Slot Recovery Method

Abstract

The present concept is a method of removing casings from a well in the oil industry, which may be used for slot recovery. The method involves running an internal cutter down the production casing to cut through a preselected number of existing casings at one or more predetermined depths before drilling around the outermost preselected casing with a hollow drill bit. The hollow drill bit drills through the preselected outermost casing cement to the predetermined depth before a removal tool is used to remove the existing casings to the predetermined depth. These steps may be repeated using appropriately sized hollow drill bits and casings to drill around the next preselected outermost casings to the next predetermined depth, continuously removing the existing casings until all desired existing casings are removed.

1 . A method of removing one or more casings cemented in a well comprising the steps of:
 a) running an internal cutter down a production casing to laterally cut through a preselected number of casings in a casing string at a first predetermined depth;   b) drilling around the outermost casing of a first number of casings of the preselected number of casings with a hollow drill bit which is attached to a core over casing, the hollow drill hit drilling through the casing cement around the outermost casing down to the first predetermined depth; and   c) attaching a removal tool to the first number of casings and removing the first number of casings from the first predetermined depth to the surface.   
     
     
         2 . The method of  claim 1 , wherein in step a), the lateral cutting is performed at multiple predetermined depths, and further comprising after step c):
 repeating steps b) and c) using appropriately sized hollow drill bits and core over casings to drill around the outermost casing of the next number of casings of the preselected number of casings to a next predetermined depth of the multiple predetermined depths to continue to remove casings until the preselected number of casings are removed.   
     
     
         3 . The method of  claim 1 , further including after step c), placing new casing. 
     
     
         4 . The method of  claim 1 , wherein the removal tool is a casing spear. 
     
     
         5 . The method of  claim 1 , wherein the internal cutter is a multi-string cutter for milling laterally through the preselected number of casings in a multiple string of casings. 
     
     
         6 . The method of  claim 1 , wherein the preselected number of casings are multi-string casings selected from among production casings, intermediate casings and conductor casings to at least the first predetermined depth. 
     
     
         7 . The method of  claim 1 , wherein the preselected number of casings comprises a production casing and an intermediate casing, leaving a conductor casing in place to at least the first predetermined depth. 
     
     
         8 . The method of  claim 1 , wherein the preselected number of casings comprises a production casing, leaving a conductor casing in place to at least the first predetermined depth. 
     
     
         9 . The method of  claim 1 , wherein the preselected number of casings comprises a production casing, an intermediate casing and a conductor casing, thereby removing all casings to at least the first predetermined depth. 
     
     
         10 . The method of  claim 1 , wherein the hollow drill bit and core over casing are connected to a drill string using a cross over sub assembly. 
     
     
         11 . The method of  claim 1 , wherein the first predetermined depth is at a conductor casing depth. 
     
     
         12 . The method of  claim 2 , wherein the first predetermined depth is at a conductor casing depth and the next predetermined depth is an intermediate cut. 
     
     
         13 . The method of  claim 9 , further including the step of:
 d) installing a cement plug above the last existing casings.   
     
     
         14 . The method of  claim 13 , further including the step of:
 e) installing a new conductor shoe on the cement plug and installing new conductor casing.   
     
     
         15 . The method of  claim 13 , further including the step of:
 e) drilling a hole through the cement plug and placing new casing.   
     
     
         16 . The method of  claim 13 , further including the step of:
 e) drilling a hole through the cement plug by side tracking below the new conductor shoe.   
     
     
         17 . The method of  claim 1 , further including prior to step a):
 a′) removing all casing to the sea bed.   
     
     
         18 . The method of  claim 1 , further including the step of:
 d) drilling a new hole by side tracking through a conductor casing.   
     
     
         19 . The method of  claim 1 , wherein the method is used for slot recovery. 
     
     
         20 . The method of  claim 1 , wherein the well is an offshore well.