Patent ID: 12203349

DETAILED DESCRIPTION

The present disclosure relates to a two-stage expandable liner hanger that includes two independently expandable tubular portions with different configurations of engagement members for engaging a casing or wellbore. The expandable portions may be coupled end to end and disposed one above the other in a wellbore and may be referred to interchangeably in any of the various examples as first and second portions, top and bottom portions, upper and lower portions, and so forth, respectively. In an example, a top portion includes one or more engagement members which may further include any of a variety of anchoring member configurations discussed below (e.g., vertical or helical anchoring ribs), either continuous or segmented, aligned or offset. These anchoring members provide for anchoring the liner hanger to the casing by biting engagement with the casing in response to expansion of the hanger, while radially spacing the casing from the liner hanger sufficiently to allow cement to pass between the liner hanger and casing. A bottom portion (i.e., lower portion or bottom portion) is also expandable, and includes another type of engagement member referred to as gripping and/or sealing member(s). These gripping and/or sealing members may frictionally engage the casing to provide grip, and may also provide a seal, such as metal to metal (“MTM”) seal with the casing after expansion.

A running tool may be assembled with the two-stage expandable hanger, creating a hanger system. Once the system reaches a setting depth, the running tool expands the first portion (e.g., the top portion) of the liner hanger to push anchoring members (e.g., anchoring ribs) of the hanger outward, thereby anchoring the hanger onto the inner diameter (“ID”) of the casing. The running tool may then be released from the hanger and cementing the liner may begin. With the benefit of the anchoring ribs disposed on the expanded first portion, the cement may flow through the space between the ribs, ensuring that the cement has passed from the bottom of the liner to the top of the hanger. Once the cementing is done the running tool is reengaged into the hanger. The running tool then expands the remaining portion of the hanger, completing the installation of the two-stage liner hanger.

Other examples may include fluid passageways through a wall of the liner hanger and disposed between the first portion and the remaining portion of the expandable body of the hanger. In further examples, the fluid passageways may be disposed in the middle of the expandable body of the hanger. The running tool may be installed in the hanger and may expand the top portion to engage the anchoring members disposed above the fluid passageways against the casing. Once the cone (running tool) reaches the fluid passageways of the hanger, the expansion stops, thereby preserving fluid communication through the fluid passageways, and the running tool is retrieved. Cement may then be pumped down the liner (e.g., with a slickjoint and packoff) and back to the hanger top via the fluid passageways, allowing complete cementing of the whole liner. Once cementing is done, the remaining portion of the hanger is expanded.

The techniques as described herein may be directed to cemented liner applications which utilize axial load bearing assemblies in conjunction with an expandable liner hanger. In some examples, the configuration of the load bearing assemblies in relation to the expandable liner hanger may allow for intrusion of cement into the annular space of one or more load bearing assemblies. In further examples, the one or more load bearing assemblies may maintain an annular conduit for cement flow-through while expanded to engage with a casing or wellbore. Other examples include independently gripping and sealing the liner hanger (expanded) against a casing or wellbore wall while allowing for cement coverage across the length of the expandable liner hanger. Some configurations may include gripping and sealing engagement between telescoped tubulars while allowing for cement passage.

FIG.1Aillustrates an expandable liner hanger system10in accordance with examples of the present disclosure. The description is provided with reference to a vertical wellbore; however, the embodiments disclosed herein can be used in horizontal, vertical or deviated wellbores. In the system10, a casing string12has been installed and cemented within a wellbore14. A liner16is to be hung, extending downhole from a lower end of the casing string12. A liner assembly, which may be relayed into wellbore14using a work string20, may include at least a liner hanger assembly22and liner16. When the liner assembly is disposed in wellbore14, but before the hanger is engaged, there exists an annulus18between casing string12and liner16, casing string12and work string20, and casing string12and liner hanger assembly22. Liner hanger assembly22includes at least an upper section of the liner hanger assembly24and a lower section of the liner hanger assembly26. Liner hanger assembly22may further include a section that extends above upper section24, a section that extends between upper section24and lower section26, and a section that extends below lower section26. In some examples, liner16may extend below lower section26or may extend below the section that extends below lower section26. Liner hanger assembly22can support additional wellbore casing, operational tubulars or tubing strings, completion strings, downhole tools, etc., for positioning at greater depths.

As used herein, the terms “liner,” “casing,” and “tubular” are used generally to describe tubular wellbore items, used for various purposes in wellbore operations. Liners, casings, and tubulars can be made from various materials (metal, plastic, composite, etc.), can be expanded or unexpanded as part of an installation procedure, and can be segmented or continuous. It is not necessary for a liner or casing to be cemented into position. Any type of liner, casing, or tubular may be used in keeping with the principles of the present disclosure.

As depicted inFIG.1A, liner hanger22is used to seal and secure an upper end of liner16near a lower end of the casing string12. Alternatively, liner hanger assembly22could be used to seal and secure the upper end of liner16above a window (not shown) formed through a sidewall of casing string12, with the liner extending outwardly through the window into a branch or lateral wellbore. Thus, it will be appreciated that many different configurations and relative positions of the casing string12and liner16are possible in keeping with the principles of the disclosure.

A setting tool28is disposed proximate liner hanger assembly22on work string20. In some examples, setting tool28may include an expansion cone29. Work string20may be used to convey setting tool28, liner hanger assembly22, and liner16into wellbore14. Work string20may further be used to conduct fluid pressure and flow, transmit torque, tensile and compressive force, etc. Setting tool28is used to facilitate conveyance and installation of the liner16and liner hanger assembly22, in part by using the torque, tensile, and compressive forces, fluid pressure and flow, as delivered by work string20.

The liner hanger assembly22is shown with generic gripping and/or sealing members30positioned on and attached to the liner hanger22. These gripping and/or sealing members30may comprise, for example, an elastomeric sealing element or a metallic region capable of metal-to-metal sealing contact with the casing when expanded. In some examples, one or more gripping and/or sealing members30may be disposed on the exterior surface of lower section26of liner hanger assembly22.

With additional reference toFIG.1B(a cross sectional view31ofFIG.1A), the upper section24of liner hanger assembly22includes one or more anchoring members, embodied in this example as anchoring ribs32, which may be disposed on the exterior surface of liner hanger assembly22. As depicted inFIG.1A, anchoring ribs32may include extrusions on the exterior surface of liner hanger which project radially outwardly and extend continuously or segmented along at least a portion of upper section24of liner hanger assembly22. The length of anchoring ribs32along the exterior longitudinal surface of liner hanger assembly22, as well as the width and spacing of anchoring ribs32around the exterior circumference of liner hanger assembly22, may vary according to application. In some examples, anchoring ribs32may be spaced circumferentially around the exterior surface of upper section24of liner hanger assembly22. As will be discussed below, various spacing schemes may be employed to orient and place anchoring ribs32on the exterior surface of linger hanger assembly22.

The tubular body of upper section24of liner hanger assembly22may be an expandable tubular34. Anchoring ribs32may be compacted or engaged into the interior surface of casing string12as the extrusion cone29of setting tool28is progressed along the length of upper section24of liner hanger assembly22. In such examples, anchoring ribs32may anchor upper section24of liner hanger assembly22into the interior surface of casing string12. As previously mentioned, anchoring ribs32may engage with the inner surface of a tubular disposed in wellbore14(for example, the interior surface of casing string12) by biting engagement. The method of engaging gripping and/or sealing members30may be similar to the method of engaging anchoring members such as anchoring ribs32in terms of expanding the respective portion of the expandable tubular to bring into engagement with the casing. However, the way sealing and/or gripping members engage with the interior surface of casing string12may be different. For example, anchoring members may bite into the casing in response to expansion, plastically deforming the material of the casing at the location of contact, and may be axially and/or circumferentially spaced. By contrast, sealing and/or gripping members may frictionally engage the casing, and may form a continuous, i.e., 360-degree circumferential/annular seal with the casing. In some examples anchoring ribs32and gripping and/or sealing members30may differ in their anchoring pattern and construction materials. When lower section26of liner hanger assembly22is expanded, such as with an expansion cone29of setting tool28, into gripping, sealing, and/or anchoring engagement with the casing, the external gripping and sealing members24sealingly, grippingly, and/or anchoringly engage the interior of the casing string12. These elements are discussed more fully below.

FIG.2A-2Cdisplay different view of upper section24of liner hanger assembly22, where anchoring ribs32have the same anchoring pattern.FIG.2Adepicts an example of liner hanger assembly22with an exposed longitudinal cross section of upper section24. As depicted, anchoring ribs32ofFIG.2Aare broken into segments along the longitudinal length of upper section24of liner hanger assembly22.FIG.2B, a cross-sectional35view ofFIG.2A, displays eight anchoring ribs32spaced equidistant in the circumferential direction of upper section24of liner hanger assembly22. In some examples, the layout of anchoring ribs32ofFIG.2AandFIG.2Cmay be described as “castellated,” in that, the anchoring ribs32are segmented, and the resulting segments are axially separated to define grooves36therebetween which may be patterned intermittently along the longitudinal length of upper section24of liner hanger assembly22. InFIG.2C, for example, anchoring ribs32and grooves36are disposed on expandable tubular34and are respectively aligned in the circumferential direction (e.g., along the circumference) such that the grooves36are located between anchoring ribs32in the longitudinal direction. Grooves36form continuous grooved sections, or rings38, in the circumferential direction on expandable tubular34. In further examples, rings38are parallel to the transverse plane of expandable tubular34which makes up the body of liner hanger assembly22. In some examples, grooves36which run both longitudinally to form longitudinal groove40and circumferentially along upper section24of liner hanger assembly22, may provide a flow conduit for cementing operations. The number and spacing of anchoring ribs32in the circumferential direction of upper section24of liner hanger assembly22may vary. For example, whileFIG.2B, a cross-sectional view ofFIG.2A, displays eight anchoring ribs32spaced equidistant in the circumferential direction of liner hanger assembly22, other counts and arrangements of anchoring ribs32will be apparent to those of skill in the art.

FIG.2Ddepicts what may described as a “staggered castellated,” anchoring pattern. In comparison to the castellated anchoring pattern, anchoring ribs32and grooves36of the staggered castellated anchoring pattern are disposed on expandable tubular34such that they are longitudinally translated relative to the location of the longitudinal set of anchoring ribs32in the lateral direction. In some examples, the pattern of anchoring ribs32may be disposed on expandable tubular34in a spiral or helical shape as depicted inFIG.2E. For example, the pathway of grooved section44ofFIG.2Emay be aligned at any angle other than parallel to the transverse plane of liner hanger assembly22. In further examples, there may be a groove46which runs parallel to the longitudinal axis of liner hanger assembly22. In some examples, groove46may be staggered or translated in the circumferential direction such that it does not create a continuous flow path in the longitudinal direction. With respect toFIGS.2A-2E, in some examples anchoring ribs32may be a subassembly of the expandable tubular which makes up part of the structure of upper section24of liner hanger assembly22. In some examples, anchoring ribs32may be integrally molded with the expandable tubular. In other examples, anchoring ribs32may be molded or directly machined. In further examples, anchoring ribs32may be created by additive manufacturing.

FIG.3depicts lower section26of the liner hanger assembly (e.g., liner hanger assembly22inFIG.1). In some examples, lower section26of the liner hanger assembly may include one or more gripping and/or sealing members (e.g., gripping and/or sealing members30inFIG.1). In some examples, and as shown inFIG.3, the gripping and/or sealing members may include anchoring ridges60and/or sealing members62. In some examples, sealing members62may be elastomeric or may include a bonded elastomeric material. Anchoring ridges60and/or sealing members62may be disposed on an expandable tubular64. When expanded, anchoring ridges60may create a metal-to-metal seal against the inner surface of a wellbore casing, wellbore tubular, or wellbore liner. In some examples, anchoring ridges60may provide improved sealing performance at elevated temperatures. Additionally, anchoring ridges60and/or sealing members62may be sub-assemblies of expandable tubular64such that the inner diameters of anchoring ridges60and/or sealing members62may abut the outer diameter of expandable tubular64. WhileFIG.3may depict four anchoring ridges60disposed between two sealing members62, there may be any number of anchoring ridges60spaced between sealing members62. Furthermore, anchoring ridges60need not be spaced equidistant within the space between sealing members62. Across the longitudinal length of lower section26of the liner hanger assembly, there may be any number, organization, configuration, or spacing of sealing members62and anchoring ridges60.

With reference toFIGS.4A-4D, liner16and liner hanger assembly22may be relayed into wellbore14using work string20and setting tool28. Once liner hanger assembly22is aligned with a target placement depth in wellbore14, the installation process may proceed. Prior to commencing the installation process, expansion cone29of setting tool28may be located up hole from (i.e., above) both top section24and bottom section26of liner hanger assembly22. At the widest point, the expansion cone29may be of a diameter such that, once it traverses the longitudinal extent of the radially expandable pipe body which contains top section24and bottom section26, the exterior surface of the expandable pipe may be rendered flush with the inner surface of the tubular in which it is disposed (e.g., casing string12ofFIG.1). Therefore, it may be desirable to retain expansion cone29in a position that prevents even partial expansion of liner hanger assembly22until liner16and liner hanger assembly22are located at an acceptable location or depth for installation. During the installation process, top section24of liner hanger assembly22may be expanded prior to expanding bottom section26of liner hanger assembly22. As depicted inFIG.4B, progressing expansion cone29through the length of top section24of liner hanger assembly22may result in the radial expansion of top section24of liner hanger assembly22. In some examples, inducing radial expansion in top section24of liner hanger assembly22involves pushing expansion cone29from a depth at or above top section24to a depth at or below top section24. Anchoring ribs32, which extend circumferentially around expandable tubular34, may anchor into the inner surface13of casing string12. This may affix top section24of liner hanger assembly22to casing string12which may secure the position of liner16and liner hanger assembly22in wellbore14. Once expanded, top section24of liner hanger assembly22may at least partially support the axial load of liner16and liner hanger assembly22such that work string20and setting tool28, along with expansion cone29may be removed from wellbore14in a process which may be known as “pulling out of hole,” or “tripping out of hole.”

As depicted inFIG.4C, cement may be pumped into the wellbore to provide annular isolation and seal off the annular space (e.g., annulus18ofFIG.1) that is formed between the inner surface13of casing string12and an external surface of liner hanger assembly22and liner16. In some examples, the annular space may include the area between an outer surface of liner16a rockface of a subterranean formation which may be exposed during drilling, the area between the outer surface of liner hanger assembly22and the inner surface13of casing string12, and/or the area between the outer surface of liner hanger assembly22and the inner surface of any other tubular which may be disposed in wellbore14. The cement slurry70may be pumped down both the inner diameter of liner hanger assembly22and liner16before progressing into and up the annular space. The required volume of cement slurry70may be calculated or pre-determined in accordance with the diameter of the wellbore and the casing design. In some examples a spacer fluid (not shown) may be pumped ahead of and/or behind cement slurry70. The spacer fluid may allow for both the proper placement of cement slurry70as well as preventing cement slurry70from contacting any displaced fluids which were utilized during the drilling process. While anchoring ribs32, may be flush with the wall of inner surface13of casing string12, the grooves (e.g., grooves36, ring38, and longitudinal groove40as depicted inFIG.2C) may provide a conduit through which cement slurry70may flow. For example, flow path72depicts that cement slurry70may flow past top section24of liner hanger assembly22. After cement slurry70has been placed in the annular space (e.g., annulus18ofFIG.1), setting tool28and expansion cone29may be returned to wellbore14in a process that may be known as “running in hole,” or “tripping in hole.” Prior to cementing, expansion cone29may only be utilized to only create radial expansion within upper section24of liner hanger assembly22. After cementing, and as depicted inFIG.4D, expansion cone29may be extended through the remainder of liner hanger assembly22thereby radially expanding lower section26of liner hanger assembly22. Upon the expansion of lower section26, anchoring ridges60and/or sealing members62may engage with the inner surface of casing string12. In some examples, anchoring ridges60may form a metal-to-metal seal with the inner surface of casing string12. In further examples, either a portion or all of liner16, which is located downhole, or below the bottom of lower section26of liner hanger assembly22may be expanded. However, in some examples, only top section24and bottom section26of liner hanger assembly are radially expanded using expansion cone29.

As depicted inFIG.5A, liner hanger assembly22may include one or more fluid passageways80which may fluidically connect the internal portion82of liner hanger assembly22with annulus18. While fluid passageways80may include any conduit that allows for the transport of fluid between internal portion82of liner hanger assembly22and annulus18, some non-limiting examples may include perforations, ports, and/or slots.FIG.5Amay depict such fluid passageways80as being disposed in the body of expandable tubular34between upper section24and lower section26of liner hanger assembly22.

With reference toFIGS.5A-5D, liner16and liner hanger assembly22may be relayed into wellbore14using work string20and setting tool28. Once liner hanger assembly22is aligned with a target placement depth in wellbore14, the installation process may proceed. Prior to commencing the installation process, expansion cone29of setting tool28may be located up hole from (i.e., above) both top section24and bottom section26of liner hanger assembly22. At the widest point, expansion cone29may be of a diameter such that, once it traverses the longitudinal extent of the radially expandable pipe body (e.g., liner hanger assembly22and/or liner16), the exterior surface of the expandable pipe may be rendered flush with the inner surface of the tubular in which it is disposed (e.g., casing string12ofFIG.1). Therefore, it may be desirable to retain expansion cone29in a position that prevents even partial expansion of liner hanger assembly22until liner16and liner hanger assembly22are located at an acceptable location or depth for installation. During the installation process, top section24of liner hanger assembly22may be expanded prior to expanding bottom section26of liner hanger assembly22. In some examples, fluid passageways80may be disposed between top section24and bottom section26of liner hanger assembly22. As depicted inFIG.5B, the progression of expansion cone29through top section24of liner hanger assembly22may result in the radial expansion of top section24of liner hanger assembly22. In some examples, the radial expansion of top section24of liner hanger assembly22may include progressing expansion cone29beyond the depth at which flow passageways80are located. In further examples, the radial expansion of expandable tubular34for top section24of liner hanger assembly22includes expanding the portion of expandable tubular34on which fluid passageways80are disposed. Anchoring ribs32, which extend circumferentially around expandable tubular34, may anchor into the inner surface13of casing string12. This may affix top section24of liner hanger assembly22to casing string12which may secure the position of liner16and liner hanger assembly22in wellbore14. In the radially expanded position, top section24of liner hanger assembly22may at least partially support the axial load of liner16and liner hanger assembly22.

As depicted inFIG.5C, cement may be pumped into the wellbore to provide annular isolation and seal off the annular space (e.g., annulus18ofFIG.1) that is formed between the inner surface13of casing string12and an external surface of liner hanger assembly22and liner16. In some examples, the annular space may include the area between an outer surface of liner16a rockface of a subterranean formation which may be exposed during drilling, the area between the outer surface of liner hanger assembly22and the inner surface13of casing string12, and/or the area between the outer surface of liner hanger assembly22and the inner surface of any other tubular which may be disposed in wellbore14. The cement slurry70may be pumped down the inner diameter of work string20before progressing into and up the annular space (e.g., annulus18ofFIG.1). An isolation packer86may be engaged with the inner surface of liner16to ensure that cement slurry70progresses up annulus18rather than entering the annular space created between the outer surface of work string20and the inner surface of liner16. In some examples a spacer fluid (not shown) may be pumped ahead of and/or behind cement slurry70. The spacer fluid may allow for both the proper placement of cement slurry70as well as preventing cement slurry70from contacting any displaced fluids which were utilized during the drilling process. As illustrated inFIG.5C, a space fluid and/or cement slurry70may progress through fluid passageways80once they have progressed up the length of the annular space (e.g., annulus18inFIG.1). The required volume of cement slurry70may be calculated or pre-determined in accordance with the diameter of the wellbore and the casing design. While anchoring ribs32, may be flush with the wall of wellbore14, the grooves (e.g., grooves36, ring38, and longitudinal groove40as depicted inFIG.2C) may provide a conduit through which cement slurry70may flow. For example, flow path72depicts that cement slurry70may flow through the annular space of the top section24of liner hanger assembly22. After cement slurry70has been placed in the annular space (e.g., annulus18ofFIG.1), setting tool28and expansion cone29may be returned to wellbore14in a process that may be known as “running in hole,” or “tripping in hole.” Prior to cementing, expansion cone29was utilized to only create radial expansion within upper section24of liner hanger assembly22. After cementing, and as depicted inFIG.5D, expansion cone29may be extended through the remainder of liner hanger assembly22thereby radially expanding lower section26of liner hanger assembly22. Upon the expansion of lower section26, anchoring ridges60and/or sealing members62may engage with the inner surface of casing string12. In some examples, anchoring ridges60may form a metal-to-metal seal with the inner surface of casing string12. Due to the flow paths created by grooves36located between the anchoring ribs32in upper section24of liner hanger assembly22, cement slurry70may be disposed in the annular space (e.g., annulus18inFIG.1) between the exterior surface of upper section24and the inner surface of the wellbore wall. In some examples, either a portion or all of liner16, which is located downhole, or below the bottom of lower section26of liner hanger assembly22may be expanded. However, in some examples, only top section24and bottom section26of liner hanger assembly are radially expanded using expansion cone29.

Accordingly, the systems and methods of the present disclosure allow for improvements over the current technology comprising increased cement coverage over the length of an expandable liner hanger. In some examples, the improvements may provide for full cement coverage across the length of an expandable liner hanger. The methods may include any of the various features disclosed herein, including one or more of the following statements.

Statement 1. A method comprises expanding a first section of an expandable tubular comprising the first section and a second section, wherein the first section comprises one or more anchoring ribs; and expanding the second section of the expandable tubular after cement is pumped into the expandable tubular.

Statement 2. The method of statement 1, wherein the expandable tubular is disposed in a wellbore.

Statement 3. The method of any of the foregoing statements, wherein the first section of the expandable tubular is expanded with a setting tool.

Statement 4. The method of any of the foregoing statements, wherein the second section of the expandable tubular is expanded with the setting tool.

Statement 5. The method of any of the foregoing statements, wherein expanding the first section of the expandable tubular further comprises disposing a setting tool in a wellbore and extending the setting tool through the first section of the expandable tubular.

Statement 6. The method of any of the foregoing statements, further comprising removing the setting tool from the wellbore before the cement is pumped into the expandable tubular.

Statement 7. The method of any of the foregoing statements, wherein the cement is pumped through the expandable tubular while the setting tool is disposed in the wellbore.

Statement 8. The method of any of the foregoing statements, wherein a fluid passageway is disposed between the first section and the second section.

Statement 9. The method of any of the foregoing statements, further comprising allowing cement to flow through the fluid passageway.

Statement 10. The method of any of the foregoing statements, wherein the second section of the expandable tubular further comprises one or more anchoring ridges, sealing members, or combinations thereof.

Statement 11. The method of any of the foregoing statements, wherein the second section is configured to create a metal-to-metal seal with the interior surface of a tubular.

Statement 12. A two-stage expandable liner hanger, comprising a first tubular portion of a liner hanger positionable inside a casing in a wellbore and having a first set of engagement members on an exterior surface, the first tubular portion being expandable for engagement of the first set of engagement members with the casing; and a second tubular portion of the liner hanger coupled to the first tubular portion and having a second set of engagement members on an exterior surface having a different configuration than the first set of engagement members, the second tubular portion being expandable independently of the first tubular portion for engagement of the second set of engagement members with the casing.

Statement 13. The two-stage expandable liner hanger of statement 12, wherein the first set of engagement members comprise anchoring members configured for biting engagement with the casing upon expansion of the first tubular portion and providing sufficient radial spacing between the first tubular portion and the casing to allow fluid flow after the expansion.

Statement 14. The two-stage expandable liner hanger of statements 12 or 13, wherein the second set of engagement members frictionally engage and circumferentially seal the casing upon expansion of the second tubular portion.

Statement 15. The two-stage expandable liner hanger of any one of the statements 12-14, wherein the anchoring members comprise vertical or helical anchoring ribs.

Statement 16. The two-stage expandable liner hanger of statement 15, wherein the vertical or helical anchoring ribs are segmented.

Statement 17. The two-stage expandable liner hanger of statement 16, wherein the segmented vertical or helical anchoring ribs have a castellated arrangement on the exterior of the first tubular portion.

Statement 18. The two-stage expandable liner hanger of claim 17, wherein the anchoring pattern is a staggered castellated anchoring pattern.

Statement 19. The expandable liner hanger of any one of the statements 12-18, further comprising a plurality of fluid passageways through a wall of the liner hanger between the first portion and the second portion providing fluid communication between an interior of the liner hanger and an annulus between the liner hanger and the casing in where the liner hanger is disposed after expansion of at least the first tubular portion.

Statement 20. The two-stage expandable liner hanger of any one of the statements 12-19, further comprising a setting tool configured for independently expanding the first tubular section prior to cementing followed by the second tubular section after cementing.

Persons of skill in the art will recognize various combinations and orders of the above described steps and details of the methods presented herein. While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments as well as other embodiments of the invention will be apparent to persons skilled in the art upon reference to the description. It is, therefore, intended that the appended claims encompass any such modifications or embodiments.