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CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a division of prior application Ser. No. 11/939,968 filed on Nov. 14, 2007, which prior application claims the benefit under 35 USC §§119 and 365 of the filing date of prior International Application No. PCT/US06/60926, filed Nov. 15, 2006. The entire disclosures of these prior applications are incorporated herein by this reference. 
    
    
     BACKGROUND 
     The present invention relates generally to equipment utilized and operations performed in conjunction with a subterranean well and, in an embodiment described herein, more particularly provides a well tool including a swellable material and an integrated fluid for initiating swelling of the swellable material. 
     Well packers and other types of well tools are known which use swellable materials. These swellable materials swell when they are contacted by a certain type of fluid. For example, a swellable material may swell when it is contacted by a hydrocarbon fluid, gas, water, etc. 
     If the particular fluid which causes swelling of the swellable material is not present in a well when it is desired for the material to swell, then the fluid can be circulated through the well to the material, for example, by spotting the fluid at the depth of the well tool. 
     Unfortunately, this method has certain disadvantages. For example, the fluid can migrate away from the well tool (e.g., if the fluid which causes the swellable material to swell has a different density or viscosity as compared to the remainder of the fluid in the well), and over the longer term the fluid will not be present to maintain the swollen condition of the swellable material. 
     Therefore, it may be seen that improvements are needed in the art of constructing well tools utilizing swellable materials, and swelling those materials in conjunction with well operations. 
     SUMMARY 
     In carrying out the principles of the present invention, well tools and associated methods are provided which solve at least one problem in the art. One example is described below in which a well tool is provided with an integral fluid reservoir for supplying fluid to a swellable material. Another example is described below in which fluid is supplied to a swellable material of a well tool to cause the material to swell while the material is in an environment containing another fluid which does not cause the material to swell. 
     In one aspect, a well tool is provided which includes a swellable material and a reservoir for containing a fluid of a type which causes the first swellable material to swell. Preferably, the reservoir is included as an integral part of the well tool, either by being internal to the swellable material, or by being positioned adjacent to the swellable material. 
     In another aspect, a method of swelling a swellable material included in a well tool is provided. The method includes the steps of: positioning the well tool in a well; and then activating a fluid to cause swelling of the swellable material. The fluid may be activated in various different ways, for example, by passage of time, by varying pressure, increasing temperature, applying force, etc. 
     In yet another aspect, a method of swelling a swellable material includes the steps of: providing the swellable material which is capable of swelling when contacted by a fluid; positioning the swellable material in an environment in which the swellable material is contacted by another fluid which does not cause the material to swell; and swelling the swellable material by contacting the swellable material with the first fluid while the swellable material remains in contact with the other fluid. 
     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, in which similar elements are indicated in the various figures using the same reference numbers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic partially cross-sectional view of a well system and associated method embodying principles of the present invention; and 
         FIGS. 2-18  are schematic cross-sectional views of alternate configurations of well tools for use in the well system of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     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., and in various configurations, without departing from the principles of the present invention. The embodiments are described merely as examples of useful applications of the principles of the invention, which is not limited to any specific details of these embodiments. 
     In the following description of the representative embodiments of the invention, directional terms, such as “above”, “below”, “upper”, “lower”, etc., are used for convenience in referring to the accompanying drawings. In general, “above”, “upper”, “upward” and similar terms refer to a direction toward the earth&#39;s surface along a wellbore, and “below”, “lower”, “downward” and similar terms refer to a direction away from the earth&#39;s surface along the wellbore. 
     Representatively illustrated in  FIG. 1  is a well system  10  and associated method which embody principles of the present invention. In the well system  10 , a tubular string  12  is installed in a wellbore  14 . In this example, the wellbore  14  is lined with casing  16  and cement  18 , but the wellbore could instead be unlined or open hole in other embodiments. 
     The tubular string  12  includes well tools  20  and  22 . The well tool  20  is depicted as being a packer assembly, and the well tool  22  is depicted as being a valve or choke assembly. However, it should be clearly understood that these well tools  20 ,  22  are merely representative of a variety of well tools which may incorporate principles of the invention. 
