Abstract:
A shape memory polymer is initially fabricated to a size where its peripheral dimension will be at least as large as the borehole wall in which it is to be deployed. After the initial manufacturing the material temperature is elevated above the transition temperature and the material is stretched on a mandrel to retain its inside dimension as its outside dimension is reduced to size that will allow running the seal to a desired subterranean location without failing the material during the stretching. The material is allowed to cool below the transition temperature to hold the new shape. The material on the mandrel is then secured to a tubular string and delivered to the desired location. Wellbore fluid at given temperature raises the material again above the transition temperature, which causes the material to revert to its originally manufactured shape.

Description:
FIELD OF THE INVENTION 
       [0001]    The field of the invention is isolation devices for downhole use and more particularly those that employ shape memory polymers and are initially shaped for the set dimension and reconfigured for a smaller dimension for run in followed by reversion to the manufactured shape when exposed to downhole fluids at given temperature and time. 
       BACKGROUND OF THE INVENTION 
       [0002]    Shape memory materials have been used in packers to isolate portions of a wellbore as illustrated in U.S. Pat. Nos. 7,743,825 and 7,735,567. In these patents a packer made of a shape memory polymer (SMP) was delivered to a subterranean location and a heat input was applied using well fluids or a heater and an auxiliary compressive force applied to the packer element when it was made softer by the application of heat. The outside compressive force continued to be applied as the set position was achieved and the heat source was removed. The SMP then grew more rigid as it cooled with the mechanical force applied and the packer was ready for service. The sealing force in those references derived from the mechanical compression under heating conditions rather than any inherent shape memory features of the material. However, the methods described in these patents may require additional heating sources or a heating element to raise the temperature above the material&#39;s soft point or transition temperature. Therefore, it is desirable to have a material that can change shape from one to another by itself at downhole conditions to create sealing. The material can be run in hole in a small diameter, and activated to expand to larger diameter to fill space between a mandrel and a surrounding borehole. The material should preferably also be strong to maintain boost loads for sealing. 
         [0003]    Relevant art to the present invention includes U.S. Pat. Nos. 6,976,537; 6,907,937; 6,907,936; 6,854,522; 6,446,717; 5,803,172; 4,475,847; 4,415,269; 4,191,254; 4,137,970 and 3,782,458 and US Patent Applications: 2006/0124304 and 2005/0205263 as well as PCT references: WO 05059304; WO 05052316 and WO 03014517. 
         [0004]    The present invention takes advantage of the shape memory feature of the material by making the material initially to the desired set dimension when the packer is placed at the desired subterranean location. Thus the ultimate set dimension is the dimension to which the packer element is initially produced. Before deployment the packer material is stretched when heated with a dummy or the actual mandrel placed inside. The material is stretched to reduce the outside dimension as much as possible without failure in a manner that keeps the inside diameter constant because the mandrel is in position. The material is cooled while retaining the stretching force so that a run in shape is developed. The run in shape has a lower profile for running in and the shape that the element will revert when heated downhole is the original manufactured shape. Regaining the original shape puts the element into contact with the surrounding wellbore wall. The seal made by such contact can be enhanced by an applied mechanical force. Those skilled in the art will better appreciate the full scope of the invention from a description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be determined from the appended claims. 
