Patent Publication Number: US-10323489-B2

Title: Apparatus and methods for treating a wellbore screen

Description:
FIELD 
     The invention relates to an apparatus and methods for treating wellbore screens. In particular, the invention relates to an apparatus and methods for applying a coating to a wellbore screen. 
     BACKGROUND 
     Various wellbore tubulars are known and serve various purposes. A wellbore screen is a tubular including a screen material forming or mounted in the tubular&#39;s wall. The wellbore screen can be used in wellbores such as those for water, steam injection and/or petroleum product production. 
     In one form, a wellbore screen is known that includes a wall of screen material held between end fittings. The wall includes screen material that may take various forms and is usually supported in some way, as by a perforated sleeve. These screens filter fluids passing through the screen material layer either into or out of the screen inner diameter. 
     In another form, a wellbore screen is an apparatus that can include a base pipe and a plurality of filter cartridges supported in the base pipe. The filter cartridges are mounted in openings through the base pipe wall. The filter cartridges screen fluids passing through the openings into the base pipe for pumping or flow up hole. Of course, the openings may be formed and/or employed to also permit flow of fluids outwardly therethrough from the inner diameter of the base pipe. 
     It is to be understood that other aspects of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein various embodiments of the invention are shown and described by way of illustration. As will be realized, the invention is capable for other and different embodiments and its several details are capable of modification in various other respects, all without departing from the spirit and scope of the present invention. Accordingly the drawings and detailed description are to be regarded as illustrative in nature and not as restrictive. 
     SUMMARY OF THE INVENTION 
     In accordance with a broad aspect of the present invention, there is provided an apparatus for treating a wellbore screen with a coating material, the apparatus comprising: a support for supporting an outer tubular wall of the wellbore screen; a support frame; an injector for injecting coating material on to the outer tubular wall of the wellbore screen; a coating material delivery line extending through the injector from a coating material supply to an injection tip positioned near the support frame; and a driver for positioning the wellbore screen relative to the support frame and injection tip, and for moving the screen axially along the support frame to allow the injector to distribute coating material on to the outer tubular wall of the wellbore screen via the injection tip. 
     In accordance with another broad aspect of the present invention, there is provided a method for treating a wellbore screen having a tubular wall with an outer tubular surface and a screening component installed to screen fluid passing through the tubular wall from the outer tubular surface to the inner bore, the method comprising: supporting at least a portion of the wellbore screen on a support frame; introducing a coating material in the form of a liquid on to the outer tubular surface via an injection tip of an injector; distributing the coating material on to the outer tubular surface such that the coating material penetrates to some extent into the screening component; and allowing the coating material to set to form a removable seal across the screening component in the outer diameter. 
     In accordance with yet another broad aspect of the present invention, there is provided an apparatus for treating a wellbore screen with a coating material, the apparatus comprising: a support for supporting an outer tubular wall of the wellbore screen; an injector for injecting coating material on to the outer tubular wall of the wellbore screen via an injection tip positioned near the support; a coating material delivery line extending through the injector from a coating material supply to the injection tip; and a driving mechanism for moving the injection tip axially relative to the support in a direction substantially parallel to a lengthwise axis of the support, to allow the injector to distribute coating material on to the outer tubular wall of the wellbore screen via the injection tip. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Drawings are included for the purpose of illustrating certain aspects of the invention. Such drawings and the description thereof are intended to facilitate understanding and should not be considered limiting of the invention. Drawings are included, in which: 
         FIG. 1  is a top elevation view of an apparatus in a mid process position for applying a coating material to the outer diameter of a wellbore tubular; 
         FIG. 2  is a side view of the apparatus in  FIG. 1 ; 
         FIG. 3  is a cross-sectional view of the apparatus, along line AB-AB, in  FIG. 2 ; 
         FIG. 4  is an end view of a portion of the injector of the apparatus; 
         FIG. 5 a    is a magnified view of the area T of  FIG. 1 ; 
         FIG. 5 b    is a cross-section of the support frame, on the left side of the apparatus of  FIG. 1 ; 
         FIG. 5 c    is a magnified side view of the area V of  FIG. 1 ; 
         FIG. 5 d    is a magnified view of the area V of  FIG. 1 ; 
         FIG. 5 e    is a magnified side view of the area T of  FIG. 1 ; 
         FIG. 6  is a side elevation of one wellbore tubular useful in the present invention; and 
         FIG. 7  is a section along line II-II of  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS 
     The detailed description set forth below in connection with the appended drawings is intended as a description of various embodiments of the present invention and is not intended to represent the only embodiments contemplated by the inventor. The detailed description includes specific details for the purpose of providing a comprehensive understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without these specific details. 
     Referring to  FIGS. 1 to 5 , an apparatus is shown and a method is described for applying a coating material to a wellbore screen. The apparatus and method can be employed to form a wellbore screen with a coating. 
     In one embodiment, the wellbore screen  2  includes a tubular wall including an inner tubular surface defining an inner bore, an outer tubular surface and a screening component installed to screen fluid passing through the tubular wall from the outer tubular surface to the inner bore; and a coating on the outer tubular surface embedded into the screening component from the outer tubular surface, the coating substantially sealing against fluid passage through the screening component until the coating is at least partially removed. 
