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BACKGROUND OF THE INVENTION 
     The present invention relates generally to operations performed in conjunction with a subterranean well and, in an embodiment described herein, more particularly provides apparatus including a high strength water soluble plug. 
     For economy of manufacture, convenience of assembly and use, etc., it would be quite desirable to fabricate certain components of apparatus used in operations performed in conjunction with subterranean wells of soluble polymeric material. In this manner, operation of the apparatus could be controlled, at least in part, by controlling contact between the polymer and the fluid in which it is soluble. 
     For example, it would be desirable to construct a plug apparatus in which a plug member blocking flow through a fluid passage included a soluble polymer. Subsequent contact between the polymer and the fluid in which it is soluble would enable the plug member to be dispersed, thereby permitting flow through the fluid passage. 
     As another example, it would be desirable to construct an apparatus in which a displacement member displaces in operation of the apparatus, and in which a blocking member blocks displacement of the displacement member. Subsequent contact between the polymer and the fluid in which it is soluble would permit displacement of the displacement member, thereby controlling operation of the apparatus. 
     Therefore, it would be advantageous to provide apparatus in which a soluble polymer is utilized to control, at least in part, operation of the apparatus. It is accordingly an object of the present invention to provide such apparatus. 
     SUMMARY OF THE INVENTION 
     In carrying out the principles of the present invention, in accordance with embodiments thereof, apparatus is provided which is used in conjunction with operations performed in a subterranean well. In one embodiment, a plug member of a plug apparatus includes a soluble polymer. In another embodiment, an apparatus blocking member, which includes a soluble polymer, blocks displacement of a displacement member. 
     In one aspect of the present invention, a plug apparatus includes a plug member blocking flow through a fluid passage. The plug member is constructed of a polymer soluble in a fluid. The fluid is placed in contact with the soluble polymer, thereby permitting the plug member to be dispersed and permitting flow through the fluid passage. The plug member may also include other soluble material, such as salt, and crack initiator material, such as sand. 
     In another aspect of the present invention, an apparatus includes a displacement member and a blocking member preventing displacement of the displacement member. In an embodiment of the apparatus disclosed herein, the apparatus is a valve in which displacement of a closure member is blocked by a member constructed of a polymer soluble in a fluid. The fluid is placed in contact with the soluble polymer, thereby permitting the closure member to displace and operate the valve. 
     These and other features, advantages, benefits and objects of the present invention will become apparent to one of ordinary skill in the art upon careful consideration of the detailed description of representative embodiments of the invention hereinbelow and the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a quarter-sectional view of a first apparatus embodying principles of the present invention; 
     FIG. 2 is a schematic cross-sectional view of a second apparatus embodying principles of the present invention; 
     FIG. 3 is a schematic quarter-sectional view of a third apparatus embodying principles of the present invention; and 
     FIG. 4 is a schematic quarter-sectional view of a fourth apparatus embodying principles of the present invention. 
    
    
     DETAILED DESCRIPTION 
     Representatively illustrated in FIG. 1 is a plug apparatus  10  which embodies principles of the present invention. In the following description of the plug apparatus  10  and other apparatus and methods described herein, directional terms, such as “above”, “below” “upper”, “lower” etc., are used for convenience in referring to the accompanying drawings. Additionally, it is to be understood that the various embodiments of the present invention described herein may be utilized in various orientations, such as inclined, inverted, horizontal, vertical, etc., without departing from the principles of the present invention. 
     The plug apparatus  10  is similar in many respects to the plug apparatus described in U.S. patent application Ser. No. 09/031,632, filed Feb. 27, 1998 and entitled Plug Apparatus Having a Dispersible Plug Member and a Fluid Barrier. The disclosure of that patent application is incorporated herein by this reference. 
     The plug apparatus  10  includes an outer housing  16  and a plug member  12 , which blocks flow through a fluid passage  14  formed generally axially through the plug apparatus. The plug member  12  includes a material  18 , and closures  20 ,  22  above and below the material. The closures  20 ,  22  prevent contact between the material  18  and fluid  24  in the fluid passage  14 . 
     To permit flow through the fluid passage  14 , the material  18  is contacted with a fluid in which at least a part of the material is soluble. The material  18  may be at least partially soluble in the fluid  24  in the fluid passage  14 , and/or the material may be soluble in another fluid  26 , which may be selectively introduced into contact with the material via another fluid passage  28  formed in the plug apparatus  10 . The material  18  is contacted with a fluid in which it is soluble, thereby weakening the material and permitting the material to be dispersed by, for example, creating a pressure differential across the plug member  12 , thereby expelling the closures  20 ,  22  and the at least partially dissolved material  18 . 
