Abstract:
A method of making an anisotropic filtration media includes, foaming a media, straining the media in a selected direction, and relieving strain of the media in the selected direction.

Description:
BACKGROUND 
     Filtration media that have anisotropic flow and filtration characteristics typically vary these characteristics in the direction of fluid flow. For example, the sizes of particles filtered out by a typical anisotropic filtration media decreases in the direction of fluid flow through the media. Some applications, however, may benefit from an anisotropic filtration media that differs in directions other than that of the fluid flow. New anisotropic filtration media and methods for making such media would therefore be well received in the art. 
     BRIEF DESCRIPTION 
     Disclosed herein is a method of making an anisotropic filtration media. The method includes, foaming a media, straining the media in a selected direction, and relieving strain of the media in the selected direction. 
     Further disclosed herein is an anisotropic filtration media. The anisotropic filtration media includes, a body having a foamed structure, and a plurality of cell walls separating a plurality of cavities defining the foamed structure, and a plurality of the plurality of cell walls oriented near parallel to a selected direction having a greater percentage of openings ruptured therein by straining of the body than a plurality of the plurality of cell walls oriented further from parallel to the selected direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike: 
         FIG. 1  depicts a partial cross sectional view of an anisotropic filtration media disclosed herein; 
         FIG. 2  depicts a partial cross sectional view of an isotropic media used in the production of the anisotropic filtration media of  FIG. 1 ; and 
         FIG. 3  depicts a tubular screen constructed of the anisotropic filtration media of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     A detailed description of one or more embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures. 
     Referring to  FIG. 1  an anisotropic filtration media disclosed herein is illustrated at  10 . The anisotropic filtration media  10  includes, a body  14  having a foamed structure defined by a plurality cavities  18  with cell walls  22  surrounding each of the cavities  18 . Some of the cell walls  22  have openings  26  therethrough that fluidically connect the cavities  18  that are adjacent to the cell walls  22  having the openings  26 . The openings  26  are not distributed evenly through the body  14  but instead are distributed such that more of them are located on the cell walls  22  that are oriented nearer to parallel to a first direction, as indicated by the arrows  34 , than are oriented further from parallel to the first direction. This nonsymmetrical distribution of openings  26  in the media  10  causes the media  10  to be anisotropic. The anisotropic nature of the media  10  results in greater restriction of fluid flow in directions parallel to the arrows  34  and less restriction to fluid flowing in directions orthogonal to the arrows  34 . 
     Referring to  FIG. 2 , the anisotropic structure of the media  10  is created from a body  48  that, as illustrated here, is an isotropic structure in the as-foamed condition. Most, and possibly all, of the cell walls  22  of the body  48  are free of any of the openings  26  (only in  FIG. 1 ). The openings  26  are formed in the cell walls  22  in response to the body  48  undergoing mechanical straining. One strain that will make tears in the cell walls is a compressive strain, or compaction, that causes buckles as described below. Another is a shear strain (that is equivalent to a superimposed tension and compression along mutually orthogonal axes oriented ±45° from the shearing direction). This also causes buckles in the cell walls  22 . Tension may also be used to preferentially open cell walls  22  by simple tearing. In the illustrated embodiment the compaction is in the direction of arrows  34 . This compaction causes the cell walls  22  that are aligned more parallel to the arrows  34  to buckle, thereby stressing the material of the cell walls  22  resulting in tearing and generation of the openings  26  therethrough. Dashed lines  52  in the cell walls  22  highlight the cell walls  22  that are aligned near enough to parallel with the arrows  34  for tearing to occur thereto. It is these cell walls  22 , as shown in  FIG. 1 , that have openings  26  therein. In contrast, the cell walls  22  without the dashed lines  52  happen to be aligned in orientations further from parallel with the arrows  34  and, as such, do not buckle under the compaction and consequently do not tear to form the openings  26 . Optionally, a structure (not shown) may be employed to support the body  48  to thereby prevent it from expanding in directions orthogonal to the arrows  34  while the compaction is taking place. Such support can minimize or prevent buckling of the body  48  itself to thereby prevent undesirable localized tearing in some of the cell walls  22 . After the mechanical compaction is removed the body  14  returns dimensionally toward the dimensions of the body  48 . Exact dimensional recovery to the original, pre-compaction dimensions, however, is not needed. For example, the recovery may be to a dimension less than, greater than or roughly equal to the original dimension. If, for instance, the foam dimension has been reduced by lower pressure inside the cavities  18  compared to ambient pressure, the recovered dimension may be greater than the initial dimension. 
     Referring again to  FIG. 1 , since the majority of the openings  26  are in the cell walls  22  aligned nearer to parallel to the arrows  34  it can be observed that fluid flow through the body  14  will have less restriction in directions orthogonal to the arrows  34  than in the direction of the arrows  34 . Arrows  54  show possible fluid flow paths through the cavities  18  and the openings  26  for fluid flowing generally in the direction of arrows  44 . Restriction to flow is determined, in part, by sizes of the openings  26 . The sizes of the openings  26  also determine the filtration characteristics of the completed media  10 . Although the number of, and sizes of the openings  26  are somewhat random they depend upon parameters of the foamed body  48  including, material, percent solid, the size of the cavities  18 , percentage of compaction employed, and a temperature at which the compaction takes place, for example. For example, compaction at room temperature may result in either larger or smaller sized openings  26 , and more or fewer openings  26  than compaction at an elevated temperature. An operator, therefore, through control of at least the foregoing parameters, can control the filtration characteristics through the anisotropic filtration media  10 . 
     Referring to  FIG. 3 , an embodiment of a screen  56  constructed of the anisotropic filtration media  10  is illustrated. The screen  56  has a tubular shape and has been compacted in a longitudinal direction along arrows  60 . The finished screen  56  therefore has anisotropic flow and filtering characteristics. Flow through the screen  56 , for example, is less restrictive in a radial direction, along arrows  64 , than it is in a longitudinal direction, along arrows  60 . Similarly, the filtration characteristics differ between these two directions as well. Such anisotropic characteristics may be desirable for certain applications. For example, the screen  56  could be employed in earth formation borehole applications concerned with hydrocarbon recovery or carbon sequestration. The screen  56  could be attached around a perforated pipe (not shown) and installed in a wellbore to filter fluid flowing therethrough in either radial direction. In a hydrocarbon recovery application the screen  56  can be employed to filter out sand and gravel particles to reduce erosion of downstream components and to help maintain the structure of the formation. The screen could also be configured to expand radially after positioning within the borehole to provide even greater support to the formation. Additionally, the longitudinal restriction to flow through the screen  56  can help isolate flow from one portion of the formation from that of another portion of the formation displaced longitudinally along the borehole, for example, such as between a highly permeable portion and a less permeable portion. 
     Radial expansion of the screen  56  could result from material selection of the media (i.e. from an expandable material), or from radial compaction of the screen  56  prior to miming into the borehole, or combinations of both. Employable materials include, elastomers/polymers, metals, glass and combinations of the foregoing, for example. 
     While the invention has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the claims. Also, in the drawings and the description, there have been disclosed exemplary embodiments of the invention and, although specific terms may have been employed, they are unless otherwise stated used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention therefore not being so limited. Moreover, the use of the terms first, second, etc. do not denote any order or importance, but rather the terms first, second, etc. are used to distinguish one element from another. Furthermore, the use of the terms a, an, etc. do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.