Abstract:
An expandable well screen having a temporary sealing substance. In a described embodiment, a method of installing a well screen in a subterranean well includes the steps of: providing the screen including a temporary sealing substance preventing fluid flow through a wall of the screen; positioning the screen in a wellbore of the well; expanding the screen in the wellbore; and degrading the sealing substance, thereby permitting fluid flow through the screen wall.

Description:
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 an expandable well screen having a temporary sealing substance. 
   It is desirable to be able to circulate through a well screen while installing the screen in a well. In the past, such circulation has been provided by a washpipe extending through the screen. The washpipe permits fluid to be circulated through the screen before, during and after the screen is conveyed into the well, without-allowing debris, mud, etc. to clog the screen. 
   Expandable screens have been used in the past, either with or without the use of a washpipe. When the washpipe is used, a separate trip into the well is typically needed to expand the screen after the washpipe is removed from the screen. When the washpipe is not used, there is no sealed path available in the screen assembly to allow fluids to be pumped from the top of the screen to the bottom. As a result, any attempts to circulate fluid in the well would result in large volumes of fluid being pumped through the screen media, potentially plugging or clogging the screen. 
   Therefore, it may be seen that improved methods and systems are needed to permit circulation through an expandable well screen during its installation in a well, while not requiring an additional trip into the well to expand the screen. Other benefits could also be provided by improved methods and systems for installing well screens in a well. 
   SUMMARY 
   In carrying out the principles of the present invention, in accordance with an embodiment thereof, systems and methods are provided for installing well screens in a well. A temporary sealing substance is used to prevent fluid flow through a wall of an expandable screen during the installation process. Preferably, the screen is conveyed into the well and expanded in a single trip into the well. 
   In one aspect of the invention, a method of installing a well screen in a subterranean well is provided. The method includes the steps of: providing the screen including a temporary sealing substance preventing fluid flow through a wall of the screen; positioning the screen in a wellbore of the well; expanding the screen in the wellbore; and degrading the sealing substance, thereby permitting fluid flow through the screen wall. 
   In another aspect of the invention, a method of installing a well screen in a subterranean well includes the steps of: providing the screen including a temporary sealing substance preventing fluid flow through a wall of the screen; conveying the screen into a wellbore of the well while the sealing substance prevents fluid flow through the screen wall; expanding the screen in the wellbore; and degrading the sealing substance, thereby permitting fluid flow through the screen wall. 
   In yet another aspect of the invention, an expandable well screen system is provided. The system includes a well screen having a filtering layer for filtering well fluid as the fluid flows through a wall of the screen. A temporary sealing substance prevents the fluid from flowing through the screen wall. The screen has an expanded configuration and an unexpanded configuration in a well. 
   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 schematic cross-sectional view of a well screen installation system embodying principles of the present invention; 
       FIG. 2  is a schematic cross-sectional view of the system of  FIG. 1 , wherein a well screen is being expanded in a well; 
       FIG. 3  is a schematic cross-sectional view of the system of  FIG. 1 , wherein a screen installation process has been completed; and 
       FIG. 4  is an isometric view of a wall of the screen used in the system of  FIG. 1 . 
   

   DETAILED DESCRIPTION 
   Representatively illustrated in  FIG. 1  is a system  10  which embodies principles of the present invention. In the following description of the system  10  and other apparatus and methods described herein, directional terms, such as “above”, “below”, “upper”, “lower”, etc., are used only 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., and in various configurations, without departing from the principles of the present invention. 
   As depicted in  FIG. 1 , a well screen assembly  12  is conveyed into a wellbore  14 . The assembly  12  includes an expandable hanger  16 , a fluid loss control device  18 , expandable screens  20  and a one-way valve  22 . The screens  20  are conveyed into an open hole portion of the wellbore  14 , while the hanger  16  is set in casing  24  above. However, it should be clearly understood that the principles of the invention are not limited to any particular details of the system  10  described herein. For example, any number of the screens  20  could be used, the screens could be positioned in a cased portion of the wellbore  14 , more, less or different tools, equipment, etc. could be included in the assembly  12 , etc. 
   The assembly  12  is preferably conveyed into the wellbore  14  with an expander tool  26  attached thereto. This permits the assembly  12  to be conveyed into, and expanded in, the wellbore  14  in a single trip into the well. The assembly  12  and expander tool  26  may be conveyed by means of a tubular string  28 , such as drill pipe or production tubing, or any other type of conveyance. 
