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FIELD OF THE INVENTION 
   This invention relates generally to a rod guide, and more particularly to an improved rod guide having increased gripping power, suitable for both rotating and reciprocating rod applications. 
   BACKGROUND OF THE INVENTION 
   In the hydrocarbon recovery industry, pumps are used at the lower ends of wells to pump oil to the surface through production tubing positioned within a well casing. Power is transmitted to the pump from the surface using a rod string positioned within the production tubing. Rod strings include both “reciprocating” types, which are axially stroked, and “rotating” types, which rotate to power progressing cavity type pumps. The latter type is increasingly used, particularly in wells producing heavy, sand-laden oil or producing fluids with high water/oil ratios. 
   Both reciprocating and rotating rods benefit from the use of rod guides to protect the interior surface of the production tubing. In practice, sucker rods and production tubing do not hang perfectly concentrically within a well, in part because well bores are never perfectly straight. Direct contact between the rod and the production tubing during reciprocation or rotation, especially while immersed in a harsh fluid environment, would otherwise cause expensive damage to the tubing and the rod. Rod guides are therefore placed between the rod and the tubing as a low cost sacrificial wear member. 
   Some rod guides have a plurality of fins projecting radially toward the ID of the production tubing, to center the rod within the tubing. The space between fins then provides a flow path for drilling fluid or hydrocarbon production flowing through the tubing. U.S. Pat. No 6,152,223 to Abdo describes such a rod guide, incorporating a low-friction wear material and a fin construction affording generous flow through. Other rod guides have a generally cylindrical outer surface having an OD substantially less than the ID of the production tubing, such that there is ample space between the guide and the tubing as a flow path. The disadvantage of this type of guide is there is less erodible wear volume (“EWV”) in the guide, which leads to greater frequency of replacement and associated costs. 
   Many rod guides require at least some assembly to the rod prior to being transported to the field where they will be used. U.S. Pat. No. 5,941,312 to Vermeeren and U.S. Pat. No. 5,339,896 to Hart, et. al, each disclose examples of such “partially field-installable” rod guides. A spool is mechanically bonded to the rod in a shop or manufacturing facility. When in the field, an outer rod guide body may be later snapped over the spool affixed to the rod. 
   The Hart patent describes a rod guide having embodiments for use with both rotating and reciprocating rods. The embodiment of the outer guide body depends on whether it is to be used with a reciprocating or rotating rod. For example, for a rotating embodiment, the body and spool may rotate freely with respect to each other, which is generally preferred for all rotating type rod guides. As the rod rotates, the spool remains stationary with respect to the rod, while the outer body is free to rotate about the spool to remain nearly stationary with respect to a sidewall of the production tubing, minimizing wear between the body and the tubing, and between the spool and the rod. The majority of the wear instead occurs between the low cost sacrificial spool and guide body. For a reciprocating embodiment, the spool may include an elongate projection, and the outer guide body may include a slot for mating with the projection, such that the guide body does not rotate with respect to the spool. 
   To minimize manufacturing and assembly costs, some existing rod guides can be installed entirely in the field. U.S. Pat. No. 4,858,688 to Edwards, et al. and U.S. Pat. No. 5,494,104 to Sable each disclose examples of such “fully field-installable” rod guides. In each of these, a generally unitary body is provided with a bore for tightly positioning about a rod, and an access channel is provided from an outer surface of the body to the bore, allowing the guide to be forcibly “snapped-on” in the field. A problem inherent to each of these rod guides is that the single-piece body must be flexed when snapped onto the rod, weakening the gripping power of the guide. The Sable patent strives to minimize this drawback, by providing a non-circular bore to place more material at the area of highest flex. Although this potentially improves the gripping power of the guide, the presence of the access channel remains a source of structural weakness during the service life of the guide. A further shortcoming of these single-piece snap-on rod guides is that a single-piece body is generally best suited for reciprocating-type rods, and is non-ideal for use with rotating type rods. 
