Method for Casing Recovery

Abstract

Method of removing casing from a well, in which an annulus between the outside of the casing and the inside of a surrounding downhole body is at least partially filled by debris, the perforated section of casing is washed in casing lengths shorter than the perforation length and an attempt made to pull the casing after each shorter length is washed. If the casing is free after washing only a shorter section of the perforated section of casing then it can be recovered and saves the washing time. A bottom hole assembly is described which includes a downhole power tool to exert a greater force to pull the section of casing between washing steps.

1 . A method of removing casing from a well, in which an annulus between the outside of the casing and the inside of a surrounding downhole body is at least partially filled by debris, comprising the steps:
 (a) determining a casing cutting target depth (CCTD) to provide a section of casing for removal;   (b) cutting the casing at the casing cutting target depth (CCTD);   (c) perforating the section of casing along a perforation length thereof;   (d) washing the annulus along a first length of the section of casing by passing fluid through the perforations, the first length being shorter than the perforation length to clear at least a portion of the debris;   (e) gripping the section of casing;   (f) pulling the section of casing;   (g) in the event that the section of casing is free, pulling the section of casing from the well,   wherein the method includes the step of anchoring a downhole power tool to the surrounding downhole body at a position uphole of the cut section of casing and in step (f) pulling is by exerting a force from the downhole power tool on the section of casing.   
     
     
         2 . The method of removing casing from a well according to  claim 1 , wherein the steps are performed in the order of the steps (a) to (g). 
     
     
         3 . The method of removing casing from a well according to  claim 1 , wherein the step (b) is performed at any point between the steps (a) and (f). 
     
     
         4 . The method of removing casing from a well according to  claim 3 , wherein the step (b) is performed between the steps (c) and (d). 
     
     
         5 . The method of removing casing from a well according to  claim 3 , wherein the step (b) is performed between the steps (d) and (e). 
     
     
         6 . The method of removing casing from a well according to  claim 3 , wherein the step (b) is performed between the steps (e) and (f). 
     
     
         7 . The method of removing casing from a well according to  claim 1 , wherein, in the event that the section of casing is not free, the method includes selecting a second length of the section of casing and repeating the steps (d) to (g) on the second length. 
     
     
         8 . The method of removing casing from a well according to  claim 7 , wherein the method includes selecting subsequent lengths of the section of casing until the section of casing is free and can be pulled from the well. 
     
     
         9 . The method of removing casing from a well according to  claim 1 , wherein the perforation length is a majority of the section of casing. 
     
     
         10 . The method of removing casing from a well according to  claim 1 , wherein the perforation length is a length between a free casing depth and the CCTD. 
     
     
         11 . The method of removing casing from a well according to  claim 7 , wherein the first and second lengths of the section of casing are sequentially located along the perforation length. 
     
     
         12 . The method of removing casing from a well according to  claim 7 , wherein the first and second lengths overlap by at least a portion. 
     
     
         13 . The method of removing casing from a well according to  claim 1 , wherein the steps (e) and (f) are performed between the steps (b) and (c) to see if the cut section of casing can be pulled free without requiring perforation and washing. 
     
     
         14 . The method of removing casing from a well according to  claim 1 , wherein a circulation test is performed during or after the step (b) to provide an indication of the level of debris in the annulus. 
     
     
         15 . The method of removing casing from a well according to  claim 1 , wherein in the step (d) a wash tool is moved along the perforated casing. 
     
     
         16 . The method of removing casing from a well according to  claim 1 , wherein the step (f) includes vibrating the section of casing to assist in freeing the section of casing.