     The well tool  20  includes a swellable material  24  for use as an annular seal to selectively prevent flow through an annulus  26  formed between the tubular string  12  and the casing  16 . Swellable materials may be used as seals in other types of well tools in keeping with the principles of the invention. 
     For example, another type of swellable seal is described in U.S. application Ser. No. 11/407,848, filed Apr. 20, 2006 for regulating flow through a well screen. The entire disclosure of this prior application is incorporated herein by this reference. 
     The well tool  22  includes a flow control device  28  (such as a valve or choke, etc.) and an actuator  30  for operating the flow control device. Swellable materials may be used in other types of actuators for operating other types of well tools. 
     For example, actuators using swellable materials for operating well tools are described in U.S. application Ser. No. 11/407,704, filed Apr. 20, 2006. The entire disclosure of this prior application is incorporated herein by this reference. 
     The swellable material used in the well tools  20 ,  22  swells when contacted by an appropriate fluid. The term “swell” and similar terms (such as “swellable”) are used herein to indicate an increase in volume of a swellable material. 
     Typically, this increase in volume is due to incorporation of molecular components of the fluid into the swellable material itself, but other swelling mechanisms or techniques may be used, if desired. Note that swelling is not the same as expanding, although a seal material may expand as a result of swelling. 
     For example, in some conventional packers, a seal element may be expanded radially outward by longitudinally compressing the seal element, or by inflating the seal element. In each of these cases, the seal element is expanded without any increase in volume of the seal material of which the seal element is made. Thus, in these conventional packers, the seal element expands, but does not swell. 
     The fluid which causes swelling of the swellable material could be water and/or hydrocarbon fluid (such as oil or gas). The fluid could be a gel or a semi-solid material, such as a hydrocarbon-containing wax or paraffin which melts when exposed to increased temperature in a wellbore. In this manner, swelling of the material could be delayed until the material is positioned downhole where a predetermined elevated temperature exists. The fluid could cause swelling of the swellable material due to passage of time. 
     Various swellable materials are known to those skilled in the art, which materials swell when contacted with water and/or hydrocarbon fluid, so a comprehensive list of these materials will not be presented here. Partial lists of swellable materials may be found in U.S. Pat. Nos. 3,385,367 and 7,059,415, and in U.S. Published Application No. 2004-0020662, the entire disclosures of which are incorporated herein by this reference. 
     The swellable material may have a considerable portion of cavities which are compressed or collapsed at the surface condition. Then, when being placed in the well at a higher pressure, the material is expanded by the cavities filling with fluid. 
     This type of apparatus and method might be used where it is desired to expand the material in the presence of gas rather than oil or water. A suitable swellable material is described in International Application No. PCT/NO2005/000170 (published as WO 2005/116394), the entire disclosure of which is incorporated herein by this reference. 
     It should, thus, be clearly understood that any swellable material which swells when contacted by any type of fluid may be used in keeping with the principles of the invention. 
     Referring additionally now to  FIG. 2 , an enlarged scale schematic cross-sectional view of one possible configuration of the well tool  20  is representatively illustrated. The well tool  20  is used for convenience to demonstrate how the principles of the invention may be beneficially incorporated into a particular well tool, but any other type of well tool may utilize the principles of the invention to enable swelling of a swellable material of the well tool. 
     As depicted in  FIG. 2 , the swellable material  24  is positioned on a generally tubular mandrel  32 . The swellable material  24  could, for example, be adhesively bonded to the mandrel  32 , or the swellable material could be otherwise secured and sealed to the mandrel. 
     Multiple relatively small reservoirs  34  are formed internally within the swellable material  24 . Although the reservoirs  34  are illustrated in  FIG. 2  as being spherical in shape, the reservoirs  34  may be formed as cavities having any desired shape. 
     The reservoirs  34  may be formed when the swellable material  24  is manufactured, or they may be formed in the material afterward. The reservoirs  34  could extend longitudinally, circumferentially, radially, or in any other direction or combination of directions. 
