones and siltstone.
By deploying oval cutting elements on the secondary layer 904 and round cutting elements on the primary layer 902, embodiments of the invention combine the advantages of both round and oval cutting elements. A similar benefit may be obtained by deploying the round cutting elements on the secondary layer 904 and the oval cutting elements on the primary layer 902. Alternatively, oval shaped cutting elements may be deployed on both the primary and secondary layers 902 and 904, but of substantially different types. For example, elliptical shaped cutting elements may be deployed on the primary layer 902 while teardrop cutting elements may be deployed on the secondary layer 904, and so on.
In addition to substantially different shapes, in some embodiment, the cutting elements of the primary layer and the cutting elements of the secondary layer may have substantially different back rake angles. The term “back rake angle,” as understood by those having ordinary skill in the art, refers to the angle formed between a line parallel to the cutting element face and a vertical line drawn through the center of the cutting element. Such back rake ankles control how aggressively the cutting element engages the subsurface formation. In general, a smaller back rake angle increases cutting element aggressiveness (i.e., high ROP), but leaves the cutting element vulnerable to impact breakage. On the other hand, a larger back rake angle decreases cutting element aggressiveness (i.e., low ROP), but gives the cutting element longer life.
Unlike the previous embodiments, the cutting elements 1008a-n deployed on the secondary layer 1004 here have a substantially different back rake angle from the cutting elements 1006a-n deployed on the primary layer 1002.
Although the embodiments described thus far have focused on the different radial positions and shear lengths (or average shear lengths as applicable), in some embodiments, it may be desirable to provide a drill bit where the primary layer cutting elements and the secondary layer cutting elements having different shear lengths. An example of such an embodiment is illustrated in
Unlike the previous embodiments, the primary and secondary layers 1102 and 1104 have cutting elements 1106a-n and 1108a-n mounted in substantially identical radial positions (see
In some embodiments, based on the specifics of an application as well as the formation types to be drilled, the primary layer cutting elements and the secondary layer cutting elements may have substantially different properties in terms of abrasion and impact resistance. For example, either the primary layer cutting elements or the secondary layer cutting elements may be made more abrasion resistant (i.e., have a finer diamond grain), or both the primary layer cutting elements and secondary layer cutting elements may have improved abrasion resistance. In a similar manner, the primary layer cutting elements may be made more impact-resistant than the secondary layer cutting elements, or vice versa, or both the primary layer and secondary layer cutting elements may have improved impact resistance.
In other embodiments, either the primary layer cutting elements or the secondary layer cutting elements may be treated to remove catalyzing material (e.g., cobalt), a process commonly referred to as “leaching.” As is well known in the art, leaching or removal of catalyzing material from cutting elements can improve their thermally stability, thus allowing them to withstand much higher drilling temperatures before failing. Improved thermal stability drastically reduces the wear initiation process of the cutting elements. This process may be used to further enhance the performance properties of the primary layer cutting elements or the secondary layer cutting elements, as described herein. Techniques for removal of catalyzing material from cutting elements are generally known and may be found, for example, in U.S. Pat. No. 8,544,408 entitled “High Volume Density Polycrystalline Diamond with Working Surfaces Depleted of Catalyzing Material,” which is incorporated herein by reference.
It should be noted that regardless of the diamond material types (e.g., fine grain or coarse grain diamond materials) that may be used for the primary layer and/or secondary layer cutting elements, or the leaching or catalyzing material depletion processes employed, all advantages, principles and teachings herein discussed for the present invention remain valid and fully applicable to these various embodiments.
In operation, the cutting elements in the primary layer of the drill bit initially bear most of the load during drilling of a specific dominant formation type (e.g., sandstone, shale, siltstone, etc.). As the cutting elements in the primary layer wears and/or deteriorates due to formation hardness and/or abrasiveness, the cutting elements in the secondary and subsequent layers define a new bit, having independent bottom hole coverage that cut different swaths in the formation, and also have different and unique ROP, durability and stability characteristics. Based on the specific layout of a drill bit according to embodiments of the invention, but mainly due to the substantially different radial positions of the cutting elements in the different layers and/or substantially different shear lengths (SL) of the different layers, such drill bits are adapted to effectively drill in chert, pyrite and or nodules due to the controlled and specifically staged durability and ROP characteristics of the drill bit of the invention. In such instances, the cutting elements in the primary layer fail, but in do doing so, expose the cutting elements in the secondary layer (and possibly tertiary layer, and so forth), which are then able to re-establish the drill bit's ROP and durability characteristics, thus enabling the drill bit to continue drilling for longer periods of time at an effective ROP. In other words, because the secondary layer cutting elements have independent bottom hole coverage and may be customized with a substantially different shear length, size, shape, thermal stability, abrasion resistance, and/or impact resistance according to embodiments of the invention, the drill bit is able to continue drilling at an economical ROP through the subsequent formation type, eventually reentering the dominant formation type or a different formation that is devoid of chert, pyrite or nodules.
While the present invention has been described with reference to one or more particular embodiments, those skilled in the art will recognize that many changes may be made thereto without departing from the scope of the invention Accordingly, each of the foregoing embodiments and obvious variations thereof is contemplated as falling within the scope of the claimed invention, as is set forth in the following claims.
Claims
1. A drill bit, comprising:
- a drill bit body;
- blades formed on said drill bit body, said blades having a plurality of cutting element positions radially located thereon; and
- cutting elements deployed on said blades, said cutting elements forming a primary layer of cutting elements and a secondary layer of cutting elements, said primary layer of cutting elements having a different height relative to said drill bit body from said secondary layer of cutting elements;
- wherein at least one primary layer cutting element and a corresponding secondary layer cutting element occupy substantially different cutting element positions on said blades such that their cutting element profiles overlap, said at least one primary layer cutting element and said corresponding secondary layer cutting element together defining a cutting zone equal to a diameter of one of said at least one primary layer cutting element and said corresponding secondary layer cutting element plus a predetermined fraction of said diameter.
