# Patent

## Title
Anisotropic filtration media

## 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.

## Background
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.

## Claims

1. An anisotropic filtration media, comprising
a perforated pipe;
a body having a foamed structure disposed around the perforated pipe; 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, the openings varying in size.

2. The anisotropic filtration media of claim 1, wherein the body has a tubular shape.

3. The anisotropic filtration media of claim 2, wherein the selected direction is longitudinal.

4. The anisotropic filtration media of claim 1, wherein the straining is in the selected direction.

5. The anisotropic filtration media of claim 1, wherein the body is configured to restrict flow therethrough in the selected direction more than in directions significantly different from the selected direction.

6. The anisotropic filtration media of claim 1, wherein the body is selected from the group consisting of elastomeric, polymeric, metal, glass and combinations of the foregoing.

7. The anisotropic filtration media of claim 1, wherein size variation of the openings is random.