Patent Application
20120312603
Not applicable.
Not applicable.
1. Field of Technology
The disclosure relates generally to earth-boring bits used to drill a borehole for the recovery of oil, gas or minerals. More particularly, this disclosure relates to methods for designing fixed cutter drill bits, and to the bits made according to those methods.
2. Background Information
To drill a well, an earth-boring drill bit is mounted on the lower end of a drill string and the drill string is rotated while weight is applied. In this manner, the rotating drill bit engages the earthen formation and drills a borehole toward a target zone. The borehole created will have a diameter generally equal to the diameter or “gage” of the drill bit.
Drilling a borehole is extremely costly, with the cost being proportional to the total time it takes to drill to the targeted depth and location. In turn, the time spent drilling the well is greatly affected by the bit's rate of penetration (“ROP”) and the number of times the bit must be changed before reaching the targeted formation, as is necessary, for example, when the bit becomes worn or damaged. Whenever a bit must be changed, the entire drill string, which is made up of discrete sections of drill pipe that have been threaded together and that may be miles long, must be retrieved from the borehole, section by section. Once the drill string has been retrieved and the new bit installed, the bit must be lowered back to the bottom of the borehole. This is accomplished by reconstructing the drill string, section by section. This process, known as a “trip” of the drill string, requires considerable time, effort and expense. Accordingly, it is desirable to employ drill bits that drill faster and for longer durations.
One type of conventional bit is a fixed cutter bit having a bit body with a number of cutter elements secured thereto. In a typical fixed cutter bit, each cutter element includes an elongate and generally cylindrical support member that is formed of tungsten carbide and retained in a pocket formed in the surface of one of several blades on the bit body. This support serves as a substrate for the cutting face made of polycrystalline diamond (“PCD”) or other superabrasive material, such as cubic boron nitride, thermally stable diamond, polycrystalline cubic boron nitride, or ultrahard tungsten carbide (meaning a tungsten carbide material having a wear-resistance that is greater than the wear-resistance of the material forming the substrate). For convenience, as used herein, reference to a “PCD cutting element” refers to a cutter element employing a hard cutting layer of polycrystalline diamond or other superabrasive material such as cubic boron nitride, thermally stable diamond, polycrystalline cubic boron nitride, or ultrahard tungsten carbide. The cutting face generally faces in the direction of bit rotation and scrapes, cuts, and removes formation material as the bit is rotated.
A bit's ROP and its durability may be substantially affected by the placement and orientation of the cutter elements on the bit. Designers face substantial challenges in designing a fixed cutter bit that is both fast-drilling (has a high ROP) and that will drill for long intervals before having to be replaced (i.e. is durable). This task often requires a compromise in design. For example, a bit design intended to have a high ROP may also be a design leading to an excessive resultant force being applied to one or more of the cutter elements, causing the elements to wear prematurely or to break. Excessive wear or cutter damage may lead to a reduction in ROP and bit life, and thus necessitate a costly and premature trip of the drill string. Thus, it may be necessary to sacrifice ROP in order to design and produce a bit with sufficient durability.
Other design criteria come into play in designing a fixed cutter bit. For example, in many applications, it is important that the forces applied to the bit during drilling be balanced to a substantial degree. Put another way, in many drilling applications, it is important that the resultant out-of-balance force that the formation applies to the bit during drilling be minimized. The positions of the cutter elements on the bit and how they are oriented will impact significantly the out of balance force applied to the bit.
Accordingly, there remains a need in the art for a fixed cutter bit and cutting structure capable of enhanced ROP and greater bit life, while minimizing certain detrimental effects. A method to optimize cutter element placement parameters to achieve important design criteria would be welcomed by the industry.
Disclosed herein are methods for designing a fixed cutter drill bit and optimizing its cutting structure. One such method includes: (a) defining initial placement parameters for primary cutter elements and backup cutter elements; (b) applying in a drilling simulation a drill bit having the defined initial placement parameters and producing a generated value of at least a first design criteria of interest; (c) determining whether the generated value meets a predetermined value for the first design criteria; (d) redefining at least one placement parameter of at least one of the backup cutter elements; (e) applying in a drilling simulation a drill bit having the redefined placement parameters and producing a new generated value for the first design criteria; (f) determining whether the new generated value meets the predetermined value; and (g) repeating steps (d), (e) and (f). Steps (d), (e) and (f) may be repeated at least until the new generated value meets the predetermined value of the first design criteria of interest, or until a plurality of new generated values are determined that meet the predetermined value. The method may also include: (h) after a new generated value is determined to meet the predetermined value of the first design criteria, selecting a second and different design criteria of interest; (i) applying in a drilling simulation a drill bit having the initial placement parameters of the primary cutter elements and the redefined placement parameters of the back up cutter elements that generated a value that met the predetermined value for the first design criteria, and producing a generated value of said second design criteria of interest; (j) determining whether the generated value of the second design criteria of interest meets a predetermined value for the second design criteria; (k) redefining at least one placement parameter of at least one of the backup cutter elements; (l) applying in a drilling simulation a drill bit having the initial placement parameters of the primary cutter elements and the redefined placement parameters for the backup cutter elements of step (k), and producing a new generated value for the second design criteria of interest; (m) determining whether the new generated value for the second design criteria of interest of step (l) meets the predetermined value for the second design criteria; and (n) repeating steps (k), (l) and (m).
