Patent Publication Number: US-2021189830-A1

Title: Reactive metal sealing elements for a liner hanger

Description:
TECHNICAL FIELD 
     The present disclosure relates to the use of reactive metal sealing elements, and more particularly, to the use of reactive metal sealing elements for sealing and anchoring liner hangers and tie-back liners in wellbore applications. 
     BACKGROUND 
     In some wellbore operations, a liner may be suspended from a casing string or set cement layer with a liner hanger. The liner hanger anchors to the interior of the casing string or set cement layer and suspends the liner below the casing string or set cement layer. The suspended liner and the liner hanger do not extend to the surface as a casing string or set cement layer may. A liner hanger forms a seal with the casing string or set cement layer to prevent fluid flow therein from outside of the suspended liner. The fluid flow may thus be directed through the liner instead. In some wellbore operations, a tie-back liner may be sealed to the liner hanger. The tie-back liner runs back to the surface and may or not be installed permanently by cementing it in place. 
     Sealing elements may be used for a variety of wellbore applications including forming annular seals in and around liner hangers and tie-back liners. The annular seal may restrict all or a portion of fluid and/or pressure communication at the seal interface. These sealing elements may seal and anchor the liner hangers and tie-back liners to the adjacent surface such as the casing, set cement layer, or to the liner hanger in the case of tie-back liners. Some species of sealing elements comprise swellable materials that may swell if contacted with specific swell-inducing fluid. 
     Many species of the aforementioned swellable materials comprise elastomers. Elastomers, such as rubber, swell when contacted with a swell-inducing fluid. The swell-inducing fluid may diffuse into the elastomer where a portion may be retained within the internal structure of the elastomer. Swellable materials such as elastomers may be limited to use in specific wellbore environments (e.g., those without high salinity and/or high temperatures). The present disclosure provides improved apparatus and methods for forming seals in wellbore applications.    
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Illustrative examples of the present disclosure are described in detail below with reference to the attached drawing figures, which are incorporated by reference herein, and wherein: 
         FIG. 1  is a cross-section illustrating an example tubing system for a wellbore penetrating a subterranean formation in accordance with the examples disclosed herein; 
         FIG. 2  is an enlarged cross-section illustrating a portion of the example tubing system of  FIG. 1  in accordance with the examples disclosed herein; 
         FIG. 3A  is a cross-section of an expandable liner hanger in accordance with the examples disclosed herein; 
         FIG. 3B  is a cross-section of the expandable liner hanger of  FIG. 3A  after a portion of it is expanded in accordance with the examples disclosed herein; 
         FIG. 4  is an isometric illustration of a liner hanger in accordance with the examples disclosed herein; 
         FIG. 5  is a cross-section illustrating an example tubing system for a wellbore penetrating a subterranean formation in accordance with the examples disclosed herein; 
         FIG. 6  is an enlarged cross-section illustrating a portion of the example tubing system of  FIG. 5  in accordance with the examples disclosed herein; 
         FIG. 7A  is a cross-section illustration of a tie-back liner in the process of being fitted with a reactive metal sealing element in accordance with the examples disclosed herein; and 
         FIG. 7B  is a cross-section illustration of a tie-back liner having a reactive metal sealing element fitted and swaged thereon in accordance with the examples disclosed herein. 
     
    
    
     The illustrated figures are only exemplary and are not intended to assert or imply any limitation with regard to the environment, architecture, design, or process in which different examples may be implemented. 
     DETAILED DESCRIPTION 
     The present disclosure relates to the use of reactive metal sealing elements, and more particularly, to the use of reactive metal sealing elements for sealing and anchoring liner hangers and tie-back liners in wellbore applications. 
     In the following detailed description of several illustrative examples, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration examples that may be practiced. These examples are described in sufficient detail to enable those skilled in the art to practice them, and it is to be understood that other examples may be utilized and that logical structural, mechanical, electrical, and chemical changes may be made without departing from the spirit or scope of the disclosed examples. To avoid detail not necessary to enable those skilled in the art to practice the examples described herein, the description may omit certain information known to those skilled in the art. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the illustrative examples is defined only by the appended claims. 
     Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and so forth used in the present specification and associated claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the examples of the present disclosure. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claim, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. It should be noted that when “about” is at the beginning of a numerical list, “about” modifies each number of the numerical list. Further, in some numerical listings of ranges some lower limits listed may be greater than some upper limits listed. One skilled in the art will recognize that the selected subset will require the selection of an upper limit in excess of the selected lower limit. 
     Unless otherwise specified, any use of any form of the terms “connect,” “engage,” “couple,” “attach,” or any other term describing an interaction between elements is not meant to limit the interaction to direct interaction between the elements and may also include indirect interaction between the elements described. Further, any use of any form of the terms “connect,” “engage,” “couple,” “attach,” or any other term describing an interaction between elements includes items integrally formed together without the aid of extraneous fasteners or joining devices. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to.” Unless otherwise indicated, as used throughout this document, “or” does not require mutual exclusivity. 
     The terms uphole and downhole may be used to refer to the location of various components relative to the bottom or end of a well. For example, a first component described as uphole from a second component may be further away from the end of the well than the second component. Similarly, a first component described as being downhole from a second component may be located closer to the end of the well than the second component. 
