Patent Publication Number: US-10309183-B2

Title: Internally degradable plugs for downhole use

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Prov. Appl. 61/901,681, filed Nov. 8, 2013, which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE DISCLOSURE 
     A number of operations in a wellbore use balls, plugs, or the like to actuate downhole tools, close off fluid flow, and perform other operations. For example, bridge plugs used in plug and perforation operations for completing a wellbore may have balls disposed therein to control fluid flow or may have balls dropped to engage the plugs during fracture operations. 
     In a staged fracturing operation, multiple zones of a formation may be isolated sequentially for treatment using dropped balls. To achieve this, operators install a fracturing assembly down the wellbore, which typically has a top liner packer, open hole packers isolating the wellbore into zones, various sliding sleeves, and a wellbore isolation valve. When the zones do not need to be closed after opening, operators may use single shot sliding sleeves for the fracturing treatment. These types of sleeves are usually ball-actuated and lock open once actuated. Another type of sleeve is also ball-actuated, but can be shifted closed after opening. 
     Initially, operators run the fracturing assembly in the wellbore with all of the sliding sleeves closed and with the wellbore isolation valve open. Operators then deploy a setting ball to close the wellbore isolation valve. This seals off the tubing string of the assembly so the packers can be hydraulically set. At this point, operators rig up fracturing surface equipment and pump fluid down the wellbore to open a pressure-actuated toe sleeve so a first zone can be treated. 
     As the operation continues, operators drop successively larger balls down the tubing string and pump fluid to treat the separate zones in stages. When a dropped ball meets its matching seat in a sliding sleeve, the pumped fluid forced against the seated ball shifts the sleeve open. In turn, the seated ball diverts the pumped fluid into the adjacent zone and prevents the fluid from passing to lower zones. By dropping successively increasing sized balls to actuate corresponding sleeves, operators can accurately treat each zone up the wellbore. 
     As background to the present disclosure,  FIG. 1A  shows an example of a sliding sleeve  10  for a multi-zone fracturing system in partial cross-section during an opened state, and  FIG. 1B  illustrates a close up view of the sliding sleeve  10 . This sliding sleeve  10  is similar to Weatherford&#39;s ZoneSelect MultiShift fracturing sliding sleeve and can be placed between isolation packers in a multi-zone completion. The sliding sleeve  10  includes a housing  20  defining a bore  25  and having upper and lower subs  22  and  24 . An inner sleeve or insert  30  can be moved within the housing&#39;s bore  25  to open or close fluid flow through the housing&#39;s flow ports  26  based on the inner sleeve  30 ′s position. 
     When initially run downhole, the inner sleeve  30  positions in the housing  20  in a closed state. A breakable retainer  38  initially holds the inner sleeve  30  toward the upper sub  22 , and a locking ring or dog  36  on the sleeve  30  fits into an annular slot within the housing  20 . Outer seals on the inner sleeve  30  engage the housing  20 ′s inner wall above and below the flow ports  26  to seal them off. 
     The inner sleeve  30  defines a bore  35  having a seat  40  fixed therein. To open the sliding sleeve  10  in a fracturing operation, operators drop an appropriately sized ball B downhole and pump the ball B until it reaches the seat  40  disposed in the inner sleeve  30 . 
     Once the ball B is seated, built up pressure forces against the inner sleeve  30  in the housing  20 , shearing the breakable retainer  38  and freeing the lock ring or dog  36  from the housing&#39;s annular slot so the inner sleeve  30  can slide downward. As it slides, the inner sleeve  30  uncovers the flow ports  26  so flow can be diverted to the surrounding formation. The shear values required to open the sliding sleeves  10  can range generally from 1,000 to 4,000 psi (6.9 to 27.6 MPa). 
     Once the sleeve  10  is open, operators can then pump proppant at high pressure down the tubing string to the open sleeve  10 . The proppant and high pressure fluid flows out of the open flow ports  26  as the seated ball B prevents fluid and proppant from communicating further down the tubing string. The pressures used in the fracturing operation can reach as high as 15,000-psi. 
