The packer (more accurately described as the'upper completion production packer') is a key piece of downhole equipment in many completions - a sealing device that isolates and contains produced fluids and pressures within the tubing string; it is a well barrier element, usually part of the well's primary well barrier, protecting the casing and creating an A-annulus. The packer is essential to the basic functioning of most wells, injectors or producers. Alternatives to using a production packer include a dynamic seal assembly, a cemented completion and a packerless completion. The slip is a wedge-shaped device with wickers (or teeth) on its face, which penetrate and grip the casing wall when the packer is set. The cone is beveled to match the back of the slip and forms a ramp that drives the slip outward and into the casing wall when setting force is applied to the packer. Once the slips have anchored into the casing wall, additional applied setting force energizes the packing-element system and creates a seal between the packer body and the inside diameter of the casing. Permanent packers can be removed from the wellbore only by milling. The retrievable packer may or may not be resettable, but removal from the wellbore normally does not require milling. Retrieval is usually accomplished by some form of tubing manipulation.