Patent Grant
7150479
Threaded connections are a prevalent method to join two or more members such as pipe sections. In certain applications, as during hydrocarbon exploration and recovery operations, a string of pipe sections joined by threaded connections may be rotated in a well bore. For example, a drill string may be rotated to urge a bottomhole assembly into a subterranean formation. The bottomhole assembly (BHA) also may include components that are mated or joined with threaded connections. In certain instances, drilling activity may cause the string and BHA to bend. As is known, the bending of threaded connection induces compression on one side of the threaded connection and a tension on the other side of the threaded connection. Because the threaded connection is rotating, the tension and compression is cyclical. It is, of course, also known that cyclical bending stresses imposed by even moderate loadings may lead to failure of the threaded connection (e.g., high cycle fatigue).
The harsh drilling conditions of the well bore environment or deviated well bores can cause such cyclical bending stresses in these threaded connections. Unfortunately, conventional threaded connections, such as those specified by the American Petroleum Institute (API), do not always possess sufficient bending fatigue resistance to support advanced drilling programs or complex well bore trajectories. For example, in some instances, drilling operations and hydrocarbon recovery may require a highly deviated well bore, e.g., a well bore having a sharp radius portion. Form deviated wellbore sections requires a BHA and drill string that can withstand a relatively high “build-up rate.” Conventional threaded connections subjected to such build-up rates can suffer reduced operational lifetime or require additional maintenance or rework. Moreover, even common drilling conditions slowly degrade conventional threaded connections such that these connections must be either changed-out or reworked. The costs incurred in such activity not only include the maintenance itself but, for example, the delay in drilling activities.
The present invention addresses these and other drawbacks of conventional threaded connections.
The present invention provides a threaded connection having high resistance against cyclical bending fatigue. In a preferred embodiment, the threaded connection is used in a pin-box arrangement that joins two drill string components. Such components include, but are not limited to, steerable assemblies, drilling motors, bottomhole assemblies, measurement-while-drilling assemblies, formation evaluation tools, drill collars or drill pipe. In addition to complementary threads, the pin and box each include a radial shoulder and abutting surface, respectively. The threads of the pin and box conform to a pre-determined profile that is defined at least by taper, pitch, and root radius. A preferred thread profile includes a relatively long pitch, a relatively large root radius and a relatively shallow taper as compared to conventional thread profile standards (e.g., API standards). The thread configuration is defined at least by pre-determined reference diameters, a pin length, and a boreback-diameter. An illustrative thread profile for an exemplary 9½ inch connection or coupling provided on preferred components is approximately as follows: Taper: 1:5; a ratio between Pitch and Root Radius (P/R) of approximately 5.40; and a ratio between Thread Height and Root Radius (H/R) of approximately 2.41. It should be appreciated that these values are provided with specificity merely for convenience and that the present invention is by no means limited to these values. Moreover, a coupling having less than all of these characteristics may provide adequate performance in many applications. It is believed that this exemplary joint will have a pin bending strength that is fifty percent greater and a box bending strength that is one hundred percent greater than a conventional threaded connection for the same size joint.
In certain embodiments to the present invention, the threads may be cold worked to increase of fatigue resistance, copper plated to increase of galling resistance, and/or shot peened to increase resistance against stress-corrosion-cracking. The threads may also include stress relief groove(s) to increase of fatigue resistance. The threaded connection can optionally include a contact ring in the shoulder to transmit power and data between different tools. In still another embodiment, the threaded connection includes a sealing system to avoid mud ingress and electrical shortage under rough drilling conditions. The threaded connection of the present invention increases the mechanical strength of conventional joined components and thus enhances the allowable operational range (e.g., rotating Build-up-Rate capacity), increases service reliability in case of harsh drilling conditions, and also reduces maintenance costs.
It should be understood that examples of the more important features of the invention have been summarized rather broadly in order that detailed description thereof that follows may be better understood, and in order that the contributions to the art may be appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject of the claims appended hereto.
For detailed understanding of the present invention, references should be made to the following detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, in which like elements have been given like numerals and wherein:
The present invention relates to an apparatus and methods for increasing the fatigue resistance of pin and box connections or couplings subjected to cyclic bending stresses, particularly in oilfield applications. The present invention is susceptible to embodiments of different forms. There are shown in the drawings, and herein will be described in detail, specific embodiments of the present invention with the understanding that the present disclosure is to be considered an exemplification of the principles of the invention, and is not intended to limit the invention to that illustrated and described herein.
Referring initially to
Referring now to
The connector 101 includes a pin end 102 and a box end 104. The pin end 102 is generally configured to mate with a complementary box end of an adjacent component (not shown). The pin end 102 includes a nose 106 having a threaded surface 108, a shoulder 110, and a through bore 112. The box end 104 includes a stepped bore 114 having a threaded interior portion 116, a shoulder 118, and a boreback 120. Upon engagement of a pin end 102 and a box end 104, the shoulders 110 and 118 mate along a ring-like surface area. The pin threaded surface 108 and box threaded interior portion 116 each include threads 124 that are best shown in
A preferred thread profile includes a relatively longer pitch, a relatively larger root radius and a relatively shallower taper as compared to conventional thread profile standards (e.g., API standards). For convenience, these thread profile elements or features will be discussed in terms of ratios, specifically the ratio between Pitch and Root Radius (P/R) and the ratio between Thread Height and Root Radius (H/R). The preferred thread profile may be determined by an iterative modeling process wherein one or more parameters, such as a connection outer diameter, are set as a design parameter. A first profile having a known thread design, e.g., an API specified profile is then formed on a test piece. This test piece preferably includes a controlled variation in one or more thread profile or configuration features. For example, the taper T may be made relatively shallow in order to provide more material on which to form threads in the box. Additionally, the root radius R may be increased to reduce local stress concentration. This test piece is subjected to bending fatigue under controlled conditions until the threaded connection or coupling fails. Thereafter, known methods such as mathematical models utilizing finite element analysis may be used to determine the extent to which an incremental variation in the same feature or another feature may reduce stresses. A second piece is then prepared and retested. This iterative design process can be used, for example, to isolate one or more features that can be modified to effect a reduction in localized stresses in the thread form. It will be appreciated that this mathematical modeling technique will produce (a) an thread design having one or more optimized features (i.e., maximized fatigue resistance); and/or (b) a table of various combinations of feature variations that produce a particular fatigue resistance that is greater than that of conventional thread designs.
The table below provides a comparison of a conventional thread profile and one preferred embodiment of a thread profile for a conventional connection having a 9½ inch outer diameter, a pin inner diameter of 3½ inches, and a box bore-back inner diameter of 145 mm:
As can be seen, the pitch-to-root radius ratio is preferably less that that of the conventional (e.g., API) thread profile, and preferably no greater than approximately 5.40. Likewise, the thread height-to-root radius ratio is preferably less that that of the conventional (e.g., API) thread profile, and preferably no greater than approximately 2.41. The preferred thread configuration for the 9 1/2 inch connection is as follows:
Referring briefly to
It is believed that the above general guidelines for a preferred thread profile and configuration will enhance the fatigue strength of a connection utilizing an exemplary thread profile of the present invention. It is, for example, estimated that the comparative endurance limits for the pin and box of the conventional and preferred thread profiles under rotating bending are as follows:
As is known, tooling for downhole applications is provided in various diameters to accommodate the several conventional sizes of well bores. Accordingly, for convenience, the following table provides numerical guidelines for preferred thread profiles for other conventional well tool and equipment diameter sizes:
Preferred thread configurations for the above listed connections or couplings are as follows:
Like the values stated for the 9½ inch coupling, it will be appreciated by one of ordinary skill in the art that the pitch-to-root radius ratios shown above are preferably less that that of corresponding conventional (e.g., API) thread profiles, and preferably no greater than the approximate values listed above. Likewise, the thread height-to-root radius ratios are preferably less that that of corresponding conventional (e.g., API) thread profiles, and preferably no greater than the approximate values listed above.
For convenience, selected thread profile values from the API specification are provided below in Tables A and B:
Table A reproduces selected numbers from Table 9.1 entitled Product Dimensions Rotary Shouldered Connections and Table B reproduces selected numbers from Table 9.2 entitled Product Thread Dimensions Rotary Shouldered Connection, both of which are found in Specification for Rotary Drilling Equipment (American Petroleum Institute) Specification 7 (SPEC 7) Thirty-Seventh Edition, Aug. 1, 1990 by the American Petroleum Institute, a reference which is hereby incorporated by reference for the purpose of defining conventional thread specifications.
It will be apparent that the embodiments of the present invention use dimensions for the above-described features that are different from those currently specified by the American Petroleum Institute (API) and that provide markedly improved strength characteristics. Generally, when compared to the corresponding conventional connection size, the embodiments of the present invention include: (i) a pitch-to-root radius ratio that is less than the API ratios (which is approximately 8 to 10), e.g., less than 6.5 to 7; (ii) a thread height-to-root radius ratio that is less than that specified by the API (which is approximately 4 to 6), e.g., less than 3.5; (iii) a flank angle that is less than that specified by the API (which is approximately 60°) and (iv) a taper that is less than that specified by the API (which runs from 1:4 to 1:8). It should be understood, however, that a coupling having less than all of these features may, in many instances, provide adequate strength characteristics.
It should be appreciated that these values are provided with specificity merely for convenience and that the present invention is by no means limited to these values. Furthermore, it should be understood that these values are subject to applicable machining tolerances. Thus, these values merely indicate the general optimization technique that may be applied to minimize local stresses under given geometric constraints. It is believed that the general relationships between the described features of the thread profile will enhance the fatigue strength of nearly any diameter size connection utilizing an exemplary thread profile of the present invention.
In alternative embodiments to the present invention, the threads may be cold worked to increase of fatigue resistance, copper plated to increase of galling resistance, and/or shot peened to increase resistance against stress/corrosion/cracking. The threads may also include stress relief groove(s) to increase of fatigue resistance.
Referring now to
It will be appreciated that the preferred threaded connection will enhance the utility of threadedly joined components or members of well tools and strings used in a well construction system. For example, a bottomhole assembly utilizing one or more preferred connections will have improved resistance to fatigue imposed during harsh drilling conditions, high cyclic or dynamic loading. Such a bottomhole assembly will allow a relatively longer time in rotation within curved boreholes and effect higher build-up rate or dogleg severity.
The foregoing description is directed to particular embodiments of the present invention for the purpose of illustration and explanation. It will be apparent, however, to one skilled in the art that many modifications and changes to the embodiment set forth above are possible without departing from the scope and the spirit of the invention. It is intended that the following claims be interpreted to embrace all such modifications and changes.
This application takes priority from U.S. Provisional Patent Application Ser. No. 60/340,756, filed Dec. 7, 2001.
| Number | Name | Date | Kind |
|---|---|---|---|
| 3067593 | McCool | Dec 1962 | A |
| 3079181 | Van der Wissel | Feb 1963 | A |
| 3917319 | Kloesel, Jr. et al. | Nov 1975 | A |
| 4549754 | Saunders et al. | Oct 1985 | A |
| 4588213 | Bollfrass et al. | May 1986 | A |
| 5127784 | Eslinger | Jul 1992 | A |
| 5221113 | Stoll | Jun 1993 | A |
| 6174000 | Nishi et al. | Jan 2001 | B1 |
| 6513840 | Krug et al. | Feb 2003 | B1 |
| Number | Date | Country |
|---|---|---|
| 975291 | Nov 1961 | DE |
| 0386373 | Dec 1990 | EP |
| WO0134936 | May 2001 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 20030156918 A1 | Aug 2003 | US |
| Number | Date | Country | |
|---|---|---|---|
| 60340756 | Dec 2001 | US |