     After the fracturing job, the well is typically flowed clean, and the ball B is floated to the surface. In some cases, the ball B cannot be floated to the surface because the ball has become wedged in the seat or for some other reason. In any event, the ball seat  40  (and the ball B if remaining) is milled out in a milling operation. The ball seat  40  can be constructed from cast iron to facilitate milling, and the ball B can be composed of aluminum or a non-metallic material, such as a composite. Once milling is complete, the inner sleeve  30  can be closed or opened with a standard “B” shifting tool on the tool profiles  32  and  34  in the inner sleeve  30  so the sliding sleeve  10  can then function like any conventional sliding sleeve that shifts with a “B” tool. 
     To reduce the need to mill out the balls B, various materials and designs have been used to make the balls disintegrate, dissolve, break apart, or otherwise degrade in the wellbore. Being able to degrade the balls B eliminates the need to flow the balls B back to surface after the fracture operation and reduces the complexity of milling operations for any balls B not floated to the surface. Degradable balls and other plugs find uses in applications other than just sliding sleeves. 
     A number of materials and designs have been developed to disintegrate, dissolve, break apart, or otherwise degrade balls in a wellbore environment when exposed to certain factors, such as temperatures, pressures, fracture fluids, other pumped fluids, hydrocarbons, time spans, etc. Examples of such materials and designs are disclosed in US 2012/0181032; US 2012/0273229; US 2011/0132621; U.S. Pat. Nos. 8,528,633; 8,403,037; 8,127,856; and U.S. Pat. No. 7,350,582. 
     The materials and designs condense down to two particular approaches. In the first approach, the structure of the ball is compromised externally when subjected to the wellbore environment. For example, U.S. Pat. No. 8,528,633 discloses a ball having perforations in its outer surface. The perforations control a rate of intrusion of the wellbore environment into the ball and below its outer surface. By controlling this rate of intrusion, the rate of reaction of the ball&#39;s material with the environment can be controlled so that the ball is weakened to a point where it can fail due to the stress applied to it. 
     In another example, US 2011/0132621 discloses a ball having two or more parts that are resistant to dissolution, but are bound together by an adherent material that can dissolve. During use, dissolution of the adherent material allows the two or more parts of the ball to move out of engagement with a ball seat so that the parts pass through the seat. 
     In the second approach, the material of the ball is compromised externally when subjected to the wellbore environment. For example, US 2012/0273229 discloses a composite downhole article (e.g., ball) having a corrodible core that corrodes at a faster rate in wellbore fluid than the rate that an outer member disposed on the core corrodes. An access point on the outer member can provide access of wellbore fluid to the corrodible core. In another example, US 2012/0181032 discloses a ball composed of a material that disintegrates, dissolves, delaminates, or otherwise experiences a significant degradation of its physical properties over time in the presence of hydrocarbons and formation heat. 
     As can be seen, both of these approaches subject the ball to the wellbore environment to initiate the degradation externally. Although these approaches may be effective, the need to maintain the structural integrity of the ball during use is a driving consideration for operators. As the industry progresses, higher pressures are being used downhole, and more and more zones are being treated downhole in a given wellbore. To operate properly, a composite ball needs to withstand high fracture pressures and needs to maintain its shape engaging a seat under such pressures. The ball may also need to function properly for longer periods of time. If the ball deforms or fails, then the fluid seal it provides with the seat will be compromised and make the fracture treatment ineffective. In light of this, the tolerances and size differences between deployed balls is becoming smaller and requiring more precision. Existing technology for manufacturing balls is approaching pressure and temperature limitations beyond which the deployed balls become less effective. In addition to fracture balls, other plugs used in other application preferably maintain their integrity while being degradable in a given application. 
     The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above. 
     SUMMARY OF THE PRESENT DISCLOSURE 
     Embodiments of the present disclosure can be characterized as a plug for deployment downhole. The plug includes a body composed of a first material and includes an activating element disposed internally in the body. The activating element has an agent configured to degrade the body. However, the agent is kept from degrading the body until occurrence of an activating trigger. 
