US20120273199A1

US20120273199A1 - Nitinol Through Tubing Bridge Plug

Info

Publication number: US20120273199A1
Application number: US12/937,039
Authority: US
Inventors: Gary Cresswell; Freeman Hill; William Befeld; Gregory Rinberg; Dan Raz; Michael Goldstein
Original assignee: Baker Hughes Inc
Current assignee: Baker Hughes Holdings LLC
Priority date: 2009-04-27
Filing date: 2010-04-27
Publication date: 2012-11-01
Also published as: WO2010129266A3; WO2010129266A2

Abstract

A bridge plug assembly having a nickel titanium alloy flexible member that can be selectively radially expanded so its outer surface sealingly engages a surrounding tubular. The flexible member can comprise an annular membrane like member having coaxial rings on the opposing ends of the flexible member. The percentage of weight of nickel can range up to about 40 to about 58%, 55% or to about 60%.

Description

BACKGROUND

1. Field of Invention
The invention relates generally to the field of oil and gas production. More specifically, the present invention relates to a system and method for plugging tubing within a borehole.
2. Description of Prior Art
Downhole plugs are used to block flow through a wellbore tubular and can be formed from an elastomeric membrane on a mandrel or coaxially stacked members. Downhole plugs can be selectively set into place by expanding the membrane or collapsing the stacked members to block the annular space within the mandrel. Plug or packer setting can occur by axially compressing the mandrel or by filling the membrane with a pressurized fluid. The tubulars can be casing or production tubing.

SUMMARY OF INVENTION

Disclosed herein is an example embodiment of a bridge member. In an example embodiment, the bridge member is used with a bridge plug assembly and includes a pair of collars that both set around an axis and spaced apart from one another. Elongated ribs are included where each rib is made from a superelastic material and have ends coupled to the collars. A mid-portion of the ribs, between the collars, projects radially outward with respect to the ends of the ribs. Webs are included that connect between each adjacently rib; the webs are also formed from a superelastic material. Thus by rotating one of the collars with respect to the other collar, the mid-portions of the ribs are drawn radially inward which lengthens the bridge member and creates folds in the webs. In an optional embodiment, the ribs and webs include an alloy having nickel of about 55% to about 57% by weight and titanium of about 45% to about 43% by weight. In an example embodiment, a portion of one of the ribs or webs that deforms due to an applied load transforms from an austenite to a deformed martensite. In alternate embodiments, the rib thickness ranges from about one to three times the thickness of the web. An annular elastomeric seal can be included that circumscribes the mid-portion of the ribs and has an outer surface that seals against an inner surface of a tubular. In an example embodiment, the web can be elastically deformed at a value of up to about 8% along the folds and can be subjected to a stress of about 7.33×10⁸N/m².
Also described herein is a method of blocking a tubular. In an example embodiment the method includes providing a bridge plug assembly that is made up of a mandrel, a bulbous membrane circumscribing the mandrel, and a pair of end collars coupled on each end of the bridge member and circumscribing the mandrel. The membrane can include a superelastic material. The method further includes configuring the membrane so it can be moved within a tubular, this can be accomplished by rotating one of the collars with respect to the other collar. This twists the membrane to elastically forming folds within the membrane and pulls the membrane radially inward toward the mandrel. In an example embodiment, the folds are oppositely facing. Energy is stored in the folds, thus to keep the membrane in the “insertion” configuration, a resistive force is kept on the collar that was rotated which elastically maintains stress in the membrane folds. The method can also include inserting the bridge plug assembly into the tubular and then removing the resistive force; this allows unloading of the elastically maintained stress and the inherent elasticity of the material reforms the membrane as it was before it was twisted so it can unfold and expand to block the tubular. Optionally, the membrane can be reloaded into the smaller diameter configuration and the bridge plug assembly removed from the tubular. In an alternative embodiment, the bridge plug assembly can also include ribs coupled with the membrane. The ribs can be substantially aligned with the mandrel when no stress is applied to the membrane, and oblique with the mandrel when the membrane is loaded. In an example embodiment, the membrane includes an alloy having nickel of about 55% to about 57% by weight and titanium of about 45% to about 43% by weight. Yet further optionally, the method can include injecting liquid into the membrane. In an example embodiment, the tubular is within a wellbore and undulations can be defined along outer circumference of the membrane.
Also described herein is a bridge plug assembly that includes a bulbous and substantially hollow member, where the member is made from a superelastic material. The member includes a membrane with a series of strategically located foldable regions. The bridge plug assembly can further include a mandrel circumscribed by the member and a pair of spaced apart and annularly shaped ends that also circumscribe the mandrel. The annularly shaped ends may be coupled to opposing ends of the member, so that when a rotational force is applied to one of the ends with respect to the other end, the outer diameter of the member reduces and folds form along the foldable regions that retain therein at least a portion of the force applied to said one of the ends. In an alternative example embodiment, the annularly shaped ends are made up of a first annularly shaped end and a second annularly shaped end, and the member further comprises elongated ribs coupled with the membrane that project from the first annularly shaped end into engagement with the second annularly shaped end. The ribs can be substantially parallel with the mandrel and moved into an oblique orientation with respect to the mandrel after the rotational force is applied to one of the ends. Optionally, the membrane may include a nickel titanium alloy. In an example embodiment, the member is made up of segments joined together, each segment having a raised mid portion aligned with the mandrel so that the outer circumference of the member defines an undulating surface.

BRIEF DESCRIPTION OF DRAWINGS

Some of the features and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which:

FIG. 1A is a side partial sectional view of an example embodiment of a bridge plug assembly being inserted into a wellbore.

FIG. 1B is a depiction of the bridge plug assembly of FIG. 1A being set in the wellbore.

FIG. 2 is a graphic illustration of an example embodiment of a crystalline structure of a superelastic material under a load.

FIG. 3 is a stress-strain plot of an example embodiment of a superelastic material.

FIG. 4 is a perspective illustration of the bridge member of FIG. 2 in a deployed configuration.

FIG. 5 is a sectional view of the bridge member of FIG. 4.

FIG. 6 is a perspective view of the bridge member of FIG. 4 in an insertion configuration.

FIG. 7 is a partial sectional view of the bridge member of FIG. 6.

FIG. 8 is an illustration of the bridge member of FIG. 4 having an annular sleeve.

FIG. 9 is a side sectional view of the bridge member of FIG. 8.

FIG. 10 is a side perspective view of an alternative bridge member for use in a bridge plug assembly in accordance with the present disclosure.

FIG. 11 is a side perspective view of the bridge member of FIG. 10 in a deployed configuration.

FIGS. 12 and 13 are respective sectional views of the bridge member of FIGS. 10 and 11.

FIGS. 14 and 15 are sectional views of an example embodiment of a bridge member segment taken along the member axis.

While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope, of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF INVENTION

