Slot recovery operation can be considered as one of the most time consuming operation. Cut and pull casings, or milling casings have been carried out as typical method of slot recovery. However there are a lot of risks with this typical method such as poor progress of milling, damaging top drive due to high vibration while milling or sudden string jumping up while overpulling and possibility of string stuck caused by poor hole cleaning while milling. We have completed slot recovery operations on numbers of wells, but there were a lot of troubles caused by above mentioned adversaries on rig equipment and taking a lot of time to complete operation.
There are several kinds of new slot recovery technologies that may save rig time and less harmful than conventional method. Casing Pulling Tool (CPT) is one of the new technologies which eliminates or mitigates risks mentioned above. CPT has piston internally and it is activated by applying pressure inside string. CPT is run with casing spear and drill pipes. Once spear is engaged with casing and apply pressure inside drill string, CPT provides pulling force on casing. Pulling force is varied depend on the applied pressure and maximum available pulling force is more than 1,000 kips. Hence upper part of string is anchored at rotary table by slips, pulling force is applied on casing and drill string below rotary table. This means no pulling force is applied on top drive and minimize the chance of getting damage on it.
As an actual case, we could successfully recover 13-3/8" casing by CPT without having any troubles and complete slot recovery operation with saving rig time compared to the conventional methods.
This paper introduces the details about the case mentioned above.