     In this embodiment of the present invention, the material  18  is a soluble polymer. Specifically, the material  18  may include a water soluble polymer, such as polyacrylic acid. However, the polymer may be produced from any water soluble monomer which can be polymerized to form a water soluble polymer. For example, the monomer may be acrylic acid, 2-hydroxyethylacrylate, vinyl pyrrolidone, N,N-dimethylacrylamide, etc. Additionally, copolymers, terpolymers, or any combination of water soluble monomers could be used. 
     Other components may be included in the material  18 . For example, the material  18  may include a material which aids in the formation of crack propagation sites, so that the material may be easily broken up for dispersal. An acceptable crack initiation material is sand. Another acceptable crack initiation material is salt, which is also water soluble, and which also aids in the formation of voids in the material if the fluid brought into contact with the material is water. 
     Referring additionally now to FIG. 2, another plug apparatus  30  embodying principles of the present invention is representatively and schematically illustrated. The plug apparatus  30  is similar in many respects to the plug apparatus  10  described above, but differs in at least one substantial respect in that a plug member  32  thereof blocking fluid flow through a fluid passage  34  is constructed of a material  36  having a coating  38  applied thereto. 
     The coating  38  isolates the material  36  from contact with a fluid  40  in the fluid passage  34 . However, the material  36  may be at least partially soluble in a fluid  42  selectively introduced into contact with the material via another fluid passage  44  formed in the apparatus  30 . The material  36  may be similar to the material  18  described above, or it may be another material, without departing from the principles of the present invention. 
     The coating  38  is preferably made of a material which is not soluble in the fluid  40 . The coating  38  may be a non-water soluble plastic or polymeric material. For example, the coating  38  could be made of polystyrene, polycarbonate, epoxy resin, etc. 
     Beneficial results may be obtained by making the coating  38  of a relatively brittle material, so that the coating may be selectively fractured to thereby permit contact between the material  36  and the fluid  40 . For example, a rod, bar or other structure  46  could be lowered into the fluid passage  34  and impacted with the coating  38  to fracture the coating. 
     Referring additionally now to FIG. 3, another apparatus  50  embodying principles of the present invention is representatively and schematically illustrated. In the apparatus  50 , a plug member  52  initially blocks flow through an opening or fluid passage  54  formed through a sidewall of a tubular housing  56  of the apparatus. The plug member  52  isolates an inner fluid passage  58  from communication with the exterior of the housing  56 . As shown in FIG. 3, the plug member  52  and opening  54  are specially constructed to resist a pressure differential directed from the exterior of the housing  56  to the fluid passage  58 , but the plug member and opening could also be constructed to alternatively resist an oppositely directed pressure differential, or to resist pressure differentials from both directions. 
     The plug member  52  includes a material  60 , which may be similar to the materials  18 ,  36  described above. The material  60  may have a coating  62  isolating the material  60  from contact with fluid  64  in the fluid passage  58  and/or from contact with fluid  66  external to the housing  56 . 
     To disperse the plug member  52  and thereby permit flow through the opening  54 , a fluid  68  in which at least a portion of the material  60  is soluble may be selectively introduced into contact with the material via a fluid passage  70  formed in the apparatus  50 , or the material may be placed into contact with one or both of the fluids  64 ,  66 . For example, a rod, bar or other structure, such as the structure  46  shown in FIG. 2, may be lowered in the fluid passage  58  and impacted with an inwardly extending portion  72  of the plug member  52 . Such application of force to the portion  72  by the structure will cause fracture of the coating  62 , or complete dislocation of the portion  72  from the remainder of the plug member  52 , thereby permitting contact between the fluid  64  and the material  60 . 
     Note that either or both of the plug members  32 ,  52  described above may be constructed to have a predetermined strength, so that when a predetermined pressure differential is created across the plug member, the material  36 ,  60  will break, thereby permitting flow through the respective fluid passage  34 ,  54 . 
     Referring additionally now to FIG. 4, another apparatus  80  embodying principles of the present invention is representatively and schematically illustrated. The apparatus  80  is depicted as including a valve  82  for selectively permitting and preventing flow through an opening or fluid passage  84  formed through a housing  86  of the valve. However, it is to be clearly understood that the apparatus  80  is merely representative of a wide variety of types of apparatus which may embody principles of the present invention. For example, an apparatus constructed in accordance with the principles of the present invention does not necessarily include a valve or other flow control device. 
