BOP with partially equalized ram shafts

A ram assembly for positioning on a BOP body having a passageway therein for receiving an oilfield tubular, the ram assembly comprising:

• a ram housing for sealing with the BOP body and having a ram cavity therein in communication with the passageway in the BOP body, the ram housing including a radially outward end plate;
• a ram piston movably responsive to hydraulic pressure within the ram cavity between an open position and a closed position;
• a ram block for sealing engagement with the oilfield tubular when the ram piston is in the closed position;
• a sleeve-shaped ram shaft interconnecting the ram piston and the ram block;
• a ram shaft seal for sealing between the ram housing and the ram shaft as the ram piston moves between the open position and the closed position;
• the sleeve-shaped ram shaft having a bore therein in fluid communication with the central passageway in the BOP body and extending radially outward to a radially outward end of the ram shaft;
• a ram shaft rod fixedly secured to the ram housing and positioned within the bore in the sleeve-shaped ram shaft, the ram shaft rod extending from the end plate radially toward the ram block;
• and
• a rod seal for sealing between the ram shaft rod and the ram shaft as the ram piston moves between the open position and the closed position, such that fluid pressure in the BOP passageway opposes closing of the ram shaft as a function of a sealing area of the ram shaft seal less the sealing area of the rod seal.

A method of closing first and second radially opposing ram assemblies of a blowout preventer to engage an oilfield tubular, the blowout preventer including a BOP body having a central passageway for receiving the oilfield tubular, first and second ram housings each sealing connected to the BOP body, first and second pistons each movably responsive to hydraulic pressure within the ram housings, first and second ram blocks, first and second ram shafts each interconnecting a respective piston and a respective ram block, and first and second ram shaft seals each for sealing between a respective ram housing and a respective ram shaft as each ram assembly moves between the open and closed positions, the method comprising:

• providing a bore in each ram shaft in fluid communication with the central passageway in the BOP body and extending radially outward from the respective ram seal to a radially outward end of the ram shaft;
• securing first and second ram shaft rods each to a respective ram housing and positioned within the bore in a respective sleeve-shaped ram shaft, each ram shaft rod extending radially from the respective ram housing toward the respective ram block;
• providing first and second rod seals each for sealing between a respective ram shaft rod and a respective ram shaft as each respective ram assembly moves between the open and closed positions;
• and
• pressurizing the first and second ram housings to move the first and second pistons and the first and second ram blocks radially inward, while fluid pressure in the BOP passageway opposes closing of each ram shaft as a function of the sealing area of the respective ram shaft seal less the sealing area of the respective rod seal.