The subject(s) of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. The subject(s) of the present disclosure may, however, be embodied in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. For the convenience in referring to the accompanying figures, directional terms are used for reference and illustration only. For example, the directional terms such as “upper”, “lower”, “above”, “below”, and the like are being used to illustrate a relational location.
It is to be understood that the subject(s) of the present disclosure described herein are not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation.
Shown in FIG. 1A is a partial sectional view of a bridge plug assembly 20 being deployed within a tubular 9 that is set in a wellbore 7. A formation 5 circumscribes the wellbore 7. The tubular 9 can be casing lining the wellbore 7 or production tubing coaxially deployed within casing. The bridge plug assembly 20 shown is being deployed on wire line 22 that is suspended downward into the wellbore 7 from a wellhead assembly 11. Alternatively, the bridge plug assembly 20 can be deployed from other means, such as coiled tubing.
In the example embodiment of FIG. 1A, the bridge plug assembly 20 includes an elongated body 24 and a bridge member 28A provided along a section of the body 24. The embodiment of the bridge plug assembly 20 is in the insertion configuration for insertion within the tubular 9. While in the insertion configuration, the bridge plug assembly 20 can be disposed to a desired location in the tubular 9; alternatively, a bridge plug assembly 20 in an insertion mode may be freely moved through the tubular 9. The bridge member 28A is selectively expandable into a configuration having an enlarged periphery. Referring now to FIG. 1B, an example embodiment of the bridge plug assembly 20 is illustrated with the bridge member 28A selectively expanded so that the outer surface of the bridge member 28A projects radially outward past the outer perimeter of the body 24. The bridge member 28A can be expanded partially into the annular space between the body 24 and inner circumference of the tubing 9, or fully into the annular space so that it is in sealing engagement with the tubular 9.
In an example embodiment, the bridge member 28A is made at least in part by pseudoelastic or superelastic materials. Generally, superelastic describes materials that can elastically endure greater strain rates than non-superelastic materials. As schematically illustrated in FIG. 2, a superelastic material transforms from an austentic phase to a deformed martensitic phase when under an applied stress. This transformation involves domain boundaries to move, which is a reversible mechanism. Thus when the stress applied to a superelastic material is released, the material returns to the original austentic phase and conforms to the original shape and configuration. Example superelastic materials include a nickel titanium alloy, wherein the nickel percentage-ranges up to about 60% by weight, in another embodiment the percentage of weight of nickel can range from about 40% to about 58%, in another embodiment the percentage of weight of nickel can range from about 48% to about 53%, and in another embodiment the percentage of weight of nickel in the alloy can be about 55%. Additional embodiments exist wherein the percentage weight of nickel can be any value within the aforementioned ranges. The balance of the alloy can be titanium, or optionally, a combination of titanium and some, all, or a mixture of other constituents, such as copper, iron, oxygen, hydrogen, cobalt, molybdenum, magnesium, and carbon.
A stress-strain curve of an example superelastic material is graphically provided in FIG. 3 illustrating elasticity at strains of up to about 8%. In the example of FIG. 3, the stress/strain ratio increases linearly under an applied load up to an inflection point, then, while undergoing continued loading, the stress remains substantially constant as the strain increases. The portion of the plot depicting relatively unchanging stress with increasing strain may be referred to as a loading plateau. Similarly, as the load is being removed, the stress/strain both decrease up to an inflection point, after which the stress remains substantially the same as the strain decreases. This portion of the plot may be referred to as an unloading plateau. As illustrated, the unloading plateau occurs at a lower value of stress than the loading plateau.
Shown in a side perspective in FIG. 4 is an example embodiment of a bridge member 28A in an expanded configuration. In this embodiment, the bridge member 28A has a bulbous pumpkin like mid-portion shown about an axis A_X. The outer surface of the bridge member 28A projects radially inward at the opposing ends of the bridge member 28A and “necks” down to define annular base rings 30 or collars at each end of the bridge member 28A. The base rings 30 are shown having substantially the same dimensions and coaxially circumscribing axis A_X. In the embodiment of FIG. 4, the bridge member 28A is a generally hollow member having a membrane-like body depending between the base rings 30. The hollow body includes elongated ribs 32 each having first and second ends connected to the base rings 30. In the embodiment of FIG. 4, although bulged radially outward from the axis A_X, the ribs 32 extend along a line generally parallel to the axis A_X. Webs 34 are shown laterally spanning between each adjacent rib 32 and tilling the space between the adjacent ribs 32.
The bridge member 28A may be formed by attaching together multiple segments 36 to form the bridge member 28A. An example method of attaching the segments 36 includes welding and/or other methods of adhesion. A line L is shown on the bridge member 28A to illustrate an example configuration of the segment 36. In this example, the segment 36 includes an angular portion of one of the base rings 30 about the axis A_Xthat extends towards the other base ring 30 up to about the mid-portion of the bridge member 28A. In the example of FIG. 4, the segment 36 includes three ribs 32 with the middle rib disposed along a curved path further away from the axis A_Xthan either of the two lateral ribs 32. The segment 36 outer surface continues its downward slope towards the axis A_Xto its terminal lateral end. Each adjacent segment 36, which has a similar configuration, therefore forms a bridge member 28A with its outer circumference having a generally undulating form along the circumference.
A sectional view of the bridge member 28A is provided in FIG. 5 wherein the section is taken substantially perpendicular to the axis A_X, this view illustrates a thickness difference between the ribs 32 and web 34. As shown, the width of each rib 32 reaches a maximum roughly at the mid-portion of the bridge member 28A along the axis A_X, then narrowing to a minimum proximate to where each rib 32 attaches to the ring 30. As noted above, in the embodiments illustrated in FIGS. 4 and 5, the ribs 32 are substantially parallel with the axis A_X. However, by rotating one of the base rings 30 with respect to the other base ring 30, the ribs 32 change orientation from being parallel with the axis A_Xto a helical type arrangement. An example of this is illustrated in FIGS. 6 and 7. Setting the ends of the rib 32 at different circumferential locations along the two base rings 30 draws the mid-portions of the ribs 32 radially inward towards the axis A_X, thereby forming the generally tubular shape of the bridge member 28 of FIGS. 6 and 7. Additionally, maintaining a torsional force on the bridge member 28 can retain the tubular shape, which may be required for insertion into the tubular 9 or retrieval therefrom.
FIG. 6 illustrates a perspective view of an example of a bridge member 28 used in combination with the bridge plug assembly 20. The bridge member 28 in this embodiment is shown as a generally annular member. In this configuration, referred to as an insertion configuration, the bridge member 28 is insertable into a downhole tubular. As noted above, applying a torsional force to the rings 30 forms flatter ribs 32 a and angles them with respect to the axis A_Xso their respective ends couple to the rings 30 at different azimuths. A partial sectional view of the member 28 of FIG. 6 is provided in FIG. 7. In this view the member 28 includes sections 36 each extending along the length of one or more ribs 32A from one of the rings 30 to about the mid-portion of the bridge member 28.
Shown in side perspective view in FIG. 8 is a bridge member 28A in the expanded deployed mode and a sleeve 40 that circumscribes its outer surface. The sleeve 40 may include an elastomeric or other polymeric material used in forming a sealing surface with a tubular inner circumference. In one example, the sleeve 40 includes a nitrile rubber material.
FIG. 9 illustrates in a side sectional view an example of a bridge plug assembly 20 shown equipped with a bridge member 28A and outer sleeve 40 radially expanded into contact with a tubular 9. In this embodiment, the bridge plug assembly 20 includes an elongated cylindrical mandrel 42 coaxial with its axis A_X. Deployment mechanisms 44 circumscribe the mandrel 42 at opposite ends of the bridge member 28A where they are shown affixed on the outer lateral sides of the respective ring members 30. The deployment mechanism 44 can axially rotate the bridge member 28A from its expanded mode into its retracted mode for passage through the tubular 9. The deployment mechanism 44 can further be locked in place to retain the member 28A in its annular configuration until the member is within the tubular 9 pre-designated location for deployment.
Deploying the bridge plug assembly 20 can include commanding the mechanism 44 to remove the torsional force applied to one or each of the base rings 30. The applied torsion force stores energy in the bridge member 28 since memory in the bridge member 28 material causes it to return to its convex shape (FIG. 4). Thus removing applied torsional force to the base ring(s) 30 in turn unloads the bridge member 28 thereby allowing a return to the bulbous configuration. Torsionally unloading the bridge member 28A enables the expansive movement of the ribs 32 and web 34 into outward blocking contact with tubular 9. The deployment mechanism 44 can include an electrical motorized means for applying and retaining the torsional force. Optionally, hydraulic lines and controls can be included to perform this function.
Shown in side perspective views respectively in FIGS. 10 and 11 is an alternative bridge member 29 shown having a generally annular configuration with coaxially and circular ring members 31 affixed at the end of the member 29. In this configuration, the ribs 33A of FIG. 10 each are angled with respect to the axis A_Xthus taking a curved path between the base rings 31. Additionally, each rib 33A is disposed at generally the same radial location away from the axis A_Xas other ribs 33A of the bridge member 29A. A web 35A spans the lateral distance between adjacent ribs 33A. Shown in FIG. 11 is a perspective view of a bridge member 29 that is an example of the bridge member 29A of FIG. 10 after having been torsioned to smaller diameter bridge member 29 for passage through a tubular. Unlike the embodiment in FIG. 6, the radius of the bridge member 29 of FIG. 11 bulges slightly proximate the mid-portion.
FIGS. 12 and 13 illustrate cross sectional views, shown parallel with the axis A_X, of the bridge member 29A, 29 respectively of FIGS. 10 and 11. More specifically, with reference to FIG. 12, depicted is an example embodiment an arrangement of the web 35 into a series of folds 37 in response to applied torsional force at the base rings 31 and around the ribs 33. Converting the ribs 33A web 35A of FIGS. 10 and 13 into the ribs 33 and web 35 of FIG. 11, reconfigures the ribs 33A and folds the web 35A to radially compact the bridge member 29. While in the compact configuration, the bridge member 29 can travel in and out of a downhole tubular.
FIG. 14 illustrates a side sectional view of the bridge member segment 36 when the bridge member 28A is radially expanded. As noted above, the section 36 includes a portion of the bridge member 28A having three ribs: that include a middle rib 32 with adjacent lateral ribs 320, 321. In the embodiment of FIG. 14, the lateral ribs 320, 321 are wider than the middle rib 32. Although illustrated as having different thicknesses, in an example embodiment, the thickness of the ribs 32, 320, 321 can range from about the same thickness as the web 34 up to about three times the thickness of the web 34. The web 34 connectively spans laterally between each adjacent rib 32, 320, 321. A reference axis A_Sis shown adjacent the segment 36. FIG. 15, shows the section 36 of FIG. 14 in a torsioned configuration for tubular passage. In response to the applied torsion, the web 34A curves between the middle rib 32 and lateral rib 321 with a radius R₁projecting from an origin O₂. The web 34A also curves along the portion projecting from the lateral side of each rib 320, 321 opposite from the middle rib 32. In the embodiment of FIG. 13, the second set of curved portions of the web 34A each have a radius R₂projecting from origins O₃and O₄. By strategically creating segments 36 having the dimensions and material, both in cross section and in contour along the segment axis A_Sthe torsional force supplied at the base rings can produce the folded arrangement of the segment 36A shown in FIG. 15. Moreover, the nature of the material used can then spring back into its original shape (FIG. 14) and adopt the configuration of a radially expanded bridge member 28A used for blocking within a tubular.

Example 1

In one non-limiting example, a proposed bridge member 28A was analyzed having the material properties shown in Table 1 and constituents as shown in Table 2.

	TABLE 1

	Property	Value

	Tensile Strength, Ultimate	1450 MPa/210,000 psi
	Tensile Strength, Yield	1280 MPa/185,000 psi
	Percent elongation, Fracture	12.5%
	Percent elongation, Yield	8.00%
	Tensile Set	0.100%
	Melting Point	1300° C./2370° F.

	TABLE 2

	Constituent	Mass Percent

	Carbon, C	≦0.0500
	Iron, Fe	≦0.0500
	Nickel, Ni	55.4-56.4
	Oxygen, O	≦0.0500
	Titanium, Ti	43.54-44.6

A finite element analysis employing COSMOS® software yielded stress values for the prophetic bridge member 28A as specified in Tables 1 and 2. In an expanded configuration, stress values ranged from about 8.29×10⁵N/m²to about 7.33×10⁸N/m²and strain values ranging from about 1.61×10⁻⁵about 5.20×10⁻². Higher stress concentrations were identified in the web portion in a region between the mid-portion of a section 36 and where the bridge member 28A “necks down” transverse to the axis A_X. Lower stress concentrations were estimated adjacent the collars 30.
In an example of use of the device described herein, a bridge plug assembly 20, as shown in FIG. 1B, is provided prior to insertion into a tubular 9. In an example, the outer diameter of the bridge member 28A is about 6 inches and the length of the bridge member 28A is about 15″. A torque T (FIG. 8) applied to one of the collars 30 folds the bridge member 28A from the expanded bulbous configuration (FIG. 4) to the insertion mode (FIG. 6). In an example, the outer diameter of a folded bridge member 28 is about 0.2 inches and the length of a folded bridge member 28 is about 15.5″. Optionally, oppositely directed torques T could be applied to both collars 30. A retaining force or torque may be applied to the bridge member 28 to maintain it in the insertion mode. An example mechanism for torquing the collar(s) 30 is illustrated in FIG. 9. In one example embodiment, the material of the bridge member 28A is superelastic, so that the stress from torquing the bridge member 28A produces a phase change from an austenite structure (bridge member 28A) to a deformed martinsite structure (bridge member 28). In an example embodiment, the material of the bridge member 28 material deforms up to about 6%, in another alternative embodiment, the material of the bridge member 28 deforms up to about 8%. In yet another alternative, the material of the bridge member 28 deforms up to about 10%.
As shown in FIG. 1B, when the bridge plug assembly 20A is in a desired location in the tubular, the retaining force on the bridge member 28 can be removed to permit reversing the material phase change of the superelastic material thereby returning to the expanded bridge member 28A. Optional embodiments involve the bridge member 28 experiencing a change in form, girth, circumference, length, or a combination thereof during transformation. In yet another option: the applied torque can be increased to exert an increased preload to induce additional rotation of the bridge member and/or more axial movement of the bridge member.
The present invention described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment of the invention has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims.

