WO2013120192A1

WO2013120192A1 - Casing centralizing device

Info

Publication number: WO2013120192A1
Application number: PCT/CA2013/000147
Authority: WO
Inventors: Frederick W. PHEASEY
Original assignee: Top-Co Inc.
Priority date: 2012-02-19
Filing date: 2013-02-19
Publication date: 2013-08-22

Abstract

A composite solid-body casing centralizer has a molded cylindrical non-metallic main body with outwardly-projecting straight or helical blades, with a circular metal wear band embedded in one end of the main body to provide wear resistance when the centralizer is in rotating contact with a coupling or a stop collar on a casing string around which the centralizer has been mounted. The inner diameter of the wear band is greater than the inner diameter of the non-metallic main body, such that the wear band will remain clear of the outer surface of the casing. Fluid passages are provided in the wear band to facilitate evacuation of any drilling fluid or cement slurry in the annular space between the centralizer and the casing into the annulus between the casing and a wellbore in which the casing is installed.

Description

CASING CENTRALIZING DEVICE

FIELD OF THE DISCLOSURE

The present disclosure relates in general to the technical field of oil and gas well completion. More particularly, the disclosure relates to the technical field of casing centralization in a wellbore.

BACKGROUND

Wellbores are often lined with a string of tubular casing, which is typically cemented into place to seal off the wellbore and to fix the casing in place in the wellbore. When running a casing string into a wellbore, it is desirable to keep the casing substantially centralized within the wellbore to prevent it from resting against the wall of the wellbore. Otherwise, the casing may become stuck to the wellbore due to the hydrostatic pressure of fluid in the wellbore being higher than the formation pressure. This problem is well known in the oil and gas industry, and is commonly referred to as "differential sticking". It is also desirable, and sometimes critically important, for the casing to be substantially centralized in order to ensure that, in the completed well installation, the casing will be completely encased with cement, with the thickness of the cement being reasonably uniform around the circumference of the casing at all locations along the length of the casing string. After a casing string has been installed in a wellbore, the casing is typically cemented in place by pumping a cement slurry (commonly referred to as simply "cement") from the surface into the casing string and out its lower end, thus displacing less dense drilling fluid (or "drilling mud") present in the wellbore annulus (i.e., the annular space between the wellbore and the casing) so that the cement slurry flows upward into the annulus and surrounds the casing string. During this cementing operation, it is desirable for the cement to find its way into all voids within the annulus to ensure that the cementing process results in a good seal against the wellbore, thus preventing formation fluids from entering the cement-filled annulus. If the casing is resting against or close to the wall of the wellbore, there will either be no cement separating the casing and the wellbore wall in such areas, or the cement thickness will be unsatisfactorily small.

To achieve these desirable objectives, cylindrical centralizing devices (or "centralizers") with external vanes or blades are commonly installed on wellbore casings to keep them generally centralized within the wellbore and, preferably, to turbulently "scour" unwanted mud cake from the wellbore, so that the cement slurry will completely envelope the perimeter of the casing. Centralizers may alternatively be referred to as "standoff devices, because they are intended to ensure that the casing "stands off from the wall of the wellbore.

It is desirable for a casing centralizer to be free to rotate about the casing to which it is mounted. It is also desirable for casing centralizers to be comparatively light in weight, for ease of on-site handling and to reduce shipping costs. For such reasons, centralizers made from polymeric materials such as thermoset resins have become popular in the industry.

When cylindrical casing centralizers are used, it is desirable for the upward- flowing cement slurry to displace any drilling mud that may have accumulated in spaces between the centralizers and the casing during casing-running operations, as the presence of such residual drilling mud will contaminate and weaken the cement layer surrounding the casing, and may impair the seal between the casing and the wellbore.

When running (i.e., lowering) a casing string into a wellbore, it may be necessary or desirable to rotate and/or reciprocate the casing, and/or to add weight to the casing string, in order to advance the casing to the bottom of the wellbore. Such operational conditions are encountered particularly often when casing is being run into deviated (i.e., non-vertical) or horizontal wellbores.

