(a) Plugging in uncased hole. In uncased portions of wells, cement plugs shall be placed to extend from total depth or at least 100 feet below each oil or gas zone, whichever is less, to at least 100 feet above the top of each zone, and a cement plug at least 200 feet long shall be placed across an intrazone freshwater-saltwater interface or opposite impervious strata between fresh- and saltwater zones so as to confine the fluids in the strata in which they are found and to prevent them from escaping into other strata.

(b) Isolation of open hole. Where there is open hole immediately below casing, a cement plug shall be placed in the deepest cemented casing string from total depth or at least 100 feet below the casing shoe, whichever is less to at least 100 feet above the casing shoe.

(c) Plugging perforated intervals. A cement plug shall be placed opposite all perforations extending to a minimum of 100 feet above the perforated intervals, liner top, cementing point, or zone, whichever is higher.

(d) Isolating zones behind cemented casing. Inside cemented casing, a cement plug at least 100 feet long shall be placed above each oil or gas zone and above the shoe of the intermediate or second surface casing; a cement plug at least 200 feet long shall also be placed across an intrazone freshwater-saltwater interface or opposite impervious strata between fresh- and saltwater zones.