Debris screen for a downhole tool

Abstract

A debris screen, sealingly and releasably latched to the top of a polished bore of a downhole tool for preventing the ingress of debris into the polished bore. Typically the debris screen is connected to a tieback receptacle of a liner hanger assembly. The debris screen is connected to a setting tool and is axially moveable on the setting tool permitting the setting tool to be stroked inside the liner hanger assembly during normal operations, such as cementing while retaining the debris screen at the top of the tieback receptacle at all times except during the final stages of retrieval. The debris screen has a tubular sleeve having a plurality of ports, covered by a wedge wire screen through which fluids can flow. Further, the latching mechanism has a plurality of ports to permit the flow of debris-free fluids from the wellbore into the annulus between the setting tool and the downhole tool.

The Embodiments of the Invention in which an Exclusive Property Or Priviledge is Claimed are Defined as Follows:  
     
         1 . A debris screen preventing the ingress of debris to a tool annulus between a setting tool inserted into a bore of a downhole tool in a wellbore, the setting tool being axially moveable within the bore, the debris screen comprising: 
 a tubular sleeve positioned about an exterior surface of the setting tool, and axially moveable thereon and defining a sleeve annulus therebetween, the sleeve having a plurality of ports formed therethrough for permitting fluid communication between the sleeve annulus and the wellbore;    a screen formed over the tubular sleeve for preventing the passage of debris therethrough;    a seal positioned at a top end of the tubular sleeve and extending between the tubular sleeve and the setting tool, the seal permitting limited fluid communication therethrough for preventing pressure locking while blocking debris; and    means for latching the tubular sleeve sealingly to a top of the bore and permitting fluid communication between the sleeve annulus and the tool annulus.    
     
     
         2 . The debris screen as described in  claim 1  wherein the means for latching the tubular sleeve sealingly to the top of the bore comprises: 
 a latching mechanism operable between the tubular sleeve and the bore wherein the latching mechanism is adapted for releasably engaging an annular groove at a top of the bore for retaining the tubular sleeve adjacent the top of the bore.  
 
     
     
         3 . The debris screen as described in  claim 2  wherein the latching mechanism further comprises: 
 a plurality of latch dogs, extendable radially outward through a plurality of corresponding openings at a lower end of the tubular sleeve, for engaging the annular groove at the top of the bore, the latch dogs being moveable between a radially extended position and a retracted position;  
 a latch dog housing, positioned in the tool annulus and releasably connected to the tubular sleeve in a downhole position for supporting the latch dogs in the extended position and being axially moveable thereupon to an uphole position following release from the tubular sleeve, to permit the latch dogs to move to the retracted position thereby releasing the tubular sleeve from the bore; and  
 ports formed in the latch dog housing for permitting fluid communication between the sleeve annulus and the tool annulus.  
 
     
     
         4 . The debris screen as described in  claim 3  further comprising a downwardly depending shoulder at a lower end of the latch dog housing wherein when the setting tool is lifted to exit the bore, the setting tool engages the shoulder and lifting pressure is applied to the latch dog housing sufficient to overcome the releasable connection and move the latch dog housing to the uphole position permitting the latch dogs to move to the retracted position and releasing the tubular sleeve from the bore.  
     
     
         5 . The debris screen as described in  claim 4  wherein the latch dog housing is releasably connected to the tubular sleeve by at least one shear screw.  
     
     
         6 . The debris screen as described in  claim 2  wherein the latching mechanism further comprises a collet system.  
     
     
         7 . The debris screen as described in  claim 6  wherein the collet system comprises: 
 a plurality of downwardly depending collet fingers, formed at a lower end of the tubular sleeve, for engaging the annular groove at the top of the bore;  
 a collet retainer positioned in the tool annulus and releasably connected to the tubular sleeve in a downhole position for supporting the collet fingers in the annular groove at the top of the bore, the collet retainer being axially moveable thereupon to an uphole position following release from the tubular sleeve, to permit the collet fingers to be released from the annular groove thereby releasing the tubular sleeve from the bore; and  
 ports formed in the collet retainer for permitting fluid communication between the sleeve annulus and the tool annulus.  
 
     
     
         8 . The debris screen as described in  claim 7  further comprising a downwardly depending shoulder at a lower end of the collet retainer wherein when the setting tool is lifted to exit the bore, the setting tool engages the shoulder and lifting pressure is applied to the collet retainer sufficient to overcome the releasable connection and move the collet retainer to the uphole position, forcing the collet fingers out of the annular groove and releasing the tubular sleeve from the bore.  
     
     
         9 . The debris screen as described in  claim 1  wherein the screen is a wedge wire screen.  
     
     
         10 . The debris screen as described in  claim 3  wherein the screen is a wedge wire screen.  
     
     
         11 . The debris screen as described in  claim 8  wherein the screen is a wedge wire screen.  
     
     
         12 . The debris screen as described in  claim 1  wherein the downhole tool is a liner hanger assembly.  
     
     
         13 . The debris screen as described in  claim 3  wherein the downhole tool is a liner hanger assembly.  
     
     
         14 . The debris screen as described in  claim 8  wherein the downhole tool is a liner hanger assembly.  
     
     
         15 . A debris screen preventing the ingress of debris to an annulus between a setting tool inserted into a bore of a liner hanger assembly, the setting tool being axially moveable within the bore, the debris screen comprising: 
 a tubular sleeve positioned about an exterior surface of the setting tool, and axially moveable thereon and defining a sleeve annulus therebetween, the sleeve having a plurality of ports formed therethrough for permitting fluid communication between the sleeve annulus and the wellbore;    a screen formed over the tubular sleeve for preventing the passage of debris therethrough;    a seal positioned at a top end of the tubular sleeve and extending between the tubular sleeve and the setting tool, the seal permitting limited fluid communication therethrough for preventing pressure locking while blocking debris; and    means for latching the tubular sleeve sealingly to a top of the bore and permitting fluid communication between the sleeve annulus and the tool annulus.    
     
     
         16 . The debris screen as described in  claim 15  wherein the means for latching the tubular sleeve sealingly to the top of the bore is a latching mechanism operable between the tubular sleeve and the bore and wherein the latching mechanism is adapted for releasably engaging an annular groove at a top of the bore for retaining the tubular sleeve adjacent the top of the bore, the latching mechanism comprising: 
 a plurality of latch dogs, extendable radially outward through a plurality of corresponding openings at a lower end of the tubular sleeve, for engaging the annular groove at the top of the bore, the latch dogs being moveable between a radially extended position and a retracted position;  
 a latch dog housing, positioned in the tool annulus and releasably connected to the tubular sleeve in a downhole position for supporting the latch dogs in the extended position and being axially moveable thereupon to an uphole position following release from the tubular sleeve, to permit the latch dogs to move to the retracted position thereby releasing the tubular sleeve from the bore:  
 ports formed in the latch dog housing for permitting fluid communication between the sleeve annulus and the tool annulus; and  
 a downwardly depending shoulder at a lower end of the latch dog housing wherein when the setting tool is lifted to exit the bore, the setting tool engages the shoulder and lifting pressure is applied to the latch dog housing sufficient to overcome the releasable connection and move the latch dog housing to the uphole position permitting the latch dogs to move to the retracted position and releasing the tubular sleeve from the bore.  
 
     
     
         17 . The debris screen as described in  claim 16  wherein the latching mechanism is a collet system comprising: 
 a plurality of downwardly depending collet fingers, formed at a lower end of the tubular sleeve, for engaging the annular groove at the top of the bore;  
 a collet retainer positioned in the tool annulus and releasably connected to the tubular sleeve in a downhole position for supporting the collet fingers in the annular groove at the top of the bore, the collet retainer being axially moveable thereupon to an uphole position following release from the tubular sleeve, to permit the collet fingers to be released from the annular groove thereby releasing the tubular sleeve from the bore; and  
 ports formed in the collet retainer for permitting fluid communication between the sleeve annulus and the tool annulus; and  
 a downwardly depending shoulder at a lower end of the collet retainer wherein when the setting tool is lifted to exit the bore, the setting tool engages the shoulder and lifting pressure is applied to the collet retainer sufficient to overcome the releasable connection and move the collet retainer to the uphole position, forcing the collet fingers out of the annular groove and releasing the tubular sleeve from the bore.