       SUMMARY OF THE INVENTION 
       [0005]    A shape memory polymer is initially fabricated to a size where its peripheral dimension will be at least as large as the borehole wall in which it is to be deployed. After the initial manufacturing the material temperature is elevated above the glass transition temperature and the material is stretched on a mandrel to retain its inside dimension as its outside dimension is reduced to size that will allow running the seal to a desired subterranean location without failing the material during the stretching. The material is allowed to cool below the glass transition temperature to hold the new shape. The material is designed and fabricated so that its glass transition temperature is preferably near downhole temperature. The material on the mandrel is then secured to a tubular string and delivered to the desired location where it contacts wellbore fluid at a wellbore temperature which is usually higher than surface temperature. The hot wellbore fluid raises the material again above the material glass transition temperature, which causes the material to revert to its originally manufactured shape. The original shape is at least as large as or larger than the borehole size so that a seal ensues. Optionally, external force can also be applied as the material is heated to cross its transition temperature and that force can be retained to provide an assist to sealing beyond that created by the reversion of the material to the initially manufactured shape. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a section view of an as manufactured element put on a mandrel; 
           [0007]      FIG. 2  is the view of  FIG. 1  showing an optional spring added on the mandrel and the element stretched while above its transition temperature and allowed to cool on the mandrel before running in to a subterranean location; 
           [0008]      FIG. 3  is the view of  FIG. 2  when the element is at the subterranean location and has reverted to its manufactured shape of  FIG. 1  due to crossing its transition temperature with the spring providing additional sealing force; 
           [0009]      FIG. 4  is an alternative embodiment to  FIG. 1  where the original manufactured shape is cylindrical; 
           [0010]      FIG. 5  shows the seal brought above its transition temperature and stretched on a mandrel and allowed to cool down prior to running into a subterranean location; and 
           [0011]      FIG. 6  is the view of  FIG. 5  with the seal at the subterranean location and the seal having crossed its transition temperature to assume a sealing position in the borehole. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0012]      FIG. 1  shows a sealing element  10  having ends  12  and  14  and a middle section  16  that is curved radially outwardly to a dimension  18  when initially manufactured. Dimension  18  equals or exceeds the borehole dimension at the deployment location  20 . The element  10  can be made in a mold or otherwise fabricated to an outer dimension  18  and further with a bore  20  that will allow a mandrel  22  to be inserted before the next manufacturing step. 
         [0013]    While in the  FIG. 1  as manufactured condition with the mandrel  22  in position, the element  10  is heated as schematically represented by arrow H. As it softens when the transition temperature of the shape memory polymer that is the preferred material for the element  10  is heated as represented by arrow H, a tensile force represented by arrow F is applied. As a result the internal dimension of the element  10  remains the external dimension  24  of the mandrel  22 . The amount of applied force represented by arrow F is controlled so that the exterior dimension  26  is reduced with respect to the manufactured exterior dimension  18  shown in  FIG. 1 . In one end position of the stretching under the force F the exterior dimension  26  winds up at the manufactured thickness of ends  12  or  14  in  FIG. 1 . Alternatively, the end dimension under the application of force F as the element is above the transition temperature can be to a smaller dimension than the manufactured dimension of the ends  12  or  14  as shown in  FIG. 1 . Those skilled in the art will realize that the smaller the run in exterior dimension the faster the element  10  can be run into a given borehole. On the other hand, care must be taken to avoid overstretching in the heated condition for there is a possibility of creating thin portions or even having the wall of the element  10  simply fail if the applied force F is too high or applied for too long. 
         [0014]    A biasing member  28  which can be a coiled spring or a stack of Belleville washers or other equivalent structure can be optionally slipped over the mandrel  22  so that it finds support off of flange  30  and bears against the lower end  32  of the element  10  after the stretching using force F is accomplished with the element above its transition temperature followed by allowing the element to be cooled down so that it holds its stretched shape shown in  FIG. 2 . The spring is optional and if used can be held in a compressed state as the element  10  is stretched as shown schematically with force F. 
         [0015]    It should also be noted that in the original manufacturing shown in  FIG. 1 , the mandrel  22  can already be in position for example in the mold that is used to manufacture the initial shape. Alternatively, the mandrel  22  can be inserted through the openings  20  past both ends  12  and  14  with preferably an interference fit so as to minimize leakage flow through the interior of the element  10  and along the mandrel  22  when ultimately deployed as in  FIG. 3 . 
         [0016]    Referring again to  FIG. 2 , when the desired dimension on the exterior of the element  10  is reached, the heat H is removed and the force F is subsequently removed as the consistency of the element  10  gets firmer. If the optional biasing member  28  is used and pre-compressed, any retainers holding the member  28  in the compressed position are released and the biasing member bears against the element  10 . 