     The wellbore screen may be produced by a method comprising: providing a wellbore screen including a tubular wall with an inner tubular surface defining an inner bore, an outer tubular surface and a screening component installed to screen fluid passing through the tubular wall from the outer tubular surface to the inner bore; introducing a coating material in the form of a liquid on to the outer tubular surface; distributing the coating material on to the outer tubular surface such that it penetrates to some extent into the screening component; and allowing the coating material to set to form a removable seal across the screening component in the outer diameter. 
     The word “liquid” as used herein includes liquid, semifluid, and colloid. A semifluid is a substance with flow properties that are between those of solids and liquids. 
     The coating material is in the form of a liquid so that it can be distributed, such as for example by spreading, on the outer wall. In one embodiment, the viscosity of the liquid can be selected such that it tends not to rapidly migrate once introduced to the screen. For example, if the liquid has a low viscosity it may pour into or out of the tubular through the screening component as it is introduced. However, the viscosity of the liquid coating material can be selected such that the material introduced can be distributed on to the surface of the outer wall of the screen and can penetrate to some extent into the screening component, but is sufficiently viscous such that it remains in place once distributed. As will be appreciated, this ability to reliably place the coating material may also be achieved by selecting a liquid that rapidly moves through a phase change from liquid to solid when a temperature difference is encountered. 
     In this invention, the coating material may take various forms provided it can be handled in a liquid state and will set to a substantially solid form capable of creating a removable seal across the screening component. The coating material should have a repeatable phase change between solid and liquid such that it can be brought to a liquid state and will set to a solid state under predictable conditions of time and temperature. When in place and set in the wellbore screen, the coating material creates a substantial seal against fluid flow through the screening component, such that the screen acts as a tubular capable of holding pressures greater than would be otherwise possible if the coating material was not in place in the screening component. However, the coating material is removable to open the screening component to fluid flow therethrough. The coating material may be a polymer, a resin, a salt, a wax, or a combination thereof, etc. and may be removable by various means such as chemical breakdown, dissolution, solubilization, melting, etc. For example, the coating material may be a polymer removed by acid treatment, it may be a salt removed by solubilization in a liquid such as water, it may be wax removed by melting, etc. 
     In one embodiment, the coating material may be a wax such as paraffin wax. One useful wax has a repeatable phase change from solid to liquid between 50 to 90° C., such as a phase change from solid at 55° C. to 85° C. This wax also exhibits an extrudable and spreadable viscosity (i.e. of about 1000 to 1000000 centipoises) at a temperature of 65 to 75° C. When wax melts it is miscible in oil and wax can be removed from the surface of the wellbore screen, including the screening component, leaving substantially no residue. The crystalline structure, if any, of wax in the melted form is small enough to pass through a typical wellbore screening component without clogging, but forms a solid of substantial strength such that a pressure holding structure can be formed by infiltration of the wax into the screening component. 
     Depending on the coating material, the properties of the coating material may have to be adjusted to ensure the viscosity is appropriate. For example, the coating material may have to be heated before being introduced to the outer diameter or before being distributed. Alternately, or in addition, the method may include heating the wellbore screen before introducing the coating material to the outer diameter so that the coating material remains liquid once it contacts the material of the wellbore screen. The method may further include cooling and/or removing heat from the wellbore screen to facilitate the setting of the coating material. 
     Spreading or spraying the coating material on to the outer wall ensures that a substantially uniform coating is applied to the outer wall and the coating material penetrates into the screening material to some degree. The spreading procedure may also be configured to remove excess coating material from the outer diameter. 
     The method may include rotating the screen until the coating material is allowed to set. The screen may be rotated, for example, about its long axis to prevent the coating material from migrating by gravity to a low spot while it remains a liquid, until the coating material sets. Alternatively or additionally, the method may include rotationally spraying the coating material about the screen&#39;s long axis on to the outer wall. 
     The method can be carried out in various ways and by employing various apparatus. One possible apparatus is shown in  FIGS. 1 to 5 . 
     The illustrated apparatus includes a support frame  40  for the wellbore screen  2 , the support  40  supporting an outer surface of the wellbore screen and presenting the wellbore screen with open access to its outer tubular wall  18 ; an injector  42  for injecting coating material on to the outer diameter of the wellbore screen; a coating material delivery line  56  extending through the injector  42  from a coating material supply  58  to an injection tip  57  positioned near a support frame  41  and a driver  54  for positioning the wellbore screen relative to frame  41  and moving the screen axially along frame  41  to allow injector  42  to distribute coating material on to the outer tubular wall of the wellbore screen. In the sample illustrated embodiment, the injector is positioned laterally beside a lengthwise side of support frame  41 . 
     In one embodiment, the driver  54  operates to drive the wellbore screen relative to the injector to position the injection tip adjacent the outer diameter and move the screen relative to the injection tip along the outer tubular surface to allow coating material to be introduced from the injector to the outer diameter along the length of the screen. 
     In one embodiment, for example, the driver  54  is incorporated with the screen support  40  and together they form a driving base on which the screen is supported and along which the screen can be moved substantially in line with the screen&#39;s long axis. In this way, the screen can be moved along a drive axis in a forward direction (as illustrated by an arrow P) and in a reverse direction (as illustrated by an arrow R) while the inner bore remains substantially concentric with the drive axis. 
