Abstract:
The removable plug features a solid material that is housed in a porous container that has its shape changed to transition from the run in shape to the set shape. A swage is moved through a passage in the container to enlarge the passage and move the container to a borehole wall. The passage is then closed such as with a flapper valve or by moving in a mandrel into the expanded passage and lodging the mandrel in the expanded passage. Various release techniques are described.

Description:
FIELD OF THE INVENTION 
     The field of the invention is removable plugs and more particularly plugs filled with a solid material that is contained in a porous member that has its shape changed to set the plug and the plug structure subsequently altered for release of the plug. 
     BACKGROUND OF THE INVENTION 
     Zones in a wellbore have been isolated from each other with sand plugs. Typically, a porous substrate is supported in the wellbore and sand is pumped onto the substrate. Pressure is applied and the sand is dewatered. If a long enough sand column is created, the pressure applied from pumped fluid above forces the sand particles together in such a manner as to create a barrier to isolate zones in a wellbore from each other. When the barrier is no longer needed a jetting tool at the end of coiled tubing or the like is run into position above the plug. The jetting action and the circulation starts to work on the compacted sand pile and eventually allows the particles to come off the cohesive plug and get lifted from the well with the circulating fluid that exits the jetting nozzles. Some examples of this technique are U.S. Pat. Nos. 5,623,993 and 5,417,285. Other efforts in horizontal wells involve recipes of a variety of granular components that have predetermined properties such as specific gravity below 1.25 to create the plug using deposition techniques. One example of this is U.S. Pat. No. 7,690,427. 
     Other designs place swelling material in porous enclosures and allow the swelling action to create relative movement that allows a packer to go from a run in to a set position as overlapping petals of swelling material in enclosures rotate relatively to reach a sealing configuration in a borehole. This technique is illustrated in U.S. Pat. No. 7,422,071. 
     What is needed and provided by the present invention is a plug that can be set with a setting tool that creates relative movement and features a solid granular material in a porous enclosure where the setting action alters the shape of the enclosure to attain the set position. This can be done by bringing one end closer to another end and preferably through a passage in an annularly shaped sheath. Alternatively a swage can be brought through a passage in an annularly shaped sheath to enlarge the passage and in so doing set up the fill material in the sheath to push against the surrounding wellbore while a valve such as a flapper closes the passage to pressure from above. The porous enclosure can then be undermined in a variety of ways to allow the granular material to escape where it can be removed with fluid circulation. In some variations, a mandrel allows flow therethrough until an object is landed on a seat for zonal isolation. In other instances the mandrel can be undermined as a way of letting the granular material escape. The retaining porous material can be dissolved or in other ways removed so that it will not interfere with the working of other tools in the borehole. For fracturing plug purposes, perfect sealing is not required as long as sufficient flow past the plug is sufficiently slowed so that the acting pressure can deliver the requisite flow into the fractures to further open them, in the known manner. The use of a mandrel can also be optional and the plug structure can comprise a granular material in a porous enclosure that folds on itself to set. An optional lock feature or a valve to prevent reverse flow in the setting location when relative movement occurs can also be incorporated. These and other features can be incorporated into the design as will be more readily apparent to those skilled in the art from review of the details of the description of the preferred embodiment and the associated drawings, while understanding that the full scope of the invention is to be determined from the appended claims. 
     SUMMARY OF THE INVENTION 
     The removable plug features a solid material that is housed in a porous container that has its shape changed to transition from the run in shape to the set shape. A running string and setting tool that creates relative movement deliver the plug and pull on its lower end while holding the top stationary against a backing plate. The container is pulled into itself as the radial dimension grows for the set. There can be a mandrel that remains in position and can lock to the backing plate or alternatively there can be no mandrel or a removable mandrel. In an alternative embodiment a setting tool pulls a swage through a passage in an annularly shaped sheath to set up the granular material in the sheath to seal against the borehole wall while the enlarged passage is closed off with a valve such as a flapper after the swage exits the passage. The porous container can be removed in a variety of ways to let the solid material escape to be removed with fluid circulating in the wellbore. Alternatively the mandrel can be undermined to let the solid material escape for recovery. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view for run in of one embodiment of the removable plug; 
         FIG. 2  is the view if  FIG. 1  in the setting process as the mandrel is raised internally of the plug; 
         FIG. 3  is the view of  FIG. 2  with the plug in the set position and the mandrel removed; 
         FIG. 4  is an alternative embodiment of the plug shown in the run in position; 
         FIG. 5  is the view of  FIG. 4  during the setting process; 
         FIG. 6  is the view of  FIG. 5  with the plug in the set position and the mandrel left in place; 
         FIG. 7  is an alternative embodiment schematically illustrated in the run in position; 