In another embodiment, the design method includes (a) defining initial primary placement parameters for primary cutter elements; (b) repeatedly: selecting back up placement parameters for back up cutter elements; applying to a simulated formation a bit design having the combination of the defined initial primary placement parameters and the selected back up placement parameters; using the combination in the simulation and generating a value representative of a first design criteria of interest (such as resultant force on a cutter element, total out-of-balance force on the bit, resistance to slip stick, and resistance to bit vibration); comparing the generated value to a first predetermined acceptable value. This method may include performing step (b) at least until one combination or a plurality of combinations are found that meet the first predetermined acceptable value. The method may also include: (c) for a combination that produces a generated value that meets the first predetermined acceptable value, repeatedly applying to a simulated formation a drill bit design having the combination; using the combination and producing in the simulation a generated value representative of a second design criteria of interest; comparing the generated value of the second design criteria to a second predetermined acceptable value.
In a further embodiment, the design method includes: (a) determining initial placement parameters for primary and backup cutter elements; (b) calculating through a simulation the resultant force on each of the primary cutter elements in at least a given region on the bit; (c) comparing the calculated resultant force on each primary cutter element in the given region to a predetermined acceptable value; (d) adjusting at least one placement parameter for at least one backup cutter element; and (e) repeating steps (b) through (d) at least until the calculated resultant force on each primary cutter element in the given region is within acceptable limits.
Thus, embodiments described herein comprise a combination of features and advantages intended to address various shortcomings associated with certain prior apparatus and methods. The various features and characteristics described above, as well as others, will be readily apparent to those skilled in the art upon reading the following detailed description, and by referring to the accompanying drawings.
For a detailed description of the embodiments of the bit and design method disclosed herein, reference will now be made to the accompanying drawings in which:
Many factors relating to the design of a fixed cutter drill bit will affect bit performance and how well the bit will meet particular design criteria. For example, the position and orientation of the cutter elements will impact specific criteria, such as the resultant force applied to each cutter element and the overall out-of-balance force seen by the bit, as well as other criteria. In turn, these can affect the bit's ROP and its durability. The methods described herein are directed to an iterative process by which the placement parameters (e.g., tip height or tip offset, radial position, backrake angle, siderake angle, and angular position) for backup cutter elements are varied while the placement parameters for the primary cutter elements remain at their initial or baseline values. Varying the placement parameters of backup cutter elements provides a means to optimize a cutting structure in an effort to achieve a better performing bit.
The following description is exemplary of embodiments of the invention. These embodiments are not to be interpreted or otherwise used as limiting the scope of the disclosure, including the claims. One skilled in the art will understand that the following description has broad application, and the discussion of any embodiment is meant only to be exemplary of that embodiment, and is not intended to suggest in any way that the scope of the disclosure, including the claims, is limited to that embodiment.
The drawing figures are not necessarily to scale. Certain features and components disclosed herein may be shown exaggerated in scale or in schematic form, and some details of conventional elements may not be shown in interest of clarity and conciseness.
The terms “including” and “comprising” are used herein, including in the claims, in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . .” Also, the term “couple” or “couples” is intended to mean either an indirect or direct connection. Thus, if a first component couples or is coupled to a second component, that connection may be through a direct engagement between the two components, or through an indirect connection, via other intermediate components, devices and/or connections.
