No well shall be drilled within the city limits without using mud as the drilling fluid after the setting of surface casing as provided in § 155.15. Prior to the time the well reaches the depth of the first known or encountered oil or gas bearing horizon, the weight of the mud laden drilling fluid shall be at all times maintained at not less than ten pounds per gallon. After the well reaches the depth of the first known or encountered oil or gas bearing horizon, the weight of the mud laden drilling fluid shall be at all times maintained at such weight as will provide a hydrostatic head of not less than 250 pounds per square inch in excess of the formation pressure. In reworking a well, a drilling fluid shall be at all times maintained at such weight as will provide a hydrostatic head of not less than 250 pounds per square inch in excess of the formation pressure.
(Prior Code, § 18-16)