Expandable Liner Hanger Milling: North Sea Case Histories

Abstract

Liner hangers are designed to provide seal and anchoring capability for installation of casing. The expandable liner hanger has a uniform body with no moving parts that will expand into the parent casing and provide a permanent and reliable seal. Unfortunately, drilling a well can be problematic in certain situations, resulting in loss of a section or the entire wellbore. This leads to additional well construction costs from milling casing, running a sidetrack, or drilling a new section. Retrieving sections of the installed casing can reduce the cost but may require removal of the liner hanger. While milling conventional hanger systems has been performed before, there has been little experience with milling an expandable liner hanger. This paper discusses the first two cases in the North Sea where expandable liner hangers required milling because of drilling issues below the liners. The milling of the expandable hanger bodies provided several benefits when compared to the milling of conventional liner hanger systems. The benefits included reduced rig time and non-productive time (NPT), less well debris than when milling movable parts/slips, and no parent-casing slip damage. In the first case, during running of an expandable liner hanger, the hanger disconnected and was lost. A backup hanger was run, cemented, and set. Options for correcting the situation will be discussed in this paper along with why milling was considered the most feasible option. In the actual job, 10.5 feet of hanger were milled out in less time than anticipated. In the second case, a liner and expandable hanger were set in a long, extended mature reservoir. During drilling of the next section, the drill string became stuck, requiring a sidetrack. Milling of the expandable liner hanger system enabled the operator to pull the liner and perform the needed sidetrack.

Numerical Analysis on the Expanding Process of Expandable Casing and Contact Evaluation of its Threaded Connection

“…Research and applications on expandable casing have been reported by various references [2,3,4,5,6,7,8,9]. Reference [10] presented their work on evaluating the sealing integrity of an expandable casing section, with specific focus on the sealing ring.…”