Abstract:
A downhole apparatus is described comprising a main body coupled with a well tubing and a swellable mantle disposed on the main body. The swellable mantle expands upon contact with at least one predetermined fluid, and the main body comprises at least one opening for fluid flow between an exterior of the main body and the bore. An insert permits the passage of fluid, through the swellable mantle, between the exterior of the apparatus and the opening. In one aspect of the invention a screen filters solids between the exterior of the apparatus and the bore, and a swellable mantle comprises a first region which allows the passage of fluid between the exterior of the apparatus and the main body and a second region, circumferentially adjacent the first region, which substantially prevents passage of fluid. Corresponding well completion and production methods are also described.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a National Stage entry from PCT Patent Application No. PCT/GB2008/001256, filed Apr. 10, 2008, which claims priority to United Kingdom Patent Application No. GB0706909.9, filed on Apr. 10, 2007, the contents of each one incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a downhole apparatus and method for use in the completion of hydrocarbon wells, and in one aspect to a downhole screen including a swellable material and a method of use. 
       BACKGROUND 
       [0003]    In the completion of hydrocarbon wells, it is known to use screens to prevent the production of solids from the formation. Expandable tubular technology has been used to expand metal screens to reduce the annular space around the screen and thereby reduce or eliminate the requirement for gravel packing and provide structural support for the formation. 
         [0004]    There are a number of drawbacks to using expanding tubulars. It can be difficult to control the force used to expand the tubular, and there may be resulting problems with the application of an undue, damaging force onto the formation. Expandable tubulars also have a limited expansion range, which means that maximum expansion can still result in an unsupported formation in a wash out zone. 
         [0005]    US 2005/0173130 describes an arrangement in which a swellable layer is located over an expanding screen to allow the apparatus to conform to the borehole shape. Holes in the swellable layer allow the passage of formation fluids. However, it is desirable in many applications to avoid the use of expanding tubulars. Additionally, by providing the screen around the expandable pipe at a location displaced from the borehole wall, there is an annular space into which solids may be produced, and along which solids may flow. This increases the risk of blocking the screen and creating so-called hotspots which are prone to erosion. 
         [0006]    The proposal of WO 2006/003112 attempts to overcome these deficiencies by providing a screen which is expanded into contact with the borehole wall by swellable rings. This approach relies on overlaid screen sheets which are forced outward by the swelling of the rings. This has the undesirable effect of restraining expansion of the swellable material, which may only be capable of exerting a pressure of 50 to 100 PSI (345 to 690 KPa). In addition, the gaps between overlaid screen sheets provide route for solid particles to enter the production tubing. 
       SUMMARY 
       [0007]    It is one aim of at least one aspect the invention to provide a downhole apparatus and method which overcomes or mitigates the deficiencies of previously proposed apparatus and methods. 
         [0008]    It is another aim of at least one aspect of the invention to provide an alternative apparatus and method to those previously proposed. 
         [0009]    It is an aim of at least one aspect of the invention to provide a downhole apparatus offering improved performance and or wider operating parameters than the apparatus of the prior art. 
         [0010]    According to a first aspect of the invention there is provided a downhole apparatus comprising a main body having a bore arranged to be coupled with a well tubing; and a swellable mantle disposed on the main body, which swellable mantle expands upon contact with at least one predetermined fluid; wherein the main body comprises at least one opening for fluid flow between an exterior of the main body and the bore, and the swellable mantle is provided with an insert to permit the passage of fluid between the exterior of the apparatus and the at least one opening through the swellable mantle. 
         [0011]    Thus the apparatus may permit fluid flow from its exterior into the bore, through the openings in the main body, and onward to the well tubing. The apparatus may therefore communicate with production tubing, and may be adapted to permit flow of production fluid from a producing zone into the production tubing. 
         [0012]    The swellable mantle may be disposed around an elongate portion of the main body, and may form a substantially cylindrical member around the main body. The elongate portion may comprise at least one opening therein, and the swellable mantle may be adapted to allow the passage of fluid between the exterior of the apparatus and the at least one opening in the elongate portion. The apparatus may therefore be arranged to permit fluid flow across an area or surface over which the swellable mantle is disposed. 
         [0013]    The main body may be a tubular, and may form a base pipe of the apparatus. The main body may comprise a liner tubular. Preferably, the main body comprises a plurality of openings. The openings may be slots or perforations. The main body may therefore be a slotted or pre-perforated tubular. 
         [0014]    In a preferred embodiment, the main body is formed to a fixed diameter, and is not adapted for expansion in use. 
         [0015]    The swellable mantle may be provided with at least one formation to promote fluid flow between the exterior of the apparatus and the at least one opening. 
         [0016]    Preferably, the swellable mantle is provided with at least one aperture therein. The aperture may be a hole, groove or slot in the swellable mantle. The aperture may be a radial opening in the swellable mantle. The aperture may comprise a groove extending circumferentially of the swellable mantle, and may comprise an annular groove in the swellable mantle. Alternatively, or in addition, the aperture may comprise a groove extending longitudinally of the swellable mantle. The aperture may comprise a groove defining a groove axis, which may be oriented longitudinally, circumferentially, or helically of the swellable mantle. 
         [0017]    The aperture may comprise a hole extending radially of the swellable mantle. 
         [0018]    The aperture may provide a fluid flow path from the exterior of the apparatus to main body. The apparatus may comprise a flow path from the exterior of the apparatus to the bore, via the aperture and the at least one opening in the main body. The flow path may be from a producing formation to the bore, via the aperture and the at least one opening in the main body. 
         [0019]    The insert may be provided in the aperture. The insert preferably permits fluid flow through the aperture. The insert may be adapted to maintain a flow path in the aperture. The insert may comprise a fluid permeable material. The insert may function as a filter for filtering solid particles from the fluid flowing through the aperture. 
         [0020]    The insert may be disposed over one or more openings of the main body. The insert may extend longitudinally and/or radially of the main body. The insert may substantially fill a volume defined by the aperture. The insert may function to support or abut a portion of the swellable mantle, and may define a bearing surface for a portion of the swellable mantle. The insert may therefore limit or prevent the expansion of the swellable mantle in at least one direction, and may be arranged to prevent the expansion of the swellable mantle into the flow path defined by the aperture. 
         [0021]    The insert may be formed from a permeable rope, a braided line or a fibrous material, which may be wound into the aperture. Alternatively, the insert may comprise a sintered metal component. 
         [0022]    In a further alternative, the insert may comprise an impermeable metal component having fluid apertures formed therein. The insert may comprise an abrasion- or erosion-resistant material such as tungsten carbide or similar. 
         [0023]    The insert may define a conduit in the swellable mantle. The insert may define a radially extending conduit through an aperture in the swellable mantle. The conduit may be a bounded conduit, which may be adapted to maintain a flow path in the aperture. The conduit may be defined by a tube. The conduit may extend from the exterior of the swellable mantle to main body. The conduit may have a first end arranged for fluid flow to and/or from an exterior of the apparatus and a second end arranged for fluid flow to and/or from the main body. The second end may be located at or adjacent to the main body. The second end may be coupled to the apparatus at an opening on the main body. Alternatively, the second end may fully or partially extend into main body. The second end may be bonded to the main body. 
         [0024]    The conduit may be of variable length. The conduit may be telescopic, and may comprise a first member at the first end, movably coupled to a second member at the second end. The first and second members may therefore move relative to one another to create a channel of variable length. Such relative movement result from expansion of the swellable mantle. The second member may be bonded to the swellable mantle. The first member may be adapted to move relative to the second member on expansion of the swellable mantle. A seal may be provided between the first and second members. 
         [0025]    In an embodiment of the invention, there is provided one or more flow-directing members or channels disposed on an outer surface of the apparatus. The flow-directing member may be adapted to couple multiple apertures, and or direct flow to multiple apertures. The flow-directing member may be provided with holes corresponding to apertures in the swellable mantle. The flow-directing member may provide a fluid path from the exterior of the apparatus to one or more apertures. The flow-directing member may be coupled to an insert to an aperture. 
         [0026]    Preferably, the flow-directing member is coupled to multiple inserts, and may be integral therewith. More preferably, the flow-directing member is coupled to multiple conduits, or first members thereof. The flow directing member may partially or fully define the inserts to the apertures. 