     The valve  82  includes a displacement member or sleeve  88 , which displaces relative to the housing  86  in operation of the apparatus  80 . Specifically, the sleeve  88  is a closure member which permits flow through the opening  84  when the sleeve is positioned as shown in FIG. 4, but which prevents flow through the opening when it is downwardly displaced relative to the housing  86 . A spring or other bias member  90  biases the sleeve  88  downward, but the sleeve is prevented from displacing downwardly by a blocking member  92 . 
     The blocking member  92  includes a material  94  which may be similar to any of the materials  18 ,  36 ,  60  described above. The blocking member  92  may be dispersed, to thereby permit the bias member  90  to downwardly displace the sleeve  88  relative to the housing  86 , by selectively introducing a fluid  96  into contact with the material via a fluid passage  98  formed in the apparatus  80 . Alternatively, a portion (similar to portion  72  shown in FIG. 3) of the blocking member  92  could extend inwardly into an inner fluid passage  100  formed through the apparatus  80 , so that a structure (similar to structure  46  shown in FIG. 2) could impact the blocking member and thereby provide contact between the material  94  and a fluid  102  in the fluid passage  100 . When the fluid  96  and/or fluid  102  contacts the material  94 , the material at least partially dissolves in the fluid, thereby permitting the blocking member  92  to be dispersed sufficiently for the bias member  90  to displace the sleeve  88  downwardly, so that flow is prevented through the opening  84 . 
     Note that the blocking member  92  may be constructed with a predetermined strength, so that when a predetermined force is applied to the blocking member, for example, by the bias member  90 , the material  94  will break, thereby permitting displacement of the displacement member  88  in operation of the apparatus  80 . 
     As described above, the materials  18 ,  36 ,  60  and  94  may include a polymer material soluble in a fluid. The material may be a mixture of a water soluble polymer, such as polyacrylic acid, along with salt and/or sand. 
     For example, the applicants have found that an acceptable material results from a mixture of 100 g acrylic acid, 700 g salt of {fraction (14/20)} grain size, along with 0.1 g of a polymerization initiator dissolved in 5 ml water, or a proportionate multiplication of these constituents. The initiator may, for example, be 2,2′-Azobis (N,N′-dimethyleneisobutyramidine) dihydrochloride marketed by Wako under the trade name VA-044. Other acceptable material may result from the following examples of mixtures: 
     a) 45 g acrylic acid, 200 g sand of {fraction (20/40)} grain size, along with 0.15 g polymerization initiator dissolved in 5 ml water; 
     b) 100 g acrylic acid, 700 g sand of {fraction (20/40)} grain size, along with 0.3 g polymerization initiator dissolved in 3 ml water; 
     c) 100 g acrylic acid, 700 g salt of {fraction (14/20)} grain size, along with 0.3 g polymerization initiator dissolved in 5 ml water; 
     d) 100 g acrylic acid, 700 g salt of {fraction (14/20)} grain size, along with 0.6 g polymerization initiator dissolved in 5 ml water; 
     e) 100 g acrylic acid, 350 g sand of {fraction (20/40)} grain size, 350 g salt of {fraction ( 14 / 20 )} grain size, along with 0.3 g polymerization initiator dissolved in 5 ml water; 
     f) 100 g acrylic acid, 700 g salt of {fraction (14/20)} grain size, along with 0.3 g polymerization initiator dissolved in 3 ml water; 
     g) 100 g acrylic acid, 700 g salt of {fraction (20/40)} grain size, along with 0.3 g polymerization initiator dissolved in 3 ml water; and 
     h) 100 g acrylic acid, 350 g sand of {fraction (20/40)} grain size, 350 g salt of {fraction (20/40)} grain size, along with 0.3 g polymerization initiator dissolved in 3 ml water. 
     To prepare the material, the monomer is placed in a suitable container or mold and mixed with crack initiator material and/or other soluble material, such as sand and/or salt, if any. Nitrogen is bubbled through the mixture to remove Oxygen from the monomer solution. The initiator dissolved in water is then added to the mixture. The mixture is then heated to the appropriate polymerization temperature. 
     Of course, a person skilled in the art would find it obvious to make modifications, substitutions, deletions, additions and other changes to the embodiments described herein, and these changes are contemplated by the principles of the present invention. Accordingly, the foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of the present invention being limited solely by the appended claims.

Summary:
Apparatus for use in operations performed in conjunction with a subterranean well is provided by the present invention. In one described embodiment, a plug apparatus includes a soluble polymer material, which is utilized in a plug member for blocking flow through a fluid passage. In another described embodiment, a soluble polymer material is utilized in a blocking member for blocking displacement of a displacement member of an apparatus.