     In general, the body can be a sphere, a cylinder, a cone, a dart, or other shape, and the first material can be composed of metal, composite, or other polymer, among other materials. The agent can be one or more of an acid, a base, a solvent, a hydrocarbon, a hydrocarbon wax, a salt (ionic compound), an organic compound, or a mixture, among other materials. A single agent can be used. Alternatively, at least two agent components can be kept separate from one another and can be allowed to interact with one another upon occurrence of the activating trigger. In general, the activating trigger can include an impact of the body against a downhole surface; a length of time; a temperature level; a pressure level; a physical deformation; a solid, liquid or gas that expands/contracts at pressure and/or temperature; thermodynamic reaction; or a combination of these. 
     To degrade the body, the activating agent can be configured to chemically react with the first material of the body. For example, the activating element can include a shell enclosing the agent therein and keeping the agent from chemically reacting with the first material. The shell can be composed of a breachable or breakable material being breached or breaking to allow the agent to react with the first material. To breach or break the shell, the activating element can further include a breaching element that breaches the shell in response to the activating trigger. 
     The foregoing summary is not intended to summarize each potential embodiment or every aspect of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  illustrates a sliding sleeve having a ball engaged with a seat to open the sliding sleeve as background to the present disclosure. 
         FIG. 1B  illustrates a close up view of the sliding sleeve in  FIG. 1A . 
         FIG. 2A  illustrates a cross-sectional view of a downhole plug according to the present disclosure with a body of the plug formed about an internal activating element. 
         FIG. 2B  illustrates a cross-sectional view of another downhole plug according to the present disclosure with an activating element inserted internally into a body of the plug. 
         FIGS. 3A-3B  illustrates a sliding sleeve having a plug according to the present disclosure engaged with a seat to open the sliding sleeve. 
         FIGS. 4A-4B  illustrate configurations of the disclosed plug having breaching elements disposed relative to the internal activating element. 
         FIGS. 5A-5B  illustrate configurations of the disclosed plug having internal activating elements with multiple agents. 
         FIGS. 6-7  illustrate cross-sectional views of additional downhole plugs with activating elements according to the present disclosure. 
         FIGS. 8-10  illustrate partial cross-sectional views of different configurations of downhole plugs according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
       FIGS. 2A-2B  show cross-sectional views of downhole plugs  50  according to the present disclosure. The plugs  50  can be used in any application were a plug activates or actuates a tool, seals an orifice, engages a seat, etc. For example, the plugs  50  can be used with sliding sleeves, stage tools, composite fracture plugs, or other downhole tools. 
     In general, the plugs  50  can be a spherical ball as shown so that reference herein may be made to the plug  50  being a ball, such as used to engage a ball seat in a downhole tool. It will be appreciated, however, that the plugs  50  as disclosed herein can have any suitable shape (dart, cylinder, cone, sphere, etc.) for deploying downhole and performing some purpose of sealing, actuating, or the like. Accordingly, reference herein to “plug”  50  connotes any suitable plug, fracture ball, trip ball, opening plug, closing plug, dart, wiper, etc. with any suitable shape for use downhole. 
     The plugs  50  have a body  52  with an exterior or external surface  53 . When deployed downhole, the external surface  53  of the body  52  may be exposed to a wellbore environment and conditions and may engage a seat or the like to form a seal or other type of engagement. Inside its interior, the body  52  includes an activating element  60 , such as an ampule, pill, seed, chemical fuse, or the like disposed therein. 
     In  FIG. 2A , the body  52  of the plug  50  completely encompasses the activating element  60  such that the body  52  has been formed, molded, wound, machined, or otherwise manufactured around the element  60 . For example, the activating element  60  may be molded in the body  52 , which can be composed of a composite material, such as commonly used for fracture balls used with sliding sleeves downhole. 
     In  FIG. 2B , the body  52  has been formed, molded, wound, machined or otherwise manufactured separately. A pocket or hole  54  in the body  52  allows the activating element  60  to be inserted into the body  52 , and a filler element  56 , material, or the like disposed in the pocket  54  can enclose the activating element  60  in the body  52 . In this arrangement, the plug  50  can be manufactured using regular practices and can have the pocket  54  drilled in it. The activating element  60  in the form of an ampule or the like is inserted into the pocket  54 . A breaching element (not shown) to break the activating element  60  upon impact with a ball seat, in response to physical (elastic or plastic) deformation of the plug  50 , or other trigger can also be inserted in the pocket  54 . To complete the plug  50 , operators then fill the pocket  53  with material  56 , which can be inert, part of the plug&#39;s body  52 , or part of a chemical fuse. 
     When the plug  50  of  FIG. 2A or 2B  is dropped into the well, impact with a ball seat, pressure from a fracture operation, or other activating event or trigger activates or ruptures the activating element  60  inside the plug  50 , which causes the element  60  to degrade the plug  50  from inside out. 
     In general, the body  52  can be composed of any suitable material for downhole use. Accordingly, the body  52  can be composed of a metallic material, including, but not limited to, aluminum, aluminum alloy, zinc alloy, magnesium alloy, steel, brass, aluminum bronze, a metallic nanostructure material, cast iron, etc. Additionally, the plug  50  can be composed of any suitable non-metallic material, including, but not limited to, ceramics, plastics, composite materials, phenolics (e.g., G-10), polyamide-imide (e.g., Torlon®), polyether ether ketone (PEEK), polyglycolic acid (PGA), thermosets, thermoplastics, or the like. (TORLON is a registered trademark of Solvay Specialty Polymers, LLC of Alopharetta, Ga.) 
     The activating element  60  is composed of or contains an activating agent  62 , which can be a solid, liquid, gas, gel, or the like, designed to react with the material of the body  52 . The reaction of the activating element  60  with the body  52  can dissolve, degrade, erode, eat away, break apart, melt, or otherwise compromise the structural integrity of the body  52  through a chemical or other reaction. As disclosed herein, the reaction between the body&#39;s material and the element&#39;s agent  62  can dissolve, erode, corrode, disintegrate, break apart, or otherwise degrade the body  52 . In that light, a number of reactions between materials can be used to achieve the purposes of the present disclosure. In general, the activating agent  62  may be composed of one or more of an acid, a base, a solvent, a hydrocarbon, a hydrocarbon wax, a salt (ionic compound), an organic compound, a mixture, or the like. 
     As shown here, the activating element  60  has the form of an ampule having an outer shell  64  holding the internal agent  62 . Thus, depending on the composition of the agent  62  and how it reacts with the body&#39;s material, the activating element  60  may have some form of preventive interface or shell  64  to initially prevent reaction between the materials of the body  52  and agent  62 . For example, the shell  64  can be composed of glass, plastic, wax, an ionic salt, calcium carbonate, ceramic, or other material. 
     The activating element  60  may begin reacting with the body&#39;s material when one or more particular activating triggers occur. In general, the activating trigger may be an impact of the plug  50  while deployed downhole; an amount of deformation of the plug  50  from applied pressure; a heat level experienced downhole; an internal pressure level experienced downhole; a length of time; a solid, liquid, or gas that expands/contracts at pressure and/or temperature; a thermodynamic reaction, or a combination of these. 
     As one example, the agent  62  of the activating element  60  can be an acid of sufficient quantity and strength to chemically react with the material of the body  52 , which can be composed of metal. When the shell  64  of glass or other material is broken or breached by impact or other trigger, the acid of the activating agent  62  can then react in an acid-metal reaction with the metal of the body  52  to form a metal salt and hydrogen. 
     Alternatively, the activating element  60  can be composed of one or more agents  62  that experience a reaction when exposed to the heat or pressure in the wellbore. When the activating agent  62  reacts to such a trigger, the agent  62  begins to degrade, rupture, break, erode, etc. the body of the plug  50 . For example, the activating agent  62  may be composed of a material that expands rapidly when subjected to the heat in the wellbore environment. Many types of materials expand when heated so any of a number of materials can be used. Eventually, the internal pressure of the reaction can break apart the plug  50 . 