Claims

1. A bridge member for use in a bridge plug assembly, the bridge member comprising:

a pair of spaced apart and substantially coaxial annular collars;

a plurality of elongated and superelastic ribs, each rib having opposing ends respectively coupled with the collars and a mid-portion projecting radially outward with respect to the ends of the ribs; and

a plurality of superelastic webs spanning between each adjacently spaced rib, so that when one of the collars is rotated with respect to the other collar, the mid-portion of the ribs is drawn radially inward, the bridge member elongates, and folds are formed in the webs.

2. The bridge member of claim 1, wherein the ribs and webs comprise material that includes an alloy having nickel of about 55% to about 57% by weight and titanium of about 45% to about 43% by weight.

3. The bridge member of claim 1, wherein when at least a portion of one of the ribs or webs is deformed from an applied load, the deformed portion undergoes an elastic phase transformation from an austenite to a deformed martensite.

4. The bridge member of claim 1, wherein the rib thickness ranges from about one to three times the thickness of the web.

5. The bridge member of claim 1, further comprising an annular elastomeric seal circumscribing the mid-portion of the ribs and having an outer surface in sealing contact with a tubular.

6. The bridge member of claim 1, wherein the web elastically deforms at a value of up to about 8% along the folds.

7. The bridge member of claim 1, wherein the web is subjected to a stress of about 733×10⁸N/m².

8. A method of blocking a tubular comprising:

(a) providing a bridge plug assembly comprising: a mandrel, a bulbous membrane circumscribing the mandrel and formed from a superelastic material, a pair of end collars coupled on each end of the bridge member and circumscribing the mandrel

(b) configuring the membrane for travel within a tubular by rotating one of the collars with respect to the other collar and elastically forming folds within the membrane thereby drawing the membrane radially inward toward the mandrel;

(c) retaining a resistive force on the said one of the collars thereby elastically maintaining stress along the folds in the membrane;

(d) inserting the bridge plug assembly into the tubular,

(e) releasing the resistive force on the said one of the collars, so that the elastically maintained stress unfolds and expands the membrane to the configuration of step (a) to block the tubular.

9. The method of claim 8 further comprising, repeating step (b) and removing the bridge plug assembly from the tubular.

10. The method of claim 8, wherein the bridge plug assembly further comprises ribs coupled with the membrane that are substantially aligned with the mandrel in step (a) and oblique with the mandrel in one of steps (b)-(d).

11. The method of claim 8, wherein the membrane comprises material that includes an alloy having nickel of about 55% to about 57% by weight and titanium of about 45% to about 43% by weight.

12. The method of claim 8, further comprising injecting liquid into the membrane.

13. The method of claim 8, wherein step (b) further comprises preloading the bridge member.

14. The method of claim 8 wherein the tubular is within a wellbore.

15. The method of claim 8 wherein undulations are defined along outer circumference of the membrane.

16. The method of claim 8, wherein the folds in step (b) are alternatingly facing

17. A bridge plug assembly comprising:

a bulbous and substantially hollow member that is formed from a superelastic material and comprising a membrane having a series of strategically located foldable regions;

a mandrel circumscribed by the member; and

a pair of spaced apart and annularly shaped ends that circumscribe the mandrel and are coupled to opposing ends of the member, so that when a rotational force is applied to one of the ends with respect to the other end, the outer diameter of the member reduces and folds form along the foldable regions that retain therein at least a portion of the force applied to said one of the ends

18. The bridge plug assembly of claim 17, wherein the annularly shaped ends comprise a first annularly shaped end and a second annularly shaped end and the member further comprises elongated ribs coupled with the membrane that project from the first annularly shaped end into engagement with the second annularly shaped end, wherein the ribs are substantially parallel with the mandrel and oblique with the mandrel after the rotational force is applied to one of the ends.

19. The bridge plug assembly of claim 17 wherein the membrane comprises material having a nickel titanium alloy.

20. The bridge plug assembly of claim 17, wherein the member comprises segments joined together, each segment having a raised mid, portion aligned with the mandrel so that the outer circumference of the member defines an undulating surface.