However, when a casing string carrying rotatable centralizers is rotated while being lowered into a wellbore, the centralizers will tend to ride upward on the casing due to friction against the wall of the wellbore, causing the upper ends of the centralizers to contact and rub against casing couplings or stop collars fixed to the casing above the centralizers. This increases the torque required to rotate the casing string, due to the frictional resistance between the centralizers and the couplings or stop collars resulting from relative rotation between the centralizers and the couplings or stop collars.

The same thing occurs when the casing string is being used as a drill string, commonly referred to as "drilling with casing" (or "DWC" for short). In certain operational situations, the lower ends of the centralizers can also rub against the couplings or stop collars. This could arise, for example, in situations where a casing running operation needs to be aborted for some reason, necessitating removal (or "tripping") of the casing string out of the wellbore. In that situation, friction between the centralizers and the wellbore during the upward withdrawal of the casing will cause the centralizers to ride move downward on the casing and into contact with the couplings or stop collars below. In the common situation where the casing string is rotated to facilitate its withdrawal from the wellbore, the lower ends of the centralizers will rub against the couplings or stop collars due to relative rotation between the centralizers and the couplings or stop collars.

Such rotational rubbing against metallic couplings and stop collars can cause severe wear to the upper and lower ends of non-metallic centralizers, and such wear may be worsened by the presence of drilling fluid incorporating or carrying abrasive materials such as drill bit cuttings. It is known to mitigate these problems, while retaining the practical advantages of non-metallic centralizers, by incorporating metallic wear bands into the ends of non-metallic centralizers. Examples of such centralizers may be seen in U.S. Patent No. 7,357,178 and U.S. Patent No. 8,141 ,629. In such a centralizer, it will be the wear bands rather than the softer polymeric material of the main body of the centralizer that will rub against the couplings or stop collars on the casing string. Any resultant wear on the wear bands, couplings, and/or stop collars typically will be acceptable and will not cause operational problems. Centralizers of this type may be referred to as "composite" centralizers in view of the fact that they incorporate both metallic and non-metallic components.

However, a problem with known composite centralizers having metallic wear bands is that the inner bore of the wear bands will inevitably come into rotating metal-to- metal contact against the outer cylindrical surface of the casing, causing undesirable wear to the casing, particularly in cases where the wear bands are made from a metal having greater hardness than the steel casing.

BRIEF SUMMARY

The present disclosure teaches a composite centralizer comprising a generally cylindrical main centralizer body made from a selected non-metallic material, and a generally cylindrical metallic wear band incorporated into one end of the centralizer body, with the inner diameter of the wear band being greater than the inner diameter of the adjacent region of the centralizer body. The inner diameter of the wear band will be sufficiently greater than the inner diameter of the centralizer body such that the wear band will not come into contact with the surface of a casing onto which the centralizer has been mounted (preferably allowing for any expected or predictable wear in the bore of the centralizer body resulting from contact against the surface of the casing).

In one embodiment, the composite centralizer is formed in a mold, with the wear band being integrated into the main centralizer body during the molding process. The wear band is preferably configured to produce a mechanical interlock with the centralizer body, such as (by way of non-limiting example) by forming the wear band with protrusions, grooves, recesses, or other features promoting embedment of the wear band into the non-metallic material of the main centralizer body so as to prevent longitudinal separation of the wear band from the centralizer body or relative rotation between the wear band and the centralize body. However, composite centralizers in accordance with the present disclosure are not limited or restricted to this method of manufacture or to the use of wear bands incorporating any particular means for fixing the wear bands to the centralizer bodies. Accordingly, in one aspect the present disclosure teaches a centralizing device comprising:

• a generally cylindrical main body having an upper end, a lower end, a main body wall, a main body bore, and a longitudinal axis, with the main body being made from one or more materials including at least one non-metallic material;

• a plurality of blades projecting outward from the main body wall;

• a generally cylindrical first wear band having an annular upper surface, a circular outer perimeter surface, and a generally cylindrical first wear band bore having a diameter greater than the diameter of the main body bore; and · anchor means whereby said first wear band is fixed to the upper end of the main body so as to be concentric therewith.

In certain embodiments, the first wear band may comprise a circular flange having a lower end and carrying said annular upper surface and said outer perimeter surface, plus a generally cylindrical skirt concentrically contiguous with the lower end of the circular flange. The skirt has a generally cylindrical outer surface with a diameter smaller than the diameter of the outer perimeter surface of the main body, and the anchor means comprises deformations formed on or into the outer surface of the skirt. The first wear band is preferably formed with one or more fluid passages extending between the first wear band bore and the outer perimeter surface of the first wear band. The fluid passages may be provided as slots formed into the annular upper surface of the first wear band, drilled radial channel, or in any other functionally effective form.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of centralizing devices in accordance with the present disclosure will now be described with reference to the accompanying Figures, in which numerical references denote like parts, and in which:

FIGURE 1 is an isometric view of a first embodiment of a composite centralizer in accordance with the present disclosure. FIGURE 2 is a partial-cutaway elevation of the composite centralizer shown in FIG. 1.

FIGURE 3 is an isometric view of a variant embodiment of the composite centralizer shown in FIG. 1. FIGURE 4 is a partial-cutaway elevation of the composite centralizer shown in FIG. 3.

FIGURE 5 is a top view of a composite centralizer as in FIGS. 1-4.

FIGURE 6 is an isometric view of a wear band as incorporated into composite centralizers as shown in FIGS. 1-4. FIGURE 7 is an isometric view of an alternative wear band.

DETAILED DESCRIPTION

FIGS. 1, 2, and 5 illustrate one embodiment of a cylindrical composite casing centralizer 100 comprising a main body 10 having an upper end 10U, a lower end 10L, a main body wall 12, and a longitudinal axis Ai₀; a plurality of vanes or blades 20 projecting outward from and circumferentially spaced around main body wall 12; and a cylindrical wear band 30 concentrically incorporated into upper end 10U of main body 10. Blades 20 are preferably formed integrally with main body 10, but this is not essential to centralizers in accordance with the present disclosure.

Main body 10 has a generally cylindrical bore 14 having an upper end 14U and a lower end 14L. Bore 14 has an upper bore diameter DHU at upper end 14U of bore 14, and a lower bore diameter D^L at lower end 14L of bore 14. In the illustrated embodiment, upper bore diameter Dj₄u and lower bore diameter DHL are equal, such that bore 14 is uniformly cylindrical. In alternative embodiments, however, upper bore diameter Di₄u and lower bore diameter D₁₄L may be unequal, such that bore 14 is of slightly frustoconical configuration (i.e., tapered). This configuration may be advantageous to simplify centralizer mold construction and to facilitate mold stripping. It is to be noted, however, that centralizers in accordance with the present disclosure are not limited or restricted to any particular configuration of bore 14 of main body 10.

The outermost surfaces 22 of blades 20 are at a radius relative to main centralizer body 10 generally corresponding to the radius of the wellbore in association with which it is intended to use centralizer 100. In the illustrated embodiments, blades 20 extend substantially the full longitudinal distance between upper end 10U and lower end 10L of centralizer main body 10, and they are angularly or helically oriented so as to induce rotation of centralizer 100, relative to a casing on which centralizer 100 has been mounted, in response to an upward flow of drilling fluid (during casing running or DWC operations) or cement slurry (during casing cementing operations) through the wellbore annulus. However, this is by way of example only, and in alternative embodiments blades 20 could be oriented parallel to axis Aio of centralizer 100, and/or could be considerably shorter in length than main body 10. Centralizer blades of many styles and configurations are known in the art, and centralizers in accordance with the present disclosure are not in limited or restricted to blades of any particular type or style.

In the illustrated embodiments, wear band 30 comprises a circular flange 32 contiguous with and projecting radially outward from a generally cylindrical skirt 34 which extends below flange 32. Flange 32 has an outer perimeter surface 31 and an annular end surface 33 (which is preferably but not necessarily planar). Wear band 30 is molded into or otherwise integrated into upper end 10U of main body 10 such that skirt 34 is fixed to main body 10 and such that flange 32 largely or completely projects beyond upper end 10U of main body 10. Skirt 34 is formed with or otherwise provided with anchor means for embedding or otherwise fixing skirt 34 in or to main body 10.

In the illustrated embodiment, wear band 30 has a cylindrical inner surface 36 having an inner diameter D36, which is a selected amount larger than upper bore diameter

Dun of main body 10. In alternative embodiments, inner diameter D36 of inner surface 36 does not necessarily have to be of constant value, but could vary without departing from the scope of the present disclosure provided that the minimum value of inner diameter

D36 is greater than upper bore diameter Di_4lJ, so as to provide a gap 15 between upper bore diameter D^u and the radially innermost surfaces of wear band inner diameter D36 around at least a substantial portion of the perimeter of wear band 30.

In alternative embodiments, inner surface 36 of wear band 30 conceivably could have one or more ribs or other protuberances projecting radially inward such that a gap 15 would not be present in some localized areas, but with such ribs or protuberances being configured such that they would not pose a risk of causing significant wear to a casing onto which centralizer 100 has been mounted. Such alternative embodiments are intended to come within the scope of the present disclosure and the appended claims.

In the illustrated embodiment, at least one and preferably several radially-oriented slots 38 are formed into the upper surface 32A of upper flange 32 of wear band 30. Slots 38 act as fluid passages extending between inner surface 36 of wear band 30 and outer perimeter surface 31 of flange 32, whereby any residual drilling fluid within the narrow annular space (or "centralizer annulus") between bore 14 of main centralizer body 10 and the outer surface of a casing (which annular space may be referred to as the centralizer annulus) onto which centralizer 100 has been mounted can flow out into the wellbore annulus in response to an upward flow of cement slurry into the centralizer annulus. During casing cementing operations, the upward flow of slurry will typically urge centralizer 100 upward into contact with the casing joint coupling or stop collar above it. In the absence of slots 38 or other fluid flow passages facilitating evacuation of drilling mud from the centralizer annulus into the wellbore annulus, such evacuation of drilling mud would be effectively prevented because the upper end of the centralizer annulus would be closed off due to upper flange 32 of wear band 30 abutting the coupling or stop collar.

In alternative embodiments, fluid flow passages could be provided in the form of radial channels 39 drilled through or otherwise formed in upper flange 32 of wear band 30. Such radial channels 39 are illustrated in the variant wear band 130 in FIG. 7.

Wear bands for centralizers in accordance with the present disclosure are not limited or restricted in terms of the materials from which they are made. In preferred embodiments, however, the wear bands are made from metallic materials, such as but not limited to steel or zinc alloy. The wear bands can be fabricated by means of any suitable process, such as but not limited to machining or die-casting.

FIGS. 3, 4, and 5 illustrate an alternative embodiment of a cylindrical composite casing centralizer 110 similar to casing centralizer 100 shown in FIGS. 1 and 2, with the only difference being that centralizer 110 comprises an upper wear band 30U plus a lower wear band 30L. In FIGS. 3 and 4, lower wear band 30L is shown with fluid flow slots 38 as shown in upper wear band 30U. In most operational conditions there may be no need for slots 38 in lower wear band 30L, but it may be convenient and beneficial for both wear bands 30U and 30L to have slots 38 (or flow passages of alternative form) so that centralizer 110 will be reversible.

Main body 10 of centralizer 100 (or 110) may be molded from any suitable non- metallic material, including but not limited to polymeric materials such as thermoplastic resins and thermoset resins, it is to be rioted, however, that central izers in accordance with the present disclosure are not limited to either of these specific materials or any other particular material.

The material from which main body 110 is molded may comprise selected filler materials for purposes of imparting selected properties to main body 110 or enhancing selected properties of main body 110, such as lubricity (to reduce friction between blades 20 and the wall of a wellbore) and hardness of the molding material (to reduce abrasive wear on blades 20).

FIG. 6 is an enlarged view of wear band 30 as incorporated into centralizer embodiments 100 and 110 in FIGS. 1 -4, and illustrating one of many possible means by which wear band 30 could be fixed to main body 10 of centralizer 100 (or 110). In this embodiment, wear band 30 incorporates skirt 34 contiguous with flange 32 as previously described, with skirt 34 incorporating anchor means for fixing skirt 34 to main body 10 being provided in the form of a series of annular ridges 40 projecting outward from the outer surface of skirt 34. When skirt 34 is molded into main body 10 as shown in FIGS. 2 and 4, ridges 40 on skirt 34 have the effect of integrating wear band 30 into main body 10 and preventing longitudinal separation of wear band 30 from main body 10. As shown in FIG. 6, ridges 40 may be discontinuous around the perimeter of skirt 34 so as to provide intermittent regions 42 of skirt 34 that do not have any ridges. These intermittent non-ridged regions 42, in combination with adjacent ridged regions 40. have the effect of preventing rotation of wear band 30 relative to main body 10.

Ridges 40 are merely one example of possible anchor means for fixing skirt 34 in or to main body 10, and persons skilled in the art will readily appreciate that numerous other functionally effective anchor means could be devised in accordance with technologies know to persons skilled in the art.

FIG. 7 illustrates one such alternative anchor means incorporated into a variant wear band 130. In this embodiment, a plurality of indentations or anchor pockets 50 are formed into the outer surface skirt 34. When wear band 130 is molded into a polymeric main centralizer body 10, the molten polymeric material will flow into anchor pockets 50, thereby providing a mechanical interlock between wear band 130 and main body 10 to prevent both longitudinal movement and rotation of wear band 130 relative to main body 10. In FIG. 7, anchor pockets 50 are shown as being of rectilinear configuration, but this is solely by way of example, as the shape of anchor pockets 50 would be purely a matter of design choice. As noted previously, the anchor means used for fixing skirt 34 of wear band 30 to main centralizer body 10 could take any of many different forms, and centralizers in accordance with the present disclosure are not restricted to the use of any particular anchor means. For example, skirt 34 could incorporate anchor means in the form of protrusions having functionally effective configurations different from the illustrated annular ridges 40.

Moreover, centralizers in accordance with the present disclosure are not restricted to embodiments in which wear bands incorporate a skirt as in the illustrated embodiments herein. In wear bands incorporating a skirt, the primary function of the skirts is to facilitate integration of the wear bands into main body 10 of the central izers, and the inclusion of such skirts for this purpose will typically be advantageously convenient when forming a central izer using a molding process. However, such skirts are not essential. What is important in the context of the present disclosure is for the inner diameter D36 of wear band 30 to be larger than the diameter D1 of bore 14 in main body 10, such that wear band 30 will not be in contact with the outer surface of a casing on which the associated centralizer 100 (or 110) has been mounted.

Persons skilled in the art will appreciate that wear bands providing this functionality could alternatively be anchored to or integrated into a centralizer using anchor means not entailing a skirt as in the illustrated embodiments. By way of one non- limiting example, the wear band could comprise a simple circular metal ring of rectilinear cross-section, with a plurality of spaced anchor elements fixed to and extending from the metal ring so as fit within a mold used for casting the composite centralizer and to become embedded in polymeric material introduced into the mold to form the composite centralizer. Centralizers having wear bands such anchor means or any other functionally effective anchor means are intended to be within the scope of the present disclosure.

It will be readily appreciated by those skilled in the art that various modifications to embodiments in accordance with the present disclosure may be devised without departing from the scope and teaching of the present teachings, including modifications which may use equivalent structures or materials hereafter conceived or developed. It is to be especially understood that the scope of the claims appended hereto should not be limited by any particular embodiments described and illustrated herein, but should be given the broadest interpretation consistent with the description as a whole. It is also to be understood that the substitution of a variant of a claimed element or feature, without any substantial resultant change in functionality, will not constitute a departure from the scope of the disclosure.

In this patent document, any form of the word "comprise" is to be understood in its non-limiting sense to mean that any item following such word is included, but items not specifically mentioned are not excluded. A reference to an element by the indefinite article "a" does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one such element. Any use of any form of the word "typical" is to be understood in the non-limiting sense of "common" or "usual", and not as suggesting essentiality or invariability. Any use of any form of the terms "mount", "fix", or any other term describing an interaction between elements is not meant to limit the interaction to direct interaction between the subject elements, and may also include indirect interaction between the elements such as through secondary or intermediary structure.

Relational and/or conformational terms such as "parallel", "concentric", "radial", "cylindrical", "circular", "annular", and "planar" are not intended to denote or require absolute mathematical or geometrical precision. Accordingly, such terms are to be understood as denoting or requiring only substantial or general conformity with the associated relational or conformational characteristics (e.g., "substantially parallel" or "generally cylindrical") consistent with the contexts in which the terms are used, and unless the context clearly requires otherwise. Wherever used in this document, the terms "typical" and "typically" are to be interpreted in the sense of representative of common usage or practice, and are not to be interpreted as implying essentiality or invariability.

In this patent document, the adjectives "upper" and "lower" are used in the descriptions of certain components and features of the disclosed centralizing devices. In such usages, these adjectives are to be interpreted with reference to a centralizing device having its longitudinal axis in a substantially vertical orientation. In use, centralizing devices in accordance with the disclosure will commonly assume horizontal and other non-vertical orientations. Accordingly, the words "upper" and "lower" are not intended to be given a strictly literal interpretation unless the context clearly requires otherwise.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A centralizing device comprising:

(a) a generally cylindrical main body having an upper end, a lower end, a main body wall, a main body bore, and a longitudinal axis, said main body being made from one or more materials including at least one non-metallic material;

(b) a plurality of blades projecting outward from the main body wall;

(c) a generally cylindrical first wear band having an annular upper surface, a circular outer perimeter surface, and a generally cylindrical first wear band bore having a diameter greater than the diameter of the main body bore; and

(d) anchor means whereby said first wear band is fixed to the upper end of the main body so as to be concentric therewith.

2. A centralizing device as in Claim 1 wherein the first wear band comprises:

(a) a circular flange having a lower end and carrying said annular upper

surface and said outer perimeter surface; and

(b) a generally cylindrical skirt concentrically contiguous with the lower end of the circular flange, said skirt having a generally cylindrical outer surface having a diameter smaller than the diameter of said outer perimeter surface;

wherein the anchor means comprises deformations on the outer surface of the skirt.

3. A centralizing device as in Claim 2 wherein the deformations comprise annular ridges projecting from the outer surface of the skirt.

4. A centralizing device as in Claim 3 wherein the annular ridges comprise multiple circumferentially-spaced groups of annular ridges.

5. A centralizing device as in Claim 2 wherein the deformations comprise indentations into the outer surface of the skirt.

6. A centralizing device as in any one of Claims 1-5 wherein the first wear band is formed with one or more fluid passages extending between the first wear band bore and the outer perimeter surface of the first wear band.

7. A centralizing device as in Claim 6 wherein at least one of the one or more fluid passages comprises a slot formed into the annular upper surface of the first wear band.

8. A centralizing device as in Claim 6 wherein at least one of the one or more fluid passages comprises a drilled radial channel.

9. A centralizing device as in any one of Claims 1-8 wherein the main body is made from a polymeric material.

10. A centralizing device as in Claim 9 wherein the polymeric material is selected from the group consisting of thermoplastic resins and thermoset resins.

1 1. A centralizing device as in Claim 9 wherein the polymeric material comprises a polyester resin.

12. A centralizing device as in any one of Claims 1-1 1 wherein the blades are formed integrally with the main body.

13. A centralizing device as in any one of Claims 1-12 wherein the blades are helically oriented relative to the longitudinal axis of the main body.

14. A centralizing device as in any one of Claims 1-12 wherein the blades are parallel to the longitudinal axis of the main body.

15. A centralizing device as in any one of Claims 1-14 wherein the wear band is made from a metallic material.

16. A centralizing device as in Claim 15 wherein the metallic material comprises steel.

17. A centralizing device as in Claim 15 wherein the metallic material comprises a zinc alloy.

18. A centralizing device as in any one of Claims 1-17, further comprising a second wear band concentrically fixed to the lower end of the main body.