Abstract:
A stop collar assembly used for axially securing and/or to resist axial sliding of a downhole tool device. The assembly provided on a housing of the downhole tool and includes a generally annular ring having an inner circumference beveled outward proximate to the ring edge. A clamp ring having a raised portion on its outer surface is disposed adjacent and substantially coaxial with the annular ring. Pushing the annular ring against the clamp ring compresses the clamp ring onto the housing to resist axial sliding of the annular ring.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to and the benefit of U.S. Provisional Application Ser. No. 61/044,559, filed Apr. 14, 2008, the full disclosure of which is hereby incorporated by reference herein. 
    
    
     FIELD OF INVENTION 
     The invention relates generally to the field of oil and gas production. More specifically, the present disclosure relates to a device and method for affixing together members to be disposed downhole with two or more opposing wedge like members. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Some of the features and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  illustrates an exploded perspective view of an embodiment of a stop collar assembly. 
         FIG. 2  is a perspective view of an assembled embodiment of the assembly of  FIG. 1 . 
         FIG. 3  depicts a side view of an embodiment of a stop collar assembly of  FIG. 1  on a downhole tool. 
         FIG. 4  is a plot of load test results for a prior art stop ring and stop collars with different beveled edges. 
     
    
    
     While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF INVENTION 
     The present invention will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. For the convenience in referring to the accompanying figures, directional terms are used for reference and illustration only. For example, the directional terms such as “upper”, “lower”, “above”, “below”, and the like are being used to illustrate a relational location. 
     It is to be understood that the invention is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. Accordingly, the invention is therefore to be limited only by the scope of the appended claims. 
       FIG. 1  provides an exploded view of one example of a stop collar assembly  20  in accordance with the present disclosure. The stop collar assembly  20  comprises annular rings  22 ,  24  having beveled surfaces  23 ,  25  on their inner diameters. The beveled surfaces  23 ,  25  lie at an angle C with respect to the annular rings  22 ,  24  axis A X . The annular rings  22 ,  24  also include apertures or passages  27  radially formed therethrough. The passages  27  may be threaded and sized to receive set screws  26  within the passages  27 . Adjacent the annular rings  22 ,  24  is a gripping wedge ring  28 , shown in this embodiment as having a split section  33 . The gripping wedge ring  28  outer surface includes a ridge at about its mid-section and is profiled away from the ridge at an angle B. Angle B and angle C can be substantially equal or at different values. The ring inner surface  31  may optionally be textured to increase its coefficient of friction. Shown adjacent the ring  24  is an optional sleeve  32  for housing the rings  22 ,  24 . The sleeve  32  is provided with elongated slots  34  so the set screws  26  can be externally accessed. 
       FIG. 2  provides a perspective view of an assembled embodiment of the stop collar assembly  20 . In  FIG. 2  the gripping wedge ring  28  resides coaxially within the sleeve  32  and stacked between the annular stop rings  22 ,  24  on opposite sides of the wedge ring  28 . Set screws  26  extend through the slots  34  and into the passages  27 . The slot  34  is elongated along the axial direction of the sleeve  32  thereby allowing the set screw  26  to laterally move within the sleeve  32  body. 
       FIG. 3  is a side view of a downhole tool  36  employing a centralizer  40  combined with a stop collar assembly  20 . The centralizer  40  comprises a pair of circular base members  42 ,  43  around the downhole tool  36  housing  38 . Centralizer arms  44  pivotingly attach on one end to a first base member  42  and on the other end of the arm  44  to the second base member  43 . As is known, the arms  44  bow out in their midsection into contacting engagement with the inner circumference of a tubular  50 , such as casing or other downhole tubing. The centralizer  40  maintains the downhole tool  36  a set distance from the walls of the tubular  50 . When the tool  36  is stationary in the tubular  50 , the tubular  50  walls exert a radially inward force on the arms  44  resulting in opposing lateral forces pushing the base members  42 ,  43  apart. When the tool  36  is being pushed into the tubular  50  its walls tangentially rub against the arms  44  urging the centralizer  40  upward on the tool  36 . This loads the base member  43  against the lower stop collar  20 . Similarly, when pulling the tool  36  from within the tubular  50 , the arms  44  rub against the tubular  50  walls resulting in the base member  42  transferring the arm  44  and tubular  50  wall frictional force against the upper stop collar  20 . 