     Examples of the methods and systems described herein relate to the use of reactive metal sealing elements comprising reactive metals. As used herein, “sealing elements” refers to any element used to form a seal. A “seal” is a barrier to the passage of a liquid and/or gas. In some examples, the metal sealing elements described herein may form a seal that complies with the International Organization for Standardization (ISO) 14310:2001/API Specification 11D1 1 st  Edition validation standard for the Grade V5: Liquid Test. The reactive metals expand by contacting specific reaction-inducing fluids to produce a reaction product having a larger volume than the base reactive metal reactant. The increase in metal volume of the reaction product creates a seal at the interface of the reactive metal sealing element and any adjacent surface. By “expand,” “expanding,” or “expandable” it is meant that the reactive metal sealing element increases its volume as the reactive metal reacts with a reaction-inducing fluid, such as a brine, thereby inducing the formation of the reaction products. Formation of the reaction products results in the volumetric expansion of the reactive metal sealing element. Advantageously, the reactive metal sealing elements may be used in a variety of wellbore applications where an irreversible seal is desired. Yet a further advantage is that the reactive metal sealing elements may swell in high-salinity and/or high-temperature environments that may be unsuitable for some other species of sealing elements. An additional advantage is that the reactive metal sealing elements comprise a wide variety of metals and metal alloys and may expand upon contact with reaction-inducing fluids, including a variety of wellbore fluids. The reactive metal sealing elements may be used as replacements for other types of sealing elements (e.g., elastomeric sealing elements), or they may be used as backups for other types of sealing elements. One other advantage is that the reactive metal sealing elements may be placed on an existing liner hanger or tie-back liner without impact to or adjustment of the liner hanger or tie-back liner&#39;s outer diameter or exterior profile. Another advantage is that the reactive metal sealing elements may be used on a variety of liner hangers including expandable, non-expandable, and drop-off species. 
     The reactive metals expand by undergoing a reaction in the presence of a reaction-inducing fluid (e.g., a brine) to form a reaction product (e.g., metal hydroxides). The resulting reaction products occupy more volumetric space relative to the base reactive metal reactant. This difference in volume allows the reactive metal sealing element to form a seal at the interface of the reactive metal sealing element and any adjacent surfaces. Magnesium may be used to illustrate the volumetric expansion of the reactive metal as it undergoes reaction with the reaction-inducing fluid. A mole of magnesium has a molar mass of 24 g/mol and a density of 1.74 g/cm 3 , resulting in a volume of 13.8 cm 3 /mol. Magnesium hydroxide, the reaction product of magnesium and an aqueous reaction-inducing fluid, has a molar mass of 60 g/mol and a density of 2.34 g/cm 3 , resulting in a volume of 25.6 cm 3 /mol. The magnesium hydroxide volume of 25.6 cm 3 /mol is an 85% increase in volume over the 13.8 cm 3 /mol volume of the mole of magnesium. As another example, a mole of calcium has a molar mass of 40 g/mol and a density of 1.54 g/cm 3 , resulting in a volume of 26.0 cm 3 /mol. Calcium hydroxide, the reaction product of calcium and an aqueous reaction-inducing fluid, has a molar mass of 76 g/mol and a density of 2.21 g/cm 3 , resulting in a volume of 34.4 cm 3 /mol. The calcium hydroxide volume of 34.4 cm 3 /mol is a 32% increase in volume over the 26.0 cm 3 /mol volume of the mole of calcium. As yet another example, a mole of aluminum has a molar mass of 27 g/mol and a density of 2.7 g/cm 3 , resulting in a volume of 10.0 cm 3 /mol. Aluminum hydroxide, the reaction product of aluminum and an aqueous reaction-inducing fluid, has a molar mass of  63  g/mol and a density of 2.42 g/cm 3  resulting in a volume of 26 cm 3 /mol. The aluminum hydroxide volume of 26 cm 3 /mol is a 160% increase in volume over the 10 cm 3 /mol volume of the mole of aluminum. The reactive metal may comprise any metal or metal alloy that undergoes a reaction to form a reaction product having a greater volume than the base reactive metal or alloy reactant. 
     Examples of suitable metals for the reactive metal include, but are not limited to, magnesium, calcium, aluminum, tin, zinc, beryllium, barium, manganese, or any combination thereof. Preferred metals include magnesium, calcium, and aluminum. 
     Examples of suitable metal alloys for the reactive metal include, but are not limited to, alloys of magnesium, calcium, aluminum, tin, zinc, beryllium, barium, manganese, or any combination thereof. Preferred metal alloys include alloys of magnesium-zinc, magnesium-aluminum, calcium-magnesium, or aluminum-copper. In some examples, the metal alloys may comprise alloyed elements that are not metallic. Examples of these non-metallic elements include, but are not limited to, graphite, carbon, silicon, boron nitride, and the like. In some examples, the metal is alloyed to increase reactivity and/or to control the formation of oxides. 
     In some examples, the metal alloy is also alloyed with a dopant metal that promotes corrosion or inhibits passivation and thus increases hydroxide formation. Examples of dopant metals include, but are not limited to nickel, iron, copper, carbon, titanium, gallium, mercury, cobalt, iridium, gold, palladium, or any combination thereof. 
