US2886111A - Centralizer - Google Patents

Description

' Filed Aug. 22. 1956 May 12,. 1959 5. D. HALL 2,886,111

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2,886,111 CENTRALIZER Elmer 1). Hall, Weatherford, Tex. Application August 22, 1956, Serial No, 605,599 Claims. Cl. 166-241 This invention relates to improvements in centralizerconstruction and refers more particularly to the design and construction of centering devices mounted on the exterior of casing or pipe used to produce fluid from wells, the inventive centralizer having extremely great radial compressional rigidity while yet retaining some flexibility under radial compression.

In the drilling of oil wells and other wells, and in the conditioning of the well bore for cementing, fluids, such as slurries of mud and water, mud and oil and cement and water are circulated in the annular'passageway between the well bore and the exterior of the casing or pipe. Well. tools in some instances are mo'unted on the exterior of the casing to center the casing in the well bore and to remove mud cake from the bore when the Well is being conditioned for cementing. The mounting of tools on the exterior of the casing inevitablyjfonns an obstruction to the passage of fluids in the annular space surrounding the casing. centralizers. usually are constructed with upper and lower collars or sleeves ,to which are attached bands or strips of metalextending between the collars and outbowed at their midsections to frictionallycontact the well bore. By spacing the centralizer'satintervals along the pipeor casing, the latter is held in a .centeredposition in the well bore, forming an annulus or passageway, of relatively uniform radial depth around the. casing forthe flow of fluid.

2,886,111 Patented May 1 2, 1959 1 2 a diameter than the greatestouter diameter of the centralizers. The lackof this is universal characteristic possessed by the more flexible centralizerslies in the fact that the bands, as formed, are too stiff and require the pipe carrying the centralizers to be snubbed into the bore hole until the weight of the pipe above them is greater than the'resistance created by their passage through the well. Additionally, such a rigid, arched band will not easily go through restrictions in the hole.

In some operations, a solid bar centralizer, comprising a plurality of solid metal barswelded right onto the wellpipe, along theentire length of the bars, is employed. The elements of this type of centralizer will not compress under radial application of force at all and thus will meet any requirement of radial compressional resistance. However, some radial compressional resiliency of thecentralizerelements is desired. Additionally, it is desirable that a centralizer be able to rotate on the pipe, and, as well, have better vertical thrust characteristics, features not shared by the solid metal bar type centralizers. i t r Typical straight band and spiral band centralizers deficient in some radial compression situations include the structures of Patents Nos. 2,515,149 (Willhoit, 1950), 2,555,628 (Baker, .1951), 2,228,648 (Welles, 1941), 2,727,57 (Hall, 1955 and 2,628,682 (Wright, 1953).

Wire centralizers alike deficient in resistance to radial compression include I. E. Hall, S12, Patents Nos.

2,731,816 (1956) and 2,717,650 (1955).

As the size .ofthe annulus or passageway is defined by the distancebetween the exterior ofthe casing and the well bore, any obstruction on. the outside of thepipe, such as the centralizers, will ,form an obstruction .to the nee flow of fluid; and since the blades or outbowedbands of eachcentralizer extend from the upper collar to the 1 well wall and thence back to the lower collar, each band forms. a double obstruction .in the fluid passageway.

Therefore, any reduction that can be made in thelwidth of the bands in their upperand lower sections will reduce to that extent the obstruction; offered to the passage of fluidsthrough the .annulus surrounding the casing.

, Previously there have been provided a numberof types and forms of centralizers which are generally adequate for actually centering the pipe in the well bore against the stresses encountered therein, but, which, under certain, circumstances, fail to ad-equately, resist the extreme radial compressional stresses encounteredby the pipe in the well bore. Thus, the ileafsspring centralizer, the concave leafspring centralizer and the wire centralizer,

to name someof the most well known conventional types are. generally adequate and operable but do not possess to application of radial compres- Previously, a number of companies have provided band type centralizers wherein-the bands extend essentially flatly between the collars adjacent theirrends and, then, toward theircenters, the bands arch sharply outwardly in aghalf-circle shape in side view. Suchbands have great radial compressional resistance but cannot be universalf in the sense that. they will fit a plurality of different diameter bore holes, including those of lesser will form less obstruction to fluid flow around the casing While materially enhancing their strengthand rigidity.