     In the example of use depicted in  FIG. 3 , the transferred frictional force between the arms  44  and tubing  50  wall (as illustrated by arrow AF) pushes the anchor  43  against the stop collar assembly  20 . The centralizer anchor  43  is in contact with the annular ring  22  of the collar assembly  20 . The set screws  26  are illustrated tightened through the annular ring  22  and against the housing  38  outer surface to provide sufficient anchoring force for the ring  22  onto the housing  38 . However, in some situations, the force AF may exceed the compression and friction forces of the set screws  26  on the housing  38  and may axially move the annular rings  22  toward the adjacent gripping wedge ring  28 . This further engages the beveled surface  23  against the wedge ring&#39;s  28  profile thereby further compressing the wedge ring  28  against the housing  38 . Further engaging the beveled surface  23  over the wedge ring  28  profile correspondingly increases the compression force applied to the housing  38  by the wedge ring  28 . Ultimately, the compressive force exceeds the axial force AF thereby preventing further lateral movement of the annular ring  22  securing the centralizer anchor  43  in place. The values of angles B and C may be selectable to produce a desired clamping force. It is within the capabilities of those skilled in the art to determine angle values to produce a particular clamping force. 
     Example 1 
     In one actual example of use, the stop collar assembly  20  has been measured to provide a multiple of seven to ten times the gripping force of traditional known stop rings under static loads and up to twenty times the kinetic gripping force.  FIG. 4  includes plots of actual applied axial pounds force (ordinate) onto a stop ring over time (abscissa). The plots represent test data for: (1) a prior art existing ring; (2) a stop ring as described herein with angles B and C equal to about 20°; and (3) a stop ring as described herein with angles B and C equal to about 12°. The rings  22 ,  24 ,  28  were coupled to a test mandrel and an increasing axial load was applied. Where a local maximum occurs for the applied load indicates the particular ring was moved from its mounting by the applied load. The test results indicated that the existing ring supported an axial load up to about 1200 lbs before releasing. The stop ring beveled at 20° withstood loads in excess of 10,000 lbs and the stop ring beveled at 12° remained stable up to the test device maximum applied load of 15,000 lbs. Accordingly, stop rings beveled at more acute angles can withstand higher applied axial loads. 
     Alternative values for the angles B and C include angles up to or greater than about 7°, up to or greater than about 8°, up to or greater than about 9°, up to or greater than about 10°, up to or greater than about 11°, up to or greater than about 12°, up to or greater than about 13°, up to or greater than about 14°, up to or greater than about 15°, up to or greater than 16°, up to or greater than about 17°, up to or greater than about 18°, up to or greater than about 19°, up to or greater than about 20°, up to or greater than about 21°, and up to or greater than about 22°. Additionally, the present disclosure includes stop collar assembly  20  embodiments that are not self locking. That is, the angles B and C are such that when applied axial loads are removed from the stop collar assembly  20 , the rings  22 ,  24 ,  28  have not become press fit together, but instead can be readily separated. Angles B and C that form a “self locking” configuration depend on the ring  22 ,  24 ,  28  material and application. 
     The centralizer  40  is but one example of a piece of auxiliary equipment on a downhole tool  36  that may be secured with the stop collar assembly  20  as disclosed herein. The stop collar assembly  20  is also useful for any other auxiliary device slideable under an axial load that may be attached to or used with a downhole tool. Other examples include a standoff type centralizer, a de-centralizer, an excluder, or a wedge coaxially disposed on the outer surface of a downhole tool for mating with slips that slide along a tool body. 
     Optionally, the downhole tool may employ more than one stop collar assembly  20  and may be on opposite ends of the devices such as the centralizer  40 . Other embodiments include a single wedge ring combined with a single annular ring. In such embodiment, the wedge ring may have an anchoring means to hinder axial movement, such as a set screw thereby negating the need for the second annular ring. 
     The present invention described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment of the invention has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. For example, the wedge ring  28  could be integrally included within the remaining portions of the assembly  20  and not as a separate member. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims.