The present invention provides apparatus and methods for expanding an expandable sand screen in the wellbore and then fracturing the wellbore. In one aspect of the invention, an expandable sand screen includes a perforated inner pipe and outer shroud. The outer shroud includes a plurality of longitudinal channels that retain their general shape after the expandable sand screen is expanded. In the expanded state, the channels provide a fluid conduit along an area between the screen and the wall of the wellbore. In a subsequent fracturing operation, slurry travels along the conduits permitting communication of the fracturing slurry with hydrocarbon bearing formations.

CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation of co-pending U.S. patent application Ser. No. 09/885,850, filed Jun. 20, 2001, which is herein incorporated by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to expandable sand screen. More particularly the present invention relates to an expandable sand screen that permits fracturing of a hydrocarbon bearing formation after the well screen is expanded in a wellbore.  
           [0004]    2. Description of Related Art  
           [0005]    Hydrocarbon wells are typically formed with a central wellbore that is supported by steel casing. The casing lines the borehole in the earth and the annular area created between the casing and the borehole is filled with cement to further support and form the wellbore.  
           [0006]    While some wells are produced by simply perforating the casing of the central wellbore and collecting the hydrocarbons, wells routinely include portions of wellbore that are left open or unlined with casing. Because they are left open, hydrocarbons in an adjacent formation migrate into these wellbores where they are affected along a perforated tubular or sand screen having apertures in its wall and some kind of filtering material to prevent sand and other particles from entering. The sand screen is attached to production tubing at an upper end and the hydrocarbons travel to the surface of the well via the tubing. In this specification “open” and “horizontal” wellbore refers to an unlined bore hole or wellbore.  
           [0007]    Because open wellbores have no support provided along their walls, and because the formations accessed by these wellbores have a tendency to produce sand and particulate matter in quantities that hamper production along a sand screen, open wellbores are often treated by fracturing and packing. Fracturing a wellbore or formation means subjecting the walls of the wellbore and the formation to high pressure solids and/or fluids that are intended to penetrate the formation and stimulate its production by increasing and enlarging the fluid paths towards the wellbore. Packing a wellbore refers to a slurry of sand that is injected into an annular area between the sand screen and the walls of the wellbore to support the wellbore and provide additional filtering to the hydrocarbons. Fracturing and packing can be performed simultaneously. A cross-over tool is typically utilized to direct the fracturing/packing material towards the annulus of the open wellbore while returning fluid is circulated up the interior of the screen and returns to the surface of the well in an annular area of the central wellbore.  
           [0008]    There are problems associated with the packing of an open wellbore. One such problem relates to sand bridges or obstructions which form in the annulus between the sand screen and the wall of the wellbore. These sand bridges can form anywhere along the wellbore and they prevent the flow of injected material as it travels along the annulus. The result is an incomplete fracturing/packing job that leaves some portion of the sand screen exposed to particulate matter and in some cases, high velocity particles that can damage the screen.  
           [0009]    Today there exists sand screen that can be expanded in the wellbore. This expandable sand screen “ESS” consists of a perforated base pipe, woven filtering material and a protective, perforated outer shroud. Both the base pipe and the outer shroud are expandable and the woven filter is typically arranged over the base pipe in sheets that partially cover one another and slide across one another as the ESS is expanded. The foregoing arrangement of expandable sand screen is known in the art and is described in U.S. Pat. No. 5,901,789 which is incorporated by reference herein in its entirety. Expandable sand screen is expanded by a cone-shaped object urged along its inner bore or by an expander tool having radially outward extending rollers that are fluid powered from a tubular string. Using expander means like these, the ESS is subjected to outwardly radial forces that urge the walls of the ESS past their elastic limit, thereby increasing the inner and outer diameter of the ESS.  
           [0010]    The biggest advantage to the use of expandable sand screen in an open wellbore like the one described herein is that once expanded, the annular area between the screen and the wellbore is mostly eliminated and with it the need for a gravel pack. Typically, the ESS is expanded to a point where its outer wall places a stress on the wall of the wellbore, thereby providing support to the walls of the wellbore to prevent dislocation of particles.  
           [0011]    While the ESS removes the need for packing the wellbore with sand, it does not eliminate the need to fracture the formation in order to improve production. Fracturing prior to expanding screen in the wellbore is not realistic because the particulate matter, like the sand used in the fracturing will remain in the annulus and hamper uniform expansion of the screen. Fracturing after expansion of the expandable sand screen is not possible because, as explained herein, the annular path for the fracturing material has been eliminated.  
           [0012]    There is a need therefore for an expandable sand screen for use in a wellbore to be fractured. There is a further need for an expandable sand screen that can be expanded prior to the fracturing of the wellbore surrounding the screen. There is yet a further need for an expandable sand screen that forms a path or conduit for the flow of fracturing material along its outer surface after it has been expanded.  
         SUMMARY OF THE INVENTION  
         [0013]    The present invention provides apparatus and methods for expanding an expandable sand screen in an open wellbore and then fracturing the wellbore. In one aspect of the invention, an expandable sand screen includes a perforated inner pipe and outer shroud. The outer shroud includes a plurality of longitudinal channels that retain their general shape after the expandable sand screen is expanded. In the expanded state, the channels provide a fluid conduit along an area between the screen and the wall of the wellbore. In a subsequent fracturing operation, a slurry travels along the conduits permitting communication of the slurry with hydrocarbon bearing formations to effectively fracture the formation. In another aspect, a method of fracturing includes expanding an expandable well screen in a wellbore whereby the expanded screen provides longitudinal channels in communication with the hydrocarbon bearing formation. Thereafter, fracturing slurry is injected and travels along the channels, thereby exposing the slurry to the formation. In yet another aspect of the invention, joints of the ESS are assembled together into sections and the channels on the outer surface of each joint are aligned to ensure that the longitudinal channels are aligned throughout the ESS section. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    So that the manner in which the above recited features, advantages and objects of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings.  
         [0015]    It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.  
         [0016]    [0016]FIG. 1 is a section view showing an open, horizontal wellbore with an expandable sand screen disposed therein.  
         [0017]    [0017]FIG. 2 is an exploded view of an expander tool.  
         [0018]    [0018]FIG. 3 is a section view of the expandable sand screen in an unexpanded state.  
         [0019]    [0019]FIG. 4 is a section view of the wellbore with the screen partially expanded.  
         [0020]    [0020]FIG. 5 is a section view of the expandable sand screen in an expanded state.  
         [0021]    [0021]FIG. 6 is a section view of the wellbore being treated with material injected from the surface of the well through a cross-over tool.  
         [0022]    [0022]FIG. 7 is a section view of the wellbore tied back to the surface of the wall with a production tubing.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0023]    [0023]FIG. 1 is a section view of a wellbore  200  with an expandable sand screen  210  according to the present invention disposed therein. The wellbore includes a central wellbore which is lined with casing  215 . The annular area between the casing and the earth is filled with cement  220  as is typical in well completion. Extending from the central wellbore is an open, horizontal wellbore  225 . A formation  226  is shown adjacent the wellbore  225 . Disposed in the open wellbore is an expandable sand screen (ESS)  210 . As illustrated in FIG. 1, the ESS  210  is run into the wellbore on a tubular run-in string  230 . Disposed at the end of the run-in string is an expander tool  100 . In the embodiment shown, the expander tool  100  is initially fixed to the expandable sand screen  210  with a temporary connection  235  like a shearable connection or some other temporary mechanical means. Typically, the ESS  210  is located at the lower end of a liner  218  which is run into the well and hung from the lower portion of the casing  215  by some conventional slip means. Below the liner top, the outer diameter of the liner  218  is reduced to a diameter essentially equal to the diameter of the ESS.  
         [0024]    [0024]FIG. 2 is an exploded view of an exemplary expansion tool  100 . The expansion tool  100  has a body  102  which is hollow and generally tubular with connectors  104  and  106  for connection to other components (not shown) of a downhole assembly. The connectors  104  and  106  are of a reduced diameter compared to the outside diameter of the longitudinally central body part of the tool  100 . The central body part has three recesses  114  to hold a respective roller  116 . Each of the recesses  114  has parallel sides and extends radially from a radially perforated tubular core (not shown) of the tool  100 . Each of the mutually identical rollers  116  is somewhat cylindrical and barreled. Each of the rollers  116  is mounted by means of an axle  118  at each end of the respective roller and the axles are mounted in slidable pistons  120 . The rollers are arranged for rotation about a respective rotational axis which is parallel to the longitudinal axis of the tool  100  and radially offset therefrom at  120 -degree mutual circumferential separations around the central body. The axles  118  are formed as integral end members of the rollers and the pistons  120  are radially slidable, one piston  120  being slidably sealed within each radially extended recess  114 . The inner end of each piston  120  is exposed to the pressure of fluid within the hollow core of the tool  100  by way of the radial perforations in the tubular core. In this manner, pressurized fluid provided from the surface of the well, via a tubular, can actuate the pistons  120  and cause them to extend outward whereby the rollers contact the inner wall of a tubular to be expanded.  
         [0025]    [0025]FIG. 3 is a section view of the expandable sand screen  210  of the present invention in a wellbore  200  prior to expansion. The ESS includes a base pipe  240  having perforation  242  formed therein, woven filter material  245  and an outer shroud  250  having perforations  255  formed therein and also having outwardly formed longitudinal channels  260  formed thereupon. The channels  260  are formed by bending the surface of the outer shroud  250  between perforations  255  to create two sides  265 ,  270  and a bottom portion  275 . In the preferred embodiment illustrated in FIG. 3, the bottom portion of each channel is welded or otherwise attached to the base pipe in at least one location  280 . The woven filter material  245  is held between the bottom  275  of the channel  260  and the base pipe  240 . The outer shroud  250  may be formed by any well-known metal working means including pressing and bending. A longitudinal seam (not shown) is formed by the cylindrical shroud after it is wrapped around the base pipe and filter material and its free ends are connected.  
         [0026]    [0026]FIG. 4 is a section view illustrating the wellbore  200  and the ESS  210  partially expanded therein. As shown in the figure, the expansion tool  100  has been activated with its rollers  116  contacting the inner wall of base pipe  240  and applying an outward radial force thereto. Typically, the temporary connection  235  between the expander tool  100  and the ESS  210  is disengaged as the expander tool is actuated and thereafter, the expander tool moves independently of the expandable sand screen  210 . By using the run-in string  230  to move the expander tool axially and rotationally within the ESS, the ESS  210  can be circumferentially expanded into or nearly into contact with the wellbore therearound.  
         [0027]    [0027]FIG. 5 is a section view illustrating the expandable sand screen  210  of the present invention after it has been expanded in a wellbore  200 . Radial force applied to the inner wall of the base pipe  240  has forced the pipe past its elastic limits and also expanded the diameter of the base pipe perforations  242 . Also expanded is the shroud  250  with its formed channels  260 . As shown in the figure, the shroud is expanded to a point wherein the upper edges of the sides  265 ,  270  of the channel  260  are either in contact or almost in contact with the wellbore  200 . The decision relating to contact between the expanded sand screen in a wellbore depends upon the needs of the user. Contact between the screen  210  and the wellbore  200  can place a slight stress on the wellbore and reduce the risk of particulate matter entering the wellbore. On the other hand, leaving a slight space between the edges of the channel and the wellbore leaves a greater fluid path for fracturing material to reach areas of the wellbore between the channels.  
         [0028]    [0028]FIG. 6 is a section view of the wellbore  200  illustrating an apparatus used to fracture the well after the ESS  210  has been expanded. As illustrated, a string of tubulars  300  is inserted into the top of the liner. An assembly at the lower end of the string of tubulars is typical of one used in fracturing operations and includes a cross-over tool  310  made up of an exit port  315  (not shown) permitting fluids to exit the tubular and a first and second packer  320 ,  325  disposed on either side of the exiting port to isolate the port from the annular area between the liner and the run-in string. A sliding sleeve (not shown) on the liner permits fluid communication between the interior of the string  300  and the exterior of the liner. As illustrated by arrows  330 , a slurry of fracturing and/or packing material is injected from the surface of the well down the tubular string  300 . At some predetermined location below the top of the liner  218 , the cross-over tool  310  permits the material to flow to an annular area outside of the liner and the expanded sand screen. In this manner, the material flows to the outer surface of the expanded sand screen and longitudinally flows along the channels  260  formed on the exterior of the ESS  210 . The particulate material is left within the annular area and within fractures extending outwardly from the wellbore and fluid (illustrated by arrows  335 ) is returned to the surface of the well in the interior of the string and subsequently, via the annular area between the string  300  and the casing  215  of the central wellbore. In use, a slurry of sand and gel or other fracturing material at an elevated pressure is carried into the central wellbore  200  in a tubular. Using a cross-over tool or other apparatus, the slurry is directed from the tubular to the outer surface of the expanded sand screen where it travels from a heel  226  of the wellbore  225  towards the toe  227  thereof. In this manner, the walls of the wellbore  225  and the formation  226  therearound are exposed to the high pressure slurry via the channels  260  formed on the outer surface of the shroud  250 . Return fluid is carried back towards the surface of the well in the interior of the base pipe  240 .  
         [0029]    One method of utilizing the expandable sand screen of the invention is as follows: A section of expandable sand screen  210  is formed at the surface of a well to an appropriate length by threading joints of screen together. The channels  260  formed in the shroud  250  of each subsequent joint are aligned as the joints are assembled together. The unexpanded section of ESS is then run into the wellbore  200  on a tubular string having an expander tool  100  disposed at the end thereof. The expander tool, or alternatively the run-in string adjacent the tool, is temporarily connected to the expandable sand screen  210  with a temporary connection  235 . As the ESS  210  reaches its desired location in the wellbore  200 , the expander tool  100  is actuated and the ESS is expanded in at least two points about is circumference. In this manner, the ESS is anchored in the wellbore. By providing a pulling, pushing or rotational movement to the string and expander tool, the temporary connection  235  between the tool  100  and the sand screen  210  is disengaged and the activated expander tool can move independently of the screen  210 .  
         [0030]    By moving the actuated tool  100  within the sand screen, both rotationally and axially, the screen is expanded to take on an appearance illustrated in FIGS. 5 and 7. With the screen  210  in its expanded position within the wellbore  200 , the expansion tool  100  and run-in string are removed and a tubular having a cross-over tool at the end thereof is run into the wellbore. The cross-over tool permits fluid communication between the tubular and the channels  260  on the outer surface of the expanded screen  210 . As pressurized slurry travels down the tubular, it is directed by the cross-over tool to the longitudinal channels and is placed in communication with the wellbore.  
         [0031]    [0031]FIG. 7 is a section view of a central  200  and a lateral  225  wellbore after the ESS  210  has been expanded into position and the well is producing hydrocarbons. A string of tubulars  400  like a string of production tubing has been inserted into the upper portion of the liner  218  and sealed therein with a packer  410 . This sealing and arrangement between the liner and the production tubing ties the liner back to the surface of the well. Hydrocarbons illustrated as arrows  415  migrate into the expanded sand screen  210  where there are collected in the interior of the screen and the liner. The hydrocarbons then move directly towards the surface of the well in the conduit provided by production tubing string  400 .  
         [0032]    While the liner  218  and ESS  210  are shown run into the wellbore on a run in string of tubulars, it will be understood that the apparatus of the invention can be transported into the wellbore using any number of means including coiled tubing. For example, using coiled tubing and a mud motor disposed thereupon, the apparatus can be utilized with rotation provided by the mud motor. A fluid powered tractor can be used to provide axial movement of the apparatus into the lateral wellbore  225 . These variations are within the scope of the invention.  
         [0033]    As the foregoing demonstrates, the present invention provides an apparatus and methods to utilize expandable sand screen in an open wellbore in a way that minimizes the need to fill an annular area around the screen with gravel. Additionally, the invention provides for an effective fracturing of an open wellbore without the risk of sand bridges being formed between the screen and the walls of the wellbore.  
         [0034]    The apparatus described herein is a sand screen intended to filter hydrocarbons. However, the structure described relating to the grooves could be utilized with any expandable wellbore component leaving a fluid path along the outer surface thereof after expansion. Other uses include water wells and injection wells.  
         [0035]    While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.