     In some examples, the reactive metal comprises an oxide. As an example, calcium oxide reacts with water in an energetic reaction to produce calcium hydroxide. One mole of calcium oxide occupies 9.5 cm 3  whereas one mole of calcium hydroxide occupies 34.4 cm 3 . This is a 260% volumetric expansion of the mole of calcium oxide relative to the mole of calcium hydroxide. Examples of metal oxides suitable for the reactive metal may include, but are not limited to, oxides of any metals disclosed herein, including magnesium, calcium, aluminum, iron, nickel, copper, chromium, tin, zinc, lead, beryllium, barium, gallium, indium, bismuth, titanium, manganese, cobalt, or any combination thereof. 
     It is to be understood that the selected reactive metal is chosen such that the formed reactive metal sealing element does not dissolve or otherwise degrade in the reaction-inducing fluid. As such, the use of metals or metal alloys for the reactive metal that form relatively insoluble reaction products in the reaction-inducing fluid may be preferred. As an example, the magnesium hydroxide and calcium hydroxide reaction products have very low solubility in water. As an alternative or an addition, the reactive metal sealing element may be positioned and configured in a way that constrains the degradation of the reactive metal sealing element in the reaction-inducing fluid due to the geometry of the area in which the reactive metal sealing element is disposed. This may result in reduced exposure of the reactive metal sealing element to the reaction-inducing fluid, but may also reduce degradation of the reaction product of the reactive metal sealing element, thereby prolonging the life of the formed seal. As an example, the volume of the area in which the sealing element is disposed may be less than the potential expansion volume of the volume of reactive metal disposed in said area. In some examples, this volume of area may be less than as much as 50% of the expansion volume of reactive metal. Alternatively, this volume of area may be less than 90% of the expansion volume of reactive metal. As another alternative, this volume of area may be less than 80% of the expansion volume of reactive metal. As another alternative, this volume of area may be less than 70% of the expansion volume of reactive metal. As another alternative, this volume of area may be less than 60% of the expansion volume of reactive metal. In a specific example, a portion of the reactive metal sealing element may be disposed in a recess within the conduit body of the liner hanger or tie-back liner to restrict the exposure area to only the surface portion of the reactive metal sealing element that is not disposed in the recess. 
     In some examples, the formed reaction products of the reactive metal reaction may be dehydrated under sufficient pressure. For example, if a metal hydroxide is under sufficient contact pressure and resists further movement induced by additional hydroxide formation, the elevated pressure may induce dehydration of the metal hydroxide to form the metal oxide. As an example, magnesium hydroxide may be dehydrated under sufficient pressure to form magnesium oxide and water. As another example, calcium hydroxide may be dehydrated under sufficient pressure to form calcium oxide and water. As yet another example, aluminum hydroxide may be dehydrated under sufficient pressure to form aluminum oxide and water. 
     The reactive metal sealing elements may be formed in a solid solution process, a powder metallurgy process, or through any other method as would be apparent to one of ordinary skill in the art. Regardless of the method of manufacture, the reactive metal sealing elements may be slipped over the liner hanger mandrel or tie-back liner mandrel and held in place via any sufficient method. The pressure reducing metal element may be placed over the mandrel in one solid piece or in multiple discrete pieces. Once in place, the reactive metal sealing element is held in position with end rings, stamped rings, retaining rings, fasteners, adhesives, set screws, or any other such method for retaining the reactive metal sealing element in position. As discussed above, the reactive metal sealing elements may be formed and shaped to fit over existing liner hangers and tie-back liners and thus may not require modification of the outer diameter or profile of the liner hanger or tie-back liner. Alternatively, the liner hanger or tie-back liner may be manufactured to comprise a recess in which the reactive metal sealing element may be disposed. The recess may be of sufficient dimensions and geometry to retain the reactive metal sealing elements in the recess. In alternative examples, the reactive metal sealing element may be cast onto the conduit body of the liner hanger or tie-back liner. In some alternative examples, the diameter of the reactive metal sealing element may be reduced (e.g., by swaging) when disposed on the conduit body of the liner hanger or tie-back liner. 
     In some optional examples, the reactive metal sealing element may include a removable barrier coating. The removable barrier coating may be used to cover the exterior surfaces of the sealing element and prevent contact of the reactive metal with the reaction-inducing fluid. The removable barrier coating may be removed when the sealing operation is to commence. The removable barrier coating may be used to delay sealing and/or prevent premature sealing with the reactive metal sealing element. Examples of the removable barrier coating include, but are not limited to, any species of plastic shell, organic shell, paint, dissolvable coatings (e.g., solid magnesium compounds), eutectic materials, or any combination thereof. When desired, the removable barrier coating may be removed from the sealing element with any sufficient method. For example, the removable barrier coating may be removed through dissolution, a phase change induced by changing temperature, corrosion, hydrolysis, or the removable barrier coating may be time-delayed and degrade after a desired time under specific wellbore conditions. 