   U.S. Pat. No. 4,343,518 discloses another type of fully field-installable rod guide that does not require an access channel for installation. Instead, the rod guide comprises two half sections which are adapted to be lockingly clamped together. One half section has grooves and the other half section includes flanges having complementary tapered surfaces so that when the two half sections are moved together vertically the flanges are wedged in the grooves to clamp the two half sections together about the rod. The tapered surfaces are very narrow, however, and do not alone produce sufficient gripping power. The half sections may use inner ridges on semi-circular recesses for contacting the rod, to cause the recesses to deform into an elliptical shape to resist slippage. Another shortcoming of the rod guide is that it is described for use only with a reciprocating type rod, and is unsuitable for use with a rotating type rod. 
   A rod guide is desired that is fully field-installable, useful with both reciprocating and rotating rods, and having an improved mechanism for attaching the guide to the rod. 
   SUMMARY OF THE INVENTION 
   A field-installable rod guide is disclosed for a rod having an outer rod surface and movable within an oilfield tubular having an interior tubular surface for driving a downhole pump to pump liquids to the surface through the oilfield tubular. 
   In one embodiment the rod guide comprises a body including first and second interfitting body members. The first body member has an outer wear surface; a pair of circumferentially spaced outer tapered surfaces radially inward of the outer wear surface and tapering radially along an axial direction, the outer tapered surfaces extending circumferentially a combined at least 70 degrees toward one another from circumferentially outer locations no greater than 180 degrees apart to circumferentially inner locations; and an inner rod-engagement surface radially inward of the outer tapered surfaces, for gripping the outer rod surface. The second body member has an outer wear surface, an inner taper-engagement surface radially inward of the outer wear surface, for axially slidably engaging the outer tapered surfaces of the first body member, to urge the first and second body member radially inward toward one another and to deform at least a portion of the first body member radially inward toward a rod gripping position about the rod; and an inner rod-engagement surface radially inward of the inner taper-engagement surface for gripping the outer rod surface. A locking member may be included for axially locking the first and second body member with respect to one another. 
   The second body member may also have a pair of circumferentially spaced outer tapered surfaces radially inward of the outer wear surface and tapering radially along an axial direction, the outer tapered surfaces extending circumferentially a combined at least 70 degrees toward one another from circumferentially outer locations no greater than 180 degrees apart to circumferentially inner locations. Likewise, the first body member may have an inner taper-engagement surface radially inward of its outer wear surface, for axially slidably engaging the pair of outer tapered surfaces of the second body member, to both urge the first and second body member radially inward toward one another and deform at least a portion of the second body member radially inward toward a rod gripping position about the rod. 
   The tapered surface outer locations of the first body member may be circumferentially spaced less than 5 degrees from adjacent tapered surface outer locations of the second body when the body is in the rod gripping position. Each outer tapered surface may circumferentially extend at least about 35 degrees. 
   Radially projecting portions may be included along the inner rod-engagement surfaces for increasing friction between the body and the rod. These may comprise axially-spaced ribs or a knurled surface. 
   For use especially with rotating type rod guides, a sleeve may be included for positioning about the first and second body member while in the rod gripping position. The sleeve may include an inner wear surface for slidably contacting the outer wear surfaces of the first and second body members, and an outer wear surface for slidably contacting the interior tubular surface of the oilfield tubular. One or more stops on the body limit axial motion of the sleeve with respect to the body. 
   A plurality of fins may be included for centering the rod within the interior tubular surface of the oilfield tubular. The fins may be included directly on the body, especially for reciprocating rod guides, or on the sleeve, for rotating rod guides. 
   The foregoing is intended to summarize the invention, and not to limit nor fully define the invention. The aspects of the present invention will be more fully understood and better appreciated by reference to the following description and drawings. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a preferred embodiment for a rotating type rod guide, with both body members slid together to form the body and an outer sleeve about the body. 
       FIG. 2  shows a perspective view of one of the body members of  FIG. 1 . 
       FIG. 3  shows a perspective view of the body members of  FIG. 1  partially slid together. 
       FIG. 4  shows a perspective view of both body members of  FIG. 1  fully slid together to form a body. 
       FIG. 5  shows a perspective view of the sleeve of  FIG. 1 . 
       FIG. 6  is a perspective view of a less preferred embodiment of a reciprocating type rod guide not having a sleeve. 
       FIG. 7  shows the rod guide including a pair of axially spaced seal grooves. 
       FIG. 8  shows the rod guide including a pair of axially spaced seal members received by a respective one of the axially spaced seal grooves. 