     Alternatively, the activating element  60  can be composed of two or more agents  62  that experience a reaction when exposed to one another. When the agents  62  of the activating element  60  reacts with one another, the reaction or its product begins to degrade, rupture, break, erode, etc. the body of the plug  50 . For example, the activating element  60  may be composed of agents  62  that undergo a rapid exothermal reaction when exposed to one another and can eventually break apart the plug  50 . Some examples of materials that can react with one another to degrade the plug include peroxide and sulfuric acid, water and strong acid, water and an anhydrous salt, water and calcium chloride, and water and calcium carbide. 
     As one example, the body  52  can be composed of a suitable material for use in a wellbore environment that may not be specifically expected to dissolve, disintegrate, break apart, or otherwise degrade under operating conditions. As such, the body  52  can be composed of several types of metal, composite, or polymer materials currently used in oilfield applications. These materials may typically be incompatible with certain chemical agents (e.g., hydrocarbons, solvents, acids, etc.) that dissolve, weaken, or degrade the material. Accordingly, the activating agent  62  of the element  60 , however, may contain a hydrocarbon, solvent, acid, etc. to degrade the body&#39;s material  52 . To prevent or hinder interaction of the activating agent  62  with the body&#39;s material  52 , the element&#39;s shell  64  may be composed of a breachable or breakable material (e.g., glass) suited for containing the acid agent  62 . The shell  64  can be composed of other materials (plastic, membrane, glass, etc.) depending on the internal agent  62  to be contained. 
     As can be seen from the above discussion, carrying the agent  62  in the plug  50  can eliminate problems found in the prior art that require accurately spotting or pumping a suitable chemical agent to a plug after fracing so as to degrade the plug externally. Moreover, most dissolvable plugs in the prior art must be weakened externally on the exterior to subsequently allow them to degrade. Therefore, carrying the agent  62  internal to the plug  50  as disclosed herein allows the plug  50  to have a stronger exterior, but still degrade after use from the inside-out. 
     Continuing with discussion of how the plug  50  is used,  FIGS. 3A-3B  shows the plug  50  of  FIG. 2A  being deployed to a seat  40  on a sliding sleeve  10  as commonly used downhole during fracture operations. As previously noted, the sliding sleeve  10  includes a housing  20  defining a bore  25  with an inner sleeve or insert  30  movable therein to open or close fluid flow through the housing&#39;s flow ports  26  based on the inner sleeve  30 &#39;s position. The inner sleeve  30  defines a bore  35  having a seat  40  fixed therein. 
     The plug  50 , which is appropriately sized, is deployed downhole and lands on the seat  40 . With the plug  50  seated, built-up pressure forces against the inner sleeve  30  in the housing  20 , shearing a breakable retainer (not shown) and freeing the inner sleeve  30  to slide downward. As it slides, the inner sleeve  30  uncovers the flow ports  26  so flow can be diverted to the surrounding formation. The shear values required to open the sliding sleeve  10  can range generally from 1,000 to 4,000 psi (6.9 to 27.6 MPa). 
     Once the sleeve  10  is open, operators can then pump proppant at high pressure down the tubing string to the open sleeve  10 . The proppant and high pressure fluid flows out of the open flow ports  26  as the seated plug  50  prevents fluid and proppant from communicating further down the tubing string. The pressures used in the fracturing operation can reach as high as 15,000-psi. 
     With the plug  50  deployed downhole, a number of triggers can be used to activate the activating agent to degrade the plug  50 . For example, as the plug  50  is deployed down the tubing string, the plug  50  impacts the seat  40  in the sliding sleeve  10 . Typically, the plug  50  also impacts a number of seats uphole of the designated seat  40 . An expected impact level of a plug  50 , such as a dropped ball, with a seat can be from about 1100-lbf to 22,000-lbf in some implementations. Accordingly, one or more of the impacts of the deployed plug  50  with seats can trigger the activating element  60  to begin degrading the plug&#39;s body  52 , for example, by compromising the shell  64  holding the activating agent  62 . 
