Casing reaming assembly

Abstract

Apparatus and methods for drilling out from a casing string in a borehole. A reaming assembly is introduced into the borehole and fixed at a predetermined location. A drillable collar is interposed between the reaming assembly and a casing. A drilling assembly introduced into the casing and is then positioned so as to drill through the drillable collar at a predetermined angle into a formation surrounding the borehole.

1 . A method for drilling out from a casing string in a borehole, the method comprising the steps of: introducing a reaming assembly into the borehole to a predetermined location; fixing the reaming assembly in position, wherein a drillable collar is attached between the reaming assembly and a casing introducing a drilling assembly into the casing; and positioning the drilling assembly so as to drill through the drillable collar at a predetermined angle into the formation surrounding the borehole.  
   
   
       2 . A method as claimed in  claim 1  wherein the point at which the drilling assembly enters the formation surrounding the borehole is at least in part determined by the thickness of the drillable collar through which the drilling assembly drills.  
   
   
       3 . A method as claimed in  claim 1  wherein the drilling assembly is a bent housing motor assembly with a drill bit.  
   
   
       4 . A method as claimed in  claim 1  wherein the drilling assembly is a rotary steerable system with a drill bit.  
   
   
       5 . A method as claimed in  claim 3 , wherein the drill bit comprises a PDC drill bit.  
   
   
       6 . A method as claimed in  claim 1  wherein the reaming assembly is fixed in place using cement.  
   
   
       7 . Apparatus for drilling out from a casing string in a borehole, the apparatus comprising a drillable collar attached between a reaming assembly and a casing string.  
   
   
       8 . Apparatus as claimed in  claim 5  wherein the drillable collar is provided with a borehole extending from the reaming assembly to the casing string.  
   
   
       9 . Apparatus as claimed in  claim 5  wherein the drillable collar is made from aluminum.