         [0017]    The element is then made a part of a tubular string (not shown) and run into a subterranean location whose opening size  21  is no larger than the manufactured outer dimension  18  shown in  FIG. 1 . As well fluid or an auxiliary heat source H′ is applied, the shape of the element  10  reverts to the  FIG. 1  as fabricated shape and the central section  16  extends to dimension  18  which seals against the borehole dimension  21  especially if the size of the borehole  21  is smaller than the manufactured outer dimension  18 . If the optional biasing device  28  is used then an additional sealing force is applied to hold the section  16  against the borehole wall whether it is in open hole or cased or lined hole. It should be noted that the length of the element  10  shrinks in the axial direction of arrow F as it grows in the radial direction, as seen by comparing  FIGS. 2 and 3 . The biasing device  28  ideally has enough axial movement capability to compensate for the axial shrinkage of the element  10  and still have an available force that can be delivered into the element  10  to create or to enhance the seal against the borehole dimension  21 . 
         [0018]    While the biasing device  28  is shown at end  14 , those skilled in the art will appreciate that other locations and more than one biasing device  28  can be used. For example, the biasing device can be installed near each end  12  and  14 . Alternatively, the biasing device can be inserted in region  34  and can be in the form of a leaf spring  29  supported by the mandrel  22 . When the element  10  is then heated and stretched after being manufactured, the leaf spring is flattened and held in that position as the temperature is then lowered and the force F removed to hold the leaf spring in the flattened position. When warmed in the subterranean location with heat H′, the element as before reverts to its manufactured shape and the spring acts to push out the central portion  16  to create or enhance the seal. 
         [0019]    As another option for a biasing member  28  or  29 , the material used can be a shape memory alloy fabricated for a long dimension and reformed above its transition temperature to a shorter length or extension when assembled to the mandrel  22 . If used as a leaf spring  29  it can be reformed to flat before insertion in an annular space  34  or in the element  10  and before the element  10  has its outer dimension reduced using force F. When at the subterranean location and heat in the form of H′ is delivered, the biasing member reverts to its manufactured shape and original length and in so doing applies a force to the element  10  to create or enhance the seal. If used as a leaf spring the manufactured shaped can be bowed and then it can be heated and reshaped above its transition temperature and inserted in space  34  or within the element  10  itself. At the subterranean location the applied heat H′ will cause the spring to bow and push out the central section  16  to initiate or enhance the seal at dimension  21 . 
         [0020]    Arrow  36  schematically represents another option of being able to deliver a fluid into space  34  and selectively retain the fluid in the space  34  to initiate or enhance the seal against dimension  21 . 
         [0021]      FIGS. 4-6  represent what was shown and discussed as to  FIGS. 1-3  with the  FIGS. 4-6  more simplified so that the mandrel or the biasing devices are not shown. The mandrel is still used and the biasing device is optional as before. The point of these three FIGS. is that the manufactured shape can be a cylinder with a bore  38  through the seal  10 ′. Comparing to the  FIG. 1  shape where there was a bowed out central section  16 , in  FIGS. 4-6  the manufactured outer dimension  40  is at least as great as the set position with the borehole at dimension  42 . Dimension  44  at the end of the fabrication and reforming steps of  FIGS. 4 and 5  is smaller than the drift dimension of the borehole shown schematically as  42 . Thus exposure to heat H″ at the subterranean location has the element  10 ′ trying to assume the manufactured dimension  40  to create a borehole seal. As with  FIGS. 1-3  the outlined options for a bias force to aid in or create the sealing contact in the borehole are still operative. 
         [0022]    Those skilled in the art will appreciate the in the past when using shape memory polymers for a sealing element such as in U.S. Pat. No. 7,735,567 it was assumed that the nature of the shape memory polymer was such that recovery of the original manufactured shape could not generate the potential energy to create a seal. The present method seeks to take advantage of shape recovery to accomplish a seal whether aided with biasing members or applied fluid force or not. Accordingly the manufactured shape is large enough to create a seal when reverting to that shape happens downhole. Further, is the step of reducing the run in diameter with stretching on a mandrel when the element is above the transition temperature so as to minimize damage during run in and to permit a faster speed for running in while still being able to create a seal when the transition temperature is crossed again at the subterranean location, whether aided by a biasing member or not. As described the biasing member can take a variety of shapes and can optionally be made of a shape memory alloy which delivers a greater potential energy force when reverting to its manufactured shape on heat input at a downhole location. The manufactured shape can be cylindrical on the outside or it can have a central segment that is bowed out to ease sealing ability during reversion to the original shape downhole. 
         [0023]    While a single element is shown, multiples can be used in a single assembly with the manufactured shapes being identical or different. 
         [0024]    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: