You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND  
       [0001]     The invention generally relates to a well completion system and more particularly relates to a sandface completion.  
         [0002]     Several downhole trips, or runs, typically are required to complete a well. For example, several trips typically are required to perforate and gravel pack the well.  
         [0003]     As an example, the following procedure may be used to perforate and gravel pack a well. First, a string with a plug running tool is run downhole to install a plug in a previously-installed sump packer. The string is withdrawn from the well, and in a subsequent trip, a string that contains one or more perforating guns is lowered into the well. The perforating charges of the gun(s) are then fired; and subsequently, this string is pulled out of the well. Next, a cleanup string that contains, for example, a circulation valve, scraper and washing tool may be run downhole for purposes of cleaning the well. The cleanup string is pulled out of the well, and subsequently, another string is run downhole to remove the plug from the sump packer. After the string that removes the plug is retrieved from the well, a string that contains a bottom hole assembly is run into the well. The bottom hole assembly typically includes a sandscreen to support a filtering gravel substrate that is deposited around the sandscreen in a subsequent gravel packing operation. The running string (the portion of the string above the bottom hole assembly) is retrieved from the well upon completion of the gravel packing operation.  
         [0004]     In general, the fluid loss in the well increases with the number of downhole trips. Fluid losses invade the formation, and may have such detrimental effects as increasing the skin, causing near wellbore damage and impairing the overall productivity of the well.  
         [0005]     Thus, there is a continuing need for better ways to reduce the number of trips into a well for purposes of performing completion operations, such as perforating and gravel packing operations.  
       SUMMARY  
       [0006]     In an embodiment of the invention, an assembly that is usable with a well includes a base pipe, a screen and at least one perforating charge. The base pipe includes at least one radial port to communicate well fluid, and the base pipe has an outer surface. The screen is mounted to the base pipe and is adapted to at least partially surround the base pipe. The radial port(s) of the base pipe are covered by the screen. The perforating charge(s) are mounted to the outer surface of the base pipe.  
         [0007]     In another embodiment of the invention, a technique that is usable with a well includes running an assembly into the well in a single trip. The assembly includes a screen, a base pipe and a perforating gun. The perforating gun has perforating charges that are located on the outside of the base pipe. The technique includes firing the perforating charges.  
         [0008]     Advantages and other features of the invention will become apparent from the following drawing, description and claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0009]      FIG. 1  is a schematic diagram of a well according to an embodiment of the invention.  
         [0010]      FIG. 2  is a more detailed schematic diagram of a segment of a string of  FIG. 1  illustrating a bottom hole assembly according to an embodiment of the invention.  
         [0011]      FIG. 3  is a flow diagram depicting a perforating and gravel packing technique according to an embodiment of the invention.  
         [0012]      FIG. 4  is a schematic diagram of the string segment illustrating the use of a plug to set a packer of the bottom hole assembly according to an embodiment of the invention.  
         [0013]      FIG. 5  is a schematic diagram of the string segment illustrating a configuration of a service tool for purposes of cleaning out an isolated interval of the well according to an embodiment of the invention.  
         [0014]      FIG. 6  is a schematic diagram illustrating a configuration of the service tool for purposes of gravel packing an isolated interval of the well according to an embodiment of the invention.  
         [0015]      FIG. 7  is a schematic diagram of the bottom hole assembly after a gravel packing operation according to an embodiment of the invention.  
         [0016]      FIG. 8  is a perspective view of a base pipe of the bottom hole assembly according to an embodiment of the invention.  
         [0017]      FIG. 9  is a cross-sectional view taken along line  9 - 9  of  FIG. 8  according to an embodiment of the invention.  
         [0018]      FIG. 10  is a partial cross-sectional view taken along line  10 - 10  of  FIG. 2  according to an embodiment of the invention.  
         [0019]      FIGS. 11 and 13  are perspective views of combined perforating and sandscreen assemblies according to other embodiments of the invention.  
         [0020]      FIG. 12  is a cross-sectional view taken along line  12 - 12  of  FIG. 11  according to an embodiment of the invention.  
         [0021]      FIG. 14  is a cross-sectional view taken along line  14 - 14  of  FIG. 13  according to an embodiment of the invention. 
     
    
     DETAILED DESCRIPTION  
       [0022]     Referring to  FIG. 1 , an exemplary embodiment of a well  10  in accordance with the invention includes a tubular string  20  that extends from the surface into a wellbore  16  of the well  10 . As depicted in  FIG. 1 , the wellbore  16  may be lined with a casing string  12 . Although  FIG. 1  depicts the wellbore  16  as being vertical, in other embodiments of the invention, the system and techniques that are described herein may likewise be applied to lateral wellbores. Additionally, the system and techniques that are described herein may be applied to both subterranean and subsea wells.  
         [0023]     The string  20  includes a bottom hole assembly (BHA)  30  that, as further described below, may be used for such purposes as isolating a particular zone, or interval, of the well  10 ; perforating the interval; installing a sandscreen in the interval; and communicating flows for purposes of cleaning and gravel packing the interval. Thus, the components of the string  20  (such as the BHA  30  and other components of the string  20 , described below) may form a single trip sandface completion system, in accordance with some embodiments of the invention. Advantages of consolidating downhole trips include (as examples) reduced rig time, reduced fluid loss and avoidance of detrimental effects that are attributable to fluid loss.  
         [0024]     Turning now to the more specific details, in accordance with some embodiments of the invention, the BHA  30  includes a combined sandscreen and perforating assembly  34  that contains a sandscreen in addition to perforating charges that are exposed between windings of the sandscreen. As further described below, the perforating charges are positioned so that after the firing of the perforating charges, the sandscreen retains its integrity, and all flow across the sandscreen is filtered.  
         [0025]     The BHA  30  also includes, in accordance with some embodiments of the invention, a firing head  36  for purposes of firing the perforating charges of the assembly  34 ; and a combined packer and sandscreen extension assembly  39 . The firing head  36  may be activated in a variety of different ways for purposes of firing the perforating charges of the assembly  34 . For example, in accordance with some embodiments of the invention, the firing head  36  is electrically coupled to a sensor  44  (a pressure sensor, for example) of the string  20 , which is located downhole with the firing head  36 . The sensor  44  may, for example, be used by the firing head  36  to detect stimuli that are communicated downhole (from the surface of the well, for example) for purposes of instructing the firing head  36  to fire the perforating charges.  
         [0026]     The stimuli may be, as examples, a particular tubing pressure or pressure signature inside the string  20 ; a particular tubing pressure or pressure signature in an annulus that surrounds the string  20 ; or a particular stimuli that is communicated downhole on the string  20 .  
         [0027]     In other embodiments of the invention, the firing head  36  may be configured to receive commands via the load, or weight, forces on the string  20 . Thus, the string  20  may be lifted up and down in accordance with a predetermined pattern for purposes of firing the perforating charges.  
         [0028]     As examples of other communication techniques, a wired connection (such as through a wireline or cable) or a slickline may be used for purposes of communicating with and controlling the firing head  36 . Therefore, many different techniques may be used to communicate with and control the firing head  36 , all of which are within the scope of the appended claims.  
         [0029]     The packer and sandscreen extension assembly  39  includes a packer  38  (depicted in its unset state in  FIG. 1 ) that is set when the BHA  30  is in the proper downhole position for purposes establishing an upper boundary of an isolated interval  53  (see  FIG. 5 ). The lower boundary of the isolated interval  53  is established by a previously-installed sump packer  24 .  
         [0030]     Still referring to  FIG. 1 , more specifically, in accordance with some embodiments of the invention, the BHA  30  is operated in the following manner to form an isolated interval (such as the isolated interval  53  that is depicted in  FIG. 5 ) in the well  10 . First, the string  20  is lowered downhole and is stabbed into the sump packer  24 . At this point, the sump packer  24  forms an annular seal between the inner surface of the casing string  12  and the outer surface of the string  20 . The packer  38  is then set (via, for example, a technique similar to the techniques described above for controlling the firing head  36 ) to form another annular seal between the string  20  and the interior surface of the casing string  12  to form the upper boundary of the isolated interval. After this point, perforating and gravel packing operations may then be performed in the isolated interval, as further described below.  
         [0031]     In addition to the packer  38 , the packer and sandscreen extension assembly  39  also includes an extension sleeve  41  that extends to connect the packer  38  to the portion of the BHA  30  below the packer  38 . As described below, after the desired gravel packing and cleaning operations are performed, the portion of the string  20  above the assembly  39  may be disconnected and retrieved from the well, thereby leaving the BHA  30  downhole as part of the completion.  
         [0032]     Among the other features of the string  20 , in accordance with some embodiments of the invention, the string  20  may include a multiple function service tool  42 . The service tool  42  provides a releasable connection for the BHA  30  with the string  20  and provides multiple fluid paths. The fluid flow through these fluid paths may be controlled (via one of the control techniques that are listed above for the firing head  36 , for example) to perform various operations, such as flowing a slurry from the central passageway of the string  20  into the annulus of the isolated interval to perform slurry gravel packing, or communicating fluid from the isolated interval into the central passageway of the string  20  for purposes of cleaning out the interval.  
         [0033]      FIG. 2  depicts a more detailed segment  50  (see  FIG. 1 ) of the string  20  near the BHA  30 , in accordance with some embodiments of the invention. Referring to  FIG. 2 , in accordance with some embodiments of the invention, the combined sandscreen and perforating assembly  34  includes a perforated base pipe  82  that contains radial openings (not depicted in  FIG. 2 ), or ports, for purposes of receiving well fluid into the central passageway of the pipe  82  when the BHA  30  is left downhole as part of the completion. The sandscreen and perforating assembly  34  also includes perforating charges  80  (lined shaped charges, as an example), which are mounted to the exterior surface of the base pipe  82 . Therefore, in accordance with some embodiments of the invention, the perforating charges  80  do not breach the base pipe  82  either before or after the perforating charges  80  are fired.  
         [0034]     As depicted in  FIG. 2 , in accordance with some embodiments of the invention, the perforating charges  80  may extend in a spiral or helical, phasing pattern around the exterior of the base pipe  82 . The perforating charges  80  may be connected to a detonating cord  85  that extends around the exterior of the base pipe  82  and is connected to the firing head  36  to communicate a detonation wave to the shaped charges  80  when the charges  80  are to be fired.  
         [0035]     The sandscreen and perforating assembly  34  also includes a screen  86  (a sandscreen, for example) that is mounted to and extends around the base pipe  82 . In accordance with some embodiments of the invention, the screen  86  extends around the base pipe  82  in the same helical, or spiral, pattern as the perforating charges  80 . The screen  86  is wrapped around the base pipe  82  in a fashion such that channels  88  are formed between adjacent windings of the screen  86  to expose the perforating charges  80 . The radial well fluid ports (not shown in  FIG. 2 ) of the base pipe  82  are arranged to coincide with the above-described wrapping so that all of the ports are covered by the screen  86 .  
         [0036]     Due to the above-described arrangement of the sandscreen and the perforating charges  80 , the screen  86  retains its integrity after the firing of the perforating charges  80 ; and all flow into the base pipe  82  during production is filtered by the screen  86 . It is noted that the screen  86  may be a direct wire wrapped screen, in accordance with some embodiments of the invention, although other types of screens may be used in other embodiments of the invention.  
         [0037]     As depicted in  FIG. 2 , in accordance with some embodiments of the invention, the sandscreen  86  may radially vary to protect the perforating charges  80 . For example, in some embodiments of the invention, screen  86  may include upper  84  and lower  85  radial extensions at its upper and lower edges, respectively. The radial extensions  84  and  85  line the channels  88  and radially extend beyond the perforating charges  80  for purposes of protecting the charges  80  and the remaining portion of the screen  86 . The radial extensions  84  and  85  may not be part of the screen  86  in other embodiments of the invention, as described below in connection with  FIG. 8 .  
         [0038]     Still referring to  FIG. 2 , among the other features of the sandscreen and perforating assembly  34 , the base pipe  82  may be concentric with a longitudinal axis  51  of the BHA  30  and may have a lower end that is configured to form a seal with the sump packer  24  when the BHA  30  is stabbed into the packer  24 . Near the sump packer  24 , the base pipe  82  may also include radial ports  90  for purposes of communicating a flow with the isolated interval  53  (see  FIG. 5 , for example). The ports  90  are located below an inner annular extension  91  of the base pipe  82 , which forms a seal with a tubing  70  that extends inside the base pipe  82  from the service tool  42 . Thus, a flow may be communicated from the central passageway of the tubing  70  to the isolated interval  53  and vice versa. The tubing  70  has a lower end  72  that is exposed near the ports  90 .  
         [0039]     In accordance with some embodiments of the invention, the service tool  42  has a body  54  that includes a passageway  56  for purposes of communicating fluid from the central passageway of the string  20  (see  FIG. 1 ) to the isolated interval  53  (see  FIG. 5 ) and a passageway  58  for purposes of communicating fluid from the central passageway of the tubing  70  to an annular region above the isolated interval  53  (i.e., above the packer  38  when set). The service tool  42  may include other passageways, such as, for example, a passageway  68 , which establishes fluid communication between the passageway  56  and the packer  38  for purposes of setting the packer  38 . A passageway  68  of the service tool  42  establishes fluid communication between the passageway  56  and the firing head  36  for purposes of communicating pressure to the firing head  36  (to cause the firing head  36  to fire, for example).  
         [0040]     As depicted in  FIG. 2 , the bottom end of the service tool  42  is received into the extension sleeve  41  of the packer and sandscreen extension assembly  39  and is aligned such that radial ports  66  of the sleeve  61  are aligned to communicate fluid between the passageway  56  and the isolated interval below the packer  38 . The sleeve  61  is generally concentric with the longitudinal axis  51  of the BHA  30 .  
         [0041]     Referring to  FIG. 3 , in general, a perforating and gravel packing technique  100  operation may be performed in the well  10  using the string  20  in accordance with some embodiments of the invention. Referring to  FIG. 3  in conjunction with  FIGS. 1 and 2 , the technique  100  includes running the BHA  30  to the appropriate depth and locating the sump packer  24 , pursuant to block  104 .  
         [0042]     After the sump packer  24  is located, the fluid in the borehole may be changed to a desired weight, pursuant to block  108 . More specifically, the targeted fluid weight may depend on the desired balance at the time of perforating. For example, in certain situations the well may be underbalanced to create a flow from the resulting perforation tunnels into the wellbore for purposes of assisting in cleaning debris from the perforation tunnels. The fluid in the well at the time of perforating may be placed prior to or at the time of the firing of the perforating charges  80 , depending on the particular embodiment of the invention.  
         [0043]     Still referring to  FIG. 3 , when the fluid condition is correct, the BHA  30  is stabbed (block  112 ) into the sump packer  24  to establish a sealing engagement with the packer  24 . The pressure in the central passageway of the string  20  may then be increased (as one example) to set the packer  38 , pursuant to block  114 . For purposes of setting the packer  38 , a plug  150  (see  FIG. 4 ) may be run downhole through the central passageway of the tubing  20  and run through the passageway  56  to lodge in a restricted portion of the passageway  56 . The set packer  38  is depicted in  FIG. 5 , which also shows the resultant isolated interval  53 . After setting the packer  38 , the weight on the string  20  may be varied (by lifting up on the string  20 , for example) to verify that the packer  38  holds differential pressure.  
         [0044]     Next, pursuant to the technique  100 , the perforating charges  80  are fired (block  118 ). The technique used to fire the perforating charges  80  may include communicating stimuli (wireless, wired-conveyed, tubing-conveyed, fluid-conveyed, string-conveyed, etc.) downhole through fluid, on the string  20 , on a cable, etc., depending on the particular embodiment of the invention. The firing of the perforating charges  80  pierces the casing string  12  and forms perforation tunnels  180  (see, for example,  FIG. 5 ) in the surrounding formation.  
         [0045]     After the firing of the perforating charges  80 , the service tool  42  may then be configured to route fluid flows through a path to clean out the isolated interval  53 . For example, referring also to  FIG. 5  in conjunction with  FIG. 3 , in accordance with some embodiments of the invention, the service tool  42  may be configured to circulate fluid from the isolated interval  53  to form a flow  154 . Thus, a flow  154  may be circulated into the annulus of the well above the packer  38  (now set) and through the fluid passageway  58 , so that the fluid exits the tubing  70  at its end  72 . The flow  154  is routed through the radial ports  90  of the tubing  70  and into the isolated interval  53 . In the isolated interval  53 , debris enters the flow  154 . The flow  154  carries the debris back to the service tool  42  and into its fluid passageway  56 , where the fluid returns to the surface of the well.  
         [0046]     In accordance with some embodiments of the invention, the well is perforated underbalanced. For these embodiments of the invention, the cleaning operation (as illustrated in  FIG. 5 ) is not performed.  
         [0047]     Still referring to  FIG. 3 , after the cleaning operation, a gravel packing operation may be performed in the isolated interval  53 , pursuant to block  122 . Referring to  FIG. 6  in conjunction with  FIG. 3 , preparation for the gravel packing operation includes configuring the service tool  42  so that the tool  42  routes a gravel packing slurry flow  160  into the isolated interval  53 . More specifically, the slurry flow  160  flows through the central passageway of the string  20  and into the passageway  56  of the service tool  42 . From the fluid passageway  56 , the slurry flow  160  exits the radial ports  66  of the sleeve  61  and enters the isolated interval  53 , where the gravel substrate is deposited. Liquid from the slurry flow flows through the radial ports  90  of the base pipe  82  and into the lower end  72  of the tubing  70 . The liquid returns into the annulus above the packer  64  via the passageway  58  of the service tool  42 .  
         [0048]     After the gravel packing operation, the service tool  42  (and the portion of the string  20  above the service tool  42 ) is retrieved from the well  10 , pursuant to block  126  of  FIG. 3 .  
         [0049]      FIG. 7  depicts the BHA  30  after retrieval of the service tool  42 . As shown, at this point, a gravel substrate  170  resides in the isolated interval  53  and may extend into the perforation tunnels  180 . It is noted that a production string may subsequently be run downhole and received into the sleeve  61 . Thus, the sleeve  61  may include a stabbing receptacle for purposes of receiving a corresponding and mating stabbing connection of the production string.  
         [0050]     Referring to  FIG. 8 , in accordance with some embodiments of the invention, the base pipe  82  includes radial openings, or ports  200 , to receive well fluid. The radial ports  200  coincide with the portions of the base pipe  82  around which the sandscreen  86  (not depicted in  FIG. 8 ) is wrapped. As also shown in  FIG. 8 , in accordance with some embodiments of the invention, the radial extensions  84  and  85  may be attached to the exterior of the base pipe  82  and thus, may be separate from the sandscreen  86 .  
         [0051]     Additionally, as depicted in  FIG. 8 , the base pipe  82  may include longitudinal ribs  210  (which are parallel to the longitudinal axis  51 ) that extend radially outwardly to form ridges, or channels  212 , in between for purposes of creating annular spaces inside the sandscreen  86 . Referring also to  FIG. 9  (depicting a cross-sectional view of the base pipe  82 ), the openings  200  are disposed in the channels  210 ; and the longitudinal ribs  210  may be uniformly distributed around the longitudinal axis  51 .  
         [0052]      FIG. 10  depicts a partial cross-sectional view taken along line  10 - 10  of  FIG. 2 . It is noted that  FIG. 10  depicts only the right hand section of the cross-sectional view, as it is understood that a corresponding left hand side exists on the left-hand side of the longitudinal axis  51  in  FIG. 10 .  FIG. 10  illustrates a particular channel  212  that is created between the openings  200  and the sandscreen  86 .  
         [0053]     Many other variations are possible and are within the scope of the appended claims. For example,  FIG. 11  depicts a combined perforating and sandscreen assembly  300  that may be used in place of the assembly  34  (see  FIG. 2 , for example), in accordance with some embodiments of the invention. Unlike the assembly  34 , the assembly  300  includes perforating charges  340  that are aligned along a longitudinal axis  301  of the assembly  300 . Thus, the assembly  300  may be used for purposes of targeting a particular azimuthal direction in the well.  
         [0054]     The assembly  300  includes a sandscreen  330  that partially circumscribes the longitudinal axis  301  to create a longitudinal channel  320  in which the perforating charges  340  are exposed. Similar to the assembly  34 , the assembly  300  includes radial extensions  306  that define the boundaries of the channel  320  for purposes of protecting the sandscreen  330  and perforating charges  340 ; and similar to the assembly  34 , the perforating charges  340  may be each located entirely on the outside of the base pipe  302  and not pierce the base pipe  302 , either before or after the perforating charges  340  are fired. The radial extensions  306  may be part of the base pipe  302  or may be part of the sandscreen  330 , depending on the particular embodiment of the invention. Referring also to  FIG. 12 , which depicts a cross-section taken along line  12 - 12  of  FIG. 11 , the sandscreen  330  may include various longitudinal slots, or openings  344 , for purposes of communicating flow of fluid through the sandscreen  330  into corresponding radial openings, or ports  345 , of the base pipe  302 .  
         [0055]     As an example of yet another embodiment of the invention,  FIG. 13  depicts a combined perforating and sandscreen assembly  400 , which may be used in place of either the assembly  300  or  34 . The assembly  400  includes groups of perforating charges  410 , which are aligned in the same plane. Each group of perforating charges  410  may be equally distributed around a longitudinal axis  401  of the assembly  400 , as depicted in the cross-section of  FIG. 14 .  
         [0056]     For this embodiment of the invention, the sandscreen is formed from multiple and separate pieces. For example, as depicted in  FIG. 13 , the assembly  400  includes an upper  420 , middle  422  and lower  424  sandscreen sections; and collectively, the sections  420 ,  422  and  424  form the sandscreen for the assembly  400 .  
         [0057]     The sandscreen sections  420 ,  422  and  424  are spaced apart to form corresponding channels  416  that expose the perforating charges  410 , which, similar to the perforating charges of the assemblies  34  and  300 , are located entirely on the outside of the base pipe  402 . Furthermore, radial extensions  406  may define the upper and lower boundaries of each channel  416 . These radial extensions  406  may be part of the base pipe  402  or may be formed on edges of the sandscreen sections  420 ,  422  and  424 , depending on the particular embodiment of the invention. The base pipe  402  also includes radial ports, or openings (not depicted in  FIGS. 13 and 14 ), to receive fluid flow into the base pipe.  
         [0058]     Although terms of direction such as “upper,” “lower,” etc., have been used herein for purposes of convenience, these orientations are not necessary to practice the invention. For example, in accordance with some embodiments of the invention, the BHA  30  and string  20  may be used in a lateral wellbore. Therefore, many variations are possible and are within the scope of the appended claims.  
         [0059]     While the present invention has been described with respect to a limited number of embodiments, those skilled in the art, having the benefit of this disclosure, will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.

Summary:
An assembly that is usable with a well includes a base pipe, a screen and at least one perforating charge. The base pipe includes at least one radial port to communicate well fluid, and the base pipe has an outer surface. The screen is mounted to the base pipe and is adapted to at least partially surround the base pipe. The radial port(s) of the base pipe are covered by the screen. The perforating charge(s) are mounted to the outer surface of the base pipe.