You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation-in-part of U.S. patent application Ser. Nos. 10/749,019, filed Dec. 29, 2003, Ser. No. 10/411,542, filed Apr. 10, 2003, and Ser. No. 10/888,523, filed Jul. 9, 2004, the entirety of each of which is hereby incorporated by reference. U.S. patent application Ser. No. 10/749,019 is a continuation of U.S. patent application Ser. No. 09/524,088, the entirety of which is hereby incorporated by reference. U.S. patent application Ser. No. 10/411,542 is a continuation of U.S. patent application Ser. No. 09/635,116, the entirety of which is hereby incorporated by reference. U.S. patent application Ser. No. 09/635,116 is a continuation of U.S. patent application Ser. No. 09/524,088, the entirety of which is hereby incorporated by reference. 
     
    
     BACKGROUND  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates generally to hybrid drill bits that are used to drill boreholes in subterranean earth formations. More specifically, the present invention relates to techniques for modeling hybrid drill bits, simulating operation of hybrid drill bits, designing hybrid drill bits, optimizing drilling performance of hybrid drill bits, and displaying hybrid drill bits.  
         [0004]     2. Background Art  
         [0005]     Drill bits are commonly used in the oil and gas industry to drill boreholes (also referred to as “well bores”) in subterranean earth formations. One example of a conventional drilling system for drilling boreholes in subterranean earth formations is shown in  FIG. 1 . The drilling system includes a drilling rig  10  that is used to rotate a drill string  12  that extends downward into a borehole  14 . Connected to the distal end of the drill string  12  is a drill bit  20 .  
         [0006]     Two common types of drill bits used for drilling boreholes are known and referred to in the art as “fixed-cutter” drill bits and “roller cone” drill bits. A fixed-cutter drill bit  21 , as shown in  FIG. 2 , typically includes a bit body  22  having (i) an externally threaded connection at one end  24  and (ii) a plurality of blades  26  extending from the other end of the bit body  22 . The plurality of blades  26  form the cutting surface of the drill bit  21 . A plurality of cutting elements  28  are attached to each of the blades  26  and extend from the blades  26 . The plurality of cutting elements  28  are used to cut through subterranean earth formations when the drill bit  21  is rotated during drilling. The plurality of cutting elements  28  may be one or a combination of polycrystalline diamond compacts or other cutting elements formed of materials hard and strong enough to deform and/or cut through subterranean earth formations.  
         [0007]     A roller cone drill bit  30 , as shown in  FIG. 3 , typically includes a bit body  32  having (i) an externally threaded connection at one end  34  and (ii) a plurality of roller cones  36  (usually three as shown) attached to the other end of the drill bit  30 . The plurality of roller cones  36  are able to rotate with respect to the bit body  32 . Attached to the plurality of roller cones  36  are a plurality of cutting elements  38  typically arranged in rows about the surface of each of the plurality of roller cones  36 . The plurality of cutting elements  38  may be one or a combination of tungsten carbide inserts, milled steel teeth, or other cutting elements formed of materials hard and strong enough to deform and/or cut through subterranean earth formations. Further, hardfacing (not shown) may be applied to the plurality of cutting elements  38  and/or other portions of the drill bit  30  to reduce wear on the drill bit  30  and/or to increase the useful life of the drill bit  30 .  
         [0008]     Another type of drill bit that may be used to drill boreholes in subterranean earth formations is known and referred to in the art as a “hybrid” drill bit. Hybrid drill bits include a combination of one or more fixed cutting elements (e.g.,  28  in  FIG. 2 ) and one or more roller cones (e.g.,  36  in  FIG. 3 ). As shown in  FIG. 4 , a hybrid drill bit  10  typically includes a bit body  12  having an externally threaded connection at one end  14  and a rock cutting structure at an opposite end. A pair of opposing roller cone legs  16  support roller cones  18  and  19 . Adjacent to the roller cones  18  and  19 , in an opposing relationship, is a pair of fixed bit legs  26  and  29  extending from and welded to the bit body  12 . Fixed bit legs  26  and  29  terminate in fixed bit faces  28  and  31 . Hydraulic nozzles or openings are formed in each fixed bit face  28  and  31 , each opening communicating with a central hydraulic chamber in the bit body (not shown). Several diamond insert cutter blanks  32  are strategically positioned in faces  28  and  31 , the diamond cutting face  34  of the insert blanks being so oriented to most effectively remove the ridges between kerfs cut by the tungsten carbide inserts in the adjacent cones  44  and  45 .  
         [0009]     The insert blanks  32 , for example, are fabricated from a tungsten carbide substrate with a diamond layer  34  sintered to a face of a substrate, the diamond layer being composed of a polycrystalline material.  
         [0010]     The roller cone  18 , journaled to leg  16  of bit body  12 , has a plurality of chisel type tungsten carbide inserts  22  inserted in the cone. The inserts are equidistantly spaced in each row and the outermost row on the cone is the gage row  21 . The chisel crown  36  of gage inserts  25  are oriented in this gage row in a radial direction substantially parallel with the journal axis of the cone. Referring to both cones  18  and  19 , the “A”, “B”, “C” and “D” rows of inner inserts  22  have their chisel crowns oriented in a circumferential direction substantially normal to the journal axis. With this orientation, the chisel crests or crowns  23  tend to penetrate more deeply into the borehole bottom rather than scrape and gouge as would be the normal function of a chisel insert with its crest oriented in a radial direction, especially in an offset type of rock bit.  
         [0011]     One example of a hybrid drill bit is disclosed in U.S. Pat. No. 4,343,371 issued to Baker, III et al., which is assigned to the assignee of the present invention.  
         [0012]     Significant resources (e.g., time, money) are needed in the design and manufacture of drill bits for use in drilling boreholes. Having accurate models for predicting and analyzing drilling characteristic of drill bits may greatly reduce costs associated with manufacturing drill bits and designing drilling operations because these models may be used to more accurately predict the performance of drill bits prior to their manufacture and/or use for a particular drilling application.  
         [0013]     Modeling and simulation techniques for fixed-cutter bits are disclosed in: Sandia Report No. SAN86-1745 by David A. Glowka, printed in September 1987 and entitled “Development of a Method for Predicting the Performance and Wear of PDC Drill Bits”; U.S. Pat. Nos. 4,815,342, 5,010,789, 5,042,596, and 5,131,478; and U.S. patent application Ser. No. 10/888,358. Modeling and simulation techniques for roller cone drill bits are disclosed in: “The Computer Simulation of the Interaction Between Roller Bit and Rock” by D. Ma et al., printed in 1995 as paper no. 29922 in the Society of Petroleum Engineers; and U.S. Pat. No. 6,516,293, which is assigned to the assignee of the present invention.  
       SUMMARY  
       [0014]     According to one aspect of one or more embodiments of the present invention, a method for designing a hybrid drill bit comprises: simulating the hybrid drill bit drilling in an earth formation; adjusting a value of at least one design parameter for the hybrid drill bit based on the simulating; and repeating the simulating and adjusting to change a simulated performance of the hybrid drill bit.  
         [0015]     According to another aspect of one or more embodiments of the present invention, a method of designing a hybrid drill bit comprises: determining a performance characteristic of the hybrid drill bit; and graphically displaying the performance characteristic as at least one design parameter for the hybrid drill bit is adjusted.  
         [0016]     According to another aspect of one or more embodiments of the present invention, a method for simulating a hybrid drill bit comprises: generating a model comprising data relating to at least one of interactions between a selected fixed cutting element and a selected earth formation and interactions between a selected roller cone cutting element and a selected earth formation; modeling the hybrid drill bit based on at least one input bit design parameter; and simulating the hybrid drill bit drilling an earth formation based on the model and the at least one input bit design parameter.  
