Well pressure compensation for blowout preventers

摘要

A method and apparatus of compensating for the closing force on a blowout preventer caused by well pressure for reducing the wear on the blowout preventer sealing element when moving a drill string through a closed blowout preventer. A hydraulic opening force is applied to the blowout preventer which is actuated by and is proportional to the well pressure. A compensating line is connected between the blowout preventer fluid supply line and the blowout preventer opening line. A control valve is provided in the compensating lines for applying an opening force on the blowout preventer and a pilot control pressure regulator is provided in the compensating line for limiting the compensating pressure. The pilot control line is connected between the regulator and the well pressure in the blowout preventer whereby the output pressure is proportional to the well pressure for compensating for the closing force on the blowout preventer caused by the well pressure.