         [0027]    The flow-directing member and the inserts can be considered in one embodiment to function as a gutter and a series of drainpipes respectively. 
         [0028]    Preferably, the apparatus comprises a screen for filtering solids between the exterior of the apparatus and the bore. Preferably the screen is arranged to filter solids from fluid flowing from the exterior of the apparatus to the bore. The screen functions to filter solids produced from the formation, such as sands or shale or the like, from the fluid. The screen may comprise a plurality of layers. The screen may comprise at least one mesh layer, but preferably comprises a plurality of mesh layers. 
         [0029]    The screen may comprise a filter mesh layer having a filter grade of 50 microns to 350 microns. The screen may further comprise one or both of an outer protective shroud or a drainage support mesh layer. Preferably, the screen comprises a first drainage support mesh layer on one side of a filter mesh layer, and a second drainage support mesh layer on an opposing side of a filter mesh layer. 
         [0030]    The screen is preferably disposed over the openings. More preferably, the screen is disposed over the apertures. The screen may be disposed in the flow-directing member. 
         [0031]    The apparatus may comprise multiple screens at discrete locations. The apparatus may comprise at least two screens having different filter grades. 
         [0032]    The swellable mantle is preferably disposed around the main body and may be arranged to expand upon contact with at least one predetermined fluid and thereby move the screen outwardly of the main body. The screen is preferably arranged such that any restraining force imparted by the screen onto the swellable mantle which acts against its expansion can be overcome by the swellable mantle. More preferably, substantially no restraining force is imparted on the swellable mantle by the screen. 
         [0033]    The apparatus may be arranged such that the surface area of the screen is maintained in use, between an unexpanded condition and an expanded condition. The screen may have a screen surface area; and the swellable mantle may be disposed around the main body between the main body and the screen. Preferably, the swellable mantle is arranged to expand upon contact with at least one predetermined fluid and thereby move the outwardly of the main body while maintaining the screen surface area. 
         [0034]    The swellable mantle may comprise a first region located between the main body and the screen which allows the passage of fluid between the exterior of the apparatus and the main body. The swellable mantle may include a second region, which may be circumferentially adjacent the first region, which substantially prevents passage of fluid between the exterior of the apparatus and the main body. 
         [0035]    Preferably, the second region is adapted to be expanded into contact with the borehole wall. 
         [0036]    The screen may be discontinuous around the circumference of the main body. The screen may consist of multiple portions of screening material, which may be discrete in an expanded condition of the apparatus. The multiple portions may additionally be discrete in an unexpanded condition of the apparatus. Preferably, the swellable member is disposed around the main body between the main body and the screen such that on expansion the screen is moved outwardly of the main body. The screen may comprise at least two discrete screens or screen sections circumferentially spaced on the apparatus. 
         [0037]    Preferably, the swellable mantle is disposed between the main body and a borehole wall in use. The apparatus may be adapted to provide stand off of the main body from the bore in the apparatus is located. More preferably the swellable mantle is further adapted to provide support to a wall of the bore in which it is located. 
         [0038]    The apparatus may be used to support a loose or unstable borehole formation, such as a sandstone or shale formation. The apparatus may be adapted for compliant expansion of the swellable mantle to the formation, such that the swellable mantle contacts the formation without unduly stressing the formation. This has the advantage of reducing rock fatigue and reducing the tendency of solids to flow out of the formation with the fluid. 
         [0039]    Although the term “swellable mantle” is used herein it should not be taken to imply a single piece of swellable material unless otherwise specified. Certain embodiments of the invention comprise multiple, separate pieces of swellable material which combine to provide the so-called swellable mantle. Other embodiments comprise a unitary swellable mantle. 
         [0040]    The swellable material may comprise an ethylene-propylene co-polymer cross-linked with at least one of a peroxide and sulphur. More specifically the swellable member may comprise ethylene propylene diene monomer rubber (EPDM). 
         [0041]    Alternatively or in addition the swellable member may contain at least one or multiple water absorbing resins or more precisely any lightly cross-linked hydrophilic polymer embedded within the main swellable member elastomer which may comprise at least one of chloroprene, styrene butadiene or ethylene-propylene rubbers. Such water-absorbing resins are termed “superabsorbent polymers” or “SAPs” and when embedded within the swellable member it may expand when in contact with an aqueous solution. 