       FIG. 9  shows a sleeve embodiment including a locking bridge for limiting outward flexing of the sleeve. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1  shows a preferred embodiment for a rotating type rod guide  10 , assembled with interfitting first and second body members  12 ,  14  slid together to form a generally cylindrical body  13 , and an outer sleeve  16  positioned about the body  13 . The rod guide  10  in general protects the rod and an interior bore of an oilfield tubular while the rod is moved within the tubular to power a pump. The rod guide embodied in  FIG. 1  is particularly useful as a rotating type rod guide, because the body  13  may rotate freely within the sleeve  16  discussed below. 
     FIG. 2  shows in greater detail the first body member  12  of  FIG. 1 . The first body member  12  is preferably substantially identical to the second body member  14 , and for the purpose of discussion the first and second body members  12 ,  14  may be assumed to include the same features, except where noted. The first body member  12  includes an outer wear surface  20 , at least one outer tapered surface  22  radially inward of the outer wear surface  20 , tapering radially along an axial direction, and an inner rod-engagement surface  24  radially inward of the outer tapered surface  22 , for gripping an outer surface of a rod (not shown). The second body member  14  includes the outer wear surface  20 , an inner taper engagement surface  26  radially inward of the outer wear surface  20 , for axially slidably engaging the at least one outer tapered surface  22  of the first body member  12 , and the inner rod-engagement surface  24  radially inward of the inner taper engagement surface  26 . Because the body members  12 ,  14  of this preferred embodiment are substantially identical, each of them thus includes the outer wear surface  20 , the outer tapered surface  22 , the inner rod-engagement surface  24 , and the inner taper-engagement surface  26 . 
     FIG. 3  illustrates how the first and second body member  12 ,  14  cooperate. The first body member  12  is shown partially slid together with the second body member  14 , between which a rod may be positioned (not shown). As the body members  12 ,  14  are axially slid together, the inner taper engagement surface  26  on one body member  12 ,  14  axially slidably engages the at least one outer tapered surface  22  of the other body member  12 ,  14 . This engagement draws the body members  12 ,  14  toward a strong, frictional engagement about the rod. 
     FIG. 4  shows a perspective view of body members  12 ,  14  fully slid together to form the body  13 . The body  13  thus has the substantially continuous outer wear surface  20  comprising the outer wear surfaces  20  of the individual body members  12 ,  14 . The body is locked together with optional locking members, which are shown as a radially projecting snap  15  on the first body member  12  (see  FIG. 2 ) and a corresponding recess  17  on the second body member  14  (see  FIG. 3 ) for receiving the snap  15 . This gripping position is discussed in more detail below, in terms of how the rod guide  10  allows a tight, secure fit that is capable of withstanding large axial and rotational forces. 
     FIG. 5  shows a perspective view of the sleeve  16  used in the embodiment of  FIG. 1 . The sleeve  16  has a plurality of radially projecting fins  32 . The sleeve  16  includes an inner wear surface  28  for slidably contacting the outer wear surface  20  of the body  13  and an outer wear surface  30  on a radially outward portion of the plurality of fins  32  in the embodiment shown. In less preferred embodiments fins  32  may be excluded, and an outer surface located at a radially outermost location  31  may alternatively serve as the outer wear surface. The outer wear surface  30  is for contacting the interior tubular surface of the oilfield tubular (not shown). One or more stops  34  are preferably included on the body  13  for limiting axial motion of the sleeve  16  with respect to the body  13 . The stops  34  as shown are a pair of axially spaced load shoulders  34  spaced a distance equal or greater than a length of the sleeve  16 . An access channel  36  is also preferably included with the sleeve  16 , for permitting installation of the sleeve  16  on the assembled body  13 . As shown, the access channel  36  passes radially through the sleeve  16 , partially severing the sleeve  16  to create circumferential side surfaces  54 ,  56 , and extends longitudinally from one end  50  of the sleeve  16  to an opposing end  52  of the sleeve  16 . Although the channel  36  in a relaxed state may be more narrow than an OD of the body  13 , the channel  36  permits flexibly spreading of the sleeve  16  to move apart circumferential side surfaces  54 ,  56  and pass the body  13  through the access channel  36 . The channel  36  may also be merely a cut, having a small or even nominally zero thickness, such that no appreciable spacing exists between circumferential side surfaces  54 ,  56 . Thus, by spreading the sleeve  36 , such as by flexing by hand, the sleeve  16  may be installed about the body  13 . The spreading force applied to the sleeve  16  may then be released, allowing the sleeve to retract about the body  13 . 
