Typically, Liner-hanger systems have relied upon the primary cement job to provide sealing of the liner/casing overlap. Liner top packers have been run either integrally with the liner hanger or separately in a second trip. In certain applications, cementing the complete liner or obtaining a primary cement seal at the liner top has not been achievable. In these situations, a liner top packer must be used as the primary seal. In cases where the top of cement is above the overlap but below the hanger, the liner-top packer is used as a back-up seal for the overlap.
Almost all liner-top packers are run integrally with the liner hanger and are set through the application of weight applied through the drill-pipe or landing string. The capability of the liner-top packer to seal at the maximum pressures rated requires that sufficient setting force of up to 80,000 lbf be applied through the drill-pipe to the packer mechanism. Recently, work performed in Latin America showed the limitations of this process when used in shallow liner-top installations where the available drill string weight is not available.
A secondary tie-back packer design offers a conventional alternative to an integral packer design, but installation of this type of configuration requires at least two extra trips into the wellbore and picking up of a string of large drill collars in order to have capability to supply the significant setting force required.
A solution that resolved the problems discussed above was an expandable liner hanger, which allows setting force to be applied locally to the hanger body through hydraulic pressure. The setting force for the packer was measurable and consistent. The expandable liner hanger was used in two subsequent jobs, and all three jobs were successful, saving the operator several days of rig time.
The case history discussion and system description presented in this paper will verify the flexibility and integrity of the expandable liner hanger.
Historically, problems obtaining a good primary cement job at the top of liner have been associated with the installation of liners in oil and gas wells. Innovations in technology to provide backup for the primary cement job had initiated the development of the conventional liner-top packer, which is mechanically set by applying weight down or by combined weight down and rotation strategies. These setting techniques have been well accepted by the industry. However, in some cases, string weight has not been sufficient to apply the minimum recommended weight to energize the element; in other cases, due to well deviation and or drag, the pipe weight deployed has not been capable of acting effectively enough on the liner-top packer to provide the required seal.
Conventional liner tops have been prone to failure, and a formal study performed among operators in the Gulf of Mexico in 1999 identified several problems associated with liner tops during the 18 months prior to the survey1 (Fig. 1). 2,3 Primary failure modes were:
Liner top integrity-lap squeezes
Packer/hanger/centralization issues-preset, or failure to set, failure to seal
Shoe integrity-shoe squeezes