     The reservoirs  34  each contain a fluid  36  which causes the material  24  to swell. In this manner, the material  24  may be externally in contact with another fluid  38  which does not cause the material to swell, but the material will still swell because the fluid  36  is internally available to the material. 
     For example, in the well system  10  of  FIG. 1 , the annulus  26  may be filled with the fluid  38  which does not cause the material  24  to swell. However, the material  24  can still be made to swell due to the fluid  36  being in contact with the material. 
     In one embodiment, the fluid  36  could initially be in a solid form, such as a wax or paraffin, and after the well tool  20  is installed in the well the increased temperature in the well will melt and liquefy the wax or paraffin, so that it is available to cause swelling of the material  24 . 
     In another embodiment, the fluid  36  could be a gas, and after the well tool  20  is installed in the well the increased pressure in the well will cause the gas to penetrate and swell the material  24 . 
     In any of these embodiments, the fluid  36  and/or material  24  may be designed so that the fluid  36  causes swelling of the material upon passage of a predetermined amount of time. 
     Of course, other types of fluids may be used in the well tool  20  of  FIG. 2  in keeping with the principles of the invention. Furthermore, any number and size of the reservoirs  34  may be used to contain the fluid  36 . 
     Referring additionally now to  FIG. 3 , an alternate configuration of the well tool  20  is representatively illustrated. In this configuration, only a single reservoir  34  is used, with the reservoir being formed as an internal chamber in the swellable material  24 . Another difference between the configurations of  FIGS. 2 &amp; 3  is that the  FIG. 3  configuration includes a way to apply annular pressure to the reservoir  34  and compensate for dissipation of the fluid  36  into the material  24 . 
     A passage  40  is formed through the material  24  and an end ring  42 . The passage  40  provides for fluid communication between the annulus  26  and another chamber  44  formed in the material  24 . 
     A pressure equalizing device  46  (such as a floating piston, a membrane, etc.) separates the annulus fluid  38  from the fluid  36  in the reservoir  34 , while transmitting pressure from the annulus  26  to the reservoir. In this manner, pressure in the annulus  26  is available to pressurize the fluid  36  and “drive” the fluid into the material  24  if needed, and the fluid  38  can enter the chamber  44  as the fluid  36  dissipates into the material  24 . 
     Referring additionally now to  FIG. 4 , a portion of the swellable material  24  is representatively illustrated in further enlarged scale from another alternate configuration of the well tool  20 . The portion of the swellable material  24  illustrated in  FIG. 4  includes the reservoir  34  which, in this embodiment, does not include the pressure transmitting and equalizing features described above for the configuration of  FIG. 3 . 
     Instead, the configuration of  FIG. 4  includes features which prevent collapse or other deformation of the reservoir  34  when the fluid  36  is dissipated into the material  24 . For this purpose, a porous material  48  (such as a wire mesh) is positioned between the material  24  and a support structure  50  (such as a helically wound flat wire spring) in the reservoir  34 . 
     The porous material  48  permits the fluid  36  (not shown in  FIG. 4 ) to contact the material  24 , but prevents extrusion of the material between the wraps of the support structure  50 . The structure  50  prevents deformation of the reservoir  34  as the fluid  36  dissipates into the material  24 . 
     Of course, other types of porous materials and support structures may be used in keeping with the principles of the invention. Furthermore, porous materials and support structures may be used in the other configurations of the well tool  20  described herein, for example, in the reservoir  34  in the configuration of  FIG. 3 . 
     Referring additionally now to  FIG. 5 , another alternate configuration of the well tool  20  is representatively illustrated. In this configuration, the reservoir  34  is positioned in the end ring  42 , and a passage  52  is formed to provide fluid communication between the reservoir and the swellable material  24 . 
     Another difference in the configuration of  FIG. 5  is that the well tool  20  includes additional swellable materials  54 ,  56 . The swellable material  54  provides sealing between a generally tubular sleeve  58  and the mandrel  32 , and the swellable material  56  provides sealing between the end ring  42  and the mandrel. 
