Method and apparatus for replacing drive pipe

Abstract

Method and apparatus are provided for replacing a conductor pipe beneath a platform and providing a slot for drilling an additional well. The original conductor pipe is cut off to form a stub at a selected distance above or below the sea floor. Apparatus including a jet sub is assembled and lowered on drill pipe within a replacement conductor pipe. Fluid is pumped down the drill pipe to force the replacement conductor pipe in a selected direction around the top of the stub of the original conductor pipe so as to allow the replacement conductor pipe to pass alongside the top of the stub. An instrument may be lowered down the drill string to determine the direction of the fluid jet and the deflection of the replacement pipe from vertical. An offset tool is provided to assist in bypassing the stub with the replacement pipe. The replacement pipe may then be driven to a selected depth.

1 . A method for placing a replacement conductor pipe beneath a platform, the replacement conductor pipe passing through the same guides on the platform as an original conductor pipe, comprising: 
 providing a jet sub having a selected nozzle size;    placing the jet sub on a drill string and placing the drill string inside the replacement conductor pipe such that the jet sub is below and in proximity to a lower end of the replacement conductor pipe;    lowering the drill string and replacement conductor pipe to a selected position beneath the platform and pumping fluid through the drill string at a selected rate to cause the lower end of the replacement conductor pipe to be displaced horizontally a distance such that the replacement conductor pipe can be lowered past a stub of the original conductor pipe; and    removing the drill string and jet sub from inside the replacement conductor pipe.    
   
   
       2 . The method of  claim 1  further comprising providing an offset tool and placing the offset tool between the jet sub and the drill string before lowering the drill string and replacement conductor pipe.  
   
   
       3 . The method of  claim 1  further comprising providing a muleshoe sub and adding the muleshoe sub to the jet sub and drill string before lowering the drill string and replacement conductor pipe.  
   
   
       4 . The method of  claim 3  further comprising placing a well surveying instrument in the drill string and seating the instrument in the muleshoe sub so as to determine the direction of a jet from the jet sub.  
   
   
       5 . The method of  claim 4  further comprising determining the deflection of the drill string by surface readout of the well surveying instrument.  
   
   
       6 . The method of  claim 2  further comprising adding an abrasive surface to the offset tool and moving the drill string vertically so as to abrade a top surface of the stub of the original conductor pipe.  
   
   
       7 . Apparatus for placing a replacement conductor pipe beneath a platform, the replacement conductor pipe passing through the same guides on the platform as an original conductor pipe, comprising: 
 a jet sub having a selected nozzle size and being adapted to pass through the replacement conductor pipe;    a drill string to support and supply fluid to the jet sub; and    a pump for supplying fluid through the drill string.    
   
   
       8 . The apparatus of  claim 7  further comprising an offset tool in the drill string for deflecting the replacement conductor pipe around a stub of the original conductor pipe.  
   
   
       9 . The apparatus of  claim 8  further comprising a muleshoe sub in the drill string.  
   
   
       10 . The apparatus of  claim 9  further comprising a well surveying instrument adapted for seating in the muleshoe sub, the well surveying instrument comprising apparatus for measuring direction in a horizontal plane.  
   
   
       11 . The apparatus of  claim 10  wherein the well surveying instrument further comprises apparatus for measuring an angle of the instrument from vertical.  
   
   
       12 . An offset tool for placing a conductor pipe beneath a platform, comprising: 
 a cylindrical body having an axis, an upper end and a lower end, the lower end being cut in a plane lying at a selected angle to the axis;    a support pipe passing through the cylindrical body and being attached thereto, the support pipe being adapted for coupling to a drill string;    a plurality of gussets on an outside surface of the cylindrical body; and    a plate covering the lower end of the cylindrical body.    
   
   
       13 . The offset tool of  claim 12  further comprising an abrasive area on the plate covering the lower end of the cylindrical body.  
   
   
       14 . The offset tool of  claim 12  wherein the selected angle is in the range from about 20 degrees to about 60 degrees.