US20090065190A1

US20090065190A1 - Oil well polish rod clamp for use with a rotator on a beam pumping unit

Info

Publication number: US20090065190A1
Application number: US12/207,026
Authority: US
Inventors: Leslie Dean Smith
Original assignee: Robbins and Myers Energy Systems LP
Current assignee: Robbins and Myers Energy Systems LP
Priority date: 2007-09-12
Filing date: 2008-09-09
Publication date: 2009-03-12

Abstract

An oil well polish rod clamp includes unitary metallic cylindrical housing and a plurality of setscrews. A textured inner surface of the housing increases longitudinal gripping capacity on a rod rotated inside an oil well by a rod rotator and reciprocated by a beam pumping unit to actuate a downhole pump. The inner housing surface may include a plurality of axially short cylindrical portions with annular gaps between upper and lower portions to increase gripping pressure by reducing the contact area with the rod.

Description

RELATED APPLICATIONS

The present invention claims priority from provisional application Ser. No. 60/993,450 filed Sep. 12, 2007.

FIELD OF THE INVENTION

The present invention relates to oil well polish rod clamps and, more particularly, to an oil well polish rod clamp for use with a rod rotator on a beam pumping unit.

BACKGROUND OF THE INVENTION

The smallest oil well beam pumping units commonly used in the oilfield are also used to de-water coal formations to allow the controlled release of methane gas for mine safety, and also for economic benefit as an additional fuel source. The depth of these “coal-bed methane” gas wells is typically less than 1,500 feet, making a standard size beam pumping unit economically wasteful in terms of physical size, capital expense, and horsepower. As a consequence, the popularity of the smallest available beam pumping units has grown substantially in the past 10 years. The beam pumping units that are most ideal for coal-bed methane production have only 4 inches of clearance between the two wire ropes forming an assembly commonly referred to as a “bridle”.
This wireline assembly or “bridle” is the flexible power and motion transmission component between the beam pumping unit's “horsehead”, and the accessory “carrier bar”, which is a generally transverse cast iron or steel cross-member with a central hole to allow the polish rod to pass through and be retained by a polish rod clamp. The polish rod must support several thousand pounds of force during transmission of power from the pumping unit and along the sucker rod string down to the pump at the bottom of the well. To facilitate rapid and easy connection of the polish rod to the carrier bar during initial installation and subsequent well servicing, a polish rod clamp is used.
Due to variations in well depth and the fact that polish rods are commonly manufactured in lengths from 11 feet to 22 feet, this clamp must be capable of gripping anywhere along the length of the polish rod, as it is impractical to simply screw a nut on the upper threaded end of the polish rod for a positive load bearing connection between the polish rod and carrier bar. A nut may have to be spaced several feet above the carrier bar, which is extremely impractical. A hinged-style polish rod clamp has been a popular method of connecting a relatively large beam pumping unit to the polish rod for oil-producing wells.
Since an oil or gas well may not be drilled perfectly straight, the string of metal sucker rods may continuously rub against the inside of the metal production tubing as they reciprocate. This will eventually cause perforation of the tubing and also more commonly a separation of the sucker rod string hundreds of feet downhole. Both are expensive failures to correct. The polish rod clamp includes a split metal housing with a hinge on one side and one or more bolts on an opposing side of the polish rod. This design mandates that the 2-piece clamp housing be “grossly asymmetrical” instead of essentially symmetrical, i.e., it is noticeably much longer in one direction compared to the dimension 90 degrees opposite.
A discontinued variation of polish rod clamp having the trade name “No-Bolt Clamp” was symmetrical and compact enough to fit between the 4 inch bridle clearance space. However, this clamp was discontinued many years ago because the rod gripping member utilized slip-like members with sharp teeth that created noticeable indentions and stress risers in the highly stressed polish rod. When used with a rod rotator, the rotary motion combined with the indentations and stress risers resulted in unacceptable breakage and separation of the polish rod due to fatigue.
A third type of polish rod clamp used in the oil field has the balance desired for powering a progressive cavity pump. The sucker rod string is driven by a rotary drive head with much clearance and no bridle around the rod clamp. Instead of a hinge pin, this clamp uses bolts on opposite sides of the polish rod. The added body material on the opposing sides makes this design unsuitable since the clamp cannot be rotated between the 4 inch wire rope spacing on bridles found on small beam pumping units.
Users of small beam pumping units that wish to prolong the life of the sucker rod string and tubing have had no practical way to utilize a rod rotator, since commercially available but grossly asymmetrical polish rod clamps cannot rotate between the 4 inch space between the wire ropes comprising the bridle assembly. Heretofore, these clamps accordingly could only be used on such small pumping units without a rod rotator. As a consequence, excessive wear and early failure of the sucker rod string and tubing, and the resulting expensive and frequent maintenance, was accepted as the norm.
The disadvantages of the prior art are overcome by the present invention, and an improved oil well polish rod clamp is hereinafter disclosed.