         FIG. 8  is the view of  FIG. 7  showing the swage advanced through the passage in the sheath and the passage closed with a flapper to differential pressure from above. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIG. 1  the wellbore  10  can be cased or open hole. An elongated porous sheath  12  can be made of a variety of materials that have the requisite strength to contain the loose solid material  24  contained inside as the shape of the sheath  12  is changed. The sheath  12  can be a mesh material using high strength fibers such as Kevlar® or it can also be made of textile materials that are more readily undermined when it is time to release the plug while at the same time minimizing the presence of large pieces of the sheath  12 . One possible such sheath material would be nylon. Another is controlled electrolytic material that degrades under certain well conditions to release the fill material  24  when a plug release is needed. The sheath  12  has an initial annular shape with a mandrel  14  extending through the sheath  12  from a top  16  to a bottom  18 . The connection at  18  between the sheath  12  and the mandrel  14  is designed to release on application of a predetermined force. A running string or wireline or some other conveyance  20  has a setting tool S that creates relative movement between the backup  22  and the mandrel  14 . Such tools are well known in the art and one such tool is the E-4 Wireline Setting Tool sold by Baker Hughes Incorporated. The fill material  24  can be sand, coated proppant, controlled electrolytic material rubber chips or some other solid granular material that will be retained by the sheath  12  as the setting tool S it actuated as shown in  FIG. 2 . For release the controlled electrolytic material can degrade with well conditions to allow the sheath  12  to go slack so that the plug can be removed.  FIG. 2  illustrates the lower end  18  being brought up with the mandrel  14  so that the overall length is shortened as the diameter is increased and the reconfigured shape brings the sheath  12  with the fill material  24  now compressed so that fluid is displaced from its void spaces and those spaces close up. This results in the mass of the fill material  24  in the sheath  12  becoming more and more or completely impervious to through fluid flow. With the radial pressure exerted against the borehole  10  there is now in the  FIG. 2  position some or total zonal isolation. As an option the set position can be  FIG. 2  with the mandrel  14  remaining in the position shown and a ratchet locking system  26  that allows the mandrel  14  to be pulled up but will prevent reverse direction motion can be used. When doing so the setting tool S can have a breakaway connection  28  to allow its removal after the setting is complete. As a different option, the mandrel  14  can be pulled free of the lower end  18  of the sheath  12  without damage to the sheath  12 . The release from the sheath  12  can be based on movement of a predetermined distance or the application of a predetermined force. The mandrel  14  is shown in dashed lines in  FIG. 3  after a release from the lower end  18  and after having been raised clear of the backup  22  which allows the flapper  30  that can be spring biased for example with a coiled spring around a pivot shaft akin to subsurface safety valves to the closed position shown in  FIG. 3 . The closing of the flapper or other type of closure  30  prevents pressure above the set plug from pushing end  18  back to its original position and undermining the set position. As seen in  FIG. 3  the space formerly occupied by the mandrel  14  is closed by the sheath changing shape so that radial sealing force can be exerted against the surrounding borehole  10 . It should be noted that particularly in fracturing application that complete sealing is not required. Rather sufficient isolation to allow the required volume at the required pressure to reach the perforations to initiate fractures, enlarge them and deliver proppant to keep them open for subsequent production works sufficiently well. As noted in the embodiment of  FIGS. 1-3  the act of setting the plug gets the desired isolation. While a hollow mandrel  14  can be used to allow initial flow through such as during running in, removal of the mandrel puts the plug in functional operating position as a barrier. 
     There are alternatives available for plug removal from the  FIG. 2  set position or the  FIG. 3  set position. The mandrel can be made from a material that will degrade in the presence of well fluids or other fluids added to the well. The mandrel  14  can be made from a controlled electrolytic material. Controlled electrolytic materials have been described in US Publication 2011/0136707 and related applications filed the same day. These materials degrade to undermine the seal and can be attached to the sheath  12  in such a manner that the degradation will also cause a failure in the sheath  12  and release of the material  24  that can be removed with circulation or reverse circulation. Alternatively a jet tool can be lowered to reach the sheath and undermine it to allow the material  24  to escape. Another way is to undermine the sheath such as by chemical reaction or melting it so that the sheath remnants and the material  24  can be moved out to the surface with flowing fluids. 
       FIGS. 4-6  are an alternative embodiment that has a hollow mandrel  32  connected to lower end  34  of sheath  36  that has fill material  44  inside. Mandrel  32  is pulled through the backup  38  by a setting tool as previously described for the  FIGS. 1-3  embodiments. The upper end  40  of the sheath  36  is held firm against the backup  38  as the lower end  34  is brought closer to the upper end  40 . The length of the sheath  36  is reduced as its diameter is increased. Eventually contact with the borehole  42  is made. Borehole  42  can be a tubular or it can be open hole.  FIG. 5  shows the onset of the setting process with the lower end  34  coming closer to the upper end  42  that is held stationary by the setting tool S. As before the particulate material  44  is rearranged by the raising of the mandrel  32  as liquids are forced out of the spaces in the material  44  and through the sheath  36  that is preferably a permeable mesh.  FIG. 6  shows the fully set position. The mandrel  32  can have a seat  46  on which an object  48  can be landed for sealing contact so that that the plug will function as a frac plug by isolating adjacent zones even if some seepage flow still occurs. The compaction of the material  44  due to raising the mandrel  32  while holding the backup  38  fixed, reforms loose granular material into a more cohesive whole making it impervious or nearly impervious to flow under differential pressure.  FIG. 6  illustrates a ratchet locking device that allows the mandrel  32  to be raised when bringing end  34  closer to end  40  while preventing movement in the opposite direction to hold the set position of  FIG. 6  against differential pressure from above. Of course, in this embodiment as in the previous embodiment differential pressure from below will merely urge further compression of the material  44  and potentially further bring location  34  closer to location  40  with the lock  50  holding the new position. 