2. The drill bit according to claim 1, wherein said predetermined fraction is from approximately 1/10 to approximately ⅓.
3. The drill bit according to claim 1, wherein said predetermined fraction is approximately ⅕.
4. The drill bit according to claim 1, wherein said diameter is a diameter of said at least one primary layer cutting element.
5. The drill bit according to claim 1, wherein said diameter is a diameter of said corresponding secondary layer cutting element.
6. The drill bit according to claim 1, wherein said cutting elements in said primary layer and said cutting elements in said secondary layer have substantially different shear lengths.
7. The drill bit according to claim 6, wherein said shear lengths are average shear lengths derived from multiple shear lengths for said cutting elements in said primary layer and said cutting elements in said secondary layer.
8. The drill bit according to claim 1, wherein said cutting elements in said primary layer and said cutting elements in said secondary layer have substantially different sizes.
9. The drill bit according to claim 1, wherein said cutting elements in said primary layer and said cutting elements in said secondary layer have substantially different shape.
10. The drill bit according to claim 9, wherein said substantially different shapes result in said cutting elements in said primary layer and said cutting elements in said secondary layer having substantially different axial volumes.
11. The drill bit according to claim 1, wherein said cutting elements in said primary layer and said cutting elements in said secondary layer have substantially different abrasion resistances.
12. The drill bit according to claim 1, wherein said cutting elements in said primary layer and said cutting elements in said secondary layer have substantially different impact resistances.
13. The drill bit according to claim 1, wherein said cutting elements in said primary layer and said cutting elements in said secondary layer have substantially different thermal stabilities.
14. The drill bit according to claim 1, wherein said cutting elements in said primary layer and said cutting elements in said secondary layer have substantially different back rake angles.
15. The drill bit according to claim 14, wherein one or more cutting elements in said primary layer have a larger back rake angle than one or more cutting elements in said secondary layer.
16. The drill bit according to claim 14, wherein one or more cutting elements in said primary layer have a smaller back rake angle than one or more cutting elements in said secondary layer.
17. The drill bit according to claim 1, wherein said cutting elements form a tertiary layer of cutting elements and said primary layer of cutting elements have a different height relative to said drill bit body from said tertiary layer of cutting elements, and wherein at least one primary layer cutting element and a corresponding tertiary layer cutting element occupy substantially different cutting element positions on said blades such that their cutting element profiles overlap, said at least one primary layer cutting element and said corresponding tertiary layer cutting element together defining a cutting zone equal to a diameter of one of said at least one primary layer cutting element and said corresponding tertiary layer cutting element plus a predetermined fraction of said diameter.
18. A method of assembling a drill bit, comprising:
- providing a drill bit body having blades formed thereon said blades having a plurality of cutting element positions radially located thereon; and
- deploying cutting elements on said blades, said cutting elements forming a primary layer of cutting elements and a secondary layer of cutting elements, said primary layer of cutting elements having a different height relative to said drill bit body from said secondary layer of cutting elements;
- wherein at least one primary layer cutting element and a corresponding secondary layer cutting element occupy substantially different cutting element positions on said blades such that their cutting element profiles overlap, said at least one primary layer cutting element and said corresponding secondary layer cutting element together defining a cutting zone equal to a diameter of one of said at least one primary layer cutting element and said corresponding secondary layer cutting element plus a predetermined fraction of said diameter.
19. The method according to claim 18, wherein said cutting elements of said primary layer and said cutting elements of said secondary layer are mounted on blades having substantially different heights relative to said drill bit body.
20. The method according to claim 18, wherein said cutting elements of said primary layer and said cutting elements of said secondary layer are mounted on blades having substantially identical heights relative to said drill bit body.
21. The method according to claim 20, wherein said cutting elements of said primary layer and said cutting elements of said secondary layer are mounted on separate blades.
22. The method according to claim 20, wherein one or more cutting elements of said primary layer and one or more cutting elements of said secondary layer are mounted on a single blade.
23. The method according to claim 20, wherein said one or more cutting elements of said primary layer and said one or more cutting elements of said secondary layer are mounted on said single blade in multiple rows.
24. The method according to claim 23, wherein at least one of said rows contains a combination of cutting elements from said primary layer and cutting elements from said secondary layer.
25. The method according to claim 23, wherein at least one of said rows contains only cutting elements from said primary layer or only cutting elements from said secondary layer.
26. The method according to claim 18, wherein said primary layer of cutting elements establishes approximately 100% bottom hole coverage.
27. A drill bit body, comprising:
- blades formed on said drill bit body, and
- cutting element positions formed on said blades, said cutting element positions radially located thereon such that when cutting elements are deployed on said blades, said cutting elements form a primary layer of cutting elements and a secondary layer of cutting elements, said primary layer of cutting elements having a different height relative to said drill bit body from said secondary layer of cutting elements;
- wherein at least one primary layer cutting element and a corresponding secondary layer cutting element occupy substantially different cutting element positions on said blades such that their cutting element profiles overlap when said cutting elements are deployed on said blades, said at least one primary layer cutting element and said corresponding secondary layer cutting element together defining a cutting zone equal to a diameter of one of said at least one primary layer cutting element and said corresponding secondary layer cutting element plus a predetermined fraction of said diameter.
Type: Application
Filed: Nov 1, 2006
Publication Date: Nov 22, 2007
Applicant: VAREL INTERNATIONAL IND., L.P. (Carrollton, TX)
Inventor: Graham Mensa-Wilmot (Spring, TX)
Application Number: 11/555,547
International Classification: E21B 10/36 (20060101);