     In a further embodiment, the driver  54  includes a drive mechanism, such as a chain or belt drive. In the illustrated embodiment, the drive mechanism comprises a motor  51 , a pair of chains  52 , and two pairs of sprockets  53 . One pair of sprockets  53  is positioned at or near one end of the screen support, while the other pair of sprockets is positioned at or near the other end of the screen support. Each sprocket is connected to the screen support near a lengthwise side of the screen support, and a face of the sprocket is substantially parallel to a face of the other sprocket in the pair. Each sprocket is connected to the driving in such a manner that allows the sprocket to rotate about its central axis, for example by extending an axle through an aperture on the lengthwise side of the screen support and through the central axis of the sprocket. Bearings may be disposed at the interface between the axle and the aperture, or between the axle and the sprocket, to allow the sprocket to rotate relative to the side of the screen support. In a further embodiment, the axle extends through both sprockets and both sides of the screen support at at least one end of the screen support. Of course, there may be other methods of rotatably connecting the sprockets to the screen support. 
     The motor  51  is configured to control the rotation of at least one pair of sprockets. In the illustrated embodiment, motor  51  is disposed near one pair of sprockets at one end of the screen support. A second motor may be disposed at the other end of the screen support, and each motor can operate independently and/or simultaneously, and each can be selectively utilized. Motor  51  may be directly connected to the axle(s) of the at least one pair of sprockets for rotating same. Motor  51  may be positioned in between the sprockets but not necessarily, as long as the motor is capable of controlling the rotation movement of the sprockets from wherever the motor is positioned. Motor  51  may be controlled locally or remotely. Motor  51  may also include a variable speed control and/or rotation direction control. 
     The distance between each pair of sprockets is preferably substantially the same as that of the other pair. Each of the chains  52  is meshed with one of the sprockets at each end of the screen support, such that the chains are substantially parallel to each other. The chains  52  preferably span across substantially the entire length of the screen support. The chains  52  are meshed with the sprockets  53 , such that when at least one pair of sprockets is rotated, the chains  52  move relative to the screen support in line with the long axis of the screen support. In another embodiment, a belt may be used instead of chains  52 . The belt has a width that is sufficient to span across and to mesh with each pair of sprockets at each end of the screen support. Alternatively, a single sprocket having a width substantially the same as that of the belt may replace the pair of sprockets at each end of the screen support. 
     The drive mechanism includes a fitting  55  is for engaging an end of the screen, for example, by threading to the threaded pin or box end of the screen. The use of threaded ends, as will be appreciated, is typical of a wellbore tubular such as a screen. In an alternative embodiment, the fitting includes a chuck, such as a scroll chuck, for engaging an end of the screen. The fitting  55  is connected to the drive mechanism in order to transfer the motion of the drive mechanism to the screen. In one embodiment, fitting  55  is connected to a section of the chains  52 , so that when the chains move as a result of the rotation of the sprockets, fitting  55  moves with the chains. The drive mechanism is thereby capable of driving the engaged screen axially along the drive axis in both the forward direction P and reverse direction R, by switching the direction of the motor (if there is only one motor) or by alternating the operation of the motors (if there are two motors). The fitting may be attached to the chains in various ways, including for example by fasteners, adhesives, bonding, welding, etc. The fitting maybe removably attached to the chains such that the fitting may be interchanged for accommodating screens of various sizes and/or for the purpose of repairs and maintenance. 
     The fitting  55  may also include a mechanism for rotating the screen about its long axis. For example, the fitting may engage the screen to drive it axially along the drive axis and have a pipe rotator component to drive the screen rotationally about the screen&#39;s long axis. In one embodiment, the rotator component is a motor; however, other similar mechanisms may be used as well. The rotator component may include a variable speed control and/or rotation direction control. 
     The drive mechanism also includes a plurality of rollers  50  on which the screen can be supported. The rollers may support any movement of the screen relative to the screen support, whether axially or rotationally. The rollers  50  are attached to chains  52  and may be positioned intermittently or continuously along chains  52 . In the illustrated embodiment, the rollers are carried on roller supports which are attached to chains  52  at substantially equally spaced-apart intervals at long chains  52 . The rollers and/or roller supports may be attached to the chains in various ways, including for example by fasteners, adhesives, bonding, welding, etc. In one embodiment, the rollers  50  are metal wheels; however, other similar mechanisms and/or materials that can withstand heat (for example, up to approximately 250° C.) may also be used for the rollers. 
     In one embodiment, the rollers  50  are attached to chains  52  in such a manner that when the fitting  55  is at or near one end of the screen support  40 , the rollers are on an upper surface of chains  52  for supporting substantially the full length of the screen above the screen support. As the drive mechanism drives the screen in the forward direction P, the rollers also move with the chains and, one by one, as the rollers reach the other end of the screen support, they disengage from screen and move with the chains peripherally around the sprockets  53  to a lower surface. As such, the screen support  40  is configured to provide sufficient clearance for the rollers to move therethrough on the lower surface of the chains. 
     When the driver engages the wellbore screen at one end, at least a portion of the outer diameter of the screening component is exposed. 
     The injector  42  handles the coating materials and operates to inject the coating material on to the outer tubular surface of the wellbore screen. The injector is preferably positioned adjacent to the support frame  41 , with tip  57  pointing towards the frame. The coating material delivery line  56  extends through the elongate injector from the coating material supply  58  to tip  57 . The delivery line  56  may be disposed inside an outer tubing  66 . 
     Tip  57  is in communication with delivery line  56 . Tip  57  may have one or more openings through which the coating material is extruded from the delivery line and introduced to the outer surface of the screen. In one embodiment, the tip  57  includes a plurality of openings arranged in a row. In a further embodiment, there are multiple rows of openings at the tip  57 , and the positions of the openings in adjacent rows may be staggered or aligned. 
     In one embodiment, the coating material supply may be a tank, a hopper, etc. In the illustrated embodiment, the apparatus is selected to handle wax as a coating material and the coating material supply  58  includes a hopper for accepting a supply of solid wax and a wax extruder  60  including a heater to convert the wax to a substantially liquid form and an auger to force the liquefied wax into the injector&#39;s delivery line. In the illustrated embodiment, the flow direction of the coating material in the delivery line when the injector is in operation is indicated by an arrow C. Injector  42  may include a mechanism to help evenly distribute coating material among the openings at tip  57 , such that the flow rate of coating material out of each of the openings is substantially the same. 
     Frame  41  has a proximal end  43  and a distal end  59 . In the illustrated embodiment, the driver drives the wellbore screen toward the distal end  59 , with the central long axis of the screen substantially parallel with the long axis of the frame, sliding a lower side of the outer tubular surface of the screen on to an upper surface of frame  41 , for example as illustrated by a screen portion  2   a  in  FIG. 2 . 
     The frame  41  may be selected to have a length, from the distal end to the proximal end, that is substantially equal to the length of the portion of the screen to be coated. For example, in one embodiment, the screen may be over 100 feet long, with the screen component supported along almost that full length and the frame is at least that long. 
     In one embodiment, for example as illustrated in the Figures, the support frame  41  includes one or more rollers  63  on which the screen can be supported as the driver slides the screen on to the frame  41 . The rollers  63  may be supported by roller supports. Preferably, the rollers form an upper surface of frame  41  that is substantially at the same height level as rollers  50 , such that as the driver slides the screen on to frame  41 , the screen can transition smoothly from the support frame  40  to support frame  41 . When the screen is supported on frame  41 , at least a portion of the outer surface of the roller is in contact with the outer tubular wall of the wellbore screen. The rollers  63  are configured to support both axial and rotational movements of the screen. The rollers  63  and/or roller supports may be attached to the support frame  41  in various ways, including for example by fasteners, adhesives, bonding, welding, etc. 
     In the illustrated embodiment, the rollers  63  are generally cylindrical in shape with an outer tubular surface and may be made of flexible and/or resilient materials such as for example, a sheet of spring steel, rubber, etc. In one embodiment, the rollers  63  are metal cylindrical members; however, other similar mechanisms and/or materials that can withstand heat (for example, up to approximately 250° C.) may also be used for the rollers. 
     The tip  57  is positioned relative to the support frame  41  so that the opening(s) at tip  57  from which coating material exits the tip is positioned sufficiently close to the outer tubular wall, when the screen is supported on rollers  63  of support frame  41 , such that the coating material can easily be applied to the outer tubular wall without requiring the coating material to exit tip  57  at a high pressure. In one embodiment, the opening at tip  57  is spaced from the outer tubular wall by a distance of approximately 1/16″± 1/64″. If wax is the coating material, the wax may be ejected from tip  57  at a pressure ranging between 1 to 2000 psi. In one embodiment, the tip  57  points towards and is in close proximity to the interface between the outer surface of the screen and the outer surface of the roller  63 , when the screen is supported by frame  41 . 
     Preferably, the rollers  63  are positioned along the length of frame  41 , on an upper surface and near one or both lengthwise sides thereof, with the central long axis of the rollers being substantially parallel to the long axis of the screen, when the screen is supported on frame  41 . In a preferred embodiment, rollers  63  engages the outer tubular wall of the wellbore screen to help spread the coating material introduced from the tip  57  to the outer tubular wall of the wellbore screen and/or drive the coating material into the screening component. 
     In one embodiment, the roller  63  is a continuous cylindrical member positioned along substantially the entire length of frame  41 . In another embodiment, rollers  63  are two or more spaced-apart cylindrical roller segments sharing the same central long axis that are positioned intermittently or continuously along substantially the entire length of frame  41 . Rollers  63  are preferably positioned along substantially the entire length of frame  41 , but not necessarily. 
     In the illustrated embodiment, one roller  63   a  is positioned along one lengthwise side of frame  41  and another roller  63   b  is positioned along the other lengthwise side of frame  41 . The roller  63   a  on one side of frame  41  may be lined up with the roller  63   b  on the other side the frame  41 , such that they are at about the same position along the length of frame  41 . Alternatively, rollers  63   a  and  63   b  are aligned and their position along the length of frame  41  may be staggered. As mentioned above, rollers  63  may comprise of a plurality of roller segments, and the roller segments on one side of frame  41  may or may not be aligned with the roller segments on the other side. In one embodiment, the roller segments on either side of frame  41  are in a staggered configuration with the roller segments on the other side. 
     In one embodiment, roller  63  is rotatable about its long axis. The rotation of the rollers  63  may be active and/or passive. For example, the rollers may be rotated actively by one or more motors. Additionally or alternatively, the rollers may rotate by the frictional forces created by the physical engagement between the outer surface of the screen and the outer surface of the rollers  63 , when the screen is rotated while being supported on the rollers  63 . 
