Hydraulically Operated Polished Rod Clamp
A polished rod clamp includes a clamp housing having a central passage passing through a tapered bore. A wedge lock is arranged in the tapered bore such that a first surface of the wedge lock is in sliding engagement with a tapered surface of the tapered bore and a second surface of the wedge lock grips a rod in the central passage in a lock position. A first reciprocating piston is arranged to apply a first force to the wedge lock that effects a relative sliding motion between the wedge lock and the tapered surface in a first direction corresponding to the lock direction of the wedge lock. A second reciprocating piston is arranged to apply a second force to the wedge lock that effects a relative sliding motion between the wedge lock and the tapered surface in a second direction that is opposite to the first direction.
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENTNot applicable.
BACKGROUNDThe present disclosure relates generally to a mechanism for coupling a power source to a rod string, such as a sucker rod string.
A string of sucker rods is used to couple a rod pump in a well with a reciprocating or rotary power source at the surface. The uppermost joint in the sucker rod string is known as a polished rod (or polish rod). The polished rod is machined to a high diametrical tolerance and has a polished external surface that enables a hydraulic seal to be made around the sucker rod string as the sucker rod string reciprocates or rotates. The polished rod passes through a wellhead stuffing box, which establishes a seal against the polished rod. Typically, a polished rod clamp is used to couple the polished rod to the surface power source, which may be a walking beam in the case of a reciprocating pump system or a rotary drive in the case of a progressive cavity pump system.
Other examples of polished rod clamps are based on hinged jaws that are held together by a bolt. See, for example, U.S. Pat. Nos. 2,260,544 and 3,114,188, each of which being incorporated herein by reference in their entirety.
BRIEF SUMMARY OF THE DISCLOSUREThe subject matter disclosed herein relates to a polished rod clamp for coupling a rotary power source to a rod string.
In one illustrative embodiment, the polished rod clamp comprises a clamp housing having a central passage and a tapered bore, where the central passage passes through the tapered bore. A wedge lock is arranged in the tapered bore such that a first surface of the wedge lock is in sliding engagement with a tapered surface of the tapered bore and a second surface of the wedge lock circumscribes the central passage. The second surface of the wedge lock is adapted for gripping a rod extending through the central passage in a lock position of the wedge lock. A first piston is arranged in a first cavity within the clamp housing to reciprocate within the first cavity in response to hydraulic pressure and to apply a first force to the wedge lock that effects a relative sliding motion between the wedge lock and the tapered surface in a first direction corresponding to a lock direction of the wedge lock. A second piston may be arranged in a second cavity within the clamp housing to reciprocate within the second cavity in response to hydraulic pressure and to apply a second force to the wedge lock that effects a relative sliding motion between the wedge lock and the tapered surface in a second direction opposite to the first direction.
In another illustrative embodiment, a drive system for a rod pump comprises a rod pump driver and a polished rod clamp as described above coupled to the rod pump driver. The rod pump may be a rotary pump or an axially reciprocating pump. The rod pump driver is a rotary drive, in the case of a rotary pump, or a mechanism that provides axial reciprocating motion to a rod string, such as a walking beam, in the case of an axially reciprocating pump.
In another illustrative embodiment, a method of coupling a rotary drive to a rod string comprises mounting a polished rod clamp on a drive shaft of the rotary drive such that a central passage of the polished rod clamp is aligned with a central bore of the drive shaft. The rod string is received in the aligned central bore and central passage. Hydraulic pressure is the applied to a first piston in the polished rod clamp to drive a wedge lock in the polished rod clamp to a lock position in which the wedge lock grips the rod string in the central passage.
It is to be understood that both the foregoing general description and the following detailed description are exemplary of the invention and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments of the invention and together with the description serve to explain the principles and operation of the invention.
The following is a description of the figures in the accompanying drawings. The figures are not necessarily to scale, and certain features and certain views of the figures may be shown exaggerated in scale or in schematic in the interest of clarity and conciseness.
In the following detailed description, numerous specific details may be set forth in order to provide a thorough understanding of disclosed embodiments. However, it will be clear to one skilled in the art when embodiments disclosed herein may be practiced without some or all of these specific details. In other instances, well-known features or processes may not be described in detail in the disclosed embodiments so as not to unnecessarily obscure the disclosure. In addition, like or identical reference numerals may be used to identify common or similar elements.
The tapered bore 68 has a tapered surface 71 that circumscribes the central passage 62. A wedge lock 76 is arranged in the tapered bore 68 and is movable between a first position to lock the polished rod 48 to the lower clamp body 56 and a second position to unlock the polished rod 48 from the lower clamp body 56. In one illustrative embodiment, the wedge lock 76 has a wedge body 77 terminating in a flange 82. In one embodiment, the wedge body 77 has a frusto-conical shape, with an inner surface 78 that is generally straight and an outer surface 80 that is tapered. The inner surface 78 is for engaging the polished rod 48 in the central passage 62, and the outer surface 80 is for engaging and sliding against the tapered surface 71 of the tapered bore 68. Typically, the taper angle of the outer surface 80 will be substantially the same as the taper angle of the tapered surface 71 of the tapered bore 68. For example, the taper angle may be in a range from 3° to 6°.
As shown in
Returning to
In
In an alternate embodiment, the upper piston 86a and lower piston 86b may be integrated into a single piston, where the upper part of the piston can function as the upper piston 86a and the lower part of the piston can function as the lower piston 86b. In other words, the term “upper piston” may mean a single piston arranged in the upper cavity 84a or an upper part of a single piston arranged in the combined cavities 84a, 84b. Similarly, the term “lower piston” may mean a single piston arranged in the lower cavity 84b or a lower part of a single piston arranged in the combined cavities 84a, 84b.
Ports 92 formed in the upper clamp body 52 are connected to the upper cavity 84a to allow hydraulic fluid to be fed into or removed from the upper cavity 84a. Similarly, ports 94 formed in the lower clamp body 56 are connected to the lower cavity 84b to allow hydraulic fluid to be fed into or removed from the lower cavity 84b. In one embodiment, the hydraulic fluid used in operating the polished rod clamp 36 is grease. Grease is chosen because it is readily available in the well operation environment and can be injected easily into either of the cavities 84a, 84b using a grease gun. However, other types of hydraulic fluids and other methods of injecting the hydraulic fluid into the cavities 84a, 84b may be used. In the embodiment shown in
In one illustrative embodiment, a method of operating the polished rod clamp 36 includes mounting the polished rod clamp 36 on a drive head of a rotary drive as shown in
In one embodiment, as shown in
Returning to
To unlock the polished rod 48 from the polished rod clamp 36, a lifting device is again connected to the polished rod 48. Then, the plug fitting 93 and grease fitting 93a shown in
Grease has been used as an example of hydraulic fluid to operate the polished rod clamp 36. However, it should be clear that other types of hydraulic fluids could be used. It is also possible to connect the ports in the upper clamp body and lower clamp body to a fluid control system that can be operated automatically or remotely to supply hydraulic fluid to either of the upper and lower cavities to lock the polished rod in the polished rod clamp or unlock the polished rod from the polished rod clamp.
The rotary drive 30 of
The polished rod clamp described above can be applied to conventional axially reciprocating pumps as well. The polished rod clamp can be coupled to a mechanism for providing axial reciprocating motion to the rod string and pump, such as a walking beam mechanism. An example of a walking beam is shown in U.S. Patent Application Publication No. 2013/0037257, which is incorporated herein by reference in its entirety.
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 systems, apparatus, and processes described herein are possible and are within the scope of the invention. For example, the relative dimensions of various parts, the materials from which the various parts are made, and other parameters can be varied. 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. Unless expressly stated otherwise, the steps in a method claim may be performed in any order. The recitation of identifiers such as (a), (b), (c) or (1), (2), (3) before steps in a method claim are not intended to and do not specify a particular order to the steps, but rather are used to simplify subsequent reference to such steps.
Claims
1. A polished rod clamp, comprising:
- a clamp housing having a central passage and a tapered bore, wherein the central passage passes through the tapered bore;
- a wedge lock arranged in the tapered bore such that a first surface of the wedge lock is in sliding engagement with a tapered surface of the tapered bore and a second surface of the wedge lock circumscribes the central passage, the second surface being adapted for gripping a rod extending through the central passage in a lock position of the wedge lock; and
- a first piston arranged in a first cavity within the clamp housing to reciprocate within the first cavity in response to hydraulic pressure and to apply a first force to the wedge lock that effects a relative sliding motion between the wedge lock and the tapered surface in a first direction corresponding to a lock direction of the wedge lock.
2. The polished rod of claim 1, further comprising a second piston arranged within a second cavity in the clamp housing to reciprocate within the second cavity in response to hydraulic pressure and to apply a second force to the wedge lock that effects a relative motion between the wedge lock and the tapered surface in a second direction opposite to the first direction.
3. The polished rod clamp of claim 1, wherein the wedge lock comprises a wedge body terminating in a flange.
4. The polished rod clamp of claim 3, wherein a longitudinal slot is integrally formed with the wedge body and flange such that the wedge lock is flexible to expand or contract.
5. The polished rod clamp of claim 3, wherein a plurality of circumferentially spaced longitudinal grooves is formed in the wedge body and a plurality of circumferentially spaced radial slots is formed in the flange to facilitate distribution of force along a circumference of the wedge lock.
6. The polished rod clamp of claim 2, wherein the first piston and second piston are arranged in opposing relation within the clamp housing.
7. The polished rod clamp of claim 6, wherein the wedge lock has a flange received in between the first piston and the second piston such that the first piston and the second piston are configured to apply the first force and the second force, respectively, to the flange.
8. The polished rod clamp of claim 1, further comprising at least a first port formed in the clamp housing for communication of hydraulic fluid to the first cavity.
9. The polished rod clamp of claim 8, further comprising a first fitting removably mounted in the at least a first port, wherein the first fitting is selected from the group consisting of grease fitting, plug, and valve.
10. The polished rod clamp of claim 8, further comprising at least a second port formed in the clamp housing for communication of hydraulic fluid to the second cavity.
11. The polished rod claim of claim 10, further comprising a second fitting removably mounted in the at least a second port, wherein the at least a second fitting is selected from the group consisting of grease fitting, plug, and valve.
12. A drive system for a rod pump, comprising:
- a rod pump driver;
- a clamp housing coupled to the rod pump driver, the clamp housing having a central passage and a tapered bore, wherein the central passage passes through the tapered bore;
- a wedge lock arranged in the tapered bore such that a first surface of the wedge lock is in sliding engagement with a tapered surface of the tapered bore and a second surface of the wedge lock circumscribes the central passage, the second surface being adapted for gripping a rod extending through the central passage; and
- a first piston arranged to reciprocate in a first cavity within the clamp housing in response to hydraulic pressure and to apply a first force to the wedge lock that effects a relative sliding motion between the wedge lock and the tapered surface in a first direction corresponding to a lock direction of the clamp.
13. The drive system of claim 12, further comprising a second piston arranged to reciprocate in a second cavity within the clamp housing in response to hydraulic pressure and to apply a second force to the wedge lock that effects a relative motion between the wedge lock and the tapered surface in a second direction corresponding to an unlock direction of the clamp.
14. The drive system of claim 12, wherein the rod pump is a rotary pump and the rod pump driver comprises a rotary drive having a drive shaft with a central bore, wherein the clamp housing is mounted on the drive shaft such that the central passage is aligned with the central bore.
15. The drive system of claim 12, wherein the rod pump is an axially reciprocating pump and the rod pump driver is a mechanism for providing axial reciprocating motion to a rod string.
16. A method of coupling a rotary drive to a rod string, comprising:
- mounting a polished rod clamp on a drive shaft of a rotary drive such that a central passage of the polished rod clamp is aligned with a central bore of the drive shaft;
- receiving the rod string in the aligned central bore and central passage; and
- applying hydraulic pressure to a first piston in the polished rod clamp to drive a wedge lock in the polished rod clamp to a lock position in which the wedge lock grips the rod string in the central passage.
17. The method of claim 16, further comprising applying hydraulic pressure to a second piston in the polished rod clamp to drive the wedge lock to an unlock position in which the wedge lock releases the rod string in the central passage.
18. The method of claim 17, wherein applying hydraulic pressure to the first piston results in sliding of a surface of the wedge lock along a tapered surface in the polished rod clamp in a first direction.
19. The method of claim 18, wherein applying hydraulic pressure to the second piston results in sliding of the surface of the wedge lock along the tapered surface in the polished rod clamp in a second direction opposite to the first direction.
20. The method of claim 19, wherein the first piston is arranged to reciprocate in a first cavity in the polished rod clamp, and wherein applying hydraulic pressure to the first piston comprises injecting grease into the first cavity to pressurize the first cavity.
21. The method of claim 20, wherein the second piston is arranged to reciprocate in a second cavity in the polished rod clamp, and wherein applying hydraulic pressurize to the second piston comprises injecting grease into the second cavity to pressurize the second cavity.
Type: Application
Filed: Nov 21, 2013
Publication Date: May 21, 2015
Inventor: Bill W. White (Spring, TX)
Application Number: 14/086,585
International Classification: E21B 17/03 (20060101);