     The swellable materials  54 ,  56  may be made of the same material as the swellable material  24 , or one or both of the materials  54 ,  56  may be different from the material  24 . The swellable materials  24 ,  54  and the sleeve  58  may be installed on the mandrel  32  in the manner described in International Application No. PCT/US06/035052, filed Sep. 11, 2006, entitled Swellable Packer Construction, having Agent File Reference 021385U1PCT (which corresponds to U.S. application Ser. No. 11/852,295 filed Sep. 8, 2007), and the entire disclosure of which is incorporated herein by this reference. 
     If the swellable material  54  is different from the swellable material  24  or  56 , then one or more separate reservoirs  60  may be used to contain an appropriate fluid  64  for causing swelling of the material  54 . A passage  62  may provide fluid communication between the reservoir  60  and the swellable material  54 . 
     Similarly, if the swellable material  56  is different from the swellable material  24  or  54 , then one or more separate reservoirs  66  may be used to contain an appropriate fluid  68  for causing swelling of the material  56 . A passage  70  may provide fluid communication between the reservoir  66  and the swellable material  56 . 
     Preferably, the swellable materials  24 ,  54 ,  56  are made of the same type of material, and the fluids  36 ,  64 ,  68  are the same type of fluid. Accordingly, note that in  FIG. 5  additional passages  72 ,  74  are provided to permit fluid communication between the reservoirs  36 ,  64  and the swellable material  56 . 
     Plugs  76  may be provided to enable filling the reservoirs  34 ,  60 ,  66  in the end ring  42 . Set screws  78  (such as carbide-tipped set screws) may be provided to secure the end ring  42  to the mandrel  32 . 
     Referring additionally now to  FIGS. 6 &amp; 7 , another alternate configuration of the well tool  20  is representatively illustrated. In this configuration, multiple reservoirs  34  are formed in a housing  80  threadedly attached between the end ring  42  and another housing  82  having the swelling material  56  therein. 
     A cross-sectional view of the housing  80  is representatively illustrated in  FIG. 7 . In this view, it may be seen that four of the reservoirs  36  are formed in the housing  80 , and that the set screws  78  are installed through the housing between the reservoirs. Of course, any number of reservoirs  34  may be used in keeping with the principles of the invention. 
     In this embodiment, the swellable materials  24 ,  54 ,  56  are made of the same type of material, and so in  FIG. 6  it may be seen that one or more passages  84  provide fluid communication between the reservoirs  34  and each of the swellable materials. However, if the swellable materials  24 ,  54 ,  56  required different fluids  36 ,  64 ,  68  to cause swelling of respective different materials, then separate passages could be provided between the materials and separate reservoirs containing the respective different fluids. 
     Furthermore, note that although separate passages  86 ,  88  are formed in the swellable materials  54 ,  24  for communication with the passage  84  on either side of the sleeve  58 , the sleeve is also perforated to allow fluid communication through the sleeve. This feature could also be incorporated into any of the other configurations of the well tool  20  described herein. 
     Referring additionally now to  FIGS. 8 &amp; 9 , another alternate configuration of the well tool  20  is representatively illustrated. In this configuration, the reservoir  34  is formed as an annular chamber within the interior of the swellable material  24 . The passages  86 ,  88  extend into the swellable material  24  to provide adequate distribution of the fluid  36  to the material. 
     As depicted in  FIG. 9 , a series of the passages  86 ,  88  are circumferentially distributed in the swellable material  24 . Eight of each of the passages  86 ,  88  are shown in  FIG. 9 , but any number or arrangement of the passages may be used in keeping with the principles of the invention. In addition, the passages  86 ,  88  may extend any distance in the material. 
     Referring additionally now to  FIGS. 10 &amp; 11 , another alternate configuration of the well tool  20  is representatively illustrated. This configuration is similar in many respects to the configuration of  FIGS. 8 &amp; 9 , except that passages  90  which provide fluid communication between the reservoir  34  and the swellable material  24  are formed only partially in the material. 