         [0042]    Examples of water absorbent resin include cross-linked polyacrylic acid salts, cross-linked copolymers of vinyl alcohol and acrylic acid salt, cross-linked products of polyvinyl alcohol grafted with maleic anhydride, crosslinked copolymers of acrylic acid salt and meth-acrylic acid salt, cross-linked saponification products of methyl acrylate-vinyl acetate copolymer, cross-linked products of starch-acrylic acid salt graft copolymer, crosslinked saponification products of starch-acrylonitrile graft copolymer, crosslinked saponification products of starch-ethyl acrylate graft copolymer, crosslinked carboxymethyl cellulose and the like. 
         [0043]    Alternatively or in addition, the swellable member may comprise an ethylene-propylene-diene polymer with embedded water absorbent resin such that expansion of the swellable member may result from contacting either an aqueous solution or polar liquid such as oil or a mixture of both. 
         [0044]    According to a second aspect of the invention there is provided a well completion or hydrocarbon production method comprising the steps of: 
         [0000]    a. Providing a swellable mantle over an opening on a main body of an apparatus;
 
b. Locating the apparatus at a downhole location;
 
c. Expanding the swellable mantle by exposing it to a predetermined fluid;
 
d. Maintaining a fluid flow path in the swellable mantle using an insert in the swellable mantle;
 
e. Allowing fluid flow between an exterior of the apparatus and the at least one opening through the swellable mantle.
 
         [0045]    The method may comprise the step of allowing fluid to flow through the insert. The method may comprise the step of receiving fluid from the formation and into a well tubing to which the apparatus is coupled. 
         [0046]    The method may include the additional step of screening solids from the fluid received from the formation. 
         [0047]    The method may include the additional step of moving a screen outwardly of the main body during expansion of the swellable mantle. 
         [0048]    The method may include the step of expanding the swellable mantle without changing the surface area of the screen. 
         [0049]    The method may include the step of expanding the swellable mantle such that the screen consists of a plurality of discrete screen sections after expansion. 
         [0050]    Other preferred and optional features of the second aspect of the invention are defined with respect to the first aspect of the invention. 
         [0051]    According to a third aspect of the invention there is provided downhole apparatus comprising a main body having a bore communicating with a well tubing, and at least one opening for fluid flow between an exterior of the main body and the bore; a screen for filtering solids between the exterior of the apparatus and the bore; and a swellable mantle disposed around the main body and arranged to expand upon contact with at least one predetermined fluid and thereby move the screen outwardly of the main body, wherein the swellable mantle comprises a first region located between the main body and the screen which allows the passage of fluid between the exterior of the apparatus and the main body; and a second region, circumferentially adjacent the first region, which substantially prevents passage of fluid between the exterior of the apparatus and the main body. 
         [0052]    Thus the invention in this aspect provides a swellable mantle with a surface which is designed to permit or prevent fluid flow through circumferentially separated areas. This facilitates the use of a screen which is not continuous around the circumference of swellable mantle. The discontinuous nature of the screen permits the screen to be moved outwardly of the main body more readily than if a continuous screen were used. 
         [0053]    Preferably, the second region is adapted to be expanded into contact with the borehole wall. 
         [0054]    The screen is preferably arranged such that any restraining force imparted by the screen onto the swellable mantle which acts against its expansion can be overcome by the swellable mantle. More preferably, substantially no restraining force is imparted on the swellable mantle by the screen. 
         [0055]    The apparatus may be arranged such that the surface area of the screen is maintained in use, between an unexpanded condition and an expanded condition. The screen may have a screen surface area; and the swellable mantle may be disposed around the main body between the main body and the screen. Preferably, the swellable mantle is arranged to expand upon contact with at least one predetermined fluid and thereby move the outwardly of the main body while maintaining the screen surface area. 
         [0056]    The screen may be discontinuous around the circumference of the main body. The screen may consist of multiple portions of screening material, which may be discrete in an expanded condition of the apparatus. The multiple portions may additionally be discrete in an unexpanded condition of the apparatus. Preferably, the swellable member is disposed around the main body between the main body and the screen such that on expansion the screen is moved outwardly of the main body. The screen may comprise at least two discrete screen sections circumferentially spaced on the apparatus. 
         [0057]    Other preferred and optional features of the third aspect of the invention are defined with respect to the first and second aspects of the invention. 
         [0058]    According to a fourth aspect of the invention there is provided a well completion or hydrocarbon production method comprising the steps of: 
         [0000]    a. Providing a swellable mantle over an opening on a main body of an apparatus;
 
b. Locating the apparatus at a downhole location;
 
c. Expanding the swellable mantle by exposing it to a predetermined fluid to thereby move a screen outwardly of the main body;
 
d. Allowing fluid to flow between an exterior of the apparatus and the at least one opening through a first region of the swellable mantle located between the main body and the screen, while substantially preventing passage of fluid between the exterior of the apparatus and the main body in a second region of the swellable mantle, circumferentially adjacent the first region.
 
         [0059]    The method may comprise the step of receiving fluid from the formation and into a well tubing to which the apparatus is coupled. 
         [0060]    The method may include the additional step of screening solids from the fluid received from the formation. 
         [0061]    The method may include the step of expanding the swellable mantle without changing the surface area of the screen. 
         [0062]    The method may include the step of expanding the swellable mantle such that the screen consists of a plurality of discrete screen sections after expansion. 
         [0063]    Other preferred and optional features of the fourth aspect of the invention are defined with respect to the first to third aspects of the invention. 
         [0064]    According to a fifth aspect of the invention there is provided a downhole apparatus comprising a main body having a bore communicating with a well tubing, and at least one opening for fluid flow between an exterior of the main body and the bore; a screen for filtering solids between the exterior of the apparatus and the bore having a screen surface area; and a swellable member disposed around the main body between the main body and the screen, wherein the swellable member is arranged to expand upon contact with at least one predetermined fluid and thereby move the screen outwardly of the main body while maintaining the screen surface area. 
         [0065]    Other preferred and optional features of the fifth aspect of the invention are defined with respect to the first to fourth aspects of the invention. 
         [0066]    According to a sixth aspect of the invention there is provided a downhole apparatus comprising a main body having a bore communicating with a well tubing, and at least one opening for fluid flow between an exterior of the main body and the bore; a screen for filtering solids between the exterior of the apparatus and the bore; and a swellable member disposed around the main body between the main body and the screen, wherein the swellable member is arranged to expand upon contact with at least one predetermined fluid and thereby move the screen outwardly of the main body, wherein the screen comprises at least two discrete screen sections circumferentially spaced on the apparatus. 
         [0067]    Other preferred and optional features of the sixth aspect of the invention are defined with respect to the first to fifth aspects of the invention. 
         [0068]    Use of the first, third, fifth and sixth aspects of the invention in well completion or production methods is within the scope of the invention. A volume of hydrocarbon obtained by using the apparatus or methods described also forms part of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0069]    There will now be described, by way of example only, various embodiments of the invention with reference to the following drawings, of which: 
           [0070]      FIG. 1  is a perspective view of an apparatus in accordance with a preferred embodiment of the invention; 
           [0071]      FIG. 2  is a perspective view of the apparatus of  FIG. 1  with the swellable mantle removed to show other components; 
           [0072]      FIG. 3  is an exploded view of the swellable mantle of the apparatus of  FIGS. 1 and 2 ; 
           [0073]      FIG. 4  is a perspective view of an insert used with the apparatus of  FIGS. 1 ,  2  and  3 ; 
           [0074]      FIGS. 5A and 5B  are schematic views of the insert of  FIG. 4  in retracted and extended conditions respectively; 
           [0075]      FIG. 6  is a schematic exploded view of a filter used in accordance with embodiments of the invention; 
           [0076]      FIG. 7  is a schematic sectional view of the apparatus of  FIG. 1  in use in a wellbore; 
           [0077]      FIG. 8  is a schematic representation of apparatus in accordance with an alternative embodiment of the invention in partial longitudinal section; 
           [0078]      FIG. 9  is a schematic representation of apparatus in accordance with a second embodiment of the invention in partial longitudinal section; 
           [0079]      FIG. 10  is a cross-sectional view of apparatus in accordance with a further embodiment of the invention; 
           [0080]      FIG. 11A  is a cross-sectional view of apparatus in accordance with a further embodiment of the invention; and 
           [0081]      FIG. 11B  is a cross-sectional view of the apparatus of  FIG. 11A  in an expanded configuration. 
       
    
    
     DETAILED DESCRIPTION 
       [0082]    Referring firstly to  FIGS. 1 to 3 , there is shown a downhole apparatus, generally depicted at  10 , in accordance with an embodiment of the invention. The apparatus  10  comprises a main body  12  formed from tubular base pipe. The body  12  is adapted to be coupled to well tubing (not shown) such that the bore  14  of the apparatus communicates with the bore of the well tubing. 
         [0083]    A section  16  of the main body  12  extending over a length of the apparatus is provided with openings  18  or perforations distributed longitudinally and circumferentially on the section  16 . The openings are through-openings from an exterior of the main body  12  to the bore  14 . In this embodiment, the openings  18  are regularly distributed, although in alternative embodiments other arrangements of openings may be provided. 
         [0084]    Disposed over the main body  12  is a swellable mantle  20 .  FIG. 2  shows the mantle removed from the apparatus  10 . The swellable mantle  20  is a substantially tubular member shaped to fit over the section  16  of the apparatus. The swellable mantle is sized to be bonded or slipped onto the main body, and is located on the section  16  by end rings  22 . The end rings  22  are secured to the main body to prevent axial and radial movement and to abut the respective ends of the swellable mantle  20 . 
         [0085]    The swellable mantle  20  is provided with apertures  24  and inserts  26  to the apertures. The inserts  26  are located in longitudinal recessed grooves  28  on the outer surface of the swellable mantle  20 . The inserts  26  will be described in more detail below. 
         [0086]    The swellable mantle  20  is formed from a material which is selected to expand on contact with a predetermined fluid. Such swellable materials are known in the art. In this example, the swellable mantle is required to swell in oil, and the material comprises ethylene propylene diene monomer rubber (EPDM). In an alternative embodiment, where the swellable mantle is required to swell in water, the material comprises any lightly crosslinked hydrophilic polymer embedded within the main swellable member elastomer, such as at least one of chloroprene, styrene butadiene or ethylene-propylene rubbers. Such water-absorbing resins are termed “superabsorbent polymers” or “SAPS” and when embedded within the swellable member may expand when in contact with an aqueous solution. In a further alternative embodiment, the swellable member comprises an ethylene-propylene-diene polymer with embedded water absorbent resin such that expansion of the swellable member results from contacting either an aqueous solution or polar liquid such as oil or a mixture of both. 
         [0087]    The apertures  24  function to allow fluid to flow from the exterior of the swellable mantle  20  to its interior. When the swellable mantle is positioned on the main body  12 , the apertures  24  allow fluid flow from the exterior of the apparatus to the main body  12  and through the openings  18  in the main body to the bore  14 . In this embodiment, the spacing of the apertures  24  corresponds to the spacing of the openings  18 , such that the apertures  24  and openings  18  may be aligned to provide minimal resistance to fluid flow from the exterior of the apparatus to the bore  14 . 
         [0088]    The swellable mantle  20  functions to expand on contact with a well bore fluid such that the outer surface of the apparatus comes into contact with the borehole wall. The dimensions and properties of the swellable mantle are selected for compliant expansion of the swellable mantle into contact with the borehole wall, such that an appropriately low force is imparted to the borehole to create a seal, but to prevent damage to the rock formation or sandface. The dimensions and material of the swellable mantle are also selected to expand into a washout zone in the borehole to similarly create a seal with a suitably low force on the formation. In this way, the formation is supported from collapse towards the main body  12 , but without damaging the formation in a way that would increase the inflow of solids. 