   Because the channel  36  allows outward flexing of the sleeve  16 , the sleeve  16  may flex and move about the body  13  during use. This creates a possibility of increased wear between the sleeve  16  and the body  13 , and the possibility that the sleeve  16  may inadvertently come off the body  13 . To decrease the chance of these occurring, a locking bridge may be included, as shown generally at  60  in the cross-sectional view of the sleeve embodiment of  FIG. 9 . The locking bridge  60  may selectively bridge the access channel  36  to at least limit outward spreading of the sleeve  16 , i.e., at least limit circumferential separation of circumferential side surfaces  54 ,  56 , and in some embodiments to draw the circumferential side surfaces  54 ,  56  toward one another. For example, as shown, the locking bridge  60  comprises a male member  62  secured to the sleeve  16  and a female member  64  secured to the sleeve  16  for lockingly receiving the male member  62 . The locking bridge  60  may comprise a plurality of members axially spaced along the sleeve, or the locking bridge  60  may have an axial length that is a considerable fraction of the length of the sleeve, such as between 50-100% of the length of the sleeve. 
   In the preferred embodiment shown, the male member  62  and the female member  64  are positioned within the access channel  36  between arcuate surfaces  66 ,  68 , each secured to a respective one of the circumferential side surfaces  54 ,  56 . The male member  62  locks into a similarly shaped female member  64 , bridging the channel  36 , and limiting spreading of the sleeve  16 . Preferably, this locking moves circumferential side surfaces  54 ,  56  into contact with one another, to seal or at least limit passing of sand, fluid, and debris through the channel  36 . In other embodiments, the locking bridge may be secured elsewhere on the sleeve  16 , such as on arcuate surface  66 , to draw surfaces  54 ,  56  toward one another and bridge the channel  36 . For example, in one embodiment (not shown), two members may be secured to the surface  66  opposite the channel  36  from one another, and a buckle included for fastening the two members, to both bridge the channel  36  and preferably draw surfaces  54 ,  56  toward one another. 
   Progressive cavity pumps are sometimes used in sand applications because they are able to move fluid with sand therein.  FIGS. 7 and 8  show another embodiment of the rod guide  10  including a pair of axially spaced seal assemblies indicated generally at  33 , circumferentially sealing between the body  13  and the sleeve  16 , each seal assembly  33  being positioned at opposing ends of the outer wear sleeve  16 . Each seal  37  ( FIG. 8 ) seals with a respective one of a pair of axially spaced circumferential grooves  35  ( FIG. 7 ). The grooves  35  are preferably positioned radially outward of the outer wear surfaces  20 , for increasing resistance to intrusion by sand. The seals  37  are preferably elastomeric o-rings, but may also be other types of seals known in the art, such as lip seals. 
   In other embodiments (not shown), the seal assemblies  33  can instead be located on or adjacent to load shoulders  34 . For example, a grooves can be included on shoulder  34 , and still accommodate a circular seal, such as an o-ring or lip seal, to seal with sleeve ends  50 , 52 . 
     FIG. 6  illustrates a less preferred alternative embodiment of a rod guide  100  for a reciprocating type rod. Body members  112 ,  114  include the same features described for engaging body members  12 ,  14  of the rotating type rod guide  10 , but lack the sleeve  16  or stops  34  of that other embodiment. Radially projecting fins similar to fins  32  may be included (but are not shown) directly on the body  13 . However, some embodiments having a sleeve  16  as in  FIGS. 1-5  may also be used with a reciprocating type rod. This would decrease tooling and associated costs, because the same body  13  and sleeve  16  may then be used for both rotating and reciprocating type rods. Because the sleeve  16  may already have fins  32 , use of the sleeve  16  with reciprocating rods would eliminate the need for a separate rod guide embodiment having fins directly on the body  13 . 
