Wiper seal assembly
A hydraulically-operated annular blowout preventer, for controlling a wellbore and comprising a wiper seal assembly, is described. The wiper seal assembly comprises a discrete wiper seal, for preventing debris and/or contaminants from the wellbore from entering the hydraulic fluid chamber of the blowout preventer, a discrete pressure seal, positioned below and abutting the wiper seal in the same seal groove, for isolating the hydraulic chamber, and a retainer member for preventing both radial and axial movement of the wiper seal.
1. In a hydraulically operated annular blowout preventer for controlling the issuance of pressurized fluid, containing debris such as solid particles, from a wellbore, comprising:
a U-shaped annular lower housing having upstanding, spaced apart inner and outer walls;
the housing forming a central bore for connection with the wellbore;
the housing containing a vertically actuated piston;
an adapter ring connected to the outer wall and extending toward the inner wall whereby the lower housing and the adapter ring form an annular hydraulic fluid chamber;
the upper end of the inner wall and the adapter ring being spaced apart to define an annular gap;
the lower end of the piston being positioned within the chamber and its upper end extending through the gap;
the inner wall and the adapter ring each forming annular peripheral grooves at the gap;
the improvement comprising a piston seal assembly associated with each groove and comprising, in combination:
a hook-shaped retainer member forming the upper end of each groove, the retainer member having a lateral flange and a lug depending downwardly from the flange;
a discrete wiper seal associated with each retainer member and extending into the upper end of the adjacent groove, the wiper seal having an inner, upwardly extending lip for interlocking with the lug and being operative to seal against the piston, the wiper seal being directly exposed to pressurized wellbore fluid when such fluid is present in the central bore, the retainer member flange and lug being embedded in the wiper seal so that the retainer member functions to secure the wiper seal against both radial and axial movement caused by movement of the piston, the wiper seal further being operative to scrape the surface of the piston as it moves past;
each wiper seal being formed of nitrile rubber having a Shore A durometer hardness of between 85 to 95; and
a discrete pressure seal positioned in each groove, said pressure seal abutting the base of the adjacent wiper seal and the bottom of the groove, said pressure seal being upwardly oriented and having at least two extending legs abutting the base of the adjacent wiper seal and operative to isolate the hydraulic fluid chamber from pressurized wellbore fluid when present in the bore;
wherein the wiper seal functions to prevent debris adhering to the piston from reaching the pressure seal.