Another object ofthe inventionis to provide a band type centralizer which has extremelygreat compressional strength and rigidity while still retaining a certain amount of compressional flexibility, the centralizer being rotatable on the pipe and un iversal" in the sense that it can be used in boreholes of Varying diameters. from less than the greatest outer dimeter of the centralizer to markedly greaterthan said greatest outer diameter.

Another object ofthe invention is to provide a band type centralizer which is extremely simple in construction, easy to manufacture, easy to install on the casing and extremely rugged r and resistant to compressional stress..

Another object of the invention is to providea band type centralizer wherein the resistance to radial compressional stress. maylbe represented either by (1) only the resistance against return to the flat state of the band itself which has-been twisted or formed in a portion thereof at an angle to the mounting collars surfaces receiving the endsfiof the bands, -or (2) wherein the resistanceto radial compressional stress may represent both a resistance setnp by. a simple bowingof the band plus tension and compression forces'set up in the band itself by the manner of mounting itin the collars when radial compressional stress is applied thereto, or, finally,(3) merely tension and compression forces set up in the band itself by the-mannerof mounting of. it in thecollars upon application of radiai compressional, stress thereto, the

latter type of band having, the greatest resistance to radial compressional stress of thethree types set forth.

Other and further objects ot theinventio n willuappear in the course of the following description thereof.

In. the. drawings, which. form a part of the instant specification and are to be read in conjunction therewith,

embodiments of the invention are shown and, in the various views, like numerals. are employed to indicate ken r 4 q r Fig 1 is, a side view-of a first modification ofthe inventive centralizerpthe modification characterized'hy; rectangular bandsattached-to the centralizer collars and twisted centrally, the bands also arched sufliciently adjaeent their points of attachment to'the collars; s o=the smallest internal diameter of the bands is not less than the. internal diameter of the collars to which the bands are attached, the centralizer being shown positioned on a c i g, V Fig. 2.is-a plan.view with parts broken awayand in section of the construction of Fig. l. Fig. 3 is a. view of asecond modification of the inventive centralizer, this modification similar to that illustrated in Fig. 1, having bands of rectangular shape twisted centrally, butthe" bands not arched relative the collars, whereby the inwardly twisted edges of the bands before mounting ofthe centralizer on the pipe have a least internaldiameter which is less than the internal di-v ameter of'the collars to'which the bandsare attached,

Fig. 4 is a plan view with parts broken away and in section of the construction of Fig; 3.

Fig. 5 is a side view of a; third modification of the inventive centralizer, trapezoidal bands being fixed to collars ateach end thereof, the long longitudinal edge of the trapezoidbeingbent outwardly'whereby; the end edges of the bands are substantially parallel, the short longitudinal.edge-remaining in anessentially straight line.

Fig. 6 is a plan View with parts broken away and in section of the construction of Fig. 5.

Fig. 7 is aside view'of one of the trapezoidal bands employed in the Fig, 5 modification before'distortion of the long longitudinal edge thereof to form a band into the shape shown in Figs. 5 and 6. V

Fig. 8 is a view of a fourth modification of the inventive centralizer, trapezoidal bands also being employed in this modification, with additionally, the shorter edge of the trapezoid beingbent, the long edge bent outwardly and-the short edge bentinwardly, the latter to a lesser degree, the portions of the bandsjadjacent the collar attachment areashaving been. arched isufiiciently whereby theleast internal'diameter of the bands is-notless than theinternal diameter of the collars. 1

Fig.7 9 is a plan view with parts broken away-and in section of theconstruction of Fig. 8,

The invention comprises a centralizer adapted to. be mounted on casingused in wells for the production of fluids, comprising upper and IOWGI'ZCO-HEIS with internal diameters enough larger than the casingto fit slidably thereon, narrow bands extending between thecollarswith their upper ends attachedto the upper collar and their lower ends attached to the lower collar, each of said bands twistedinat leasta. portion thereof centrally. of theends thereof whereby atleast one 'edgethereot' is positioned radiallyoutwardly past the surfaceof the collarsto' which theends of the bands are attached:

'There are three basic modifications of the invention. The--first=- modification (Figs. 1-4)- employs: centrally twisted rectangular bands which resist deflection 'ofthe "bent portions thereof only bythe radial compressional force'required-to straighten out the curved bentportion "of the band. The second modification ofthe invention (Figs; 5-7) employs a'trapezoidal band bent only. in the long-longitudinal-edge thereof, the radial-compressional force required to reduce'the-bend therein being that re- 'quired to compress the long-longitudinal edge and lengthen the *short longitudinal edge, the force thus actually tending todistort the structure-of- 'the band itself and necessarily being much 'greater than-the previous modification. The'third modification of the invention comprises a trapezoidal band which is bentbotlr in the long longitudinal edge and the short longitudinal edge,

part of an applied compressive force acting to merely straighten the bend in the band and part then acting on the structure of the band as described in the previous modification.

Referring to Fig. l, at 10 is shown a casing such as an oil well casing on whichxtheinventive centralizer is mounted. Collars 11 and 12 form the upper and lower ends of the centralizer and are-of an internal diameter slighlty greater thanthe outerdiameter. of the casing 10, whereby to slidably fit thereon. A'plurality of relatively narrow rectangular bands 13=are fixedtoitheiupper and lower collars at their upper and lower ends, preferably by welding as at 14 in slots 15" formed in the centralizers. Before mounting in the collars, the rectangular bands are bent or formed centrally with one longitudinal edge16 thereofbent outwardly and the other longitudinal edge 17 thereof bent inwardly, the'longitudinalicdges'of iapart. radial'compression of one band will tend to flattensaid band out in a very low arch. Equal radial'compression the band preferably each'being bent inwardly. and'outwardly the same. amount. To ensure that the internal diameter. of. opposed. bands -13 at every portionthereof Willbe' not'le'ss' than ,the internal-diameter of the collars 11 and 12, the bands arearched'slightly as shownat'18 at .each end-whereby. the, inward'bending. of the inner longitudinal" edgef17" does ,not carry, it'pastthe outer diameter of'th'e collars. As .seen in Fig, 2, the. greatest outer diameter of'the bands is greater than the outer diameter ofthecollars whereby to center the casingwith-v in the well bore. A radial compressional force acting on a particular bandtends to straighten theband outiby pushingthe outer longitudinal. edge inwardly and'thus moving the inward longitudinal edge, if it abuts the casing,flaterally. Ifneither or justjone collar is fixed'to the vcasing, the particular band which is being compressed may flatten against the casing, thus tending to push the collars 11 and 12 further apart. The adjacent bands oneither side of. the compressed band, however, tend to resist such movement" of the collars away from one an.- other and thus. the radial compressional force mustalso affect theother bands to move the collars any distance If'both the collars are fixed to the casing, the

of all the bands simultaneously would'merely flatten them all on the. casing if only one or none'of the collars is fixed to the .casing,' .thus moving the collars apart. 'Depending upon the clearance between the casing 10 and the well bore,. the width of.the bands 13: determines the angles at which they may' be bent; The greaterthe angle of bending'of the bands, the greater radial'compressional force is required tounbend the bands. Preferably the, angles of bending are less than'90'. Thethickness of-the' bands as well as the material thereof determines the resistance'to radial compression. Fora given width of band, the greater the central bend of the band, the greater thearch 18"required at'the areas of attachment' to the collars to maintain the proper internal, diameter'of the bands attheir central portions. The number of bands may be varied as desired and, of course, depends upon the width of'the bands, the diameter of the collars, thespacing of 'the bands, etc. It'is: also evident that the central twist of the bands reduces'the.annuhrobstruction between the casing and the well bore.

The second modification of the invention shown in-Figs. 3 and 4 comprises collars 19 and 20 having slots '21 formed on the inner edges thereof. Bands 22'are welded as at23 to the collars and slots zl thereof. The :bands 22 are rectangular in shape, as in the previous modification, the difference in; the two modifications being that" the bands22 in the second modification are not archedadjacent their points ofiattachment to the collars whereby thebending-of the' centralportions o'f'thje bands" forces the inner longitudinal edges24 thereof-past" the line-of the inner diameter of" the collars 19 and 20. Thus, when the centralizer-of Figs. and4 is pos'itioned onthe it must beforced thereon, the bands unbending or unposed twisted bands permits, the same width band as the first modification to be angled at a greater angle before mounting on the casing to. have the same outer diameter on the bands themselves. When the centralizer, however, is positioned on the casing, the bands will changeangle slightly asthe inner longitudinal edge is forced outwardly again. t

It should be noted-that all of the bands in all of the modifications in this application may be formed by either actual bending of bands of the original shapes described or casting of bands to the final form described. Preferably, the collars and bands are of metal and preferably steel of a predetermined desired resiliency and strength.

