Abstract:
In a particle or sand screen control assembly for mounting on a base pipe used in a well, a sealing strip preferably in the form of a metal strip is used in a weld joint that joins the metal mesh screen of filter media to a solid metal structure or “safe edge”. The sealing strip covers the pores in the screen proximate the metal structure to which it is welded. The sealing strip is a separate thin sheet of metal that is compatible with the welding metal used in the weld joint, such that the sealing strip becomes unitary with the weld joint. Prior to welding, the sealing strip may be bent around the screen if desired, or may lie flat along the top or bottom surface of the screen.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to welding processes, and more particularly to weld joints and welding processes for welding finer metal particle control screens to compatible metallic structures for control screen assemblies adapted to mount on a perforated pipe used in a well. 
     BACKGROUND OF THE INVENTION 
     It is well known to provide a particle control screen assembly for a perforated pipe used in a well, the assembly typically including at least one outer cylindrical perforated plate and at least one inner fine mesh control screen contained therein. For example, exemplary arrangements of particle control screen assemblies assembly for a perforated pipe used in a well are disclosed in U.S. Pat. Nos. 5,782,299, 5,899,271, and 5,937,944, all to Simone et al., and commonly owned by the present assignee of the instant patent application. Other arrangements of particle screen assemblies for a perforated pipe used in a well are disclosed in U.S. Pat. No. 5,411,084 to Padden, U.S. Pat. No. 5,232,048 to Whitebay, U.S. Pat. No. 4,064,938 to Fast. All six of these patents listed in the two preceding sentences are hereby incorporated by reference for the purpose of illustrating possible uses of the present invention as will later be more greatly appreciated. 
     In this art, it is desirable to minimize leakage of sand or other particulate into the perforated pipe for obvious reasons. As will be appreciated by those skilled in the art when viewing the present invention, the prior art attempts are deficient in minimizing leakage of sand or other particulate into the perforated pipe. 
     SUMMARY OF THE INVENTION 
     It is an objective of the present invention to further minimize leakage of sand and other particulate past particle control screen assemblies for a perforated pipe used in a well. 
     It has been discovered that the welding processes used in providing high strength permanent joints in particulate screen assemblies for a perforated pipe used in a well can tend to burn the thin wire material in the mesh screens due to the intense heat necessary for welding adjacent metal structures. This can occasionally result in the formation of gaps larger than the pore sizes in the screen and therefore the increased possibility of leakage of larger particles. The problem is particularly acute at weld locations between the particulate screen medium and a solid metal support structure. The present invention provides a solution to the problem through the arrangement of a sealing strip preferably in the form of a metal strip to cover the pores in the screen proximate the metal structure to which it is welded. The sealing strip ensures that large particles can not pass at locations near the weld regardless of whether or not wires of the mesh screen have been burned too extensively creating the possibility of gaps larger than the pore size of the mesh screen. 
     In the preferred embodiment, the sealing strip is a separate thin sheet of metal that is compatible with the welding metal used in the weld joint, and is arranged along the edge of the mesh screen prior to welding, such that the metal strip becomes integral or unitary with the weld joint. Prior to welding, the sealing strip may be bent around the mesh screen if desired, or may lie flat along the top or bottom surface of the screen. 
     Other object and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings incorporated in and forming a part of the specification, illustrate several aspects of the present invention, and together with the description serve to explain the principles of the invention. In the drawings: 
     FIG. 1 is a partial cross section showing the novel weld joint in conjunction with one of the exemplary embodiments of a sand control screen assembly mounted on a base pipe in a well, according to one embodiment of the present invention. 
     FIG. 2 is an enlarged cross section of the novel weld joint illustrated in FIG.  1 . 
     FIGS. 3-4 illustrate alternative embodiments of the weld joint of FIG. 2 shown in cross section. 
     FIGS. 5-7 illustrate further alternative embodiments of the novel weld joint shown in cross section but with different types and arrangements between the filter media and the metal structure to which the media is welded as compared to FIG.  1 . 
    
    
     While the invention will be described in connection with certain preferred embodiments, there is no intent to limit it to those embodiments. On the contrary, the intent is to cover all alternatives, modifications and equivalents as included within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, the present invention is illustrated as being incorporated into a sand or other particle filter system  20  that comprises a well screen or particle control screen assembly  22 . The particle control screen assembly  22  is mounted on a base pipe  24  that is disposed, for example, in a wellbore  26 . In order to draw in petroleum or natural gas from the wellbore  26 , a portion of the base pipe  24  is perforated with holes  28 . To prevent sand and other particles from being drawn into the base pipe  24  through such holes  28 , the perforated portion of the base pipe is covered by the particle control screen assembly  22 . In the illustrated embodiment illustrated in FIG. 1, the screen assembly  22  comprises a preferably multi-layer woven mesh filter media  30  surrounded by a protective wrapper  32  that includes inner and outer perforated layers  34 ,  36  of relatively thin metal plate material, each constructed into a cylindrical tube. 
     Further general details of the structural configuration of this embodiment depicted in FIG. 1 with the exception of the improved weld joint can be had with reference to U.S. Pat. No. 5,899,271, but with the understanding that the particle filter system  20  shown in FIG. 1 of this application illustrates one of the many possible configurations for sand screen assemblies. It will be appreciated by those skilled in the art that the improved weld joint and process of the present invention can be utilized various other structural configurations of particle control screen assemblies (eg. such as those disclosed in any of the aforementioned patents) where it is necessary or desirable to weld a particulate screen to another structure. 
     Before turning to further details of the present invention, it should be first noted that the woven mesh filter media  30  has a selected pore size to selectively prevent the inflow of certain sizes of particles through the basepipe. This filter media  30  is preferably a diffusion bonded or sintered wire mesh metal material, typically comprising stainless steel material. Exemplary filter media  30  material is commercially available from Purolator Facet, Inc. (and its predecessor Purolator Products Company), 8439 Triad Drive, Greensboro, N.C. and are sold under the trademarks POROPLATE® and POROPLUS®. Although the filter media  30  can be made of a single layer, it is preferably comprised of several layers of differing pore or mesh size. For example, the filter media  30  illustrated in the present embodiment includes two layers, including a coarser mesh layer  38  and a finer mesh layer  40 . The present invention is also applicable to single layer or three or more layers if desired. Because the base pipe  24  is generally cylindrical, the filter media  30  is formed into a cylindrical structure. As such, the term cylindrical as used herein also is meant to include pleated filter media configurations as shown in the aforementioned U.S. Pat. No. 5,411,084. 
     To provide sufficient sand and particulate filtering in this application, the filter media is adapted for a perforated pipe used in a well. In particular the pores of the filter media  30  have an effective size between about 50 micron and about 250 micron such that particles larger than that in diameter do not pass, although pore sizes of up to about 500 micron may be acceptable in some well applications. It should also be noted that the cylindrical filter media has an cross sectional thickness or radial thickness of between about 0.02 inch and about 0.38 inch, preferably between about 0.05 and 0.07 of an inch. In well applications, the filter media  30  typically also has an axial length of between about 3 feet and about 10 feet. It will be appreciated that actual size ranges listed in this paragraph can vary depending upon actual well requirements. 
     It should also be noted that welded joints are often used in particle control screen assemblies for purposes of providing strength. In particular, the metal of the weld integrally unitizes two separate compatible metal structural components because during the welding process, the metal material in the edge portions of both structural components melts and becomes integral or unitary with the weld. The weld  42  provides a very strong joint that is able to reliably carry the axial and radial forces imparted on the filter media  30  during operation of the well. 
     With the foregoing in mind, it has been discovered that the welding processes used in providing high strength permanent joints in particulate control screen assemblies for a perforated pipe used in a well can create small gaps or holes sized larger than the pores in the filter media. In particular, it has been realized that achieving the strength of a weld  42  causes the filter media  30  to melt or “burn up” an undesirable amount during the welding process. Part of the reason for this is that the corresponding metal structure (shown as a “safe edge” or steel support tube  44  in FIGS. 1 and 2) to which the filter media  30  is welded is typically much more solid and does not have the thin individual screen wires  46  of the filter media  30 . The result is that leakage may result in locations where the screen wires  46  have been melted too much leaving too large of gaps or holes in the screen mesh material. 