     In some optional examples, the reactive metal sealing element may include an additive which may be added to the reactive metal sealing element during manufacture as a part of the composition, or the additive may be coated onto the reactive metal sealing element after manufacturing. The additive may alter one or more properties of the reactive metal sealing element. For example, the additive may improve sealing, add texturing, improve bonding, improve gripping, etc. Examples of the additive include, but are not limited to, any species of ceramic, elastomer, glass, non-reacting metal, the like, or any combination. 
     The reactive metal sealing element may be used to form a seal between any adjacent surfaces that are proximate to the reactive metal sealing elements. Without limitation, the reactive metal sealing elements may be used to form seals on casing, formation surfaces, cement sheaths or layers, and the like. For example, a reactive metal sealing element may be used to form a seal between the outer diameter of the liner hanger and a surface of an adjacent casing. Alternatively, the reactive metal sealing element may be used to form a seal between the outer diameter of the liner hanger and a surface of an adjacent set cement layer. As another example, a reactive metal sealing element may be used to form a seal between the outer diameter of the tie-back liner and a surface of an adjacent liner hanger. Moreover, a plurality of the reactive metal sealing elements may be used to form multiple seals between adjacent surfaces. 
     As described above, the reactive metal sealing elements comprise reactive metals and as such, they are non-elastomeric materials. As non-elastomeric materials, the reactive metal sealing elements do not possess elasticity, and therefore, they may irreversibly expand when contacted with a reaction-inducing fluid. The reactive metal sealing elements may not return to their original size or shape even after the reaction-inducing fluid is removed from contact. 
     Generally, the reaction-inducing fluid induces a reaction in the reactive metal to form a reaction product that occupies more space than the unreacted reactive metal. Examples of the reaction-inducing fluid include, but are not limited to, saltwater (e.g., water containing one or more salts dissolved therein), brine (e.g., saturated saltwater, which may be produced from subterranean formations), seawater, or any combination thereof. Generally, the reaction-inducing fluid may be from any source provided that the fluid does not contain an excess of compounds that may undesirably affect other components in the sealing element. In the case of saltwater, brines, and seawater, the reaction-inducing fluid may comprise a monovalent salt or a divalent salt. Suitable monovalent salts may include, for example, sodium chloride salt, sodium bromide salt, potassium chloride salt, potassium bromide salt, and the like. Suitable divalent salt can include, for example, magnesium chloride salt, calcium chloride salt, calcium bromide salt, and the like. In some examples, the salinity of the reaction-inducing fluid may exceed 10%. Advantageously, the reactive metal sealing elements of the present disclosure may not be impacted by contact with high-salinity fluids. One of ordinary skill in the art, with the benefit of this disclosure, should be readily able to select a reaction-inducing fluid for inducing a reaction with the reactive metal sealing elements. 
     The reactive metal sealing elements may be used in high-temperature formations, for example, in formations with zones having temperatures equal to or exceeding 350° F. Advantageously, the use of the reactive metal sealing elements of the present disclosure may not be impacted in high-temperature formations. In some examples, the reactive metal sealing elements may be used in both high-temperature formations and with high-salinity fluids. In a specific example, a reactive metal sealing element may be positioned on a liner hanger and used to form a seal after contact with a brine having a salinity of 10% or greater while also being disposed in a wellbore zone having a temperature equal to or exceeding 350° F. 
       FIG. 1  is a cross-section of an example tubing system, generally  5 , for a wellbore  10  penetrating a subterranean formation  15 . The tubing system  5  comprises a surface casing  20  and a surface cement sheath  25  descending from the surface  30 . The tubing system  5  further comprises an intermediate casing  35  and intermediate cement sheath  40  deployed and nested concentrically within the surface casing  20 . Although only one layer of intermediate casing  35  is illustrated, it is to be understood that more than one layer of intermediate casing  35  may be deployed in any example. A liner hanger  45  is deployed within the intermediate casing  35 . The liner hanger  45  may be used to suspend a liner  55  from within the intermediate casing  35 . The liner  55  may be any conduit suitable for suspension within the wellbore  10 . The liner hanger  45  comprises a conduit body  60 . The liner  55  is a conduit that does not run to the surface  30 . The liner hanger  45  seals within the intermediate casing  35  allowing the liner  55  to functionally act as an extension of the intermediate casing  35  without having to extend to the surface  30  as a separate casing string would. 
       FIG. 2  is an enlarged cross-section of a portion of the example tubing system  5  of  FIG. 1 . Intermediate casing  35  extends from the surface (i.e., surface  30  as illustrated in  FIG. 1 ) and may be held in place with the intermediate cement sheath  40 . Although only one layer of intermediate casing  35  is illustrated, it is to be understood that as many layers of intermediate casing  35  may be used as desired. Any subsequent layers of the intermediate casing  35  may be nested concentrically within one another within the illustrated intermediate casing  35 . The liner hanger  45  is deployed within the intermediate casing  35 . The liner hanger  45  may be any species of liner hanger and may be expandable or non-expandable. The liner hanger  45  suspends a liner (i.e., liner  55  as illustrated in  FIG. 1 ). The liner hanger  45  is anchored to the intermediate casing  35  with a reactive metal sealing element  50  after the reactive metal sealing element  50  has reacted and expanded. The reactive metal sealing element  50  is disposed on and around the conduit body  60  of the liner hanger  45 . The reactive metal sealing element  50  forms an external seal with the adjacent interior surface of the intermediate casing  35  after the reactive metal sealing element  50  has reacted and expanded. The reactive metal sealing element  50  expands after exposure to a reaction-inducing fluid. The reactive metal sealing element  50  reacts to produce the expanded metal reaction product described above. As the expanded metal reaction product has a larger volume than the unreacted expendable metal, the reactive metal sealing element  50  is able to expand and form an annular seal at the interface of the adjacent surface of the intermediate casing  35  as described above. The reactive metal sealing element  50  may continue to expand until contact with the adjacent surface is made. The formed seal prevents wellbore fluid from bypassing the liner and liner hanger  45 . 