SUMMARY OF THE INVENTION

An oil well polish rod clamp includes a unitary metallic cylindrical housing and a plurality of axially spaced set screws for pressing the rod into secure engagement with the housing. A textured inner surface of the housing increases the longitudinal or axial gripping capacity on the rod, which may be rotated inside an oil well by a rod rotator and reciprocated by a beam pumping unit to actuate a downhole pump. The housing may include a plurality of axially short cylindrical portions with annular gaps between upper and lower portions to increase gripping pressure by reducing the contact area with the rod. A plurality of bolts or other force applying member may be used to force the rod into gripping engagement with the housing.
These and further features and advantages of the present invention will become apparent from the following detailed description, wherein reference is made to the figures in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified pictorial view illustrating the lower end of a horsehead, a bridle between the horsehead and a carrier bar, a tubing rotator, and a polish rod clamp according to the present invention.

FIG. 2 is a cross-sectional view illustrating an inner surface of the cylindrical housing engaging the polish rod.

FIG. 3 is a cross-sectional view illustrating an alternative inner surface of a cylindrical housing.

FIG. 4 is a top view of the oil well polish rod clamp housing shown in FIG. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to FIG. 1, oil well polish rod clamp 10 of the present invention includes a unitary and generally cylindrical housing 12 with a central bore sized to receive a polish rod 14. FIG. 1 illustrates the lower portion of the horsehead 16 of a beam pumping unit, an accessory carrier bar 18, which is a transverse cross member with a hole sized to allow the polish rod 14 to pass therethrough, and a rod rotator 20 mounted above the carrier bar 18. For the depicted embodiment, the rod rotator has a simple handle 22 for manually rotating the rod. Bridle 24 extends in the conventional manner between the horsehead and the carrier bar, and for small pumping units provides a minimum space between the bridle cables.
By providing a unitary, monolithic, donut-shaped body, the clamping mechanism associated with a split body and a hinge on one side and bolts or other clamping members on the opposing side are avoided. Also, reliable gripping engagement between the rod and the housing can be more easily obtained with a unitary housing rather than a split housing. The outer circumference of the rod is generally the same as the inner surface of the housing. With a unitary housing, any differences between the diameter of these surfaces can be closely controlled. With a split body housing, the effective diameter of the housing in engagement with the rod is to some extent a function of the spacing between the clamped ends of the housing. When the bolts, as shown in FIG. 4, engage the rod to force the rod into engagement with the housing, only a small arcuate portion of the housing is actually in engagement with the rod, and that limited engagement area is further decreased by the grooves discussed above. The difference between the diameter of these engaging surfaces can be more reliably controlled with a unitary body, thereby obtaining highly reliable gripping engagement and desired repeatability for the polish rod clamp.
As shown in FIG. 2, the inner surface 26 of the housing 12 may provide axially short cylindrical sections, with an upper gap and a lower gap 28 between these sections. The plurality of gaps may collectively occupy approximately 25% or more of the interior surface area of the housing, so that the area of these gaps significantly increases the area force on the cylindrical surfaces 26.
In an alternate embodiment, as shown in FIG. 3, the inner surface of the housing may be textured with grit-like material 30. Suitable grit-like materials are disclosed in U.S. Pat. Nos. 4,643,740, 4,778,730, 5,221,099, and 7,036,397. The presence of this grit does not result in excessive marking of the polish rod since the grit particles themselves are quite small in size, but does concentrate gripping forces to reliably hold the polish rod in place.
FIG. 4 depicts a top view of the housing 12, as shown in FIG. 1, and specifically illustrates the generally cylindrical configuration of the housing, and the circumferential positioning of the lock down bolts 32. Each of these bolts pass through the housing and are threaded in a bore in the sidewall of the housing so that the bolt tip end engages rod 14. By providing upper and lower lock down bolts, and more importantly by providing circumferentially spaced lock down bolts, the rod 14 may be effectively forced into gripping engagement with an interior surface of the housing which is generally opposite the bolts, thereby tightly securing the polish rod in place. At least one force applying member may be used, although at least a pair of circumferentially spaced force applying members, and also axially spaced force applying members, is preferred.
In alternate embodiments, recesses other than grooves may be provided in the inner surface, accomplishing the same purpose. Although convenient to form each groove about the entire circumference of the housing interior surface, it is most important that recesses or grooves be provided radially opposite the force applying members, since the gripping surfaces opposing such members (bolts) are supporting the load by engagement. Grooves may be axially spaced as disclosed herein, although spiral grooves, vertical grooves, pockets, or other forms or recesses alternatively may be provided on the inner surface of the housing. A highly reliable and compact polish rod clamp is obtained by minimizing the rod/housing engagement. Also, the clamp must have a sufficient height to accommodate the bolts or other force applying member. A plurality of grooves, as compared to one large (axially long) groove is preferred to minimize stress connection points.
Although specific embodiments of the invention have been described herein in some detail, this has been done solely for the purposes of explaining the various aspects of the invention, and is not intended to limit the scope of the invention as defined in the claims which follow. Those skilled in the art will understand that the embodiment shown and described is exemplary, and various other substitutions, alterations and modifications, including but not limited to those design alternatives specifically discussed herein, may be made in the practice of the invention without departing from its scope.

