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If a well is dry, or if the hydrocarbons found in it are only in non-commercial quantities, then the well is plugged and abandoned. This process requires the isolation of various formations with cement. Wellsite personnel take particular care to block the reservoir zones and any high-pressure zones that may have been encountered.

In other cases, wells can be suspended with cement plugs set, as just described. At a later date, a producing company may re-enter the well for re-evaluation. In such situations, the cement plugs are simply drilled out, using standard drilling techniques.

However, if the well has successfully tested commercial quantities of hydrocarbons, it is usually completed as a producing well or suspended for completion that will be carried out at a later date.

A completed well has production tubing installed, and the well casing is perforated in the reservoir zone. A system of valves, known in the industry as a christmas tree, is placed at the wellhead on the surface for later hook-up to the production system.

Offshore, a successful well is often plugged and temporarily abandoned, until the oil and gas company can conduct a deliberately scheduled program of production or development drilling from one or more fixed or floating platforms in the field. An exception to this process is for small offshore fields, where subsea completions are installed on individual wells directly on the seafloor, or where small, single-well platforms are utilized. In these cases, the original exploration wells are frequently used as later producers.