     It should be clearly understood that the examples illustrated by  FIGS. 1-2  are merely general applications of the principles of this disclosure in practice, and a wide variety of other examples are possible. Therefore, the scope of this disclosure is not limited in any manner to the details of any of the FIGURES described herein. 
       FIG. 3A  is a cross-section of an expandable liner hanger  100 . Expandable liner hanger  100  may be deployed in a wellbore similarly to liner hanger  45  illustrated in  FIGS. 1 and 2 . Liner hanger  100  may be expanded to increase its diameter. An expansion cone  105  may be run through the interior of the liner hanger  100  to apply force to the interior surface  110  of the liner hanger  100 . The applied force may expand the conduit body  130  of the liner hanger  100  outward increasing the outer diameter of the conduit body  130  such that at least a portion of the exterior surface  135  of the conduit body  130  may contact the interior surface  140  of an adjacent casing  115 . A reactive metal sealing element  120  may be positioned around the exterior surface  135  of the liner hanger  100  and held in place with end rings  125 . The end rings  125  may also protect the reactive metal sealing element  120  as it is run to depth.  FIG. 3A  illustrates the initiation of the expansion of the liner hanger  100 . 
       FIG. 3B  is a cross-section of an expandable liner hanger  100  after a portion of it has been expanded by the expansion cone  105 . As illustrated, the reactive metal sealing element  120  may be expanded alongside the conduit body  130  of the liner hanger  100 . The reactive metal sealing element  120  may be retained in its orientation after expansion by the end rings  125 . After reaction with a reaction-inducing fluid, the reactive metal sealing element  120  may expand to fill any voids or irregularities in the exterior surface  135  of the conduit body  130  or the interior surface  140  of the casing  115 . The expanded reactive metal sealing element  120  may seal any proximate annular space remaining between the liner hanger  100  and the casing  115  after expansion of the liner hanger  100 . The end rings  125  may create an extrusion barrier, preventing the applied pressure from extruding the seal formed from the reactive metal sealing element  120  in the direction of said applied pressure. Although  FIGS. 3A and 3B  herein may illustrate end rings  125  as a component of the expandable liner hanger  100 , it is to be understood that the end rings  125  are optional components in all examples described herein, and are not necessary for any species of liner hanger or tie-back liner described herein to function as intended. The reactive metal sealing element  120  may be held in position with other apparatus or may be positioned in a recess on the exterior surface  135  of the conduit body  130  of the liner hanger  100  to retain its position. 
     It should be clearly understood that the examples illustrated by  FIGS. 3A-3B  are merely general applications of the principles of this disclosure in practice, and a wide variety of other examples are possible. Therefore, the scope of this disclosure is not limited in any manner to the details of any of the FIGURES described herein. 
       FIG. 4  is an isometric illustration of a liner hanger, generally  200 . The liner hanger  200  couples to and forms a seal inside a casing at the coupling end  205 . The liner hanger  200  comprises a conduit body  210 . Reactive metal sealing elements  215  form external seals to seal against the surface of the casing and anchor the liner hanger  200  to the casing. A liner (not illustrated) may be coupled to and suspended from the suspending end  220 . Elastomeric sealing elements  225  may be positioned on the ends of and in-between the reactive metal sealing elements  215  to prevent the applied pressure from extruding the seal formed from the reactive metal sealing element  215  in the direction of said applied pressure, and also to supplement the sealing of the reactive metal sealing elements  215 . In some alternative examples, the elastomeric sealing elements  225  may be replaced with other species of sealing elements such as non-reactive metal sealing elements. In some other alternative examples, the elastomeric sealing elements  225  may be replaced with retaining rings as discussed above. 
     In the illustrated example of  FIG. 4 , the reactive metal sealing elements  215  and the elastomeric sealing elements  225  alternate in a series. It is to be understood that the reactive metal sealing elements  215  may be placed in any pattern or configuration-either by itself or in conjunction with other components such as other species of sealing elements or retaining elements. As an example, a single reactive metal sealing element  215  may be used. As another example, multiple reactive metal sealing elements  215  may be used. As a further example, multiple reactive metal sealing elements  215  may be used in a series adjacent one another with individual other species of sealing elements or retaining elements placed at the ends of the series. Further to this example, multiple other species of sealing elements or retaining elements may be placed at the ends of the series. As another example, the multiple reactive metal sealing elements  215  may alternate in the series with other species of sealing elements or retaining elements. 