   During installation of the assembly  12 , it is beneficial to be able to circulate through the assembly, including circulating through a passage  30  formed longitudinally through the screens  20 . For example, debris in the wellbore  14  may be displaced by circulating if problems are encountered in conveying the screens  20  into the uncased wellbore portion, specialized fluid pills may be spotted in the wellbore as needed (such as, to remediate a fluid loss problem), an appropriate completion fluid may be circulated into the wellbore prior to expansion of the screens, etc. The one-way valve  22  (such as a float shoe or float collar) prevents fluid circulated down through the passage  30  and into the wellbore  14  from flowing back into the interior of the screens  20 . 
   To provide this circulation capability, and also to prevent solids from clogging the screens  20  during installation, a sealing substance  32  (not visible in  FIG. 1 ) is used to prevent fluid flow through sidewalls of the screens. The sealing substance  32  provides the function of a washpipe, without requiring an additional trip into the well to remove the washpipe and install the expander tool  26 . 
   As depicted in  FIG. 1 , the liner hanger  16  has been set in the casing  24 . Referring additionally now to  FIG. 2 , the expander tool  26  is being used to expand the screens  20  in the wellbore  14 . The same expander tool  26  may have previously been used to expand the hanger  16  (as depicted in  FIG. 1 ), or another tool may be used if desired. An acceptable expander tool for use in the system  10  is available from Halliburton Energy Services, Inc. of Houston, Tex. 
   Referring additionally now to  FIG. 3 , the screens  20  have all been expanded, and the expander tool  26  has been retrieved from the well, along with the tubular string  28 . Note that only a single trip into the well is required to convey the screen assembly  12 , position the assembly in the wellbore  14 , set the hanger  16  and expand the screens  20 . This is accomplished in the system  10  while also providing the ability to circulate through the assembly  12  during the installation. 
   The fluid loss control device  18  is closed as depicted in  FIG. 3 , in order to prevent loss of well fluid after the tubular string  28  and expander tool  26  are retrieved. An acceptable fluid loss control device is the Quick Trip Valve available from Halliburton Energy Services, Inc. of Houston, Tex. 
   Referring additionally now to  FIG. 4 , an enlarged view of a sidewall  34  of one of the screens  20  is representatively illustrated, apart from the remainder of the screen. The screen sidewall  34  includes a perforated tubular outer shroud  36 , an outer relatively coarse wire mesh drainage layer  38 , a relatively fine wire mesh filtering layer  40 , an inner relatively coarse wire mesh drainage layer  42 , and a tubular perforated inner base pipe  44 . The filtering layer  40  is sandwiched between the drainage layers  38 ,  42 , and these are positioned between the outer shroud  36  and the base pipe  44 . 
   Preferably, at least the filtering layer  40  has the sealing substance  32  therein, for example, by impregnating the filtering layer with the sealing substance, so that the sealing substance fills voids in the filtering layer. However, any of the other layers  38 ,  42 , shroud  36  or base pipe  44  could have the sealing substance  32  applied thereto, in keeping with the principles of the invention. For example, the sealing substance  32  could block fluid flow through the perforations in the shroud  36  or base pipe  44 , or the sealing substance could be impregnated in the wire mesh of the drainage layers  38 ,  42 , or any combination of the above. 
   Preferably, the sealing substance  32  is degradable when exposed to a subterranean well environment. More preferably, the sealing substance  32  degrades when exposed to water at an elevated temperature in a well. Most preferably, the sealing substance  32  is provided as described in copending U.S. patent application Ser. No. 10/609,031, filed Jun. 27, 2003, the entire disclosure of which is incorporated herein by this reference. 
   The sealing substance  32  may be a degradable polymer, such as one or more of a polysaccharide, chitin, chitosan, protein, aliphatic polyester, poly(actide), poly(glycolide), poly(ε-caprolactone), poly(hydroxybutyrate), poly(anhydride), aliphatic polycarbonate, poly(orthoester), poly(amino acid), poly(ethylene oxide), or a polyphosphazene. The sealing substance  32  may include a plasticizer, poly(lactic acid), a poly(lactide), or poly(phenyllactide). 
   The sealing substance  32  may degrade in the presence of a hydrated organic or inorganic compound solid, which may be included in the screens  20 , so that a source of water is available in the well when the screens are installed. For example, the hydrated organic or inorganic compound could be provided in the wire mesh of the drainage layers  38 ,  42 . Alternatively, another water source, such as an aqueous solution, may be delivered to the sealing substance  32  after the screens  20  are conveyed into the well, such as by circulating the water source down to the screens. 
   Note that the sealing substance  32  may be degraded, thereby permitting fluid flow through the screen sidewall  34 , either before or after the screens  20  are expanded in the wellbore  14 . For example, formation water may be used as the water source to degrade the sealing substance after expansion of the screens  20 . 
   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 these 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.