The current oil and gas industry uncertainty encourages innovative, efficient, and simple drilling and workover solutions. Challenging and problematic formations cause various design complications and operational risk. These include lost circulation, well control incidents, high density drilling fluid systems, tool design limitations, etc. Such troubles can also lead to liner and casing leaks downhole and eventually undesired surface pressure buildups across the tubing-casing and casing-casing annuli.
The case study well was drilled and completed, but prior to production a tubing-casing annular pressure of 6,500 psi was recorded. With two liners in the well casing designs (4-1/2 in. and 7 in.), a well leak was suspected to be at the top of the 7 in. liner as it was laying across a deep and over-pressurized formation with a 152.5 pcf gradient. After commencing the workover operations and due to downhole leaks and washouts, the well had to be killed off-bottom with 160 pcf manganese tetroxide (Mn3O4) mud. The well was fully decompleted, except for the production packer, which was left in hole. Investigation and diagnostic operations showed leaking 7 in. liner body and liner top packer.
To repair the leaking 7 in. liner, the team introduced an innovative design with a 4-1/2 in. x 7 in. tapered scab liner to sting into the newly installed repair packer and extend above the existing 7 in. top of liner to set on the 9-5/8 in. casing, and so cover the leaks. A mechanical 7 in. x 9-5/8 in. hanger and liner top packer system was deployed to allow for cementing the scab liner then setting these mechanical tools, where hydraulically actuated systems were impractical. Due to the high kill mud density of 160 pcf, a special 165 pcf Mn3O4 -Hematite cement recipe was adapted. Despite the high slurry density, this formulation allowed for optimal mixing, pumping, and leak isolation operations.
This paper will highlight the case study well history and challenges leading to liner leaks while emphasizing the nature of the over-pressurized formation. It will demonstrate the mechanical tapered scab liner design and deployment procedures in comparison to the conventional scab and tie-back liner jobs.