     In another form of trigger, the plug  50  engaged in the seat  40  can be deformed by the high pressure applied against during the fracture operation. For example, the plug  50  in the form of a composite ball may be expected to deform by the impact of the plug  50  hitting a seat and/or the pumping of fracturing fluid against the seated plug  50 . These can provide the necessary force(s) to deform the plug  50  by tending to compress, squeeze, flatten, elongate, or otherwise alter the shape of the plug  50 . Additionally, variations in pressuring up and down can allow the plug  50  to seat and then float alternatingly, which may also repeatedly deform and ultimately alter the shape of the plug  50 . The deformation of the plug  50  during the fracture operation can then trigger the activating element  60  to begin degrading the plug&#39;s body  52 , for example, by breaching, cracking, breaking, or otherwise compromising the shell  64  containing the internal agent  62 . 
     In another form of trigger, the plug  50  engaged in the seat  40  can be subjected to high temperatures during the fracture operation. Over time, the temperature can trigger the activating element  60  to begin degrading the plug&#39;s body  52 , for example, by compromising the shell  64  containing the internal agent  62 . As disclosed herein, these and other triggers can be used alone or in combination with one another to activating the element  60  to degrade the plug  50 . 
     Once triggered, reaction between the internal agent  62  and the body&#39;s material commences and begins to degrade the plug  50  from the inside-out. All the while, the plug  50  at least externally maintains its integrity, allowing the plug  50  to achieve its purposes of sealing, engagement, and the like at least until the body  52  is internally degraded to a point where it is structurally compromised. The compromised body  52  can dissolve, erode, break into pieces, collapse, implode, etc. 
     After the fracturing job, the well is typically flowed clean, and any remaining material of the plug&#39;s body  52  can be floated to the surface. In cases where the remaining material cannot be floated, the body&#39;s material can be readily milled out in a milling operation. Because the plug&#39;s body  52  is no longer uniform or whole, the milling operation can better mill up any the remnants of the body  52  regardless of its material composition. 
     As shown in  FIG. 3B , a given plug  50  can include an RFID tag or other sensor element  100 . As the plug  50  degrades, the sensor element  100  is free to pass through any seat  40 , landing, or the like. Downhole of the various tools, the tubing string can include a detector  110  (e.g., RFID reader) to detect passage of the freed sensing element  100 . Using the detector  110 , operators can determine that the given plug  50  has degraded, which can be used as a confirmation that the tool, sliding sleeve  20 , tubing string, or the like is cleared. 
       FIGS. 4A-4B  show alternative configurations of plugs  50  having an activating element  60  disposed therein. As shown in  FIG. 4A , breaching elements  70 , in the form of pins, spikes, or the like, can be disposed in the plug&#39;s body  52  and can extend roughly from the plug&#39;s exterior surface  53  to the activating element  60 . These breaching elements  70  can be composed of the same or different material than the plug&#39;s body  52 , and they may be inserted in machined holes or channels. When the plug  50  is subjected to pressures, the breaching elements  70  may move, adjust, or the like so that the elements  70  breach the activating element&#39;s shell  64  and initiate the desired degradation of the plug&#39;s body  52 . 
       FIG. 4B  shows another arrangement in which breaching elements  72  are disposed adjacent the activating element  60  and are enclosed primarily inside the plug&#39;s body  52 . All the same, these breaching elements  72  can function in a similar manner to those described above. 
       FIGS. 5A-5B  show additional configurations of plugs  50  having an activating element  60  disposed therein. As shown in  FIG. 5A , the activating element  60  includes at least two separate agents  62   a - b  that are initially kept separate from one other. When the agents  62   a - b  combine, they may initiate the reaction with the plug&#39;s body  52  to achieve the intended degradation. The activating element  60  may have a breachable container or shell  64  having chambers with a division  63  for the agents  62   a - b . When the plug&#39;s body  52  is deformed, the shell  64  or the division  63  may break, rupture, etc. so that the agents  62   a - b  combine to produce the desired reaction. Alternatively, one of the agents  62   a  may act to degrade the shell  64  so that the other agent  62   b  can interact with the plug&#39;s body  52 . In this sense, the shell  64  may not be intended to physically break, as the interaction of the agent  62   a  is intended to breach the shell  64  after a trigger (pressure, heat, impact, etc.) and allow the reaction to follow. 