     Those skilled in the art will appreciate that one or more plugs can be commonly mounted and actuated on a common mandrel. While textiles in mesh form are preferred for the sheath other flexible and porous materials are also envisioned while preference is given to materials that can be more easily undermined for the release of the set plug. Alternatively the mandrel can be undermined to remove the compressive stress from the plug in a set position and to optionally also undermine the sheath at the location of attachment to the mandrel. The sheath or mandrel can respond to well conditions that occur naturally for the release or well conditions can be altered deliberately for the release feature. Another way to release is to simply lower a jet tool and size the backup such that some of the jet streams can go around the backup and impact the sheath to cause openings to form in the sheath and thus to start the release process. 
     In essence, an annular sheath contains the solid material that will serve as the barrier and is turned inside out in the setting process that brings a lower end up through a central opening in the sheath shape and toward an upper end that is held fixed by the setting tool. The use of the sheath minimizes the amount of material needed to form a reliable barrier as compared to prior techniques of simply pumping sand onto a porous barrier. While one type of filler material can be used, blends of differing materials are also envisioned. 
       FIGS. 7 and 8  represent an alternative embodiment where the solid material  60  is inside a toroid shaped sheath  62  as before. A passage  64  is the internal void that defines the toroid shape of sheath  62  to define the annular shape for the sheath inside of which resides the solid material  60 . A swage  66  is shown at the lower end of the passage  64  and is connected to a setting tool  68  suspended by a string such as wireline  70 , coiled tubing or other elongated conveyance. Support  72  is retained by swage  66  that is in turn supported by the setting tool  68  while the swage  66  is drawn into the passage  64  as an opposing force is braced against support  72 . As a result the size of the passage  64  increases as the overall dimension of the sheath increases until contact is made with the borehole  74  which can be a tubular or an open hole at the setting location. The increase in dimension of the passage  64  and the contact of the sheath  62  to the borehole  74  compacts the material  60  pushing out fluid and packing the solid material into a cohesive whole that becomes impervious to fluid. The setting tool  68  moves the swage clear of the passage to allow a valve such as a flapper  76  to either fall to the closed position by its own weight or through the use of a biasing member acting on the flapper  76  or its pivot pin  78 . Flow is possible in an uphole direction but is prevented in the opposite direction against the closed flapper  76 . Optionally the force of the biasing can be retained by a latch that is released by the passing swage  66 .  FIG. 8  shows the flapper  76  in the closed position with the setting tool  68  and the swage  66  pulled away from the support  72  that remains behind supported by the material  60  so that differential pressure from above can be sufficiently retained to perform an operation above the plug in the  FIG. 8  set position. The plug need not be leak free and the operation above the plug can be fracturing. 
     As an alternative to the flapper  76 , a mandrel such as  80  that can be positioned with movement of the swage  66  or in the alternative can be expanded by the swage  66  if it is initially in position in the passage  64  can have a seat as described with the previous embodiment so that an object can be dropped on such seat to seal off the passage  64  in this alternative manner. Leaving the passage  64  open after setting the plug allows easy removal of an associated perforating gun that is initially delivered with the plug and the delivery by pumping of a replacement gun through the passage  64  that is still open because an object has yet to be dropped onto the seat in the mandrel. It should be noted that if the mandrel is initially in position in the passage  64  then the swage  66  would start expanding from a location past the seat to avoid damage to the seat and allow the seat to maintain its initial size. 
     The swage  66  can be fixed or variable and the swage direction can also be in the downhole direction as opposed to the uphole direction shown in  FIGS. 7 and 8 . If swaging in the downhole direction, the swage  66  can either be dropped in the hole after expansion or simply passed back through the enlarged passage  64  that its original movement has just created. 
     While relative movement described in the embodiments of  FIGS. 1-6  has been to bring ends such as  34  and  40  together, relative movement in the opposite direction is also contemplated to accomplish the setting. Additionally, when the setting occurs by bringing ends together the release can also be accomplished by forcing the ends apart while forcibly overcoming any latching device designed to hold the set position. For example a tool can find support against the plate  38  while pushing the mandrel  32  and overcoming the ratchet  50 . 
     Optionally a releasable mandrel  80  can be releasably attached to the swage  66  to be deposited in the expanded passage  64  after the swage  66  passes. The mandrel  80  can be solid or it can have a passage therethrough that is later closed by the flapper  76 . 
     The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below: