Downhole circulation apparatus

Abstract

A downhole circulation apparatus includes a body defining a longitudinal bore. At least one annular port forms a fluid path from longitudinal bore to the outside of the apparatus. A slidable sleeve is mounted in the longitudinal bore and has a closed position blocking annular port and an open position in which the annular port is open to the longitudinal bore. The slidable sleeve also comprises a ball seat in which a non-deformable ball is sized to fit to block the longitudinal bore. An abutment surface is configured to dislodge the non-deformable ball when the slidable sleeve moves into the open position.

1 . A downhole circulation apparatus comprising:
 a body defining a longitudinal bore, the body comprising at least one port defining a fluid path from said longitudinal bore out of the body;   a slidable sleeve mounted in said longitudinal bore, said slidable sleeve having a closed position blocking said at least one port and an open position in which said port is open to said longitudinal bore;   wherein said slidable sleeve comprises at least one ball seat configured to receive at least one first non-deformable ball to block fluid flow through said slidable sleeve and cause said slidable sleeve to move from the closed to the open position; and   an abutment surface configured to dislodge said at least one non-deformable ball in used when said slidable sleeve moves into said open position.   
     
     
         2 . An apparatus according to  claim 1 , wherein said abutment surface is disposed on an end of an abutment assembly comprising:
 a nose portion; and   at least one internal port to permit fluid to flow through said abutment assembly when the slidable sleeve is in the closed position, wherein said slidable sleeve blocks said at least one internal port when said slidable sleeve is in the open position.   
     
     
         3 . An apparatus according to  claim 1 , wherein said abutment surface is formed by a second ball supported in a second restriction formed in the longitudinal bore. 
     
     
         4 . An apparatus according to  claim 1 , wherein said slidable sleeve is biased into the closed position by a biasing structure. 
     
     
         5 . An apparatus according to  claim 1 , further comprising a plurality of ball seats formed in said slidable sleeve configured to receive a plurality of non-deformable balls. 
     
     
         6 . An apparatus according to  claim 1 , further comprising two or more ports defining multiple fluid paths from said longitudinal bore out of the body. 
     
     
         7 . An apparatus according to  claim 2 , wherein said abutment surface is formed by a second ball supported in a second restriction formed in the longitudinal bore. 
     
     
         8 . An apparatus according to  claim 7 , wherein said slidable sleeve is biased into the closed position by a biasing structure. 
     
     
         9 . An apparatus according to  claim 8 , further comprising a plurality of ball seats formed in said slidable sleeve configured to receive a plurality of non-deformable balls. 
     
     
         10 . An apparatus according to  claim 9 , further comprising two or more ports defining multiple fluid paths from said longitudinal bore out of the body. 
     
     
         11 . A method of creating a surge of pressurised fluid in a wellbore in which a drill string is located, the method comprising:
 deploying a downhole circulation apparatus according to  any one of the preceding claims  in a drill string in a wellbore;   operating the downhole circulation apparatus to move said slidable sleeve from the closed to the open position;   placing a deformable ball in the longitudinal bore of the downhole circulation apparatus such that the deformable ball locks said at least one port defining a fluid path from the longitudinal bore out of the body; and   increasing fluid pressure in the longitudinal bore until the deformable ball is deformed and blows through said port to temporarily increase fluid pressure in the wellbore.