is a very productive oil well, a 7" production tubing might be installed in a larger diameter casing. Gas wells may only require a small 2 ⅞" tubing set in 4 ¾" casing, so the hole might be relatively small. With rank wildcats in geological basins that have not been explored extensively, the first holes might be large enough to provide for a couple of contingency strings of casing. See also Oil Well Extraction of petroleum External links Illustration, Schlumberger Oilfield Glossary Plastik Askı Petroleum production