Referring to
In the embodiment illustrated in
Each blade 31-38 includes a cutter-supporting surface 40 for mounting a plurality of primary cutter elements 52 and a plurality of backup cutter elements 54. As best shown in
As best shown in
The arrangement by which backup cutter elements 54 trail behind corresponding primary cutter elements 52 is best described with reference to
Referring to
Given the cutting structure 20 thus described, it will be understood that, as between a primary cutter element 52 and a backup cutter element 54 on the same blade, the primary element will be subject to substantially higher loading and will perform substantially greater cutting duty, at least until significant wear to the primary cutter element 52 occurs. This is because cutter element 54 trails closely behind the primary cutter element 52, is positioned at substantially the same radial position, but has a cutting tip that is less exposed to the formation (i.e., its tip height is less than the tip height of the primary cutter 52). In one conventional design, backup cutter elements have been positioned and oriented to perform in the sense of a “spare” cutter element that does not significantly engage the formation or perform significant cutting duty until the primary cutter element which it is following becomes worn or damaged. In particular, and referring to
In conventional bit design, a common method is to define initial placement parameters for the primary cutter elements in order to optimize one or more design criteria, and then to provide backup cutter elements that have a uniform degree of tip height, radial position, backrake and siderake without considering the effects that such placement parameters might have on the primary cutter elements. In such designs, although each backup cutter element played a role in the resultant force experienced by the primary cutter elements, the overall out-of-balance force on the bit, as well as other design criteria, the uniform placement parameters assigned to the backup cutter elements did not offer a means to optimize the cutting structure to achieve a design criteria.
In a design method disclosed herein, beginning with a baseline cutting structure where the primary cutter elements 52 and the backup cutter elements 54 each have a predetermined initial set of placement parameters, the bit performance may be evaluated via drilling simulations to generate values of design criteria of interest, such as the resultant force on each cutter element, the overall out-of-balance force on the bit, resistance to slip stick, and resistance to bit vibration. Thereafter, the generated values for the design criteria of interest are compared against predetermined values. Then, by redefining the placement parameters for certain or all of the backup cutter elements 54, a new cutting structure can designed and then tested in a drilling simulation to determine the “new” values for the design criteria of interest. In an iterative process, the placement parameters of one or more of the backup cutters 54 may be varied and the results compiled such that, ultimately, through the iterative process, an optimum backup cutting structure may be created without having to alter the placement parameters of the primary cutter structure. Specific placement parameters will now be described.
The cutting profiles of primary cutter element 52d and backup cutter element 54d of blade 31 are shown in
Each primary and backup cutter element 52, 54 is also provided with an initial radial position. Varying the radial position of the backup cutter element 54 relative to its corresponding primary cutter element 52 may, like tip height, impact design criteria, such as the resultant force on the bit's cutter elements 52, 54 and also affect the total out-of-balance force seen by bit 10. Accordingly, iteratively varying the radial position of each backup cutter element 54 relative to its corresponding primary cutter element 52, running drilling simulations, and comparing generated values of certain criteria, such as resultant force and out-of-balance force, may, in turn, provide enhancements in ROP, bit durability or both,
Referring to
Referring to
Varying the backrake angle of backup cutter elements 54 can again affect the resultant force on the cutter elements 52, 54, the total out-of-balance force on bit 10, and other design criteria.
According one of the methods described herein, a backup cutter element 54d corresponding to a primary cutter element 52d will be assigned initial backrake of, for example, a +5° as shown in
The siderake angle exhibited by a backup cutter element 54 is also a placement parameter that may be iteratively adjusted and its effect compared in simulations. Referring to
The angular position of a back up cutter element 54 relative to a primary cutter element 52 is best understood with reference again to
Exemplary bit 10, described above, includes twenty-four backup cutter elements 54. Further, as discussed above, associated with each cutter elements are at least five placement parameters: tip height, radial position, backrake angle, siderake angle, and angular position. Further, for each placement parameter, there are multiple values that may be applied. For example, with respect to tip height, depending on the diameter of the bit, the diameter of the cutter element, the formation being drilled and other factors, the tip height of a backup cutter element 54 may be adjusted to three or more positions. Likewise, subject to certain dimensional constraints, radial position of the backup cutter 54 may typically be moved radically inward or radially outward a millimeter or two in each direction (as examples). As will thus be understood, the number of permutations (twenty-four backup cutter elements, considering only five placement parameters, with several possibilities for each placement parameter) leads to an extremely large number of placement parameter combinations that can be employed. Such a large number of combinations is most effectively evaluated by means of a computer. Thus, the methods contemplated herein utilize iterative design technologies to first establish, and then test in drilling simulations, cutting structures to achieve the design criteria, and to do so prior to going to the great expense of manufacturing a test bit. According to these methods, a baseline or initial cutting structure is first defined in which each primary cutter element 52 and backup cutter element 54 is assigned initial or baseline placement parameters. The initial placement parameters for primary cutter elements 52 will remain unchanged during this exemplary design process. With the initial placement parameters for primary and backup cutter elements 52, 54 established, the program will generate baseline values for various design criteria of interest, such as a baseline resultant force on each cutter element 52, 54 and a baseline out-of-balance force for the bit 10. Thereafter, the placement parameters of one or more of the backup cutter elements 54 are changed, iteratively, in order to determine the effect on the design criteria of interest (in this example, resultant force on each cutter element 52, 54 and the overall out-of-balance force on the bit 10) for each iteration. More specifically, after baseline values are determined, one placement parameter for one backup cutter element 54 is varied from the initial or baseline placement parameter, and the resultant force on the cutter elements 52, 54 and the overall out-of-balance force on the bit 10 calculated, with the results stored in memory. In a next iteration, another placement parameter is varied for a backup cutter element 54 with the drilling simulation then being run with the revised placement parameters. This will generate new data with respect to resultant force on the cutter elements 52, 54 and the out-of-balance force on the bit 10, with those values again being stored in memory. This process may continue until each placement parameter (taken alone or in combination) for each backup cutter element 54 has been run in the simulation, or until enough have been run to determine placement parameters that will yield a bit that meets particular design criteria. From the data now in memory, the designer can make narrowing choices in order to choose those combinations of placement parameters yielding desirable or at least acceptable resultant forces on cutter elements 52, 54 and out-of-balance force on bit 10.