     The elastomeric sealing elements  225  may be any species of swellable elastomer. The elastomeric sealing elements  225  may comprise any oil-swellable, water-swellable, and/or combination of swellable non-metal material as would occur to one of ordinary skill in the art. The swellable elastomeric sealing elements  225  may swell when exposed to a swell-inducing fluid (e.g., an oleaginous or aqueous fluid). Generally, the elastomeric sealing elements  225  may swell through diffusion whereby the swell-inducing fluid is absorbed into the structure of the elastomeric sealing elements  225  where a portion of the swell-inducing fluid may be retained. The swell-inducing fluid may continue to diffuse into elastomeric sealing elements  225 , causing the elastomeric sealing elements  225  to swell until they contact an adjacent surface. The elastomeric sealing elements  225  may work in tandem with the reactive metal sealing elements  215  to create a differential annular seal around the liner hanger  200 . 
     It should be clearly understood that the example illustrated by  FIG. 4  is merely a general application of the principles of this disclosure in practice, and a wide variety of other examples are possible. Therefore, the scope of this disclosure is not limited in any manner to the details of any of the FIGURES described herein. 
       FIG. 5  is a cross-section of an example tubing system, generally  305 , for a wellbore  310  penetrating a subterranean formation  315 . The tubing system  305  comprises a surface casing  320  and a surface cement sheath  325  descending from the surface  330 . Tubing system  305  further comprises an intermediate casing  335  and intermediate cement sheath  340  deployed and nested concentrically within the surface casing  320 . Although only one layer of intermediate casing  335  is illustrated, it is to be understood that more than one layer of intermediate casing  335  may be deployed in any example. A liner hanger  345  is deployed within the intermediate casing  335 . The liner hanger  345  may be used to suspend a liner (not illustrated for clarity) from within the intermediate casing  335 . The liner hanger  345  comprises a conduit body  360 . The liner hanger  345  seals within the intermediate casing  335 . A tie-back liner  365  is coupled to the liner hanger  345 . The tie-back liner comprises a conduit body  375 . The tie-back liner  365  runs to the surface  330 . The tie-back liner  365  may be a temporary or permanent component of the tubing system  305 . If the tie-back liner  365  is to be permanent, it may be cemented into place. 
       FIG. 6  is an enlarged cross-section illustration of a portion of the example tubing system  305  of  FIG. 5 . Intermediate casing  335  extends from the surface (i.e., surface  330  as illustrated in  FIG. 5 ) and may be held in place with the intermediate cement sheath  340 . Although only one layer of intermediate casing  335  is illustrated, it is to be understood that as many layers of intermediate casing  335  may be used as desired. Any subsequent layers of the intermediate casing  335  may be nested concentrically within one another within the illustrated intermediate casing  335 . The liner hanger  345  is deployed within the intermediate casing  335 . The liner hanger  345  may be any species of liner hanger and may be expandable or non-expandable. The liner hanger  345  suspends a liner (not illustrated). The liner hanger  345  is anchored to the intermediate casing  335  with a reactive metal sealing element  350  after the reactive metal sealing element  350  has reacted and expanded. The reactive metal sealing element  350  is disposed on and around the conduit body  360  of the liner hanger  345 . The reactive metal sealing element  350  forms an external seal with the adjacent interior surface of the intermediate casing  335  after the reactive metal sealing element  350  has reacted and expanded. 
     Tie-back liner  365  is deployed within the interior of the intermediate casing  335 . The tie-back liner  365  may be any species of tie-back liner. The tie-back liner  365  extends to the surface (not illustrated). The tie-back liner  365  is anchored to the liner hanger  345  with a reactive metal sealing element  370  after the reactive metal sealing element  370  has reacted and expanded. The reactive metal sealing element  370  is disposed on and around the conduit body  375  of the tie-back liner  365 . The reactive metal sealing element  370  forms an external seal with the adjacent interior surface of the liner hanger  345  after the reactive metal sealing element  370  has reacted and expanded. 
     The reactive metal sealing elements  350  and  370  expand after exposure to a reaction-inducing fluid. The reactive metal sealing elements  350  and  370  react to produce an expanded metal reaction product described above. As the expanded metal reaction product has a larger volume than the unreacted expendable metal, the reactive metal sealing elements  350  and  370  are able to expand and form an annular seal at the interface of the adjacent surface of the intermediate casing  335  or the liner hanger  345  as described above. The reactive metal sealing elements  350  and  370  may continue to expand until contact with the adjacent surface is made. The formed seal prevents wellbore fluid from bypassing the liner and liner hanger  345  or the tie-back liner  365 . 
     It should be clearly understood that the examples illustrated by  FIGS. 5-6  are merely general applications of the principles of this disclosure in practice, and a wide variety of other examples are possible. Therefore, the scope of this disclosure is not limited in any manner to the details of any of the FIGURES described herein. 
       FIG. 7A  is a cross-section of a tie-back liner  400  illustrating the coupling of the tie-back liner  400  with a reactive metal sealing element  405 . The tie-back liner  400  may be deployed in a wellbore similarly to the tie-back liner  365  illustrated in  FIGS. 5-6 . The tie-back liner  400  may comprise one or more reactive metal sealing elements  405  for sealing and anchoring to a liner hanger. The reactive metal sealing elements may be slid over the conduit body  410  of the tie-back liner  400 . The reactive metal sealing elements  405  may be positioned in a recess  415  within the exterior surface  420  of the conduit body  410 . Alternatively, the reactive metal sealing elements  405  may be cast onto the conduit body  410 . Elastomeric sealing elements  425 , or other species of sealing elements, may also be disposed on the exterior surface  420  of the conduit body  410 . 
       FIG. 7B  is a cross-section of a tie-back liner  400  illustrating a reactive metal sealing element  405  fitted and swaged thereon. When the one or more reactive metal sealing elements  405  are positioned in the recesses  415 , the diameter of the reactive metal sealing elements  405  may be reduced as desired. The reactive metal sealing elements  405  may be swaged down to a desired diameter such that the run-in-hole configuration of the tie-back liner  400  may not be impacted. Although the reactive metal sealing elements  405  are illustrated as being level with the exterior surface  420  of the conduit body  410 , it is to be understood that the reactive metal sealing elements  405  may not be level with the exterior surface  420  and may extend out of or be reduced into the recess  415  as much as desired. 
     In the illustrated examples of  FIGS. 7A and 7B , the reactive metal sealing elements  405  are disposed between the elastomeric sealing elements  425 . It is to be understood that the reactive metal sealing elements  405  may be placed in any pattern or configuration either alone or in conjunction with other components such as other species of sealing elements or retaining elements. As an example, a single reactive metal sealing element  405  may be used. As another example, multiple reactive metal sealing elements  405  may be used. As a further example, multiple reactive metal sealing elements  405  may be used in a series adjacent one another with individual other species of sealing elements or retaining elements placed at the ends of the series. Further to this example, multiple other species of sealing elements or retaining elements may be placed at the ends of the series. As another example, the multiple reactive metal sealing elements  405  may alternate in the series with other species of sealing elements or retaining elements. 
     The elastomeric sealing elements  425  may be any species of swellable elastomer. The elastomeric sealing elements  425  may comprise any oil-swellable, water-swellable, and/or combination of swellable non-metal material as would occur to one of ordinary skill in the art. The swellable elastomeric sealing elements  425  may swell when exposed to a swell-inducing fluid (e.g., an oleaginous or aqueous fluid). Generally, the elastomeric sealing elements  425  may swell through diffusion whereby the swell-inducing fluid is absorbed into the structure of the elastomeric sealing elements  425  where a portion of the swell-inducing fluid may be retained. The swell-inducing fluid may continue to diffuse into elastomeric sealing elements  425  causing the elastomeric sealing elements  425  to swell until they contact an adjacent surface. The elastomeric sealing elements  425  may work in tandem with the reactive metal sealing elements  405  to create a differential annular seal around the tie-back liner  400 . 
     It should be clearly understood that the examples illustrated by  FIGS. 7A-7B  are merely general applications of the principles of this disclosure in practice, and a wide variety of other examples are possible. Therefore, the scope of this disclosure is not limited in any manner to the details of any of the FIGURES described herein. 
     It is also to be recognized that the disclosed reactive metal sealing elements may also directly or indirectly affect the various downhole equipment and tools that may come into contact with the reactive metal sealing elements during operation. Such equipment and tools may include, but are not limited to: wellbore casing, wellbore liner, completion string, insert strings, drill string, coiled tubing, slickline, wireline, drill pipe, drill collars, mud motors, downhole motors and/or pumps, surface-mounted motors and/or pumps, centralizers, turbolizers, scratchers, floats (e.g., shoes, collars, valves, etc.), logging tools and related telemetry equipment, actuators (e.g., electromechanical devices, hydromechanical devices, etc.), sliding sleeves, production sleeves, plugs, screens, filters, flow control devices (e.g., inflow control devices, autonomous inflow control devices, outflow control devices, etc.), couplings (e.g., electro-hydraulic wet connect, dry connect, inductive coupler, etc.), control lines (e.g., electrical, fiber optic, hydraulic, etc.), surveillance lines, drill bits and reamers, sensors or distributed sensors, downhole heat exchangers, valves and corresponding actuation devices, tool seals, packers, cement plugs, bridge plugs, and other wellbore isolation devices, or components, and the like. Any of these components may be included in the systems generally described above and depicted in any of the FIGURES. 
     Provided are conduits for a wellbore in accordance with the disclosure and the illustrated FIGURES. An example conduit comprises a conduit body; and a reactive metal sealing element disposed on the conduit body; wherein the reactive metal sealing element comprises a reactive metal. The conduit may be a liner hanger or a tie-back liner. 
     Additionally or alternatively, the apparatus may include one or more of the following features individually or in combination. The reactive metal may comprise a metal selected from the group consisting of magnesium, calcium, aluminum, tin, zinc, beryllium, barium, manganese, and any combination thereof. The reactive metal may comprise a metal alloy selected from the group consisting of magnesium-zinc, magnesium-aluminum, calcium-magnesium, aluminum-copper, and any combination thereof. If the conduit is the liner hanger, the liner hanger may be expandable. If the conduit is the liner hanger, the liner hanger may be non-expandable. The reactive metal sealing element may further comprise a removable barrier coating. The conduit body may comprise a recess, and the reactive metal sealing element may be disposed in the recess. 