     In one embodiment, the position of injector  42  relative to frame  41  is substantially fixed during the operation of the apparatus. More specifically, injector  42  is stationary relative to the support frame  41  while the screen is moved in the axial direction relative to frame  41  on rollers  63 . Further, injector  42  may be positioned anywhere along the length of frame  41 , but injector  42  is preferably positioned near the proximal end  43  or distal end  59  of frame  41 , with tip  57  pointing in the direction of the frame. 
     In another embodiment, injector  42  is movable relative to frame  41 , in the axial direction of the frame (i.e. in the forward direction P and the reverse direction R). While the injector  42  moves in the axial direction, the lateral and vertical position of the tip  57  relative to the frame  41  preferably remains substantially the same. The injector may be moved in the axial direction by a driving mechanism. For example, to achieve axial movement of the injector  42 , the injector  42  may be disposed on wheels that are drivable by a motor. Alternatively, injector  42  may be installed on a movable track (for example, a chain and sprocket mechanism driven by a motor) that runs substantially parallel to the long axis of frame  41  and injector  42  is moved in the axial direction by moving the track. In this embodiment, where injector  42  is movable in the axial direction, support frame  40  along with all its components (i.e. driver  54 , fitting  55 , chains  52 , sprockets  53 , etc.) may be omitted from the apparatus such that screen  2  can be placed on support frame  41  by other means without having the screen slidingly placed on to frame  41 . In a further embodiment, where the injector  42  is movable axially relative to the frame  41 , frame  41  may include a fitting having a rotator component (similar to fitting  55 ) that can be secured to one end of the screen for rotating same about its long central axis. Alternatively or additionally, the screen may be rotated about its long central axis by actively rotating rollers  63 . 
     In another embodiment, the apparatus may include two or more injectors  42  disposed at various locations along the length of support frame  41 , and the two or more injectors  42  may be stationary or movable relative to support frame  41  while the apparatus is in operation. 
     Alternatively or additionally, tip  57  is configured to be movable in the axial direction relative to frame  41 , whether or not injector  42  is movable relative to frame  41 . Preferably, when tip  57  moves in the axial direction, the lateral and vertical position of the tip  57  relative to the frame  41  remains substantially the same. However, the lateral and vertical position of tip  57  is preferably adjustable relative to frame  41  to accommodate screens of various sizes and outer diameters. 
     In one embodiment, the injector may include a heater (not shown) along the length of the delivery line to ensure the wax remains sufficiently liquid. The delivery line  56  may include an inner tubing  64  through which the wax moves and outer tubing  66  forms an annular space between the inner tubing and the outer tubing. Heaters, for example induction heaters, may be installed in the annular space and may be operated to maintain the wax at a selected temperature in the inner tubing sufficient to prevent the wax from hardening therein. In one embodiment, heaters line substantially the full length of delivery line  56 . 
     In one embodiment, intended for use to inject wax or the like, the apparatus includes a heating element for heating the screen before and/or while the wax is injected thereon. For example, a substantially annular external heater may be positioned substantially concentrically about the screen when the screen is supported on frame  41 . The external heater may be placed near at least a portion of the outer surface of the screen and can act to heat the screen from a position adjacent its outer surface. The external heater may be positioned adjacent to either or both sides of the injector  42 . In one embodiment, the heating element is selectively movable axially relative to frame  41  such that the heating element can be placed at any axial location along the length of frame  41 . 
     In another example, as shown in  FIGS. 1 and 3 , a heater is provided in the form of an arm  47  pivotably connected to frame  41 , the arm having an inner surface with a heating element for placement adjacent to a portion of the outer surface of a length of the screen. The arm  47  is pivotable about an axis substantially parallel to the central long axis of the frame  41 , such that the arm can be pivoted radially relative to the frame  41  to allow: (i) the arm to be raised to provide clearance when a portion  2   a  of the screen is first placed on to the frame  41 ; (ii) the arm to be selectively lowered to place the heating elements adjacent to a portion of the outer surface of a length of the screen that is on frame  41 ; and (iii) the arm to be raised or lowered to accommodate screens of various diameters. The arm  47  is placed somewhere along the length of frame  41 , preferably at or near the location of tip  57  of injector  42 . The heating element of the arm heats up the screen portion adjacent thereto and, as the screen is rotated, the heating element can substantially evenly heat the entire circumferential outer surface of a length of the screen. 
     The external heater may be selectively switched on or off. A section of the screen is preferably heated by the heating element before wax is injected thereon. For example, if the wax is to be distributed on to the outer tubular wall of the screen, while the screen moves in the forward axial direction on the support frame  41 , as described in more detail hereinbelow, then the heating element should be positioned adjacent to the side of the injector  42  that is closer to the proximal end  43 . If the wax is to be distributed on to the outer tubular wall while the screen moves in the reverse axial direction on the support frame  41 , as described in more detail hereinbelow, then the heating element should be positioned adjacent to the side of the injector  42  that is closer to the distal end  59 . If the wax is to be distributed on to the outer tubular wall during both the forward and reverse movement of the screen, then preferably a heating element is positioned adjacent each side of the injector  42  and is selectively turned on or off depending on the direction of movement of the screen relative to the support frame  41 , such that the screen is heated before the injection of wax thereon. 
