Abstract:
A system and method is provided for filtering in a wellbore during various well related operations while limiting the potential for plugging. A well screen is used for filtering particulates from a fluid at a wellbore location. To remove accumulated material and avoid plugging, the well screen may be flexed via pressure differentials created across the well screen. The flexing of the well screen breaks free the accumulated materials, thereby avoiding premature job failure.

Description:
BACKGROUND 
   In many wellbore applications, sand laden fluids are filtered to return a clean fluid to the surface or to dehydrate a slurry at a desired location in a wellbore. The filtering is performed by a filtering media created from a wire wrapped or wire mesh structure. This type of filtering media is susceptible to plugging over a period time which can cause premature job failure. 
   Attempts have been made to reduce plugging by using powered tools associated with the filtering media. For example, screens have been designed with rotatable sleeves to help reduce plugging. Other screens utilize movable components that can be actuated to close off the screen during certain operations. However, such devices have limited effectiveness. Additionally, these devices tend to be complex, expensive devices requiring a power source for operation. 
   SUMMARY 
   In general, the present invention provides a system and method of filtering in a wellbore during various well related operations. A well screen is combined with a tool string for movement downhole into a wellbore. The well screen may be flexed via pressure differentials created across the well screen. For example, pressure inputs create pressure differentials able to flex the well screen between a normal mode and one or more deflection modes. Examples of deflection modes comprise a radially inward deflection mode and/or a radially outward deflection mode. Once the actuating pressure differential is diminished, the well screen automatically returns to the normal mode. The flexing of the well screen is used for adjusting flow gap size and for removing accumulated materials to unplug the well screen for continued use, thereby avoiding premature job failure. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Certain embodiments of the invention will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and: 
       FIG. 1  is a front elevation view of a wellbore assembly disposed in a wellbore, according to an embodiment of the present invention; 
       FIG. 2  is an isometric view of a well screen, according to an embodiment of the present invention; 
       FIG. 3  is a side view of the well screen illustrated in  FIG. 2 , according to an embodiment of the present invention; 
       FIG. 4  is a cross-sectional view of a well screen mounted on a support structure, according to an embodiment of the present invention; 
       FIG. 5  illustrates an enlarged portion of the embodiment illustrated in  FIG. 4 ; 
       FIG. 6  is a schematic illustration of a well screen in a normal deflection mode, according to an embodiment of the present invention; 
       FIG. 7  is a schematic illustration of a well screen in a radially inward deflection mode, according to an embodiment of the present invention; 
       FIG. 8  is a schematic illustration of a well screen in a radially outward deflection mode, according to an embodiment of the present invention; and 
       FIG. 9  is a flowchart illustrating utilization of a compliant well screen, according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   In the following description, numerous details are set forth to provide an understanding of the present invention. However, it will be understood by those of ordinary skill in the art that the present invention may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible. 
   The present invention generally relates to a system and methodology for filtering particulates from a fluid stream at a location within a wellbore. A compliant well screen is moved downhole into a wellbore for use in one or more well related operations. The well screen is compliant and cooperates with the overall system in a manner that enables removal of or prevention of plugging along the well screen. The well screen also can be used to facilitate downhole operations, such as the dehydration of a slurry in the wellbore. The compliant well screen is flexed between different modes of deflection via differential pressures across the well screen. For example, the pressure inputs resulting from the differential pressures across the well screen can be used to flex the well screen between a normal or intermediate mode and, for example, a radially inward mode of deflection or a radially outward mode of deflection. 
   Referring generally to  FIG. 1 , a system  20  is illustrated according to an embodiment of the present invention. In the particular embodiment illustrated, system  20  comprises a wellbore assembly  22  disposed in a well  24  that comprises a wellbore  26  drilled into a formation  28 . Formation  28  may hold desirable production fluids, such as oil. Wellbore assembly  22  extends downwardly into wellbore  26  from, for example, a wellhead  30  that may be positioned along a surface  32 , such as the surface of the earth or a seabed floor. The wellbore  26  may comprise open hole sections, e.g. open hole section  34 , cased sections lined by a casing  36 , or a combination of cased sections and open hole sections. Additionally, wellbore  26  may be formed as a vertical wellbore or a deviated, e.g. horizontal, wellbore. In the embodiment illustrated in  FIG. 1 , wellbore  26  comprises a vertical section  38  and a deviated section  40  which is illustrated as generally horizontal. One or more packers  42  also may be used with or included as part of wellbore assembly  22  to seal off desired sections of wellbore  26 . 
   In the example illustrated, wellbore assembly  22  further comprises a well screen  44  that is carried downhole into wellbore  26  on a tool string  46 . Well screen  44  is a compliant well screen that may be moved between a plurality of deflection modes via pressure differentials created between an exterior region  48  surrounding well screen  44  and an interior region  50  within well screen  44  and tool string  46 . Tool string  46  may be formed in a variety of configurations and with a variety of components depending on the specific well application for which it is designed. In some operations, for example, tool string  46  comprises a bottom hole assembly  52  coupled to a tubing  54 . However, other components and component arrangements can be used with well screen  44  to facilitate a variety of well related operations. 
   One embodiment of well screen  44  is illustrated in  FIG. 2 . In this embodiment, well screen  44  is generally tubular in shape and able to undergo deflections away from a normal mode, such deflections being radially inward and/or radially outward deflections depending on the pressure inputs applied to the well screen. The illustrated well screen  44  comprises a first well screen end  56  and a second well screen end  58 . Well screen ends  56  and  58  are substantially rigid in the sense that the ends do not flex outwardly or inwardly when pressure differentials are applied between exterior region  48  and interior region  50 . Extending between well screen ends  56  and  58  are a plurality of elongate members  60  separated by slots  62 . The elongate members  60  extend in a longitudinal direction generally aligned with the axis of well screen  44 . 
   The slots  62  provide gaps for fluid flow across well screen  44  from exterior region  48  to interior region  50  or from interior region  50  to exterior region  48 . The gap size of slots  62  controls the size of particulars that are filtered from the flow of fluid. However, this gap size is adjusted as the compliant well screen  44  is transitioned between different deflection modes via flexing of elongate members  60  in, for example, a radially inward direction or a radially outward direction between screen ends  56  and  58 . 
   As further illustrated in  FIG. 3 , elongate members  60  may be formed as beams that extend in a generally linear and parallel arrangement between well screen ends  56  and  58 . Each elongate member or beam  60  has linear ends  64 ,  66  affixed to well screen ends  56 ,  58 , respectively. Thus, the linear ends  64 ,  66  of elongate members  60  are substantially fixed with respect to movement in a radial direction. However, the portion of elongate members  60  between ends  64 ,  66  can be flexed in a radially inward or a radially outward direction to change the gap size of slots  62 . In the embodiment illustrated the design of elongate members  60  and slots  62  ensures the gap size is never reduced to zero. In other words, at least some fluid flow is allowed across well screen  44  between interior region  50  and exterior region  48  even when the well screen  44  is transitioned to a maximum deflection. It should also be noted that the amount of deflection, the pressure differential required to cause deflection, and the shape or pattern of deflection can be controlled by changing the length or cross-section of elongate members  60 . Additionally, these compliancy characteristics also can be controlled by selecting the appropriate material composition of elongate members  60  for a given application. For example, a variety of steels, other metals, phenolics, composites and non-metallic materials can be used in the construction of well screen  44 . 
   Well system  20  also may comprise a support structure  68  positioned to limit deflection of compliant well screen  44 . One example of support structure  68  is illustrated in  FIG. 4 . In this embodiment, support structure  68  is positioned along an interior of well screen  44  to limit deflection of well screen  44  in a radially inward direction. However, alternate or additional support structures also can be located along an exterior of well screen  44  to limit deflection of well screen  44  in a radially outward direction. Additionally, support structure  68  may have a variety of other configurations that enable the limiting of well screen deflection. 
   In the specific example illustrated, support structure  68  comprises a tubular member having a plurality of radial openings  70  to accommodate fluid flow between exterior region  48  and interior region  50 . Support structure  68  further comprises standard connection ends  72  and  74  that allow support structure  68  to be coupled to tool string  46 . By way of example, standard connection ends  72  and  74  may comprise threaded connection ends or flange-style connection ends. Support structure  68  also comprises a tubular midsection  76  sized to fit within compliant well screen  44  so as to limit the radially inward deflection of well screen  44 . 
   As best illustrated in  FIG. 5 , support structure  68  may further comprise a plurality of support elements  78  positioned to block radially inward movement of well screen  44  at a predetermined limit. For example, support elements  78  may be sized to insure the maximum deflection of well screen  44  remains within the elastic limits of the elongate members  60 . The maximum deflection within the elastic regime of elongate members  60  is a function of material choice as well as length of elongate members  60 . 
   In the embodiment illustrated, support elements  78  are mounted to tubular midsection  76  and are interchangeable to enable adjustment of the maximum deflection limitation. By way of example, each support element  78  may comprise a cap  80  of predetermined thickness. The cap  80  is mounted to tubular midsection  76  by a fastener  82 , such as a threaded fastener received in a threaded opening  84  formed in tubular midsection  76  of support structure  68 . Accordingly, the maximum deflection limitation can be changed by unthreading each threaded fastener  82 , removing each corresponding cap  80 , and reattaching the same or different threaded fasteners  82  with alternate caps  80  of a different thickness. 
   In some embodiments, the compliant well screen  44  can deflect in both an expanding mode and a collapsing mode to remove accumulation and prevent plugging of well screen  44 . The ability to deflect well screen  44  also facilitates a variety of well operations, such as dehydration of slurry in the wellbore during, for example, a gravel packing operation. The prevention of plugging is accomplished without employing any powered control mechanism downhole. Instead, elongate members  60  of well screen  44  are flexed upon application of sufficient pressure inputs created by internal and/or external pressure differentials formed along the well screen  44 . The application of pressure differentials also alters slots  62  which, in turn, changes the gap size through which fluid flows through well screen  44 . Pressure differentials may be generated by, for example, flow, mechanical crushing or drag resulting from movement of the bottom hole assembly  52 , mechanical radial force from a tool having a sliding sleeve, or other mechanisms or procedures for developing pressure differentials. 
   Until the pressure differential between exterior region  48  and interior region  50  is sufficiently great, elongate members  60  remain in an intermediate or normal mode, as illustrated schematically in  FIG. 6 . In this illustration, the orientation of the pressure differential is indicated by a plurality of arrows  86 . The pressure differential acts on elongate members  60  which have ends  64 ,  66  held radially stationary by well screen ends  56 ,  58  as represented by triangles  88  in  FIG. 6 . 
   Once the predetermined differential pressure is reached as a result of fluid flow from the exterior annulus region  48  to the interior region  50  within the tool string, the elongate members or beams  60  collapse, as illustrated schematically in  FIG. 7 . The beams  60  collapse until the flexing is limited by support structure  68 . As described above, the deflection is limited such that elongate members  60  remain in their elastic state and thus remain free to return to the intermediate mode illustrated in  FIG. 6  after sufficient reduction of the pressure differential. This radially inward mode of deflection does not completely remove the gaps created by slots  62  and thus allows some liquid flow therethrough. The retained gaps enable slurry, for example, to continue to dehydrate over a given period of time. 
   The radially inward deflection mode also forces the elongate members  60  into closer proximity with each other, thereby crushing particles that are within the gaps or slots  62  between elongate members  60 . Upon sufficient reduction or removal of the pressure differential across well screen  44 , the well screen  44  returns to its intermediate deflection mode. Fluid flow can then be directed into interior region  50  within tool string  46  to create an outward flow of fluid through well screen  44  from interior region  50  to exterior region  48 . The fluid flow can be directed to interior region  50  via flow through coiled tubing or jointed pipe of system  20 , for example. This backflow can be used to create a pressure differential able to transition the well screen to a radially outward deflection mode in which elongate members  60  are bowed radially outwardly, as illustrated schematically in  FIG. 8 . The outward flexing of well screen  44  increases the gap size by opening slots  62  and further facilitates the washing away of any remaining debris previously trapped in the gaps between elongate members  60 . Upon removal or reduction of the pressure differential, well screen  44  returns to its intermediate deflection mode. 
   The ability to flex well screen  44  between radially inward and/or outward deflection modes and to control the gap size between elongate members  60  effectively allows well screen  44  to breathe by removing plugging proppant or other materials. Furthermore, the well screen gap size can be adjusted to an optimum size during usage of well screen  44  simply by using internal and external differential pressures across well screen  44 . One result is an increase in running time for well screen  44  which, in turn, facilitates the performance and efficiency of well operations by reducing the running in and out of the wellbore to change screen assemblies. 
   In some well applications, the deflection due to expansion is controlled by pressure drop because flow to the interior of tool string  46  can either leave through well screen  44  or through the bottom of bottom hole assembly  52 . In these embodiments, flushing at a predetermined, controlled rate provides the pressure differential needed to expand well screen  44  to the radially outward deflection mode. 
   Well system  20  can be designed for a variety of well related operations that can benefit from the ability to use simple pressure differentials in controlling gap size for conducting flow through the well screen  44  and in preventing plugging of the well screen  44 . As illustrated by the flowchart of  FIG. 9 , the compliant well screen  44  can benefit a variety of well related operations. In operation, the compliant well screen  44  is initially connected to a tool string  46  designed for a specific well operation or operations, as indicated by block  90  in  FIG. 9 . The compliant well screen  44  is then run downhole into wellbore  26  on tool string  46 , as indicated by block  92 . Once well screen  44  is positioned at a desired location within wellbore  26 , the well screen is utilized in the desired well operation, as indicated by block  94 . 
   The utilization of compliant well screen  44  may be incorporated into a variety of well operations. For example, compliant well screen  44  can be used in a producing well or to facilitate the return of clean fluid to a surface location in a gravel packing operation. Compliant well screen  44  also can be used to facilitate a fracturing operation or a well stimulation operation. Additionally, compliant well screen  44  can be used in a clean-out operation or to facilitate the reverse circulation of fluid through a bottom hole assembly. Furthermore, the well screen  44  can be flexed to create a desired gap size and/or to remove accumulation along the well screen while the well screen is moved along wellbore  26 . For example, well screen  44  can be flexed to prevent plugging and/or to adjust gap size as the well screen is run in hole, pulled out of hole, or moved between wellbore zones. 
   In any of these operations, well screen  44  is flexed via a created pressure differential to remove accumulation and prevent plugging and/or to adjust the gap size between elongate members  60 , as indicated by block  96 . During or after flexing of compliant well screen  44  to a desired deflection mode or modes, the well operation is continued without any need to pull well screen  44  from the wellbore, as represented by block  98 . Accordingly, no separately powered tools are required to clean the well screen, and well screen  44  can be operated with simple pressure differentials between an exterior and an interior of the well screen. 
   It should be noted that well system  20  may have a variety of configurations and components for use in many types of well operations. Additionally, the diameter, length, shape and materials of well screen  44  can be adjusted to accommodate system requirements, environmental factors or other design considerations. 
   Accordingly, although only a few embodiments of the present invention have been described in detail above, those of ordinary skill in the art will readily appreciate that many modifications are possible without materially departing from the teachings of this invention. Accordingly, such modifications are intended to be included within the scope of this invention as defined in the claims.