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Publication numberUS3200884 A
Publication typeGrant
Publication dateAug 17, 1965
Filing dateSep 25, 1963
Priority dateSep 25, 1963
Publication numberUS 3200884 A, US 3200884A, US-A-3200884, US3200884 A, US3200884A
InventorsHempel William C, Solum James R
Original AssigneeB & W Inc
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Close tolerance centralizer with interconnecting stop collar
US 3200884 A
Abstract  available in
Images(2)
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Claims  available in
Description  (OCR text may contain errors)

1965 J. R. SOLUM ETAL 3,200,884

CLOSE TOLERANCE CENTRALIZER WITH INTERCONNEG'IING STOP COLLAR Filed Sept. 25. 1963 2 Sheets-Sheet 2 BY Zia/4 ATTQR/VEKE' United States Patent 3,269,884 CLOSE 'ltllLllEANrCE CENTRALEZER WlTH INTE CGNNECTENG Si l)? (IGLLAR James Solurn, Los Augeles, and William C. lilienapel,

Manhattan Beach, Csliii, assignors to it W incorporated, Torrance, Qalih, a corporation oi Caliiornia Filed Sept. 25, E63, Ser. No. Mllfltil) 9 @laims. (-Cl. low-d ll) This invention relates to centralizers for use in centering a well pipe or casing on which they are mounted in a surrounding well bore and, in particular, is directed to an arrangement for mounting a particular type of centralizer that is adapted to pass through well bores or well casings of a size very close to the size of the well pipe on which the centralizer is mounted.

The functions and numerous conventional styles of centralizers are well known. The most common type of centralizer is comprised of a pair of axially spaced collars with a plurality of outwardly bowed spring bows extending between and mounted on the collars in circumiierentially spaced relationship. Under the majority of conditions and requirements there is an abundance of annular space between the outer surface of the well pipe on which the centralizers are mounted and the inner surface of the well bore, well casing or the like through which the centralizer and well pipe are passed.

However, in certain situations the well pipe and centralizer must be run through or into a casing or a bore where there is a very minimal clearance between the outer surface of the well pipe and the casin or bore and, therefore, the centralizer must be capable of being collapsed to a very minimum radial thickness. A particular style of centralizer has been developed for acconnnodating these situations and this style of centralizer is commonly known as a close tolerance centralizer, very restricted clearance type centralizer or similar design tions. Such centralizers are substantially similar to the more conventional types except that the spring bows are usually butt welded to the longitudinal edges of the collars or set into slots in the longitudinal edges of the collars and welded into such slots. in this manner the centralizer may be collapsed to a minimum outside diameter equal to the outside diameter of the supporting well pipe plus twice the thickness of the material of the spring bows or the collars, whichever is thicker. As a practical matter, the collars usually have an inside diameter larger than the well pipe diameter to permit ease of alignment of the collars and to accommodate variances in the actual outside diameter of the pipe and, therefore, the outside diameter or" the collars may be the minimum diameter to which the centralizer may be collapsed.

it is common to mount a centralizer on the well pipe for limited axial movement of the centralizer on the well pipe. Moreover, it is well known that it is advantageous for the centralizer to cooperate with the well pipe on which it is mounted whereby the centralizer is pulled by leading collar of the centralizer without regard to the direction of movement of the pipe. Thus, with the conventional centralizers, it is common to position a stop collar or the like between the two collars of a centralizer and secure the stop collar to the well pipe so that the stop collar will always engage the leading centralizer collar upon movement of the well pipe in either direction. However, with centralizers of the close tolerance type, as heretofore described, a stop collar positioned between the centralizer collars would not engage the collars but would engage the bows tending to pry the bows away from the collars or even expand the entire assembly. Moreover, a stop collar so positioned would objectionably increase the radial thickness of the assembly, thereby increasing the minimum diameter to which the close tolerance centralizer could be collapsed.

As a result of these inadequacies of conventional arrangements when used with close tolerance centralizers, it has become somewhat conventional to provide lugs or collars which are welded to the pipe longitudinally beyond the close tolerance centralizer collars or even to weld one or" the centralizer collars to the well pipe. While such methods do not objectionably increase the radial thickness of the assembly, they often do not accomplish the desired arrangement of pulling on the leading collar of the centralizer. Moreover, with certain types of well pipe it is objectionable and difficult to weld on the pipe.

it is, therefore, an object of this invention to provide a novel arrangement for interconnecting each of the collars of a close tolerance type centralizer to individual stop collars mounted on the well pipe wherein the interconnecting means have a very minimal radial thickness.