         [0089]    The insert includes a screen support  30  and screen material  32 . The insert  26  therefore defines screen sections  33  of the apparatus along circumferentially spaced longitudinal regions of the swellable mantle  20 . Disposed between the screen sections are longitudinal regions of the swellable mantle  20  which substantially prevent fluid flow to the interior of the mantle  20 . In this regard, it is noted that the swellable material may permit fluid penetration by diffusion through the swellable material, but does not permit fluid flow such as that required for the inflow of production fluids into the bore  14  or the injection of fluids from the bore  14  into the formation. 
         [0090]      FIGS. 4 ,  5 A and  5 B show the insert  26  in more detail, with the screen material  32  removed. The insert  26  includes a plurality of conduits  34  which extend through the swellable mantle to the main body. Multiple conduits are connected by a channel  35  defined by the screen support  30 . The conduits  34  each comprise a first member  36  received in a second member  38 . The first and second members  36 ,  38  are movable relative to one another to accommodate expansion of the swellable mantle  20 . The conduits function to maintain the flow path of the aperture after expansion. In alternative embodiments of the invention, the conduits, or a subset of conduits, are provided with flow control members such as valves or check valves to restrict fluid flow therethrough. 
         [0091]    When assembled, the second member  38  is an interference fit with the aperture  24  of the swellable mantle into which it locates. The undersurface  42  of the screen support  30  is bonded to the surface of the swellable mantle  20  along the longitudinal groove  28 . When the swellable mantle expands, the first member  36  moves relative to the second member  38  such that the conduit telescopically extends. 
         [0092]    In alternative embodiments, the second member  38  may be fixed to the main body  12  and/or may be received in the opening  18  in the main body. 
         [0093]    Referring now to  FIG. 6 , the screen material  32  is shown as comprising a plurality of overlaid layers. Adjacent the screen support  30  is provided a drainage support mesh  44 , onto which is overlaid a filter mesh  46 . The filter mesh is selected to have an appropriate mesh grade for filtering solids which may be produced from the formation. Typically, the filter mesh will have a mesh grade of around 100 to 300 microns. Over the filter mesh  46  is a further drainage support mesh  48 , and finally an outer protective shroud  50 , having relatively large apertures, is provided on the exterior of the screen material. 
         [0094]    The present invention encapsulates embodiments in which different screen sections are provided with different filter grades. The invention also facilitates customisation of the apparatus by selecting appropriate filter grades during assembly of the apparatus. 
         [0095]      FIG. 7  shows the apparatus  10  in use in a borehole, in a swelled condition. The apparatus  10  has been run to a location in a sand-producing formation  51 , and exposure to wellbore fluids has caused the swellable mantle  20  to expand into contact with the borehole wall  52 . As expansion takes place, the conduits  34  defined by the inserts  26  telescopically extend such that a bounded conduit is formed between the exterior of the apparatus and the openings  18  in the main body  12 . The inserts prevent the swellable mantle  20  from expanding to close the apertures  24 . 
         [0096]    The screen sections  33  are placed adjacent to the sandface by expansion of the swellable mantle under the insert, and adjacent regions  54  of the swellable mantle form a compliant seal on the borehole wall  52 . Fluid flow from the formation is permitted in the areas at which the screen sections  32  are provided, and is directed through the apertures  24 , via the conduits  34 , and into the bore  14 . Flow is not permitted through the regions  54 . 
         [0097]    This embodiment of the invention provides compliant expansion of a swellable member to a borehole wall, providing structural support to the borehole without damaging the sandface. The screen sections  33  are carried or moved in a radial direction to be placed adjacent to the sandface. This minimises the annular space in which solids produced from the formation can flow. The flow of fluid is only permitted in the regions at which the screen material is provided, with adjacent sections supported and sealed by the swellable mantle. By providing the plurality of discrete screen sections, movement of the screen outwardly from the main body of the apparatus is accomplished effectively without restraining swelling of the mantle. The embodiment of the invention is also conducive to customisation and configuration of the filter grades used, which may differ between screen sections. 
         [0098]    There will now be described alternative embodiments of the invention with reference to  FIGS. 8 to 11 . 
         [0099]    Referring to  FIG. 8 , there is shown a downhole apparatus, generally depicted at  100  consisting of the main body  112  formed from a tubular base pipe and adapted to be coupled to well tubing in the same manner as apparatus  10 . In a similar fashion to apparatus  10 , the main body  112  is provided with a plurality of through-openings  118  distributed on the body. 