     The passages  90  are also bounded radially inwardly by the mandrel  32 . Note that the passages  90  could also, or alternatively, be formed on or in the mandrel  32 , if desired. 
     Referring additionally now to  FIG. 12 , another alternate configuration of the well tool  20  is representatively illustrated. In this configuration, the reservoir  34  is formed in the end ring  42  and the pressure equalizing device  46  separates the reservoir from the chamber  44  which is also formed in the end ring. 
     The configuration of  FIG. 12  is somewhat similar to the configuration of  FIG. 3 , except that the reservoir  34  and chamber  44  are formed in the end ring  42 , instead of in the swellable material  24 . Accordingly, one or more passages  92  are used to provide fluid communication between the reservoir  34  and the interior of the swellable material  24 . The passages  92  may extend any distance into the material  24 . 
     Referring additionally now to  FIG. 13 , another alternate configuration of the well tool  20  is representatively illustrated. This configuration is very similar to the configuration of  FIG. 12 , except that two sets of the end rings  42  with the reservoir  34  and chamber  44  therein are used, with one at each opposite end of the swellable material  24 . 
     Referring additionally now to  FIG. 14 , another alternate configuration of the well tool  20  is representatively illustrated. This configuration is very similar to the configuration of  FIG. 13 , except that the passages  92  are formed completely through the swellable material  24  and interconnect the reservoirs  34 . 
     Referring additionally now to  FIG. 15 , another alternate configuration of the well tool  20  is representatively illustrated. This configuration is very similar to the configuration of  FIGS. 13 &amp; 14 , except that the upper reservoir  34  is used to supply the fluid  36  to the swellable material  24 , and the lower reservoir  34  is used to supply the fluid  36  to the swellable material  54  separated from the material  24  by the sleeve  58  (as in the configurations of  FIGS. 5 &amp; 6 ). 
     Of course, if the material  24  is different from the material  54  then different fluids  36 ,  64  may be used to cause swelling of the respective materials, as described above. 
     Another difference in the configuration of  FIG. 15  is that flow control devices  94 ,  96  are used to determine when the reservoirs  36  are pressurized by the fluid  38  in the annulus  26 . As depicted in  FIG. 15 , the flow control devices  94 ,  96  are in the form of rupture discs which rupture when a predetermined pressure is applied to the annulus  26 , but other types of flow control devices (such as valves, eutectic devices which melt at a predetermined temperature, flow control devices such as sliding sleeves which operate in response to application of mechanical force, etc.) may be used in keeping with the principles of the present invention. 
     Referring additionally now to  FIG. 16 , another alternate configuration of the well tool  20  is representatively illustrated. In this configuration, a flow control device  98  (similar to the flow control devices  94 ,  96  described above) is positioned between the reservoir  34  and the passage  92 . 
     In this manner, the fluid  36  is not permitted to contact the material  24  until the flow control device  98  is opened. This allows swelling of the material  24  to be delayed until such swelling is desired (for example, after the well tool  20  has been appropriately positioned downhole in a well), at which time a predetermined pressure, temperature, force, etc. may be applied to cause the flow control device  98  to open and permit fluid communication between the reservoir  34  and the interior of the material. 
     Note that the flow control devices  94 ,  96 ,  98  depicted in  FIGS. 15 &amp; 16  may be used in any of the other configurations of the well tool  20  described herein to control application of pressure to the reservoir  34 , and/or to control fluid communication between the reservoir and the swellable material  24  or a passage in communication with the material. 
     Referring additionally now to  FIG. 17 , another alternate configuration of the well tool  20  is representatively illustrated. This configuration is similar in many respects to the configuration of  FIG. 8 . However, in the configuration of  FIG. 17 , the reservoir  34  is collapsible, in order to allow for pressure equalization between the interior of the reservoir and the exterior of the tool  20  as the fluid  36  is dispersed into the material  24 . 