Another object of this invention is to provide a novel arrangement for interconnecting a centralizer collar to a conventional stop collar of the type that may be secured to the well pipe wherein such interconnection permits limited axial movement of the centralizer collar relative to the stop collar and well pipe.

A further object of this invention is to provide a novel centralize: assembly with a stop collar interconnected to each centralizer collar in a manner for permitting sulficiently free movement of such centralizer end collars for allowing collapsing and expanding of the centralizer spring bows and yet engaging the leading centralizer end collar upon movement of the well pipe in either axial direction for consistently pulling the centralizer.

A still further object of this invention is: to provide a novel interconnecting means for extending between a stop collar and a centralizer collar to produce a strong and rugged interconnection with a very minimum radial thickness. 7

Other and more detailed objects and advantages of this invention will appear from the following description and the accompanying drawings.

in the drawings:

FIGURE 1 is an elevation view of the device of this invention installed on a well pipe with the centralizer spring bows in their uncollapsed condition.

FIGURE 2 is an elevation view similar to FlGURE l with the spring bows collapsed and the well pipe moving in a downward direction.

FEGURE 3 is an elevation similar to PEGURE 2 with the well pipe moving in an upward direction.

FIGURE 4 is a fragmentary perspective view of the lower centralizer end collar and the interconnected stop collar.

FIGURE 5 is a fragmentary sectional view taken substantiaily on the line 5-5 of FIGURE 4 aaoossa FIGURE 6 is a fragmentary elevation view taken from inside the centralizer end collar and viewing a portion of the interconnecting means.

FIGURE 7 is a perspective view similar to FlGURE 4 illustrating a modified form.

Referring in general to FIGURE 1, the illustrated close tolerance type centralizer, generally designated ill, includes upper and lower end collars it and 12, respectively, with a plurality of outwardly bowed spring bows 13 extending between and connecting the collars. Notches 14 are provided in the longitudinal edge of each collar l1, 12 for positioning the end portion llfi of a how 13 in such notch and securing the bow to the collar by Weld means 16. This is the preferred arrangement for strength, ease of assembly, and close tolerance although it will readily be appreciated that other variations could be employed such as merely butt welding the ends of the bows to the longitudinal edges of the collars. The collars ill and 12 are axially aligned and closely fit the well pipe 9. As thus far described, the centralizer Jill is somewhat conventional.

A pair of stop collars l7 and 13 are respectively connected to centralizer end collars 121. and 12 by interconnecting means, generally designated Ztl, and hereinafter described in further detail. As will appear hereinafter more fully, the interconnecting means permit a limited amount of relative axial movement between the collar 11 and stop collar 17 and between collar 12 and stop collar 18. In mounting the centralizer ill) on the well pipe 9, the stop collars 1'7 and 18 are positioned the maximum distance away from the interconnected centralizer collar 11 and 12, respectively, with the bows 13 in their uncollapsed condition and the stop collars are secured to the well pipe in the appropriate manner. The stop collars l7 and 15 may be of any conventional type but for accomplishing the purposes of this invention, it is extremely desirable that the stop collars be of a type having a minimum radial thickness. For example, the stop collars disclosed in US. Letters Patents Nos. 2,872,226 and 2,998,848, assigned to the assignee of this invention, have been found to be satisfactory and this is the type that has been here illustrated.

Referring now more particularly to FIGURES 4, 5 and 6, the centralizer end collar 15, stop collar 18 and interconnecting means Ztl are illustrated in greater detail. The centralizer end collar 14, stop collar 1'7 and interconnecting means Zll therebetween are identical except inverted from that shown in FIGURE 4. it is preferred that two interconnecting means 26 be provided and diametrically spaced from each other for more evenly distributing the loads between the centralizer end collar and the stop collar, and since such pair of interconnecting means are identical only one will be described in detail. The centralizcr end collar 12 is of substantial longitudinal length and is provided with a longitudinal slot 21 extending a relatively substantial portion of the longitudinal length of the collar. The slot 21 is open at Zita at the longitudinal end of collar 12 adjacent the stop collar 13. The slot 21 is also of relatively substantial width in a circumferential direction.

