Application of retrieving cemented production casing technology to sidetrack surface casing

Some production platforms have no spare slots to drill adjustment well in Bohai Bay, so it is proposed that some failure wells can be used to sidetrack adjustment wells. Sidetracking from production casing is impossible in some of the wells because of the small size, and it is necessary to sidetrack from surface casing, so it is necessary to retrieve production casing from wellhead to side-tracking point, which is cemented partly. One failure well has been taken as the experiment well to try to retrieve production casing. By designing and manufacturing special washover shoes and optimizing assembly of washover, the sections of production casing, which are concentric and slightly eccentric in surface casing, are washovered and retrieved. By designing and optimizing cutting pilot mill shoes and flat bottom mill shoes, the badly eccentric section of production casing is cut at a higher speed than by ordinary mill shoes. Finally the production casing is successfully retrieved, which meets sidetracking requirement. The technique makes a break in Bohai Bay and can be extended.