Referring to
The design process next includes an initial definition of placement parameters for all cutter elements 52, 54 in step 104. An automated bit design tool is used to create a bit design file in which the placement parameters for each cutter element are defined. The bit design tool may comprise menu-based input prompts and graphics generation routines that execute on a Microsoft Windows operating system. In one implementation, solid modeling computer aided design (CAD) software may be utilized. In step 104, each cutter element 52, 54 will be assigned a particular tip height, radial position, backrake, siderake, and angular position. In a drilling simulation, a calculation is then performed in step 106 to generate the resultant force applied to each primary cutter elements 52 and backup cutter element 54. It should be understood that certain aspects of the method disclosed herein may be defined and implemented in cooperation with kinematic force models such as that developed by Amoco Research and through other cutting analysis tools and graphics design programs run on personal computers or workstations. As already discussed, the forces on primary cutter element 52 will be substantially greater than those of the corresponding backup cutter elements 54; however, the resultant force on each backup cutter element 54 is also calculated in order to ultimately calculate the out-of-balance force on the bit in step 110, discussed below. Techniques for determining resultant force on individual cutter elements and a resultant out-of-balance force on bits are known, as described in U.S. Pat. Nos. 4,932,484, 5,010,789, 5,042,596, in U.S. Patent Application Publication No. US2009/0166091 A1, and in the published Sandia Report entitled “Development of a Method for Predicting the Performance and Wear of PDC Drill Bits” by David Glowka dated June 1987, the disclosures of which are all incorporated herein by this reference. With the resultant force on each cutter element 52, 54 calculated, the force is measured against a predetermined design criteria in step 108 to determine whether that resultant force is too high. That predetermined design criteria is based on prior calculations, lab tests, field tests and run data and will depend in part, on the strength of the materials employed in making the cutter elements, as one example.
If the resultant force on each primary cutter element 52 is acceptable, the out-of-balance force on the bit 10 is calculated in step 110. The output of the kinematic force model produces a total out-of-balance force vector. The total out-of-balance force on the bit is defined as the sum of the total radial and total drag forces for all the cutter elements, and can be expressed as a percentage of the weight on bit (WOB) by dividing the total imbalance force by the total WOB. Depending upon the drilling application, an out-of-balance force of a particular magnitude or force direction may be desirable or undesirable. For example, in many drilling applications, it is desirable that the resultant out-of-balance force be as low as possible. In certain directional drilling applications, force of a particular magnitude and directed towards a particular gauge pad is desired. In either instance, the calculated out-of-balance force is compared in step 112 to a predetermined design criteria for out-of-balance force. If the criteria is met, then the placement parameters defined in step 104 are passed on to be incorporated into the final design in step 114.
If after either calculation in step 106 or 110 the calculated forces are unacceptable because they do not meet the predetermined design criteria, then the design process moves to step 116 where, keeping the placement parameters of the primary cutter elements as initially defined in step 104 in this exemplary method, the placement parameters of backup cutter elements 54 are redefined and thus varied from their initial, baseline values. Following step 116, the method then recalculates the resultant forces on cutter elements 52, 54 and returns to step 106 after the placement parameters of backup cutter elements 54 have been redefined in step 116, and the process continues as described above. Although in this example, resultant force is calculated in step 106, and the calculation of out-of-balance force takes place in subsequent step 110, the order of these steps can be reversed.