     To permit the reservoir  34  to collapse, an outer wall  102  of the reservoir is relatively thin and flexible. The outer wall  102 , thus, functions as a flexible membrane and pressure equalizing device between the reservoir  34  and the exterior of the tool  20 . 
     As the fluid  36  is dispersed into the material  24 , the outer wall  102  will deflect inward, thereby allowing the volume of the reservoir  34  to decrease without creating a “negative” pressure differential which would hinder further dispersal of the fluid into the material. A rigid wall  104  is preferably provided between the reservoir  34  and the material  24 , so that collapse of the reservoir is unaffected by the swelling of the material and vice versa. 
     Referring additionally now to  FIG. 18 , another alternate configuration of the well tool  20  is provided in which the reservoir  34  is collapsible. This configuration is similar in many respects to the configuration of  FIG. 12 . However, in the configuration of  FIG. 18 , the pressure equalization device  46  is not a piston, but instead is a flexible membrane or bag in which the fluid  36  is contained. 
     As the fluid  36  is dispersed into the material  24 , the device  46  collapses, thereby allowing the volume of the reservoir  34  to decrease without creating a “negative” pressure differential which would hinder further dispersal of the fluid into the material. A flow control device  106  is provided to regulate flow into the chamber  44 . The flow control device  106  could be, for example, a check valve (such as a spring-loaded check valve, flexible sealing washer, etc.), another type of one-way valve (such as a one-way lip seal), a one-way pressure equalizing valve, etc. 
     It may now be fully appreciated that the well tool  20  described above in its various configurations provides for swelling of the swellable materials  24 ,  54 ,  56 , even though the materials are positioned in an environment in which the fluid  38  therein does not cause swelling of the materials. The well tool  20  includes at least one swellable material  24  and at least one reservoir  34  for containing a fluid  36  of a type which causes the swellable material to swell. The fluid  36  is at least one of a gas, gel, liquid, hydrocarbon fluid and water. The fluid  36  could be a solid material which liquefies at a predetermined elevated temperature. The reservoir  34  is in fluid communication with the swellable material  24 . 
     The reservoir  34  may be collapsible. A flow control device  106  may equalize pressure between an interior of the reservoir  34  and a pressure source exterior to the reservoir. 
     A flow control device  98  may selectively permit fluid communication between the reservoir  34  and the swellable material  24 . The reservoir  34  may be positioned within the swellable material  24 , or the reservoir may be positioned external to the swellable material. 
     The well tool  20  may include a second reservoir  34 ,  60 ,  66 . The second reservoir may also contain the fluid  36 , or it may contain another type of fluid  64 ,  68 . The second reservoir may be fluid communicable with the swellable material  24 , or with another swellable material  54 ,  56 . 
     The fluid  36  may be activated to cause the swellable material  24  to swell in response to passage of time or application of at least one of heat, pressure and force. The fluid  36  may be operable to cause the swellable material  24  to swell when the well tool  20  is immersed in another fluid  38  which does not cause the swellable material to swell. The swellable material  24  may be included in an actuator  30  of a well tool  22 , so that swelling of the swellable material is operable to actuate the well tool. 
     Of course, a person skilled in the art would, upon a careful consideration of the above description of representative embodiments of the invention, readily appreciate that many modifications, additions, substitutions, deletions, and other changes may be made to the specific embodiments, and such 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 and their equivalents.

Summary:
A well tool including swellable material and integrated fluid for initiating swelling. A well tool includes a swellable material and a reservoir for containing a fluid of a type which causes the swellable material to swell. A method of swelling a swellable material included in a well tool includes the steps of: positioning the well tool in a well; and then activating a fluid to cause swelling of the swellable material. A method of swelling a swellable material includes the steps of: providing the swellable material which is capable of swelling when contacted by a fluid; positioning the swellable material in an environment in which the swellable material is contacted by another fluid which does not cause the material to swell; and swelling the swellable material by contacting the swellable material with the first fluid while the swellable material remains in contact with the other fluid.