       FIG. 5B  shows an example where activating elements  60   a - b  includes separate agents  62   a - b  disposed in separate ampules, shells, pills, or the like. These two agents  62   a - b  can operate in much the same way as discussed above. Therefore, one agent  62   a  may act to degrade the shell  60   b  of the other agent  62   b  so the other agent  62   b  can interact with the plug&#39;s body  52 . Alternatively, the two agents  62   a - b  may combine together when triggered to react with the plug&#39;s body  52 . Breaching elements (not shown) may also be provided. 
       FIG. 6  illustrates a cross-sectional view of another downhole plug  50  according to the present disclosure having an activating element  60  with an internal breaching element  66 . As before, the activating element  60  can include a shell  64  containing an activating agent  62 . The breaching element  66  in this arrangement is contained in the shell  64 . Impact of the plug  50 , deformation of the plug  50 , or other physical trigger may cause the breaching element  66  to breach the shell  64  and allow the activating agent  62  to interact with the material of the plug&#39;s body  52 . 
       FIG. 7  illustrates a cross-sectional view of yet another downhole plug  50  according to the present disclosure with an activating element  60  inserted in a formed pocket or hole  54 . As discussed previously, the pocket or hole  54  in the body  52  allows the activating element  60  to insert into the body  52 , and a filler element  56 , material, or the like disposed in the pocket  54  can enclose the element  60  in the body  52 . As shown here, a breaching element  74  may be inserted into the pocket  54  along with the activating element  60  so the breaching element  74  can break the activating element  60  (upon impact with a ball seat, in response to pressure deformation of the plug  50 , or other activation). 
     As discussed above, the disclosed plugs  50  can be balls, although plugs can be used. For example,  FIGS. 8-10  illustrate partial cross-sectional views of different configurations of downhole plugs  50  according to the present disclosure. In  FIG. 8 , the downhole plug  50  has the form of a closing or wiper plug, which can be composed of a combination of materials and can be used for closing a stage tool or the like downhole. In  FIG. 9 , the downhole plug  50  has the form of a cone, which can be composed of metal (e.g., aluminum) and can be used for opening a stage tool or the like downhole. In  FIG. 10 , the downhole plug  50  has the form of a dart, which can be composed of a combination of materials and can be used in cementing and other operations. 
     Because such plugs  50  may have more material or denser material than a fracture or trip ball, more than one activating agent or a larger activating agent may be used inside the plug  50 . For example, the cone  50  in  FIG. 9  has more than one activating element  60   a - b . Also, the denser components of the plug  50 , such as the core  51  of the closing plug  50  in  FIG. 8  may have an activating element  60 , while the sealing skin  55  is not expected to degrade or is degraded separately or concurrently with the activating element  60 . 
     Finally, because these plugs  50  may be less prone to deformation, the activating agent  60  may include embodiments disclosed herein that react to impact, heat, breaching elements, or other such trigger rather than a deformation to start the degradation process. 
     As can be seen, the activating elements  60  degrade the plugs  50  from the inside-out. This is in contrast to how plugs are typically degraded externally from the outside-in due to exposure to the conditions in the wellbore or due to intrusion of the wellbore fluid into the plug. 
     The foregoing description of preferred and other embodiments is not intended to limit or restrict the scope or applicability of the inventive concepts conceived of by the Applicants. It will be appreciated with the benefit of the present disclosure that features described above in accordance with any embodiment or aspect of the disclosed subject matter can be utilized, either alone or in combination, with any other described feature, in any other embodiment or aspect of the disclosed subject matter. 
     In exchange for disclosing the inventive concepts contained herein, the Applicants desire all patent rights afforded by the appended claims. Therefore, it is intended that the appended claims include all modifications and alterations to the full extent that they come within the scope of the following claims or the equivalents thereof.