     Provided are methods for treating a wellbore in accordance with the disclosure and the illustrated FIGURES. An example method comprises positioning a conduit in the wellbore; wherein the conduit is a liner hanger or a tie-back liner; and wherein the conduit comprises: a conduit body; and a reactive metal sealing element disposed on the conduit body; wherein the reactive metal sealing element comprises a reactive metal having a first volume. The method further comprises contacting the reactive metal with a fluid that reacts with the reactive metal to produce a reaction product having a second volume greater than the first volume; and contacting a surface adjacent to the reactive metal sealing element with the reaction product. 
     Additionally or alternatively, the method may include one or more of the following features individually or in combination. The reactive metal may comprise a metal selected from the group consisting of magnesium, calcium, aluminum, tin, zinc, beryllium, barium, manganese, and any combination thereof. The reactive metal may comprise a metal alloy selected from the group consisting of magnesium-zinc, magnesium-aluminum, calcium-magnesium, aluminum-copper, and any combination thereof. If the conduit is the liner hanger, the liner hanger may be expandable. If the conduit is the liner hanger, the liner hanger may be non-expandable. If the conduit is the liner hanger, the adjacent surface may be a casing. If the conduit is the tie-back liner; the adjacent surface may be an exterior surface of a liner hanger. The reactive metal sealing element may further comprise a removable barrier coating. The conduit body may comprise a recess, and the reactive metal sealing element may be disposed in the recess. The contacting a surface adjacent to the reactive metal sealing element with the reaction product may further comprise forming a seal against the adjacent surface. The contacting a surface adjacent to the reactive metal sealing element with the reaction product may further comprise anchoring the conduit to the adjacent surface. 
     Provided are systems for forming a seal in a wellbore in accordance with the disclosure and the illustrated FIGURES. An example system comprises a conduit comprising: 
     a conduit body; and a reactive metal sealing element disposed on the conduit body; wherein the reactive metal sealing element comprises a reactive metal. The conduit is a liner hanger or a tie-back liner. The system further comprises a liner. 
     Additionally or alternatively, the system may include one or more of the following features individually or in combination. The reactive metal may comprise a metal selected from the group consisting of magnesium, calcium, aluminum, tin, zinc, beryllium, barium, manganese, and any combination thereof. The reactive metal may comprise a metal alloy selected from the group consisting of magnesium-zinc, magnesium-aluminum, calcium-magnesium, aluminum-copper, and any combination thereof. If the conduit is the liner hanger, the liner hanger may be expandable. If the conduit is the liner hanger, the liner hanger may be non-expandable. The reactive metal sealing element may further comprise a removable barrier coating. The conduit body may comprise a recess, and the reactive metal sealing element may be disposed in the recess. If the conduit is the liner hanger, the system may further comprise a casing and the liner hanger may be sealed to the casing with the reactive metal sealing element, and the liner may be suspended from the liner hanger. If the conduit is the tie-back liner, the system may further comprise a liner hanger, and the tie-back liner may be sealed to the liner hanger with the reactive metal sealing element, and the liner may be suspended from the liner hanger. 
     The preceding description provides various examples of the apparatus, systems, and methods of use disclosed herein which may contain different method steps and alternative combinations of components. It should be understood that, although individual examples may be discussed herein, the present disclosure covers all combinations of the disclosed examples, including, without limitation, the different component combinations, method step combinations, and properties of the system. It should be understood that the compositions and methods are described in terms of “comprising,” “containing,” or “including” various components or steps. The systems and methods can also “consist essentially of” or “consist of the various components and steps.” Moreover, the indefinite articles “a” or “an,” as used in the claims, are defined herein to mean one or more than one of the element that it introduces. 
     For the sake of brevity, only certain ranges are explicitly disclosed herein. However, ranges from any lower limit may be combined with any upper limit to recite a range not explicitly recited, as well as ranges from any lower limit may be combined with any other lower limit to recite a range not explicitly recited. In the same way, ranges from any upper limit may be combined with any other upper limit to recite a range not explicitly recited. Additionally, whenever a numerical range with a lower limit and an upper limit is disclosed, any number and any included range falling within the range are specifically disclosed. In particular, every range of values (of the form, “from about a to about b,” or, equivalently, “from approximately a to b,” or, equivalently, “from approximately a-b”) disclosed herein is to be understood to set forth every number and range encompassed within the broader range of values even if not explicitly recited. Thus, every point or individual value may serve as its own lower or upper limit combined with any other point or individual value or any other lower or upper limit, to recite a range not explicitly recited. 
     One or more illustrative examples incorporating the examples disclosed herein are presented. Not all features of a physical implementation are described or shown in this application for the sake of clarity. Therefore, the disclosed systems and methods are well adapted to attain the ends and advantages mentioned, as well as those that are inherent therein. The particular examples disclosed above are illustrative only, as the teachings of the present disclosure may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown other than as described in the claims below. It is therefore evident that the particular illustrative examples disclosed above may be altered, combined, or modified, and all such variations are considered within the scope of the present disclosure. The systems and methods illustratively disclosed herein may suitably be practiced in the absence of any element that is not specifically disclosed herein and/or any optional element disclosed herein. 
     Although the present disclosure and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the disclosure as defined by the following claims.