In another example, in some instances, bit stability may be a critical design criteria, such that minimizing the overall out-of-balance force on the bit would be a primary goal of the design. In this example, the simulation program would run all possible combinations of placement parameters for the backup cutter elements 54 and rank the combinations from those generating in a simulation the lowest out-of-balance force to those having the highest out-of-balance force. Based on existing data or other studies by which a maximum resultant force on the cutter elements 52, 54 is determined, those combinations of placement parameters resulting in a low out-of-balance force, but where the predetermined maximum resultant force on the cutter elements was exceeded, would be discarded. Of those combinations/permutations remaining, the resultant force on the cutter elements 52, 54 would be less than the predetermined maximum, and so the combination exhibiting the lowest out-of-balance force (in this example), would be selected for the bit design, and a bit may be manufactured pursuant to that design.
In a variation of this method, there may be instances where a specific out-of-balance force may be desirable, as in directional drilling applications. In those instances, after eliminating the combinations in which the resultant force on the cutter elements 52, 54 exceed a predetermined maximum, the computer would sort the remaining combinations and choose the one generating the out-of-balance force that is closest to the out-of-balance force that is desired for the particular drilling application.
In another example, where the total out-of-balance force on the bit is not as important as avoiding designs having an excessive resultant force on a cutter element, the combinations would be run in a simulation and ranked to first eliminate all placement parameter combinations for backup cutter elements yielding a resultant force on any cutter element that exceeded a predetermined maximum. Then, the remaining combinations would be ranked by the computer from those having the lowest out-of-balance force to those having the highest. In applications where it is also desirable to have a low out-of-balance force, then the combination having the lowest out-of-balance force of those remaining combinations could then be selected for implementation, and the bit then manufactured in accordance with those placement parameters.
In another example of a design method disclosed herein, initial placement parameters for primary cutter elements and backup cutter elements are assigned, and a bit having that cutting structure is run in a simulation in order to determine the baseline resultant force on all cutter elements. Theoretically, the most efficient loading distribution would be to load all the primary cutter elements 52 in a particular region of the bit equally, so that the design would be less likely to overload any single cutter element in that region. For example, and referring to
Referring to
Referring to
Starting with the baseline cutting structure 20′ shown in
As shown, adjustments to even a single placement parameter (in this example) of only a single secondary cutter element 54 can affect the resultant force on the primary cutter elements and the out-of-balance force on the bit. Varying more placement parameters and for more backup cutter elements 54 (even while keeping the placement parameters for the primary cutter elements 52 unchanged as in this example), provides the bit designer with the substantial opportunities to optimize the cutting structure and to enhance bit performance.
The bit design method has, to this point, been described most particularly in terms analyzing resultant force and how to balance force across the entire bit face. It should be understood that the methods described may also be applied to other design criteria of interest, such as slip stick and resistance to bit vibration. Further, these methods may be applied with respect to only certain regions of the bit, rather than to the entire bit face. In fact, it is typically the case that the highest resultant force is applied to primary cutter elements in the nose region of the bit, meaning that, if the placement parameters of backup cutter elements are adjusted to ensure that the resultant forces experienced by the primary cutter elements in the nose region are below a predetermined acceptable value, then the resultant forces on cutter elements in all other regions will likewise be below their acceptable values.
Referring momentarily to
Accordingly, the method described herein may be applied, for example, only to the shoulder region 72 of the bit, or the nose portion 76 rather than the entire bit face 18. Using the shoulder region as an area of most interest in this example, then the same methodology explained with reference to
Analyzing and optimizing the cutting structure in only a particular region may be appropriate where past history has shown cutter elements in that particular region being susceptible to breakage, but where cutter elements in other regions do not exhibit similar damage.
After it has been determined that the resultant force on all the primary cutter elements in the region of interest (here, the shoulder region 72) are below a predetermined maximum value, then the out-of-balance force on the entire bit can be evaluated to determine whether that design criteria is satisfied.
When varying a placement parameter of one of more back up cutter elements, it is to be understood that the methods disclosed herein allow for varying only some of the placement parameters, and varying placement parameters for only some back up cutter elements. Thus, for example, although some conventional bit designs incorporate back up cutter elements that all have the same tip height (for example), when redefining the placement parameters of the back up cutters to optimize certain criteria according to the teachings herein, it may be that one or more of the back up cutters have their tip height changed from their initial value to a new first value, while others are changed to a new second value that differs from the new first value, while still others remain unchanged. In other words, the methods disclosed herein do not require that the redefined placement parameters all be changed, or that they all be changed in a like manner or to a uniform value.
While preferred embodiments have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teachings herein. The embodiments described herein are exemplary only, and are not limiting. Many variations and modifications of the disclosed apparatus are possible and are within the scope of the invention. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims.