Claims

1. An oil well polish rod clamp, comprising:

a unitary, generally cylindrical housing;

the housing having a radially inner surface for engagement with a polish rod, and a plurality of grooves in the inner surface for decreasing the contact area between the rod and the housing, the inner surface engaging the rod comprising a plurality of generally arcuate inner surfaces with recesses between the inner surfaces; and

at least one force applying member passing through the housing for engagement with the sucker rod to force the sucker rod into gripping engagement with the inner surface of the housing.

2. A polish rod clamp as defined in claim 1, wherein a plurality of recesses collectively occupy 25% or more of the interior surface of the housing between an uppermost inner surface and a lowermost inner surface.

3. A polish rod clamp as defined in claim 1, wherein the recesses on the inner surface are axially spaced grooves.

4. A polish rod clamp as defined in claim 1, wherein the force applying member is one or more bolts for threaded engagement with the housing.

5. A polish rod clamp as defined in claim 1, wherein the force applying member comprises at least two circumferentially spaced force applying members.

6. A polish rod clamp as defined in claim 5, wherein the force applying member comprises at least two axially spaced force applying members.

7. An oil well polish rod clamp, comprising:

a unitary, generally cylindrical housing;

a plurality of circumferentially spaced and axially spaced force applying members passing through the housing for engagement with the sucker rod to force the sucker rod into gripping engagement with the inner surface of the housing.

8. A polish rod clamp as defined in claim 7, wherein a plurality of recesses collectively occupy 25% or more of the interior surface of the housing between an uppermost inner surface and a lowermost inner surface.

9. A polish rod clamp as defined in claim 7, wherein the plurality of recesses on the inner surface are axially spaced grooves.

10. A polish rod clamp as defined in claim 7, wherein the force applying members are a plurality of bolts for threaded engagement with the housing.

11. An oil well polish rod clamp, comprising:

a unitary, generally cylindrical housing;

the housing having a radially inner surface for engagement with a polish rod, and a plurality of grooves in the inner surface for decreasing the contact area between the rod and the housing, the inner surface engaging the rod comprising a plurality of generally arcuate inner surfaces with recesses between the inner surfaces, the plurality of recesses collectively occupying 25% or more of the interior surface of the housing between an uppermost inner surface and a lowermost inner surface; and

a plurality of force applying members each passing through the housing for engagement with the sucker rod to force the sucker rod into gripping engagement with the inner surface of the housing.

12. A polish rod clamp as defined in claim 11, wherein the plurality of recesses on the inner surface are axially spaced grooves.

13. A polish rod clamp as defined in claim 11, wherein the plurality of force applying members are bolts for threaded engagement with the housing.

14. A polish rod clamp as defined in claim 11, wherein the plurality of force applying members comprise at least two circumferentially spaced force applying members.

15. A polish rod clamp as defined in claim 14, wherein the plurality of force applying members comprise at least two vertically spaced force applying members.