         [0100]    Disposed on the body  112 , and shown in the Figure in longitudinal section, are end rings  122  and a swellable mantle  120  consisting of three longitudinally spaced sections  121   a ,  121   b , and  121   c . Apertures  124  are provided in the form of circumferential grooves to the swellable mantle  120  extending from its outer surface to the main body  112 . Provided in the apertures  124  are inserts  126 , which in this embodiment are constructed from a permeable rope which is wound around the main body into the aperture. The insert  126  is wound tightly on the main body and provides an abutting surface for the adjacent portions of the swellable mantle  120 . In use, the swellable mantle expands outwardly and partially over the insert  126 , but without covering the aperture to prevent fluid flow. 
         [0101]    The inserts  126  function to permit fluid flow through the aperture and into the main body, while maintaining the flow path and limiting or preventing the expansion of the swellable mantle in the longitudinal direction. The insert additionally functions as a filter for solid particles in the fluid flowing through the aperture. 
         [0102]    In an alternative embodiment, the insert  126  is wound from a braided line or wire, or a fibrous material. 
         [0103]      FIG. 9  shows an alternative embodiment, generally depicted at  130 , similar to the embodiment of  FIG. 8  and with like components identified by like reference numerals. This embodiment differs in the form of the inserts  136 ,  138  provided to the apertures  124 . 
         [0104]    Insert  136  is in the form of a cylinder sized to slip onto the main body  112 , and provided with first and second flange members  137   a ,  137   b  extending outwardly from the main body. Holes are provided in the insert  136  to allow fluid flow to the main body. The flange members  137   a  and  137   b  function to provide an abutting surface to adjacent portions of the swellable mantle to limit or prevent expansion of the swellable mantle across the aperture  124 . Insert  138  consists of a pair of flange portions extending outwardly from the main body, and exposing the main body to the aperture  124 . 
         [0105]    In this embodiment, one or both of the inserts of  136 ,  138  may comprise a hardened, erosion-resistant material such as tungsten carbide. This functions to resist erosion caused by solid particles contained in the fluid, which would have a tendency to erode the swellable mantle and/or the openings in the main body  112 . It will be appreciated that the apparatus may comprise only one type of the inserts  136 ,  138 . 
         [0106]      FIG. 10  shows a further alternative embodiment of the invention, generally depicted at  140 . In this embodiment, the apertures  144  and the swellable mantle  146  are longitudinal grooves, at the inserts  146  are formed from blocks of sintered metal material. The blocks of sintered metal material are overlaid with screen sections  148  before filtering solids from fluid flowing through the apertures  144  and into the main body. In use, the swellable mantle expands outwardly and partially over the screen section, but without covering the aperture to prevent fluid flow. In alternative embodiments, the apertures  144  are helical or circumferential slots or holes in the swellable mantle. 
         [0107]    A further alternative embodiment is shown in  FIGS. 11A and 11B . In this embodiment, shown generally at  150 , a substantially tubular screen  152  is embedded into a swellable mantle  153 . Apertures  158  are provided in the mantle  153  to allow fluid flow to the main body  159 . The screen  152  comprises longitudinal support members  154  which function to provide support to the relatively flexible screen material  156 . In  FIG. 13A , the screen material is folded, bent or creased to such that is radial dimension is less than the maximum radial dimension which can be defined by the screen  152 . The screen has a fixed surface area, but is embedded into the swellable mantle such that it may expand radially on expansion of the swellable material to a position shown in  FIG. 13B , without stretching the screen material or affecting the filter grade. 
         [0108]    Variations to the above-described embodiments are within the scope of the invention. For example, any of the described insert configurations could be used in combination on the same apparatus in the scope of the invention. Combinations of features other than those expressly claimed are within the scope of the invention. 
         [0109]    In further alternative embodiments of the invention, the apertures, or selected apertures in the swellable mantle, are provided with flow control members such as valves or check valves to restrict fluid flow therethrough. 
         [0110]    The present invention in its various aspects provides an improved and alternative downhole apparatus and method offering improved performance and/or wider operating parameters than the apparatus of the prior art.