US 3343608 A
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Description (OCR text may contain errors)
Sept. 26, 1967 J. R. soLuM 3,343,608.A
Two-STAGE'CENTRALIZER Filed Aug. 10, 1966 wz l M United States Patent O 3,343,608 TWO-STAGE CENTRALIZER James R. Solum, Los Angeles, Calif., assignor to B & W
Incorporated, Torrance, Calif., a corporation of California Filed Aug. 10, 1966, Ser. No. 571,604 Claims. (Cl. 166-241) This invention relates to a device for centering a well pipe in a Well bore commonly known as a centralizer and, in particular, is directed to a centralizer which produces a substantially higher centering force after an initial amount of resilient deiiection thereby forming two distinct through continuons stages of centering capability.
It is relatively common to use centralizer devices for various purposes in the completion of oil wells. One of the primary uses for centralizers is in the cementing of well pipe in the well bore since it is highly desirable that no portion of the well pipe be in contact with the well bore which would result in a space devoid of cement. The use of centralizers for this purpose is particularly important in well bores which are sharply curved or inclined at an angle to the vertical. It is well recognized that as the curvature or angle of inclination of the well bore increases the spacing between centralizers must be decreased or a dilferent type of centralizer producing higher centering forces must be used. In some situations both the spacing and the centralizer must be appropriately changed. The most common type of centralizer employs spring steel bows which resiliently engage the well bore wall but it is well known that such centralizers will be deected completely at with no resultant centering in well bores which are extremely curved or inclined a substantial degree from vertical. As a result, devices known as rigid centralizers which employ inflexible ribs that are not subject to such deiiection are often used in these eXtreme well bore conditions. However these rigid centralizers are also objectionable in many respects such as being completely inflexible and more likely to adversely affect the well bore wall.
Accordingly it is a principal object of this invention to provide a novel form of well pipe centralizer employing outwardly bowed and resilient staves for engaging the well bore wall in the usual manner and having curved straps of a lesser height mounted on the interior of said stavesl which are urged against the well pipe by the initial resilient deiiection of the bore-engaging staves and in such pipe-engaging condition the straps resiliently prevent further substantial deiiection of the bore-engaging staves thereby providing a second, higher stage of deection resisting forces.
It is an object of this invention to provide a two-stage centralizer having a plurality of bows extending between collars and abutment strap means on the interior of staves to limit resiliently the magnitude of deflection of the bows.
Another object of the invention is to provide a novel form of centralizer employing a plurality of spring bows functioning both as resilient centering elements and substantially rigid centering elements in the partially deflected condition.
Other and more detailed objects and advantages of this invention will appear from the following description of the accompanying drawings, wherein:
FIGURE l is a perspective View of the centralizer of this invention.
FIGURE 2 is a sectional plan view of the centralizer of this invention taken substantially at the midpoint of the bows.
FIGURE 3 is a fragmentary sectional elevation take through a spring bow substantially on the line 3 3 in FIGURE 2 and with the bow in the substantially undeected condition.
3,343,6@3 Patented Sept. 26, 1967 FIGURE 4 is a fragmentary sectional elevation similar to FIGURE 3 but with the bow deected to the condition for imposing the second stage high forces in resisting further deflection.
Referring now in greater detail to the drawings, the two-stage centralizer of this invention is generally designated 10. The centralizer 10 is comprised of a pair of collars 11 and 12 and a plurality of bows or staves 13 extending longitudinally between the collars. The collars 11 and 12 may be of any conventional type or style and are provided with an inside diameter for tting the well pipe on which the centralizer is to be mounted. Although it is not important to this invention, the collars 11 and 12 may be comprised of two half collars hinged together as at 15 for convenience in mounting the centralizer on the well pipe by permitting the centralizer to be hinged open and applied laterally to the pipe. As is conventional the collars 11 and 12 are axially aligned.
Any number of bowed staves 13 may be employed in the centralizer 10 commensurate with accomplishing the desired centering forces and according to the size of the device. An arrangement of eight bows is shown in the drawings. The bows or staves 13 are of a preselected prole, as shown in FIGURE 3, and material width and thickness adapted to produce the desired resilient centering forces when used in a particular well bore. That is to say, the length of the stave and the magnitude to which it is bowed outwardly is selected in the usual manner to provide the overall dia-meter at the midpoints of the bows and the resilient centering forces which are desired in the particular situation. Normally the diameter formed at the mid-points of the bows 13 will be slightly larger than the nominal well bore diameter thereby assuring that the well pipe will be resiliently held in the center of the well bore, at least in vertical portions of the Well bore. The plural staves 13 are circumferentially spaced abut the collars 11 and 12 and are secured thereto by any convenient means such as welding 16. As thus far described, the centralizer 10 is substantially conventional.
Means are provided for limiting the amount of free resilient deflection of each of the bows 13 and, as shown in the drawings, these means may be comprises of a curved strap 14 mounted on the inside of each bow 13. Each of the straps 14 is of a length substantially less than the length of the bows 13 and is comprised of at end portions 17 and a bowed or curved portion 18. The straps 14 are located at the rnidportions of bows 13. The end portions 17 make surface contact with the interior side of the bow 13 on either longitudinal side of the most outwardly bowed portion of the bowed staves 13 and are secured to the bowed staves 13 by any convenient means such as welding 19. The straps 14 are curved or bowed inwardly a distance substantially less than the amount of outward bow of the staves 13 as shown in FIGURES 2 and 3. The straps 14 are preferably of a spring steel for limited resilient deection and are of suticient width and thickness to withstand the forces encountered.
Referring more particularly to FIGURES 3 and 4, the centralizer 10 is normally mounted on a well pipe 9 in any conventional manner such as with a conventional stop collar 8 or other stop means positioned between the collars 11 and 12 and secured to the well pipe 9. The stop collar 8 serves to locate the centralizer 10 on the well pipe and functions to pull the centralizer into the well bore 7 by engagement with the lower collar 12 as the well pipe is lowered into the well bore as shown. In the substantially undeflected condition of -bowed staves 13 shown in FIGURE 3 the straps 14 are curved inwardly a distance short of engaging the well pipe 9. As the lateral forces tending to urge the well pipe 9 toward the wall of the bore 7 are increased, such as in an inclined well bore, the bowed staves 13 on that side of the centralizer will be deflected producing a resilient resistive centering force. The deflection of bowed staves 13 causes some straightening of straps 14 due to the straightening of the bowed portion of staves 13 between the secured ends 17 of straps 14. The force required to tend to straighten the bowed straps 14 of course slightly increases the forces that would otherwise be required to deect the staves 13. Continued deection of staves 13 ultimately results in the curved portion 18 of the straps 14 engaging the exterior of the well pipe 9 as shown in FIGURIE 4 whereupon any further attempted inward deflection of staves 13 subjects the straps 14 to compressive bending stresses. Since the ends of straps 14 are xed to the bows 13, any further substantial deilection would require elongation of that portion of bows 13 or complete collapse of curved straps 14. The end result is that the staves 13 are restrained from further inward deection by the straps 14 thereby assuring that the well pipe 9 will be spaced from the wall of the well bore 7 by the amount shown in FIGURE 4 regardless of the magnitude of the lateral forces.
Thus it may be seen that by this invention there is provided a well pipe centralizer which produces two stages of centering forces with the rst stage comparable to the resilient centering forces of conventional bow type centralizers and the second stage producing forces comparable to rigid type centralizers. While the result is two distinct magnitudes of centering forces these forces are applied successively without interruption upon continuing `deilection of the centralizer. Although this invention has been described in connection with a particular embodiment it is to be understood that the scope of this invention is not to be considered as limited to the details herein set forth but rather is of the full scope of the appended claims.
1. -In a well pipe centralizer, the combination of: a pair of axially spaced and aligned collars adapted to fit the well pipe, a plurality of circumferentially spaced and outwardly bowed staves extending longitudinally between and mounted on said collars, and a strap means extending longitudinally of and having ends secured to the interior side of each stave for engaging the well pipe during inward deection of said staves and substantially resisting further inward deflection of said staves.
2. The centralizer of claim 1 in which each said strap means is of a length substantially less than the length of said staves.
3. The centralizer of claim 2 in which each said strap most outward bowed portion of the stave.
` means is centrally located on said stave in relation to the 5 4. The centralizer of claim 1 in which each said strap means is curved inwardly between its secured ends for resiliently engaging the well pipe.
5. The centralizer of claim 4 in which each said inwardly curved portion of each said strap means is spaced from the well pipe in the undeflected condition of the staves for rfirst engaging the well pipe after preselected initial inward `dellection of said staves.
6.'The centralizer of claim 1 in which each said strap means is a short curved bow of spring steel located at the most outwardly bowed portion of said stave and bowed inwardly short of engaging the well pipe in the undeected condition of said stave, and said strap means having a radius of curvature substantially less than that of the portion of the stave to which the strap means is attached.
7. The centralizer of claim 6 in which each said strap means has a at end portion engaging the interior of the stave in surface contact.
8. The centralizer of claim 7 in which said end portions are welded only at their extreme ends to the stave.
9. In a well pipe centralizer of the type having a pair of axially spaced and aligned collars adapted to lit the Y well pipe and a plurality of circumferentially spaced and outwardly bowed staves extending longitudinally between and mounted on said collars, the improvement comprising: a strap means extending longitudinally of and having ends secured to the interior of each stave for imposing only a slight resistance to the initial inward deection of said staves, said strap means engaging well pipe to impose a substantial resistance to further inward dellection of said staves beyond said initial amount.
10. The centralizer of claim 9 in which each said strap means is a short curved bow of spring steel located at the most outwardly bowed portion of said stave and bowed inwardly short of engaging the well pipe in the undeflected condition of said stave, and said strap means having a radius of curvature substantially less than that of the portion of the stave to which the strap means is attached.
References Cited UNITED STATES PATENTS 1,412,213 4/1922 Mowers 166-202 X 1,835,377 12/ 1931 Clark e al 166-241 X 2,368,737 2/ 1945 zBadgley 166--241 X 2,656,890 10/ 1953 Brandon 166-241 3,312,285 4/ 1967 Solum 166-241 CHARLES E. -OCONNELL, Primary Examiner.
DAVID H. BROWN, Examiner.