A production packer is a standard component of the completion hardware of oil or gas wells used to provide a seal between the outside of the production tubing and the inside of the casing, liner, or wellbore wall.
Based on its primary use, packers can be divided into two main categories: production packers and service packers. Production packers are those that remain in the well during well production. Service packers are used temporarily during well service activities such as cement squeezing, acidizing, fracturing and well testing.
It is usually run in close to the bottom end of the production tubing and set at a point above the top perforations or sand screens. In wells with multiple reservoir zones, packers are used to isolate the perforations for each zone. In these situations, a sliding sleeve would be used to select which zone to produce. Packers may also be used to protect the casing from pressure and produced fluids, isolate sections of corroded casing, casing leaks or squeezed perforations, and isolate or temporarily abandon producing zones. In waterflooding developments in which water is injected into the reservoir, packers are used in injection wells to isolate the zones into which the water must be injected.
There are occasions in which running a packer may not be desirable. For example, high volume wells that are produced both up the tubing and annulus will not include a packer. Rod pumped wells are not normally run with packers because the associated gas is produced up the annulus. In general, well completions may not incorporate a packer when the annular space is used as a production conduit.
A production packer is designed to grip and seal against the casing ID. Gripping is accomplished with metal wedges called "slips." These components have sharpened, carburized teeth that dig into the metal of the casing. Sealing is accomplished with large, cylindrical rubber elements. In situations where the sealed pressure is very high (above 5,000 psi), metal rings are used on either side of the elements to prevent the rubber from extruding.
A packer is run in the casing on production tubing or wireline. Once the desired depth is reached, the slips and element must be expanded out to contact the casing. Axial loads are applied to push the slips up a ramp and to compress the element, causing it to expand outward. The axial loads are applied either hydraulically, mechanically, or with a slow burning chemical charge.
Most packers are "permanent" and require milling in order to remove them from the casing. The main advantages of permanent packers are lower cost and greater sealing and gripping capabilities.
In situations where a packer must be easily removed from the well, such as secondary recoveries, re-completions, or to change out the production tubing, a retrievable packer must be used. To unset the tool, either a metal ring is sheared or a sleeve is shifted to disengage connecting components. Retrievable packers have a more complicated design and generally lower sealing and gripping capabilities, but after removal and subsequent servicing, they can be reused.