   The at least one outer tapered surface  22  of the first and second body members  12 ,  14  are preferably a pair of circumferentially spaced outer tapered surfaces  22 , as shown in  FIG. 1 . The pair of outer tapered surfaces  22  should circumferentially extend at least a combined 70 degrees from circumferentially outer locations  40  no greater than 180 degrees apart to circumferentially inner locations  42 . The outer tapered surfaces  22  preferably extend at least a combined 90 degrees, as shown. Individually, each outer tapered surface  22  should extend circumferentially at least 35 degrees, and preferably at least 45 degrees as shown, i.e. the distance between the outer location  40  and inner location  42  of each tapered surface  22  is preferably at least 35-45 degrees. As best seen in  FIG. 3 , the circumferentially outer locations  40  of the first body member  12  may be spaced very closely (preferably less than 5 degrees) to adjacent circumferentially outer locations  40  of the second body member, creating a substantially continuous outer tapered surface  22 . This novel geometry is largely responsible for the rod guide&#39;s strong engagement with the rod. First, the circumferentially outer locations  40  of the tapered outer surfaces  22  cause the body members to deform inwardly in proximity to the circumferentially outer locations  40 . This deformation pinches the rod at these locations  40  and may induce a non-circular inner rod-engagement surface  24 , to increase frictional engagement with the rod. Second, because opposing tapered surfaces  22  circumferentially extend to circumferentially inner locations  42  spaced less than 180 degrees, the opposing tapered surfaces  22  induce a radially inward force component to draw the body members  12 ,  14  radially inward toward one another about the rod. Third, because each tapered surface  22  preferably extends at least 45 degrees, and a combined distance of at least about 90 degrees, a gripping force is applied over a large area of the rod. As compared with the prior art, this causes a stronger total force and results in a very robust engagement with the rod. As discussed further below, these features are therefore highly important for use with reciprocating type rod guides, which may experience higher forces downhole than do rotatable rod guides. 
   As best seen in  FIGS. 3 and 4 , an intermediate flange  44  may be included, extending between the pair of outer tapered surfaces  22  of the first and second body members  12 ,  14 . The intermediate flange  44  defines a portion of the outer wear surface  20 . An intermediate channel  46  may also be included, dividing a portion of the outer wear surface  20 , such that the channel  46  on one body member  12 ,  14  receives the intermediate flange  44  on the other body member  12 ,  14 . The intermediate flange  44  of one body member  12 ,  14  preferably substantially fills the intermediate channel of the other body member  12 ,  14 , forming a substantially continuous combined outer wear surface  20  along a circumferential direction. In simple terms, this feature is what helps the substantially identical body members  12 ,  14  “fit together” to form a single body  13  having a continuous outer wear surface  20 . 
   In the preferred embodiments, as discussed, the body members  12 ,  14  are substantially identical. Thus, each body member  12 ,  14  has an outer wear surface  20 , a pair of outer tapered surfaces  22 , an inner taper engagement surface  26  for engaging the outer tapered surfaces  22  of the other body member  12 ,  14 , and an inner rod-engagement surface  24 . In less preferred embodiments, however, the invention may work conceptually with less symmetry and identity between parts. At a minimum, the first body member  12  should include the outer wear surface  20 , the at least one outer tapered surface  22 , and the inner rod-engagement surface  24 , and the second body member  14  should include the outer wear surface  20 , the inner taper-engagement surface  26 , and the inner rod-engagement surface  24 . In other words, only one of the body members  12 ,  14  needs the outer tapered surface  22 , and the other of the body members  12 ,  14  needs the taper-engagement surface  26 . 
   A reciprocating type rod guide  100  may require greater holding power than a rotating type guide  10 , due to the large axial forces of the former as compared with the low rotational forces of the latter. Thus, the aspects of the invention discussed above whereby the outer tapered surfaces  22  provide large gripping power is particularly advantageous for reciprocating type guides  100 . 
   Although specific embodiments of the invention have been described herein in some detail, it is to be understood that this has been done solely for the purposes of describing 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 the spirit and scope of the invention.

Summary:
A field-installable rod guide for a rod moveable within an oilfield tubular having an interior tubular surface for driving a downhole pump to pump liquids to the surface through the oilfield tubular. The rod guide comprises a body including interfitting body members. An outer tapered surface on one body member is engaged by an inner taper-engagement surface on the other body member, to urge the body members toward a rod gripping position about the rod. The mechanism disclosed provides a particularly strong engagement with the rod, so that the rod guide may be used for either reciprocating or rotating rods. For rotating type rod guides, an outer sleeve may be included about the body.