Background
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This invention relates generally to downhole motors used in drilling wells and more specifically to the flexible connecting rods utilized in such motors.
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Downhole motors of the type disclosed in U.S. Patent No. 2,898,087 generally comprise a motor section at the up-hole end and an output shaft and bearing assembly located at the other, down-hole end. The motor section comprises a fluid operated motor of the Moineau type having an outer stator and an inner rotor. The shaft and bearing assembly includes a shaft that is rotatable about the axis of the motor housing.
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The lower end of the rotor moves in a gyratory path with respect to the bearing shaft. Consequently, some form of flexible connection must be provided between the lower end of the rotor and the bearing shaft which will translate the eccentric movement of the rotor to the concentric rotation of the bearing shaft while transmitting torque therebetween. Such a connection must not only be flexible and capable of transmitting torque but also must be capable of transmitting thrust so that the rotor will not be expelled from its stator by the circulating fluid.
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One such flexible connection utilized by assignee prior to the present invention is shown in U.S. Patent No. 3,260,069. Such a connection utilized lobed couplings which operated satisfactorily but was quite complex in construction and relatively expensive to manufacture.
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Another flexible connection utilized in downhole motors is shown in U.S. Patent Nos. 4,679,638 and 4,676,725. Such a connection includes an overload sub connected to a flexible rod through a plurality of splines. Such an assembly is complex and relatively costly to manufacture. In addition, threaded connections were provided at the connection ends. Quite often in operation, these threaded connections would be over torqued and the female connections would tend to swell out and enlarge, thereby losing thread engagement. This is a common mode of failure for such components.
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Still another flexible connection utilized in downhole motors is shown in U.S. Patent No. 4,636,151. Such a connection includes a flexible rod connected to an upset section of each end, and a rubber jacket mounted over the rod. As with the aforementioned devices, such a multiple-piece assembly is complex and relatively costly to manufacture.
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Other forms of flexible connecting rods between a motor and bearing assembly is shown in published U.K. Patent Applications Nos. 2,152,588 and 2,084,697. However, some of the connections are not shown in sufficient detail to understand how the connections are made.
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A very early patent to Clark, U.S. Patent No. 2,898,087, shows a flexible connecting rod having hinge pin connections at its ends.
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An even earlier disclosure is made by Moineau in U.K. Patent Specification No. 400,508. This disclosure shows some early construction of helical pumps and motors utilizing flexible connecting rods.
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It is therefore desirable to have a flexible connection for a downhole motor that is simple in construction and more economical to manufacture. Preferably the flexible connection is a one-piece construction that is simple to machine and has a high power transferring capability. Preferably, threaded interconnections are avoided along with the problems commensurate therewith.
Brief Summary of the Invention
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The flexible connection includes a one-piece flexible metal rod, having an upset portion located at each end thereof. Each end of the rod is shrunk fit or otherwise attached within each upset portion and further includes locking means for preventing relative rotation therebetween.
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An advantage of the present invention over the prior art is revealed. Due to gyration of the rotor, a space of twice the gyration is required between the rotor head outside diameter and the inside diameter of its housing to allow full movement between. This limits the cross-section available to give strength to the rotor-connecting rod connection. The methods of attachment described are stronger in torque than a threaded connection in this limited space.
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Newer motors are being designed that require more torque for the same diameter. The threaded connection at the rotor is a weak member. A more efficient use of space provided is required.
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The lower connection of the connecting rod has more room for a thicker cross-section because of true rotational motion.
Brief Description of the Drawings
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These and other features and advantages of the present invention will be more fully understood upon a study of the following description in conjunction with the detailed drawings wherein:
- FIGURE 1 is a perspective view of a bottom hole assembly including a downhole motor having the flexible connecting rod assembly in accordance with the present invention;
- FIGURE 2 is an enlarged view, partially in section, of the connecting rod assembly;
- FIGURE 3 is an enlarged sectional view of the upper end of the connecting rod assembly;
- FIGURE 4 is a sectional view taken along lines 4-4 of FIGURE 3;
- FIGURE 5 is a similar view of a modified connecting rod assembly;
- FIGURE 6 is a view of a second modified connecting rod assembly;
- FIGURE 7 is an enlarged sectional view of the bottom end of the connecting rod assembly;
- FIGURE 8 is a sectional view taken along lines 8-8 of FIGURE 7;
- FIGURE 9 is a similar view of a modified connecting rod assembly;
- FIGURE 10 is a view of a second modified connecting rod assembly;
- FIGURE 11 is a sectional view of a further modification of the upper connecting rod assembly;
- FIGURE 12 is a sectional view taken along lines 12-12 of FIGURE 11;
- FIGURE 13 is a similar view of a modified connecting rod assembly;
- FIGURE 14 is a sectional view of a further modification of the lower connecting rod assembly;
- FIGURE 15 is a sectional view taken along lines 15-15 of FIGURE 14;
- FIGURE 16 is a similar view of a modified connecting rod assembly;
- FIGURE 17 is a sectional view of a further modification of the lower connecting rod assembly;
- FIGURE 18 is a sectional view of the second embodiment of the connecting rod assembly;
- FIGURE 19 is a sectional view of the upper end of the second embodiment;
- FIGURE 20 is a longitudinal sectional view of the upper end of an additional embodiment of connecting rod assembly;
- FIGURE 21 is a transverse sectional view of the end of the connecting rod assembly at line 21-21 of FIGURE 20; and
- FIGURE 22 is a longitudinal sectional view of a variation of the embodiment of FIGURES 20 AND 21.
Description
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FIGURE 1 illustrates a bottom hole assembly, generally indicated by arrow 10, comprising a plurality of drill collars 11 interconnected to form a drill string. A downhole motor 12 is connected to the lowermost drill collar 11 and comprises a motor section 13, a bent connecting rod section 14 and a lower bearing assembly section 15. A stabilizer 16 is mounted on the bearing housing 15. An output shaft 17 is rotatably mounted within the bearing assembly section 15 and extends out the lower end thereof and forms a box connection 18. A drill bit 19 is attached to the box connection 18 for drilling a borehole.
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Referring now to FIGURE 2, the downhole motor 12 includes a rotor (only rotor head 22 shown) located within the motor housing 13. A connecting rod assembly 20 is provided to interconnect the rotor to the output shaft 17.
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The connecting rod assembly 20 comprises an elongated flexible metal rod 21 extending within section 14.
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As shown in FIGURES 2 and 3, the upper end of the rod 21 is interconnected to the rotor head 22. The rod 21 is shrunk fit within the rotor head 22, and a pin 23 extends through both members as shown in FIGURES 2, 3 and 4 to prevent relative rotation therebetween. The surfaces shown are on straight cylindrical diameters. However, the diameters could be tapered. A shrink fit is the preferred connection.
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FIGURES 5 and 6 show other modifications to prevent such relative rotation. In FIGURE 5, the connecting rod 21' is modified to have a flat section 24 which mates with a flat section 25 of a rotor head 22'. In FIGURE 6, a locking screw 26 extends through the rotor head 22 and into the connecting rod 21.
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FIGURES 2 and 7 show the lower end of the connecting rod 21 which is shrunk fit within a lower upset 27. As shown in FIGURES 7 and 8, a pin 8 extends through the connecting rod 21 and the upset 27 to prevent relative rotation therebetween.
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FIGURE 9 is similar to the construction shown in FIGURE 5 for the upper upset, in that flats 28 and 29 are provided on the rod 21' and the upset 27', respectively, again to prevent relative rotation.
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FIGURE 10 likewise shows a lock screw 30, similar to that shown in FIGURE 6 to prevent rotation between the rod 21 and the upset 27.
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The upset 27 includes a threaded pin section 31 for connection to the output shaft 17.
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FIGURES 11 and 12 show a further modification of the connecting rod in which the rod 40 has a polygon connection. A three-sided polygon connection cross-section is shown in FIGURE 12. A polygon connection with any different number of sides could be used (not shown). Only straight diameter designs are illustrated. In addition, all diameters could be tapered (not shown). The rod 40 may be shrink fit or mechanically secured into a mating portion of the upper upset 41. A lock screw 42 is further provided to ensure against fret wear from relative rotation of the interconnected members.
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FIGURE 13 shows a further modification in which the upper end of rod 43 can be splined at 44 to be received within a mating section of the upset 45, as shown. Only straight diameter designs are shown. However, all diameters could be tapered. The rod 43 may be shrink fit or mechanically secured into a mating Section of the upset 45 as shown.
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FIGURES 14 and 15 show the lower end of the connecting rod 40 that is modified like that shown in FIGURES 11 and 12 to mate with and engage a lower upset 47. A lock screw 48 is also provided.
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FIGURE 16 shows the lower end of the connecting rod 43 modified like that shown in FIGURE 13 to mate with and engage a lower upset 49. A lock screw 50 is also provided.
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FIGURE 17 shows a rod 55 having an integrally formed upset 51 having a rotary shouldered box connection 52 for connection with the pin section 53 of the output shaft 54.
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FIGURES 18 and 19 show a second embodiment of the connecting rod 60 which is a hollow cylinder made of a filament wound composite material. The composite may be made of glass fibers, carbon fibers or the like bonded with an epoxy resin. The winding angle of the filament wound cylinder is chosen for carrying the required torque as well as retaining flexibility. The upper end of the rod 60 extends around an upper upset 61 and is pinned thereto by a plurality of radial pins 63. The lower end of the rod 60 is connected to a lower upset 64 by a plurality of pins 65 in a similar fashion. The lower end of upset 64 is threadedly connected to the output shaft 66.
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FIGURES 20 to 22 show additional embodiments of composite connecting rod with enlarged ends for connection to the rotor and output shaft. Only the upper end is illustrated. In the embodiment illustrated in FIGURE 20, a hollow composite connecting rod 71 has an enlarged end 72 in the end of a rotor 73. The connecting rod is wound with the end portion around a steel core 74 which is captured inside the end of the rod. The core has a gradual tapered lower end 76 and a more steeply tapered upper end 77. In between is a drive section 78 which has an octagonal cross-section as seen in FIGURE 21. The composite connecting rod has an internal surface complementary to the outside of the core 74.
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The end of the rotor 73 has a hollow cavity with an inside surface complementary to the outside octagonal surface of the connecting rod. The upper end of the cavity has a steeply tapered shoulder 79. The lower end of the cavity has a female thread 81. A split locking nut 82 is threaded into the lower end of the cavity. The inside surface of the locking nut has a taper similar to that on the core and matching that on the outside of the connecting rod. The halves of the split nut are held in alignment by dowels 83 press fitted into transverse holes in the two halves. A spring pin (not shown) in a lateral hole through the thread secures the nut so that it does not inadvertently come out of the cavity. A longitudinal dowel or spring pin could be used instead.
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The enlarged end of the connecting rod 71 with its captured core 74 is inserted into the cavity. The split nut is threaded into the end of the cavity and its internal taper engages the external taper on the enlarged end of the connecting rod. This forces the end of the rod against the shoulder 79 inside the cavity. Thrust loads are carried by the shoulder and split nut. Torque load is carried by the octagonal connection between the rod and rotor.
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The embodiment of FIGURE 22 is similar to that in FIGURE 20, and in fact, the cross-section illustrated in FIGURE 21 is equally appropriate for showing the cross-section of the embodiment of FIGURE 22. This embodiment differs by not connecting the enlarged end of the connecting rod directly to the rotor, but instead providing a linking member 85. The end of the connecting rod is fastened into the linking member in exactly the same manner as the rod is connected into the rotor in the embodiment of FIGURE 20. The linking member has a cylindrical shaft 86 at its upper end. The shaft is shrink fitted into the end of the rotor 87 of the motor. A transverse pin 88 secures the linking member, exactly the same as the embodiment illustrated in Figs. 3 and 4.
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It will of course be realized that various modifications can be made in the design and operation of the present invention without departing from the spirit thereof. Thus, while the principal preferred construction and mode of operation of the invention have been explained in what is now considered to represent its best embodiments, which have been illustrated and described, it should be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.
