Permian Basin operators are using a cup-type tool system to economically recomplete old wells that have deteriorated casing. The system employs high pressure cups, similar to those used on retrievable bridge plugs, to pack off the annulus below the damaged portion of the old casing. New casing installed inside the old casing is limited by the collar OD the old casing will permit.
This tool system was developed in response to the recent oil price downturn, which prompted many operators to plug and abandon water injection wells rather than repair casing leaks with squeeze cementing processes. The technique of recompletion with smaller diameter casing inside the old casing evolved, requiring installation of a barrier at the bottom of the new casing to prevent cementing off the injection formation. Barriers of many forms were developed.
Cast iron bridge plug set below new casing, inside old casing. Expensive and difficult to drill out through new casing.
Mechanically set packer system to pack off annulus. Economical but capable of holding only about 1000 psi differential pressure.
Inflatable packer system. More costly than mechanical, but rated for high differential pressure.
Both 2 and 3 above require use of small ID inner casing due to the packer configuration.
Cup-type packoff systems offer the following advantages.
Size is limited only by casing collar OD.
Well can be put back on production without drilling out.
A slotted liner can be run below packoff tool.
Tool can be passed through damaged casing without affecting its capability.
Subject paper presents (1) discussion of barrier systems in use in the Permian Basin, (2) design variations of the new system, (3) job design considerations, and (4) case histories of Permian Basin wells in which the system was used to recomplete wells having damaged casing.
Many injection wells in the Permian Basin have casings in some degree of deterioration due to corrosion from brines and other fluids. These conditions were brought on by a variety of events, including performance of inadequate primary cement jobs at the time of completion. Completion practices prevalent in the 1950's and earlier placed cement at the surface and bottom of the casing, but left 2000 ft or more uncemented between these cemented areas. Brines corroded the casing severely in the uncemented spans.
Squeeze cementing techniques have been successfully used to restore wellbore integrity; foam cements and a special chemical that gels on contact with brine have been used by Garvin and Creel to repair these casings.
As a result of the recent oil price decline, many owners in the Permian Basin have elected to abandon damaged water injection wells rather than restore the casing by squeeze cementing.