Preparation of a well for production. Above ground the blow-out preventer is replaced with a production wellhead and other surface facilities are installed. Downhole additional casing, a liner (q.v.), and/or small-diameter tubing (to bring produced fluids to the surface) may be installed. Packers (q.v.) are used to isolate reservoirs. In open-hole completion the casing shoe is just above the reservoir (usually limestone). Liner completion may involve placing a screen or slotted liner below the casing to exclude sand from entering; the region around the liner may be gravel-packed. Casing that has been set through the reservoir may be perforated by shaped charges (jets) or bullets. Production may be stimulated (increased) by fracturing or acidizing (q.v.).