         [0017]     According to another aspect of one or more embodiments of the present invention, a method of designing a hybrid drill bit comprises: inputting a plurality of parameters relating to characteristics of the hybrid drill bit; and graphically displaying a model of the hybrid drill bit based on the plurality of parameters, where a displayed property of the model is changeable by changing at least one of the plurality of parameters.  
         [0018]     Other aspects of the present invention will be apparent from the following description and the appended claims. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0019]      FIG. 1  shows a conventional drilling system.  
         [0020]      FIG. 2  shows a fixed-cutter drill bit.  
         [0021]      FIG. 3  shows a roller cone drill bit.  
         [0022]      FIG. 4  shows a hybrid drill bit.  
         [0023]      FIG. 5  shows a flow process in accordance with an embodiment of the present invention.  
         [0024]      FIG. 6  shows a user interface for modeling a hybrid drill bit in accordance with an embodiment of the present invention.  
         [0025]      FIG. 7  shows a user interface for modeling a hybrid drill bit in accordance with an embodiment of the present invention.  
         [0026]      FIG. 8  shows a user interface for modeling a hybrid drill bit in accordance with an embodiment of the present invention.  
         [0027]      FIG. 9  shows a flow process in accordance with an embodiment of the present invention.  
         [0028]      FIG. 10  shows a graphical display in accordance with an embodiment of the present invention.  
         [0029]      FIG. 11  shows a graphical display in accordance with an embodiment of the present invention.  
         [0030]      FIG. 12  shows a graphical display in accordance with an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0031]     Generally, embodiments of the present invention relate to techniques for modeling/simulating, designing, optimizing, and displaying hybrid drill bits. In the following description of embodiments of the present invention, a “hybrid” drill bit is a drill bit that includes both at least one fixed surface having one or more cutting elements disposed thereon/therewith and at least one roller cone surface having one or more cutting elements disposed thereon/therein. Cutting elements disposed on/with a fixed surface of a hybrid drill bit are herein referred to as “fixed cutting elements.” Cutting elements disposed on/with a roller cone surface of a hybrid drill bit are herein referred to as “roller cone cutting elements.” References herein to “cutting elements” in general include both fixed cutting elements and roller cone cutting elements.  
         [0032]      FIG. 5  shows an exemplary flow process in accordance with an embodiment of the present invention. The simulation and subsequent design and optimization of a hybrid drill bit may depend on data characterizing the interactions between (i) fixed cutting elements and an earth formation and (ii) roller cone cutting elements and an earth formation. Determining such data results in building a cutting element/formation interaction model ST 50 . Modeling the hybrid drill bit is based on input parameters (e.g., number of blades, number of roller cones) provided to a simulation tool ST 52 . The modeled hybrid drill bit, which may be graphically displayed in one or more embodiments of the present invention, is then simulated based on, for example, the cutting element/formation interaction model and the provided input parameters ST 54 .  
         [0033]     U.S. patent application Ser. No. 10/888,358, the assignee of which is the assignee of the present invention and the entirety of which is hereby incorporated by reference, discloses techniques for building a formation interaction model for fixed cutting elements. U.S. Pat. No. 6,516,293, the assignee of which is the assignee of the present invention and the entirety of which is hereby incorporated by reference, discloses techniques for building a formation interaction model for roller cone cutting elements. In one or more embodiments of the present invention, techniques for building formation interaction models in U.S. patent application Ser. No. 10/888,358 and U.S. Pat. No. 6,516,293 may be used in any combination to build a formation interaction model for the fixed cutting elements and roller cone cutting elements of a hybrid drill bit.  
         [0034]     In other embodiments, mathematical techniques, such as finite element analysis, may be used in conjunction with or in lieu of, the interaction model. Also, it should be noted that in building and using the model, techniques such as linear interpolation may be used. Further discussion of these points is found in U.S. Pat. No. 6,516,293 and U.S. patent application Ser. No. 10/888,358.  