     In accordance with the present invention, a sealing strip is used at the screen edge and in the weld  42  that may take the form of a separate thin, solid metal strip  48 . The metal strip  48  is arranged along the filter media edge  50  that is welded to metal support tube  44 . The support tube  44  provides a “safe edge” that protects the filter media  30  at its end and that can in turn be welded to other structures or welded upon as desired without concern about burning up the screen wires  46  of the filter media  30 . In any event, the metal strip  48  covers an axial length of the filter media  30  greater than the maximum length of screen wire  46  bum that is induced as a result of the welding process such that no holes or gaps larger than the effective pore size of the filter media  30  are formed. The support tube  44  or other metal support structure may have a radial thickness or cross sectional thickness of between about 0.02 inch and 0.38 inch, and is preferably solid. It has been found that a metal strip having a thickness of about 0.005 inch and about 0.02 inch works sufficient for this application. 
     The material of the weld  42  is conventional and is selected such that it is compatible with the metal of the support tube  44  (which is preferably stainless steel) and the filter media  30  (which is preferably stainless steel). The metal strip  48  which may be Inconnel type steel or stainless steel and melts during the welding process. The metals of the support tube  44  and the filter media  30 , have a sufficiently similar melting point such that during the welding process the edge of the support tube  44  and the edge  50  of the filter media  30  melt and integrally bond with the weld  42  such that the weld  42  unitizes the filter media  30  with the metal support tube  44 . Likewise the metal strip  48  also has a similar melting point such that the metal of the strip  48  melts and integrally bonds with the weld  42 . 
     FIGS. 2-4 illustrate some of the various arrangements and locations for the metal strip  48 ,  48   b ,  48   c  relative to the weld  42 ,  42   b ,  42   c  in arrangements where the cylindrical support tube  44  and cylindrical filter media  30  are axially butted up against each other such that they may be welded together (the tube  44  and the media  30  having similar diameters). In the embodiment of FIG. 2, the metal strip  48  takes the form of a cylindrical ring including a first axially extending portion  60  covering the inner radial periphery of the finer mesh  40  of the filter media  30  and a second axially extending portion  62  covering the edge of the metal tube  44 . In the second embodiment shown in FIG. 3, the metal strip  48   b  is bent at two locations to include a first cylindrical portion  64  covering the edge of the coarser mesh  38  and a second cylindrical portion  66  covering the edge of the finer mesh  40  and an intermediate radially planar portion  68  disposed between the ends of the filter media  30  and the metal tube  44 . In FIG. 4, the metal strip  48 c is a cylindrical member arranged between the terminating edges of the coarser mesh  38  and finer mesh  40 . The metal strip  48   c  may also be integrally formed with or attached to either or both of the meshes  38 ,  40  if desired prior to the welding step. The second and third embodiments have the advantage of being able to cover any leakage holes on both the coarser mesh and finer mesh material by being in direct contact with both meshes. It should be noted that in each of these embodiments the metal strip  48  is in contact with and covers the edge of the finer mesh  40  where particulate leakage is of particular concern. 
     Other possible applications of the invention are illustrated in the further alternative embodiments of FIGS. 5-7. The embodiment of FIG. 5 illustrates a novel weld joint  42 d at a T-Bone integrally joining a cylindrical tube of filter media  30  to a planar metal structure in the form of a end plate or disk  70 . Such end plates have been used in well screens as shown in U.S. Pat. No. 5,232,048. The metal strip  48   d  extends axially along the edge of the filter media  30  and in contact with the finer mesh  40 , and may be bent or straight. Another possible application is in overlapping or telescopically interfitting metal structures as shown in FIG. 6 wherein the tube  72  or the filter media  74  have different diameters such that end portions of the two metal structures overlap joined by weld  42   e.    
     Other uses of the invention are also contemplated. For example, the improved weld joint of the present invention may also be used to form a seam between two edges of the filter media  30  with strip  48   f  and weld  42   f  as shown in FIG. 7, or may be used to join the filter media  30  with other metal structures such as perforated plate if desired. 
     The foregoing description of various preferred embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments discussed were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.