The second modification as shown in Figs. 3 and 4, when forced onto the casing responds to radial compressional stress on one or more of the bands in the same manner as the Figs. 1 and 2 modification, compression of the totality of bands tending to separate the collars, compression of one band tending to separate thecollars against the resistance of the adjacent bands, compression of one or more bands when the two collars are fixed to the casing tending to form the compressed band or bands into a very low-arch, etc.

Figs. 5-7 show a third modification of the invention. In this modification, collars 25 and 26 have slots 27 therein. Bands 28 have their endportions Welded as at 29 to the slots in the collars. The bands 28 are formed, if produced by a bending process, from a flat trapezoidal shaped piece of metal30 as shown in Fig. 7. Preferably,

the long longitudinal edge 31 is bent evenly upward cenj trally while the short longitudinal edge 32 is maintained as a straight line. In this manner, the least internal diameter of opposed bands is never less than thatof the collars 25 and 26. The long longitudinal edges 33 of the centrallizer bands howeyer, are bent outwardlyyto a position so that the end edges 34 and 35 are substantially parallel one with the other as set into the slots 27 in the collars. When this centralizer is on the casing or pipe, radial compressional stress applied to the outer longitu- 'dinal edge of one of the bands will tend to compress the long longitudinal edge 33 to a shorter length and lengthen the short longitudinal edge 36 to a greater length. Thus the strain is within the band itself and also tends to twist the ends of the band in its attachment in the collars. This modification of the invention has extremely great resistance to radial compression-a1 force and, when sufficient compressional force is applied to the band 28 itself to depress the outer longitudinal edge 33,

' the band 28 itself ridges and dimples laterally at right angles to the long axis of the band. This modification of the invention may ride free on the casing, having one end attached thereto or both ends attached. The adjacent bands to a given compressed band tend to resist any twisting of the collars 25 and 26 themselves.

The fourth modification of the invention, as shown in Figs. 89, is, in a sense, a combination of the first three modifications. Upper and lower collars 37 and 38 have slots 39 therein. Bands 40 are welded as at 41 in the slots 39. The form of the bands 40 is trapezoidal as in Fig. 7, with one longitudinal edge 42 of the band shorter than the other longitudinal edge 43. However, in the Figs. 8 and 9 modification, the long longitudinal edge 42 is first bent or formed upwardly as in the Fig. 5 modification so that the end edges 44 and 45 of the bands are substantially parallel and then the entire band is bent centrally as in the Figs. 1 and 3 modifications. Additionally, preferably, the portions 46 and 47 of the bands adjacent the collar attachments are arched whereby opposite inner longitudinal edges 43 of the bands 40 have a least internal diameter not less than the internal diameter of the collars 37 and 38. Another modification wherein the least internal diameter of opposed bands 40 is less than that of the collars 37 and 38 without any arching of the end portions 46 and 47 of the bands 40 (analogous to the Pigs. Zand 3 modifications) is contemplated also. It is evident that, when the modification of Figs. 8 and 9 is applied to the casing, radial compressional stress applied to the outerlongitudinal edge 42 of one or more. of the bands 40 will first tend to straightenthe bands, as in the Figs. 1 and 3 modifications, until the inner longitudinal edge, the shorter longitudinal edge 43, is straight. At this point, further compression ofone or more bands will tend to compress and shorten the long longitudinal edge 42 and lengthen the short longitudinal edge 43 with the same effect as in the Fig. 5 modification. Thus the lesser resistance motion will occur first and the greater resistance motion follow it. Inthis way, a two stage centralizer, as far as resistancegoes, is achieved. If the internal diam eter of the center of the bands is equal to or; greater than the internal diameter of the collars, the centralizer may be readily slipped on the casing. If not, the centralizer must be forced on the casing. As in the other modifications, either one, none, or both of the collars may be fixed to the casing, the modification wherein both ends of the collar are fixed to the casing providing the greatest resistance from the beginning against both stages of compressional stress. i

From the foregoingit will be seen that this invention is one well adapted to attain all of the ends and objects hereinabove set forth, together with other advan tages which are obvious and which are inherent to the structure.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations.

This is contemplated by and is within the: scope of the claims.

As many possible embodiments may be made of the invention without departing from the scope thereof, it

attached at least substantially flatly to the lower collar whereby to permit use of flat collars of minimum thickness, each said band so formed that one longitudinal edge thereof extends in at least a portion thereof outwardly past the outer surfaces of the collars when the centralizer is mounted on the casing a distance equal to a substantial portion of the width of the band, the other longitudinal edge of each band extending between the collars at a radial level at least substantially that of the outside surfaces of the collars whereby to provide a centralizer with at least a portion thereof of markedly greater outer diameter than the outer diameters of the collars, the bands of relatively rigid construction whereby to strongly resist flattening of the outwardly formed edges of the bands.

2. A centralizer. as in claim 1 wherein the ends of the bands closely adjacent the collars are angled outwardly relative the surfaces of the collars whereby the internal diameter of opposed bands of the centralizer adjacent the center of the bands is not substantially less than the internal diameter of the collars.

3. A centralizer as in claim 2 wherein at least a portion of each of said bands extends substantially at right angles to the surface of the collars to which the ends of said bands are attached.

4. A centralizer adapted to be mounted on casing used in wells .t'or production of fluid comprising upper and lower collars whoseqinternal'diameters are enough larger thanuthe casing .to' fit slidably thereon, narrow, substantiallydrapezoidal bands extending between :the collars with-theirupperends attached at least substantially flatly to-the upper collar and lower'ends attached at least substantially flatly to-"the lower collar, whereby to permit use ofcollars ofminimum thickness each ofsaid bands so formed that the longlongitudinal edge thereof extends inqatgleast 'a portion thereof outwardly past the-outer'surfaces of the collarswhen the centralizer is mounted on the'casing: a distance equal-to asubstantial portion of .the 'w'idth of the band, the other longitudinal edge of :each "band extending between the'collars at a radial level at least substantially that of the outside surfaces of the collars whereby to provide-a centralizer with at least a portion thereof of markedly greater outer diameter than the outer diameter. of. thecollars, the bands of relativelygrigid construction whereby-to strongly resist flatteningJof the outwardly. formed edges of the bands.

5. A centralizer as in claim 4 wherein a portion of :the long longitudinal edge of each band is positioned substantially at right angles to the surfaces of the collars to which the ends of the band are attached.

6. A centralizer as in claim 4 wherein the longer longitudinal edges of the trapezoidal bands are formed outwardly relativethe collar surfaces to a position whereby the ends of the long and short longitudinal edges of the 'bandaasreceived in the collars aresubstantially equal distances apart.

7. A centralizer as in claim 4 wherein the short longitudinal edges of thebandslie essentially in straight lines between the collars and essentially parallel to the surfaces thereof.

8. A centralizer as in claim 4 wherein the long longitudinal edges of the trapezoidal bands are formed outwardly relative the surfaces ofthe collarsto position peripheral to the surfaces of said collars and the short longitudinal edges of the trapezoidal bands are formed than the internal diameter of the collars.-

-9. "A centralizer asin claim 4 wherein'the long longitudinal edges ofth'e trapezoidal bands are twisted outwardly relative the collar surfaces and the shorter longitudinal edges of the trapezoidal bands are twisted inwardly relative the collar surfaces, the ends of the bands adjacent the collars essentially in line with the surfaces of the collars whereby the internal diameters of opposed 'bands'of ithe centralizer adjacent the centers thereof are less than the internal diameter of the collars.

10. A centralizer adapted to be mounted on casing used vin wells for the production of fluids comprising upper and lower collars with internal diameters enough larger that the casing can fit slidably thereon, narrow bands extending between the collars with their upper ends attached at least substantially to the upper collar and I their lower ends attached at least substantially flatly to the lower collar, each of said bands so formed that one edge thereof extends in at least aportion thereof outwardly past the outer surfaces of the collars when the centralizer is mounted on the casing a distance equal to a substantial portion of the width of the band, the other longitudinal edge of each band extending between the collars at a radial. level substantially that of the outside surface of the collars whereby. to provide a centralizer with at least a portion thereof of markedly greater outer diameter than the outer diameter of the collars, the bands of relatively rigid construction whereby to strongly resist flattening of the outwardly formed edges of'the bands.

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