     If the apparatus includes an external heater, as noted above as an option, the screen can be heated from the outside and/or from the inside. By heating the screen, the surface can be prepared such that the wax does not immediately harden when it is injected thereon. The wax can therefore remain substantially liquid such that it can be spread and form a substantially continuous seal infiltrated to some degree into the screening component. For example, the external heater may be an induction heater, a resistance heater, or a combination thereof. The external heater can be controlled by thermocouples. 
     It can be appreciated that at least some of the parts of the apparatus can be removably attached, such that they may be replaced and/or removed for the purpose of maintenance and repairs. 
     The components of the apparatus, such as supports  40 ,  41 , fitting  55 , chains  52 , arm  47 , sprockets  53 , inner tube  64 , and outer tubing  66 , are preferably made of materials that have sufficient structural integrity to support various loads and that can withstand high temperatures (for example, up to approximately 250° C.). In one embodiment, supports  40  and  41  are made of steel; fitting  55 , chains  52 , sprockets  53 , arm  47 , and inner tube  64  are made of stainless steel; and outer tubing  66  is made of aluminum. Other materials that have similar physical properties as those mentioned above may also be used in the apparatus. 
     In operation of the apparatus, a screen  2  can be installed on the driving base, supported by the rollers  50  and with the fitting secured to the screen such that the screen can be moved by the drive mechanism. The coating material can then be prepped for injection. Using wax, the coating material can be supplied as a solid and melted and prepared for injection to the screen. In the illustrated apparatus, the wax is melted on an as needed basis from the hopper through the wax extruder. The heaters in the elongate injector and the external heaters are operated to generate heat. The heaters along the delivery line are operated as necessary to maintain the liquid state of the coating material in the delivery line. 
     The driver is then operated to slidingly move the screen on to support frame  41 . If the external heater is included, the external heater is positioned relative to the frame  41  to provide sufficient clearance for the screen to pass thereby or therethrough, and to rotate about its central long axis, but the external heater is also positioned close enough to the outer surface of the screen to allow heat from its heating elements to be transmitted to the screen. For example, if the external heater is the pivotable arm  47 , the arm may be raised before the driver moves the screen on to frame  41 . When the screen reaches or passes the axial location of the arm, the arm is lowered until the heating elements are close to but not touching the outer surface of the screen. 
     In one embodiment, where the injector is stationary and positioned near the proximal end of frame  41 , as the screen moves on to support frame  41  in the forward direction P, the screen itself is heated as it moves past the external heater and is injected with coating material from tip  57  on to its outer tubular wall as the screening component moves past the tip  57 . Alternatively or additionally, as the screen is moved in the reverse direction R from frame  41  to frame  40 , the screen is heated as it moves past the external heater and is injected with coating material from tip  57  on to its outer tubular wall as the screen component moves past the tip  57 . 
     In one embodiment, regardless of whether the coating material is injected on to the screen while the screen is moving in the forward P and/or reverse R direction, the screen is rotated by fitting  55  as it moves relative to frame  41 , such that the coating material can be injected circumferentially on to the outer tubular wall of the screen. The rotation of the screen on support frame  41  may cause one or more rollers  63  to rotate passively, as a result of the frictional engagement between the outer surface of the rollers and the screen. The direction of rotation of the rollers is opposite that of the screen. 
     Alternatively or additionally, at least one of the rollers  63  actively rotates the screen while the screen is supported thereon. The direction of rotation of the actively rotating roller(s) is selected to be the opposite of the desired direction of rotation of the screen. Any non-actively rotating rollers  63  may rotate passively as a result of the rotation of the screen. 
     In an alternative embodiment, support frame  40  and the components thereon are omitted, and at least a portion of the screen is placed on support frame  41  at the start of the coating process. The screen is rotated about its central long axis by one or more actively-rotating rollers  63  (or by a fitting having a rotator component attached to one end of the screen), but the screen is substantially stationary axially relative to the support frame  41 . Any non-actively rotating rollers  63  may rotate passively as a result of the rotation of the screen. In this embodiment, the injector  42  moves axially along the length of the support frame  41  from at least the start of the screening component of the screen to at least the end of the screening component, while injecting coating material on to the outer tubular surface of the screen. The axial movement of the injector allows coating material to be injected on to at least the entire length of the screening component, and the rotation of the screen, whether by the actively-rotating roller(s) or the fitting, allows coating material to be injected on to the outer tubular wall around the circumference thereof. If an external heater is included, the external heater may be configured to be movable axially relative to frame  41  at substantially the same speed as the injector, such that the external heater can heat the screen before or while coating material is injected on to the screen. The external heater may be configured to be movable relative to the frame  41  in the same or similar manner as the injector, examples of which are described above. 
     Whether the screen moves axially while injector  42  (and tip  57 ) remains stationary, or vice versa, once the tip  57  reaches where the screening components to be coated begin, the coating material is introduced from the opening(s) at tip  57  and is injected on to the outer wall. Simultaneously, the screen (or the injector) is moved in the forward direction P (or the reverse direction R) such that the injector continues to move relative to the screen as the coating material is injected along a length of the screen. 
     In addition to injection, the coating material may be further distributed on to the outer tubular wall by the rollers  63 . Additionally, excess coating material may be scraped from the outer surface and/or inner wall of the screen. Once a desired length of the outer tubular wall has been coated with coating material, the injection of coating material from tip  57  is stopped and the screen (or injector) may be moved in the opposite direction, for example to remove the screen from support frame  41 . In a further embodiment, the injector injects additional coating material over the previously coated section of the screen while the screen (or injector) moves in the opposite direction. Alternatively, the outer surface of the screen is only injected with coating material while the screen (or injector) moves in the opposite direction. 