A bridge element 22 of an arcuate shape for conforming to the outer surface of collar 12 is mounted over the slot 21 and secured to the outer surface of collar 12 by any convenient means such as welding 23. Bridge element 22 is provided with a square or rectangular aperture 24 superimposed over the slot 231 and preferably narrower than slot 21 in a circumferential direction. A portion 25 of bridge element 22 remains between aperture 24 and the stop collar 18, and this portion is radially spaced from the well pipe a distance substantially equal to the thickness of the material of end collar 12. A guide key 26 is mounted on the inside of bridge element 22 and spans the aperture 24 in a longitudinal direction. A bifurcated strap 27 has two longitudinally extending strap portions 28 and 29 which are secured to the longitudinal edge of the stop collar 18 by weld means 36. Strap portions 28 and 29 are circumferentially spaced a distance slightly greater than the circumferential width of guide key 26 and are positioned on either side thereof. Each strap portion 28 and Z9 is therefore located and confined in a radial direction between the inner surface of bridge element 22 and the well pipe, and in a circumferential direction between the guide key 26 and one longitudinal edge of the slot 21. The end of strap 2'7, remote from stop collar 1%, is preferably comprised of an integral portion 31 joined to and extending between the strap portions 23 and Portion 31 is folded back over the outside of guide key 26 and strap portions 2d and 29, and is secured to strap portions 28 and 29 by any convenient means such as welding 32. it is to be noted that, due to this interlocking relationship, in actual manufacturing it is necessary for the strap 27 and portion 31 to be properly positioned within slot Eli and aperture 24 before the guide ltey 26 is secured to the bridge element 2-2.

By this arrangement it is to be seen that the intercom necting strap 27 is confined within the slot 21 of the collar 12 and that portion 31 of the strap is confined within aperture 24 of the bridge element 22. Appropriate small amounts of clearance in a circumferential direction are provided between the associated members to prevent restriction of longitudinal relative movement but such members serve to guide such longitudinal movement. Portion 31 of the strap provides a downwardly facing edge or abutment 33 for engaging the upwardly facing lowermost edge 34 of aperture 24. In this manner, the distance of axial separation of collar 12 away from shop collar is limited. The longitudinal length of aperture 24 is substantially greater that the longitudinal length of portion 31 of the strap 27 and, therefore, a certain limited amount of axial movement of portion within aperture 24 is possible.

Thickness of the materials employed for collar 12, bridge element 22, guide key 26 and strap 27, i.e., the radial thickness of such members in the completed assembly, may vary substantially for different sizes and requirements. Further, although FIGURE 5 illustrates each of these members as being comprised of material substantially equal in thickness, the thickness of each member may vary independly of other members without departing from this invention. However, it may readily be seen that the greatest thickness of any portion of the interconnecting means Ztl is equal to two thicknesses of material. Thus, by this arrangement the maximum radial thickness of the close tolerance centralizer i is increased by only one thickness of material and yet an interlocking connection between the end collar and a stop collar is formed which is extremely strong, de-

pendable and offers no protuberance for becoming hung up inside a well casing or well bore.

Referring now more particularly to FIGURES 1, 2 and 3, it may be seen that, as heretofore broadly described with respect to FIGURE 1, when installing the centralizer on the well pipe, the abutment 33 of each of the interconnecting means 263 is placed in engagement with the edge 34 of the aperture 24 nearest the attached stop collar. In this manner, the end collars 11 and 12 of the centralizer are in effect prevented from axial movement toward each other although it is to be realized that there is no tendency to cause such axial movement. When the spring bows 13 are radially collapsed such as by running the well pipe into a well bore or Well casing, represented by lines 8 in FIGURES 2 and 3, the distance between collars 11 and 12 increases. This increase in distance is accommodated by the heretofore described permissible longitudinal movement of portion 31 of the strap within the aperture 24. When the Well pipe 9 is moved in a downward direction, as shown in FIGURE 2, with bows l3 frictionally resisting such downward movement, the portion 31 of strap 27 connected to the lower stop collarlt; engages the bridge element 22 attached to the lower ccntralizer end collar 12 and therefore the centralizer it is pulled downwardly by the leading centralizer collar. Upon upward movement of well pipe 9, as illstrated in FIGURE 3, the portion 31 of strap 27 connected to the upper stop collar 17 will engage the associated bridge element attached to upper centralizer end collar Ill and therefore the centralizer will be pulled upwardly by the leading collar. In either of these situations, the portion 31 of the strap 27 connected to the stop collar which is trailing with respect to the direction of movement of the well pipe does not engage either end of the aperture 24 of the bridge element and therefore no longitudinal force is transmitted between the trailing stop collar and the trailing centralizer end collar. Thus, it may be seen that the aforementioned desirable condition of always pulling on the leading end collar of a centralizer is accomplished by the arrangement of this invention. While a condition has been illustrated in FIGURES 2 and 3, wh rein lines 8 are so closely spaced from well pipe 9 that spring bows 13 re collapsed nearly flat, it is to be noted that in actual practice, under extreme situations, the radial space between the outer surface of the well pipe and the surrounding casing is even smaller.

Referring now to FIGURE 7, a modified form of this invention is illustrated that is of somewhat simpler construction. In this arrangement the end collar 112 of the centralizer is again provided with a longitudinally extending slot 121 that is open at the longitudinal extrcmity Lila adjacent the associated stop collar 118. A bridge element 122 of arcuate shape extends across slot lZll adjacent extremity 121a and is secured to the outer surface of collar I112 by any convenient means such as welding 512 3. A strap 127 of preferably arcuate crossscction is secured to one longitudinal edge of stop collar lit? by weld means 139 and extends in a longitudinal direction into slot 121 between bridge element 122 and well pipe. An abutment element 131i is mounted on the outer surface of strap 12? at the end of the strap remote from the stop collar and serves substantially similar functions as the heretofore described portion 3?. of strap of interconnecting means Ztl. Abutment element 131 extends circumterentially beyond the edges of slot 121 and thereby limits the inward movement of strap 127 which otherwise would permit disassembly of stop collar from collar lllfi when the apparatus is not mounted on a well pipe. Abutment element 131 provides a shoulder or abutment 1% for engaging the upwardly facing edge 134 of bridge element 122. in this manner longitudinal movement of stop collar 113 in a direction away from end collar 112 will result in abutment element 131i engaging the bridge element 22 and pulling end collar 112 in that direction.

Th is it may be seen that an arrangement has been provided whereby stop collars of any conventional design may be mounted on a well. pipe longitudinally beyond each end of a centralizer and the interconnecting means of invention causes the leading stop collar to pull the leading end collar of the centralizer in the direction of movement upon movement of the Well pipe in either direction whereas it would normally be expected that by mounting stop collars beyond each end of the centralizer that the trailing stop collar would push on the trailing end collar of the ccntralizer upon movement of the well pipe in either direction. Further, the interconnecting means or" this invention are of extremely minimal radial thickness and yet produces a rugged interlocking connection which permits only limited longitudinal movement beween the stop collar and end collar. While a specific could be employed it such stop collars are of a maximum radial thickness commensurate with that which is tolere able. In fact, it has been found even with the relatively thin stop collar disclosed that it is beneficial under numerous conditions to appropriately machine the outer surface of the stop collar to reduce its outer diameter as much as possible without affecting the operation of the stop collar.

Having fully described our invention it is to be understood that we do not wish to be limited to the details herein set forth or to the details illustrated in the drawings, but our invention is of the full scope of the appended claims.

We claim:

1. In an assembly for mounting a device for limited movement on a well pipe, the combination of: the device having a circumferentially extending portion for slidably engaging the well pipe, a longitudinal slot in said portion of the device extending through one longitudinal end of said portion, a bridge element extending circumferentially across said slot at that said one longitudinal end and spaced radially outward from the well pipe, means for securing to the well pipe adjacent that said one longitudinal end and having an interconnecting strap means extending longitudinally along the well pipe and into said slot radially inside of said bridge element, and means on said strap means beyond said bridge element for engaging said bridge element and limiting the axial movement of said portion of the device in a direction away from said means for securing to the well pipe.

2. In an assembly for mounting a device for limited movement on a well pipe, the combination of: the device having a circumferentially extending portion for slidably engaging the well pipe, a longitudinal slot in said portion of the device extending through one longitudinal end of said portion, a bridge element extending circumferentially across said slot at that said one longitudinal end and spaced radially outward from the well pipe, means for securing to the well pipe adjacent that said one longitudinal end and having an interconnecting strap means, said strap means having a pair of circumferentially spaced and parallel portions extending longitudinally along the well pipe and into said slot radially inside of said bridge element, a guide key extending longitudinally and positioned between said parallel portions of said strap means for guiding longitudinal movement of said strap means, said guide key mounted in said slot and on said circumferentially extending portion of the device, and an abutment on said strap means extending between and connecting said parallel portions beyond said bridge element and radially outside of said guide key for engaging saidbridge element and limitim axial movement of said portion of the device in a direction away from said means for securing to the well pipe.

in an assembly for mounting a device for limited movement on a Well pipe, the combination of: the device having an annular collar for slidably engaging the well pipe, a longitudinal slot in said collar extending through one longitudinal end of said collar, a bridge element extending circumferentially across said slot at that said one longitudinal end and spaced radially outward from the Well pipe, a second collar having means for securing saic second collar to the well pipe, an interconnecting strap means provi ed on one longitudinal edge of said second collar and extending longitudinally along the well pipe into said slot radially inside of said bridge element, and means on said strap means beyond said bridge el ment for engaging said bridge element and limiting the axial movement of the first said collar in a direction away from said second collar.

4 In an assembly for mounting a device for limited movement on a well pipe, the combination of: the device having an annular collar for slidably engaging the well pipe, a longitudinal slot in said collar extending through one longitudinal end of said collar, a bridge element extending circumferentially across said slot and having a anodes i central rectangular aperture therein communicating with said slot, a portion of said bridge element positioned at that said one longitudinal end, and spaced radially outward from the well pipe, a second collar having means for securing said second collar to the well pipe, an interconnecting strap means provided on one longitudinal edge of said second collar, said strap means having a pair of circumferentially spaced and parallel portions extending longitudinally along the well pipe and into said slot radially inside of said bridge element, a guide key extending longitudinally and positioned between said parallel portions of said strap means for guiding longitudinal movement of said strap means, said guide key mounted on the inside of said bridge element, and an abutment means on said strap means extending between and connecting said parallel portions, said abutment means positioned radially outside of said guide key and within said central aperture for interlocking the strap means and the first said collar and for engaging said portion of the bridge element at said one longitudinal end to limit the relative longitudinal movement of said first and second collars.

5. In an assembly for mounting a device for limited movement on a well pipe, the combination of: the device having an annular collar for slidably engaging the well pipe, 21 pair of longitudinal slots in said collar diametr-ically located from each other and each extending through one longitudinal end of said collar, a bridge element extending circumferentially across each said slot at that said one longitudinal end of the collar each said bridge element spaced radially outward from the well pipe, a second collar having means for securing said collar to the well pipe, a pair of interconnecting strap means provided on one longitudinal edge of said second collar at diametric locations, each said strap means extending longitudinally along the well pipe and into a said slot radially inside of the said bridge element associated with that said slot, and means on each said strap means beyond said bridge element for engaging said bridge element and limitin g the axial movement of the first said collar in a direction away from said second collar.

6. In a close tolerance centralizer assembly for mounting on a well pipe for limited movement thereon, the combination of: a first pair of axially spaced and aligned collars for slidably engaging the well pipe, a plurality of circumferentially spaced bows extending longitudinally between and connected to said collars for centering the well pipe, a longitudinal slot in each said collar extending through the longitudinal end of each collar remote from the other collar, a bridge element means extending circumferentially across each said slot at that said longitudinal end of each said collar, a pair of stop collars each having means for securing same to the well pipe, each said stop collar axially aligned with and positioned adjacent one of the collars of said first pair and on the same longitudinal side as the longitudinal slot in that one collar, an interconnecting strap means provided on the longitudinal edge of each said stop collar, each said strap means extending longitudinally along the well pipe and into a said longitudinal slot radially between the well pipe and said bridge element means associated with that said slot, and means on each said strap means on the longitudinal side of said bridge element means remote from the attached stop collar for engaging said bridge element means and limiting the axial movement of the associated collar of the first pair of collars in a direction away from the adjacent stop collar.

7. In a close tolerance centralizer assembly for mounting on a well pipe for limited movement thereon, the combination of: a first pair of axially spaced and aligned collars for slidably engaging the well pipe, a plurality of circumferentially spaced bows extending longitudinally between and connected to said collars for centering the well pipe, a pair of longitudinal slots in each said collar diametrically located from each other and extending through the longitudinal end of each collar remote from the other collar, a bridge element means extending circumferentially across each said slot at that said longitudinal end of each said collar, a pair of stop collars each having means for securing same to the well pipe, each said stop collar axially aligned with and positionedadjacent one of the collars of said first pair and on the same longitudinal side as the longitudinal slot in that one collar, a pair of interconnecting strap means provided on the longitudinal edge of each said stop collar, each said strap means extending longitudinally along the well pipe and into a said longitudinal slot radially between the well pipe and said bridge element means associated with that said slot, and means on each said strap means on the longitudinal side of said bridge element means remote from the attached stop collar and at the same radial distance from the well pipe as the bridge element means for engaging said bridge element means and limiting the axial movement of the associated collar of the first pair of collars in a direction away from the adjacent stop collar.

8. In a close tolerance centralizer assembly for mounting on a well pipe for limited movement thereon, the combination of: a first pair of axially spaced and aligned collars'for slidably engaging the well pipe, a plurality of circumferentially spaced bows extending longitudinally between and connected to said collars for centering the well pipe, a pair of longitudinal slots in each said collar diametrically located from each other and extending through the longitudinal end of each collar remote from the other collar, a bridge element means extending circumferentially across each said slot at that said longitudinal end of each said collar, a pair of stop collars each having means for securing same to the Well pipe, each said stop collar axially aligned with and positioned adjacent one of the collars of said first pair and on the same longitudinal side as the longitudinal slot in that one col lar, a pair of interconnecting strap means provided on the longitudinal edge of each said stop collar, each said strap means extending longitudinally along the well pipe and into a said longitudinal slot radially between the well pipe and said bridge element means associated with that said slot, and abutment means on each said strap means on the longitudinal side of said bridge element means remote from the attached stop collar for engaging said bridge element means and limiting the axial movement of the associated collar of the first pair of collars in a direction away from the adjacent stop collar, said stop collars mounted on the well pipe at an axial spacing in a predetermined amount greater than the overall longitudinal dimension of the first pair of collars tor axial movement of said first pair of collars upon radial collapsing or" said bows and for the said abutment means associated with the stop collar leading in the direction of movement of the well pipe to engage the associated collar of said first pair for pulling the said bows and first pair of collars in that direction.

9. In a close tolerance centralizer assembly for mounting on a well pipe for limited movement thereon, the combination of: a first pair of axially spaced and aligned collars for slidably engaging the well pipe, a plurality of circumferentially spaced bows extending longitudinally between and connected to said collars for centering the well pipe, a pair of longitudinal slots in each said collar diametrically located from each other and extending through the longitudinal end of each collar remote from the other collar, a bridge element means extending circumferentially across each said slot at that said longitudinal end of each said'collar, a pair of stop collars each having means for securing same to the well pipe, each said stop collar axially aligned with and positioned adja cent one of the collars of said first pair and on the same longitudinal side as the longitudinal slot in that one collar, a pair of interconnecting strap means provided on tne longitudinal edge of each said stop collar and having a pair of circumferentially spaced and longitudinally parallel portions, said parallel portions of each said strap means extending longitudinally along the well pipe and into a said longitudinal slot radially between the well pipe and said bridge element means associated with that said slot, a guide key extending longitudinally and positioned between said parallel portions of said strap means for guiding longitudinal movement or" said strap means, said guide key mounted in said slot and to said collar of said first pair, and abutment means on each said strap means extending between and connecting said parallel portions and positioned on the longitudinal side of said bridge element means remote from the attached stop collar, said abutment means positioned radially outside of said guide key for engaging said bridge element means and limiting the axial movement of the associated collar of the first pair of collars in a direction away from the adjacent stop collar.

References Cited by the Examiner UNITED STATES PATENTS Hartman et al. 166-241 Hall 166-172 Crawford 166241 Clark 166-241 Atkinson 166-241 De Iarnett 166-173 Park 166-241 Welles.

6/54 Atkinson.

CHARLES E. OCONNELL, Primary Examiner.

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Classifications
U.S. Classification166/241.6, 285/302
International ClassificationE21B17/10, E21B17/00
Cooperative ClassificationE21B17/1028
European ClassificationE21B17/10C2B