         [0035]     Those skilled in the art will note that methods for modeling hybrid drill bits based on cutting element/formation interaction data derived from laboratory tests conducted using the same or similar cutting elements on the same or similar formations may advantageously enable the more accurate prediction of the drilling characteristics for proposed hybrid drill bit designs. These methods may also enable optimization of hybrid drill bit designs and drilling parameters, and the production of new hybrid drill bit designs that exhibit more desirable drilling characteristics and/or longevity.  
         [0036]     In one or more embodiments of the present invention, modeling a hybrid drill bit involves a user interface by which a designer may input bit design parameters. Input bit design parameters may include: (i) cutting structure information such as, for example, fixed cutting element location and orientation and roller cone cutting element location and orientation; and (ii) cutting element information such as, for example, fixed cutting element size(s) and shape(s) and roller cone cutting element size(s) and shape(s). This information may be input using a CAD interface, for example.  
         [0037]      FIG. 6  shows an exemplary user interface by which a designer may enter bit design parameters relating to the fixed cutting elements of a particular hybrid drill bit. In  FIG. 6 , the designer has modeled the hybrid drill bit as having three blades with a total of sixteen cutting elements. Further, as shown in  FIG. 6 , a designer may enter bit design parameters relating to, for example, a radius and a height of a particular fixed cutting element.  
         [0038]      FIG. 7  shows an exemplary user interface by which a designer may enter bit design parameters relating to roller cone cutting elements of a particular hybrid drill bit. In  FIG. 7 , the designer has modeled the hybrid drill bit as having a single roller cone. Further, as shown in  FIG. 7 , a designer may enter bit design parameters relating to, for example, a diameter and position of the single roller cone. Those skilled in the art will note that the hybrid drill bit model shown in  FIG. 7  shows the relation of fixed cutting elements of the modeled hybrid drill bit to the single roller cone.  
         [0039]      FIG. 8  shows another exemplary user interface by which a designer may enter bit design parameters relating to roller cone cutting elements of a particular hybrid drill bit. In  FIG. 8 , the designer has modeled the hybrid drill bit as having three roller cones. Further, as shown in  FIG. 8 , a designer may enter bit design parameters relating to, for example, diameters and positions of the three roller cones. Those skilled in the art will note that the hybrid drill bit model shown in  FIG. 8  shows the relation of fixed cutting elements of the modeled hybrid drill bit to the three roller cones.  
         [0040]     Upon generation of a model of a hybrid drill bit, a drilling operation of the modeled hybrid drill bit in an earth formation may then be simulated  FIG. 9  shows an exemplary flow process for simulating a hybrid drill bit in accordance with an embodiment of the present invention. Simulation involves entering (i) input parameters for a hybrid drill bit, (ii) parameters of an earth formation to be drilled, and (iii) drilling operation parameters  100 .  
         [0041]     Input parameters for the hybrid drill bit may include, for example, a number of fixed surfaces having cutting elements disposed thereon, a number of cutting elements disposed on at least one of the number of fixed surfaces, a location of a cutting element disposed on at least one of the number of fixed surfaces, a type of cutting element disposed on at least one of the number of fixed surfaces, an orientation of a cutting element disposed on at least one of the number of fixed surfaces, a height of a cutting element disposed on at least one of the number of fixed surfaces, a radius of a cutting element disposed on at least one of the number of fixed surfaces, a diameter of a cutting element disposed on at least one of the number of fixed surfaces, a back rake angle of a cutting element disposed on at least one of the number of fixed surfaces, a side rake angle of a cutting element disposed on at least one of the number of fixed surfaces, a working surface shape of a cutting element disposed on at least one of the number of fixed surfaces, a bevel size of a cutting element disposed on at least one of the number of fixed surfaces, a bevel shape of a cutting element disposed on at least one of the number of fixed surfaces, a bevel orientation of a cutting element disposed on at least one of the number of fixed surfaces, a hardness of a cutting element disposed on at least one of the number of fixed surfaces, a shape of a cutting element disposed on at least one of the number of fixed surfaces, a number of roller cones having cutting elements disposed thereon, a number of cutting elements disposed on at least one of the number of roller cones, a location of a cutting element disposed on at least one of the number of roller cones, a type of cutting element disposed on at least one of the number of roller cones, an orientation of a cutting element disposed on at least one of the number of roller cones, a height of a cutting element disposed on at least one of the number of roller cones, a radius of a cutting element disposed on at least one of the number of roller cones, a diameter of a cutting element disposed on at least one of the number of roller cones, a working surface shape of a cutting element disposed on at least one of the number of roller cones, a hardness of a cutting element disposed on at least one of the number of roller cones, a spacing between cutting elements disposed on at least one of the number of roller cones, a shape of a cutting element disposed on at least one of the number of roller cones, an axis offset of at least one of the number of roller cones, a diameter of at least one of the number of roller cones, and a diameter of the hybrid drill bit.  
         [0042]     Earth formation parameters may include, for example, a type of the earth formation, a mechanical strength of the earth formation, a density of the earth formation, a wear characteristic of the earth formation, a strength of the earth formation, an orientation of the earth formation, a diameter of a borehole, and a depth of a layer of the earth formation.  
         [0043]     Drilling operation parameters may include, for example, a weight-on-bit, a bit torque, a rate of penetration, rotary speed of the hybrid drill bit, a mud type, a mud density, an angle of drilling, a load, and an axial force on the hybrid drill bit.  
         [0044]     Referring still to  FIG. 9 , in one or more embodiments of the present invention, the simulation may involve: generating a numerical representation of the hybrid drill bit, generating a numeral representation of the earth formation, and simulating the hybrid drill bit drilling the earth formation by incrementally rotating the hybrid drill bit on the earth formation  102 .  
         [0045]     Upon an incremental rotation of the hybrid drill bit  102 , new positions of fixed cutting elements and roller cone cutting elements of the hybrid drill bit are calculated. In one or more embodiments of the present invention, techniques for determining new positions of cutting elements upon an incremental rotation of a drill bit in U.S. patent application Ser. No. 10/888,358 and U.S. Pat. No. 6,516,293 may be used in any combination to determine positions of the fixed cutting elements and roller cone cutting elements of a hybrid drill bit.  
         [0046]     The interference between the fixed cutting elements and the earth formation and between the roller cone cutting elements and the earth formation during the incremental rotation are determined  104 . Such interference may be determined using a cutting element/formation interaction model such as described above.  FIG. 10  shows an exemplary graphical display showing a simulation of a hybrid drill bit in engagement with an earth formation.  
         [0047]     Those skilled in the art will note that with respect to the roller cone cutting elements, there is an added level of complexity in determining interference due the roller cone cutting elements being disposed on roller cones which themselves are rotating with respect to the rotation of the hybrid drill bit. Analyses of interference between cutting elements of a roller cone and an earth formation are detailed in U.S. Pat. No. 6,516,293.  
         [0048]     In addition to determining interference between the fixed cutting elements and the earth formation and between the roller cone cutting elements and the earth formation, forces on the fixed cutting elements and the roller cone cutting elements resulting from the interference may be determined  106 .  FIG. 11  shows an exemplary graphical display showing determined cutting forces during simulation of a hybrid drill bit. Such determined force information may be used to determine which cutting elements are experiencing the most force. For example,  FIG. 12  shows an exemplary distribution of radial forces on blades of a hybrid drill bit.  
         [0049]     Finally, the bottomhole geometry is updated to remove the portion of the earth formation cut by the fixed cutting elements and the roller cone cutting elements as a result of the interference during the incremental rotation of the hybrid drill bit  108 . The steps of incrementally rotating  102 , determining interference  104 , determining forces  106 , and updating  108  may be repeated to simulate the hybrid drill bit drilling through the earth formation with results determined for each incremental rotation being provided as output  110  (e.g., via a graphical interface).  
         [0050]     Those skilled in the art will note that while  FIG. 9  shows a general flow process for simulating a hybrid drill bit in accordance with an embodiment of the present invention, U.S. patent application Ser. No. 10/888,358 and U.S. Pat. No. 6,516,293, the entirety of both having been incorporated by reference, disclose detailed simulation techniques for fixed-cutter drill bits and roller cone drill bits, respectively, that may be applied, at least in part, to the simulation of a hybrid drill bit in accordance with one or more embodiments of the present invention.  
         [0051]     Based on simulation of a hybrid drill bit as described above, a designer may design a hybrid drill bit by selectively changing/adjusting certain parameters to effectuate certain performance characteristics and/or drilling behavior. For example, a method in accordance with one or more embodiments of the present invention includes selecting bit design parameters, drilling parameters, and an earth formation to be represented as drilled. Then, a hybrid drill bit having the selected bit design parameters is simulated as drilling in the selected earth formation under the conditions dictated by the selected drilling parameters. The simulating includes calculating the interaction between the cutting elements on the hybrid drill bit and the earth formation at selected increments during drilling. This includes calculating parameters for the cuts made in the formation by each of the cutting elements on the hybrid drill bit and determining the forces and the wear on each of the cutting elements during drilling. Then, depending upon the calculated performance of the hybrid drill bit during the drilling of the earth formation, at least one of the bit design parameters is adjusted. The simulating is then repeated for the adjusted bit design. The adjusting of the at least one design parameter and the repeating of the simulating are repeated until a desired set of bit design parameters is obtained. Once a desired set of bit parameters is obtained, the desired set of bit parameters may be used for an actual hybrid drill bit design.  
         [0052]     A set of bit design parameters may be determined to be a desired set when the drilling performance determined for the hybrid drill bit is selected as acceptable. In one embodiment of the present invention, the drilling performance may be determined to be acceptable when the calculated imbalance force on the hybrid drill bit during drilling is less than or equal to a selected amount.  
         [0053]     In another aspect of one or more embodiments of the invention, a method for optimizing drilling parameters of a hybrid drill bit is provided. Such an exemplary method involves selecting initial drilling parameters and selecting earth formation(s) to be represented as drilled. The method also includes simulating the hybrid drill bit having the selected bit design drilling the selected earth formation(s) under drilling conditions dictated by the selected drilling parameters. The simulating may involve calculating interaction between cutting elements on the selected hybrid drill bit and the earth formation at selected increments during drilling and determining the forces on the cutting elements based on cutting element/formation interaction data in accordance with the description above. The method further includes adjusting at least one drilling parameter and repeating the simulating (including drilling calculations) until an optimal set of drilling parameters is obtained. An optimal set of drilling parameters may be any set of drilling parameters that result in an improved drilling performance over previously proposed drilling parameters. In one or more embodiments of the present invention, drilling parameters are determined to be optimal when the drilling performance of the bit (e.g., calculated rate of penetration) is determined to be maximized for a given set of drilling constraints (e.g., within acceptable WOB or ROP limitations for the system).  
         [0054]     Methods in accordance with the above aspect may be used to analyze relationships between drilling parameters and drilling performance for a given hybrid drill bit design. This method may also be used to optimize the drilling performance of a selected hybrid drill bit design.  
         [0055]     While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments may be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.

Summary:
A hybrid drill bit is modeled, simulated, designed, optimized, and displayed. The hybrid drill is modeled based on input bit design parameters. The modeled hybrid drill bit is then simulated as drilling an earth formation, where at least a portion of the simulation may be graphically displayed so as to allow a user to adjust one or more parameters of the hybrid drill bit, drill string, and/or earth formation. Formation interactions between a fixed cutting element of the hybrid drill bit and the earth formation and between a roller cone cutting element of the hybrid drill bit and the earth formation are determined based on models developed using, for example, laboratory-based formation interaction tests. Simulation of the modeled hybrid drill bit may be selectively repeated so as to allow a user to adjust one or more design parameters of the hybrid drill bit to affect a simulated drilling characteristic. Such designing of the hybrid drill bit may be performed until one or more bit design parameters are accepted as being optimized.