     Further, as coating material is applied on to the screen, the screen is rotated about its long axis by either or both of a fitting (i.e. fitting  55  on frame  40  or a fitting on frame  41 ) and one or more rollers  63 . Whether achieved by the rotation of the fitting and/or one or more of rollers  63 , rotating the screen helps distribute the coating material circumferentially around the outer tubular surface. Further, the engagement between the outer surface of the rollers and the outer tubular surface of the screen helps spread the coating material introduced from injector  42  over the outer tubular wall and drive some of the coating material into the screening component. 
     In one embodiment, the apparatus includes a mechanism for scraping off excess coating material from the inner wall and/or outer surface of the screen. 
     The conditions of the coating materials and receiving surface of the screen and speed of screen movement and rotation are selected to ensure proper placement and set up of the coating material. More specifically, the speed of rotation of the fitting (i.e. fitting  55  on frame  40  or a fitting on frame  41 ) and/or one or more rollers  63 , and the speed at which fitting  55  moves axially or injector  42  and external heater move axially, whichever is applicable, relative to support frame  41 , and the number of times the screening component moves past tip  57 , are selected to allow the screening component to be substantially covered with coating material. The speed of rotation of the fitting (i.e. fitting  55  on frame  40  or a fitting on frame  41 ) and/or one or more rollers  63  may also be selected to help reduce pooling and loss of coating material by gravity. In a further embodiment, using wax, the temperatures of the wax and screen are selected to avoid the wax from dripping directly into the screen and to avoid the wax from immediately setting up (before it can be spread and/or driven into the screening components) and the speed of moving and rotating the screen relative to the tip  57  are selected with consideration of the foregoing. 
     Wellbore screens can take many forms. As noted above, in one form of a wellbore screen the wall of the screen is substantially entirely formed of screening component. The wall includes screen material held between end fittings. The screen material may take various forms and is usually supported in some way, as by a perforated sleeve. These screens filter fluids passing through the screen material layer either into or out of the screen inner bore. 
     In another form, the one termed the cartridge-type screen, the wall of the screen is a base pipe that has a plurality of discreet filter cartridges supported therein. The filter cartridges are mounted in openings through the base pipe that forms the wall. The filter cartridges screen fluids passing through the openings into the base pipe for pumping or flow up hole. Of course, the openings may be formed and/or employed to also permit flow of fluids outwardly therethrough from the inner diameter of the base pipe. 
     While the wellbore screen treated in the present invention can take many forms, one type of wellbore screen is disclosed here for clarity. Referring to  FIGS. 6 and 7 , a wellbore screen is shown including a perforated wall with fluid passages therethrough, which is illustrative of a cartridge-type screen. A cartridge-type screen includes a base pipe  10  including substantially circular such as circular or ovoid openings  5  that extend from the base pipe inner bore surface  16  to the base pipe outer surface  18  and a filter cartridge  12  is supported in each opening. Such a screen is durable and is useful in various wellbores operations such as those for water production, water/steam injection, oil and/or gas production, etc. The filter cartridges permit fluid flow through the openings into or out of the base pipe, but the integrity of the base pipe provides the screen with increased durability and strength not achievable in screens with walls entirely formed of screening components. 
     The filter cartridge  12  useful in a wellbore screen can include a filter media  20 . In one embodiment, the filter cartridge can also include one or more retainer plates positioned about the filter media. In one embodiment, as illustrated, the filter cartridge includes an exterior retainer plate  22 , an interior retainer plate  24  and filter media  20  contained therebetween. In one embodiment, the exterior retainer plate and the interior retainer plate may be coupled to one another by any of a plurality of methods, such as adhesives, welding, screws, bolts, plastic deformation and so on. In another embodiment, the retainer plates are not secured together but held in position by their mounting in the base pipe. 
     If used, the exterior retainer plate and the interior retainer plate may contain one or more apertures  26  through which fluid may flow, arrow F. Exterior retainer plate  22  and interior retainer plate  24  may be constructed of any suitable material, such as plastic, aluminum, steel, ceramic, and so on, with consideration as to the conditions in which they must operate. 
     Filter media  20  of the filter cartridge can be any media, such as including a layer of compressed fiber, woven media, ceramic and/or sinter disk that is capable of operating in wellbore conditions. The filter media must be permeable to selected fluids such as one or more of steam, stimulation fluids, oil and/or gas, while able to exclude oversized solid matter, such as sediments, sand or rock particles. Of course, certain solids may be permitted to pass, as they do not present a difficulty to the wellbore operation. Filter media can be selected to exclude particles greater than a selected size, as desired. The present screen can employ one or more layers or types of filter media. In one embodiment, a filter media including an inner woven screen, an outer woven screen and a fibrous material is used. In another embodiment, a filter cartridge may include a single layer of filter media, as shown in  FIG. 7 , to facilitate manufacture. Sintered material may be useful as a single layer filter media. 
     Openings  5  may be spaced apart on the base pipe wall such that there are chambers of solid wall therebetween. The openings extend through the base pipe sidewall and may each be capable of accommodating a filter cartridge  12 . The filter cartridges can be mounted in the openings by various methods including welding, threading, etc. In one embodiment, at least some filter cartridges may be installed by taper lock fit into the openings. In such an embodiment, each of the filter cartridge and the opening into which it is to be installed may be substantially oppositely tapered along their depth so that a taper lock fit can be achieved. For example, the effective diameter of the opening adjacent the base pipe&#39;s outer surface  18  may be greater than the effective diameter of the opening adjacent inner bore surface  16  and cartridge  12  inner end effective diameter, as would be measured across plate  24  in the illustrated embodiment, may be less than the effective diameter at the outer end of filter cartridge  12  and greater than the opening effective diameter adjacent inner bore surface  16 , so that the filter cartridge may be urged into a taper lock arrangement in the opening. In particular, the outer diameter of the filter cartridge can be tapered to form a frustoconical (as shown), frustopyramidal, etc. shape and this can be fit into the opening, which is reversibly and substantially correspondingly shaped to engage the filter cartridge when it is fit therein. In one embodiment for example, the exterior retainer plate may exceed the diameter of the interior retainer plate of the filter cartridge. Of course, the filter cartridge may be tapered from its inner surface to its outer surface in a configuration that is frustoconical, frustopyramidal, and so on and the openings of the base pipe may be tapered correspondingly so that their diameter adjacent the inner bore surface is greater than that adjacent the side wall outer surface, if desired. However, installation may be facilitated by use of an inwardly directed taper, as this permits the filter cartridges to be installed from the base pipe outer surface and forced inwardly. 
     The filter cartridges may be secured in the base pipe openings by any of various means. For example, in one embodiment, the filter cartridge may be press-fit into the opening of the base pipe. In another embodiment, the filter cartridge may be secured to the opening of the base pipe by an adhesive  28  (for example epoxy), by welding, by soldering, by plastic deformation of the base pipe over the cartridge, by holding or forcing the cartridge into engagement behind a retainer or extension over of the opening and so on, at one or more of the interface points between the filter cartridge and the base pipe. A seal, such as an o-ring, may be provided between the filter cartridge and the opening, if desired. 
     In a wellbore screen, as shown, the coating applied by the apparatus and method may form a selectively openable impermeable layer  30  relative to at least some of the plurality of openings. The impermeable layer can be normally closed and when closed is impermeable to solid matter as well as substantially impermeable to fluid flow, such as any or all of wellbore fluids, drilling fluids, injection fluids, etc. 
     Impermeable layer  30 , however, can be selectively opened at a selected time, such as when the screen is in a selected position downhole, such as when it is in a finally installed position. 
     The impermeable layer may act at one or a plurality of openings to plug fluid flow therethrough. As described above, the impermeable layer will be positioned to infiltrate into filter media  20  from the inner diameter side. The impermeable layer may serve to cover/block/plug the openings and the filter cartridge in order to prevent the flow of fluid therethrough and/or to prevent access of solids to the filter media, until the impermeable layers are selectively opened. 
     The impermeable layer may be opened to permit fluid flow once the wellbore screen is in position down hole. The method of opening can vary based on the material of the impermeable layer, and may include pressure bursting and/or removal by solubilization, melting, etc. as by acid, caustic or solvent circulation, temperature sensitive degradation, and so on. 
     In one application, a wellbore screen including impermeable layers relative to its openings, may be useful to increase buoyancy of the screen during installation, which is useful in horizontal installations. The impermeable layer also resists plugging of the openings, which can result for example from the rigors of running in. In another application, the impermeable layers are used to selectively allow flow along or from a certain section of the wellbore, while flow is blocked through other openings. In yet another application, a wellbore screen including impermeable layers relative to its openings, may be useful to allow fluid circulation through the screen during run in, which reduces hole stuck and cave in problems. Removable layers in the screening components also permit drilling of the screen into the hole, as by liner drilling. In such an application, the impermeable layers can be selected to hold the pressures encountered during drilling, for example, pressures of a few hundred psi. In such an embodiment, the impermeable layers will be present to plug the openings at least when the wellbore screen is being run down hole so that the wellbore screen may be drilled directly into the hole. Once the screen is drilled into position, the impermeable layers may be opened, as by residence time at wellbore conditions, circulating fluids to breakdown and remove the coating material (i.e. circulating heated fluids to melt the coating material) or bursting with application of fluid pressure above that which the layers can hold. 
     Depending on the application, it may be useful to seal all of the openings of a wellbore screen or it may be useful to block only certain of the openings, while others are left open. In another embodiment, it may be useful to use selected materials to form the impermeable layers on a first group of openings while another impermeable layer material is used over the openings of a second group so that some openings within a liner, for example those of the first group, can be opened while others, for example the openings of the second group, remain closed until it is desired to remove or break open that impermeable material. 
     One or more impermeable layers can be used, as desired. The layers may be positioned to provide protection to certain filter cartridge components. 
     The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to those embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein, but is to be accorded the full scope consistent with the claims, wherein reference to an element in the singular, such as by use of the article “a” or “an” is not intended to mean “one and only one” unless specifically so stated, but rather “one or more”. All structural and functional equivalents to the elements of the various embodiments described throughout the disclosure that are known or later come to be known to those of ordinary skill in the art are intended to be encompassed by the elements of the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. For US patent properties, it is noted that no claim element is to be construed under the provisions of 35 USC 112, sixth paragraph, unless the element is expressly recited using the phrase “means for” or “step for”.