Rod lock for ram blowout preventers

Abstract

A blowout preventer to hydraulically seal a wellbore includes a housing configured to be positioned above a wellhead and to surround a drillstring, a plurality of rams positioned perpendicular to an axis of the drillstring to engage the drillstring and hydraulically isolate an annulus between the wellbore and the drillstring when in a closed position, and a roller lock positioned about a thrust rod of each ram configured to maintain the rams in the closed position.

1 . A blowout preventer to hydraulically seal a wellbore, comprising: 
 a housing configured to be positioned above a wellhead and to surround a drillstring;    a plurality of rams positioned perpendicular to an axis of the drillstring, the rams configured to engage the drillstring and hydraulically isolate an annulus between the wellbore and the drillstring from components located above the housing when the rams are a closed position; and    a roller lock positioned about a thrust rod of each ram, the roller locks configured to maintain the rams in the closed position.    
     
     
         2 . The blowout preventer of  claim 1 , wherein the roller lock includes a plurality of spherical rollers in contact with inclined surfaces, the inclined surfaces configured to thrust the spherical rollers into compressive engagement with the thrust rods when the rams are displaced away from the drillstring.  
     
     
         3 . The blowout preventer of  claim 2 , wherein the spherical rollers and the inclined surfaces allow movement of the rams into engagement with the drillstring.  
     
     
         4 . The blowout preventer of  claim 2 , wherein the roller lock includes a release cage configured to retrieve the spherical rollers out of compressive engagement with the thrust rods to allow movement of the rams out of the closed position.  
     
     
         5 . The blowout preventer of  claim 4 , wherein the release cage is also configured to retain the spherical rollers within contoured pockets containing the inclined surfaces.  
     
     
         6 . The blowout preventer of  claim 2 , wherein the inclined surfaces comprise planar surfaces.  
     
     
         7 . The blowout preventer of  claim 2 , wherein the inclined surfaces comprise contoured surfaces.  
     
     
         8 . The blowout preventer of  claim 1 , wherein the roller lock comprises a plurality of cylindrical rollers in contact with inclined planes, the inclined planes configured to thrust the cylindrical rollers into compressive engagement with the thrust rods when the rams are displaced away from the drillstring.  
     
     
         9 . The blowout preventer of  claim 1 , wherein the roller lock includes a release mechanism to allow the rams to be displaced from the closed position.  
     
     
         10 . The blowout preventer of  claim 1 , wherein the roller lock includes a release mechanism actuated when hydraulic pressure is applied to retract the piston.  
     
     
         11 . A locking apparatus to be used with a blowout preventer comprising: 
 a plurality of spherical locking elements to engage and restrict movement of thrust rods connected to rams of the blowout preventer;    a plurality of receptacles for the spherical locking elements, each receptacle including an inclined surface configured to thrust the spherical locking elements into compressive contact with the thrust rods when the operating rams are urged open; and    a release cage to retract and retain the spherical locking elements into the receptacles and to direct them out of compressive contact with the thrust rods when the operating rams are to be opened.    
     
     
         12 . The locking apparatus of  claim 11 , wherein the spherical locking elements permit movement of the operating rams in a direction of closure when in contact with the thrust rods.  
     
     
         13 . The locking apparatus of  claim 11 , wherein the inclined surfaces of the receptacles are planar surfaces.  
     
     
         14 . The locking apparatus of  claim 11 , wherein the inclined surfaces of the receptacles are contoured surfaces.  
     
     
         15 . The locking apparatus of  claim 14 , wherein the contoured surfaces correspond to the spherical locking elements.  
     
     
         16 . The locking apparatus of  claim 11 , wherein the receptacles include pockets into which the spherical locking elements can be fully retracted away from the thrust rods.  
     
     
         17 . The locking apparatus of  claim 11 , wherein the release cage prevents the loss of the spherical locking elements when no tubular objects extend through the blowout preventer.  
     
     
         18 . A method to lock rams of a blowout preventer, comprising: 
 positioning spherical locking elements inside receptacles located adjacent to thrust rods of the rams, wherein the receptacles include inclined surfaces configured to engage the spherical locking elements into the thrust rods when the rams are urged open;    locking the thrust rods with compressive engagement of the spherical locking elements therewith; and    retracting the spherical locking elements into their respective receptacles with a release cage to unlock the rams.    
     
     
         19 . The method of  claim 18 , further comprising: 
 retaining the spherical locking elements in the receptacles with the release cage, wherein the release cage includes apertures to allow the spherical locking elements to contact the thrust rods without falling out of the receptacles.    
     
     
         20 . The method of  claim 18 , wherein the release cage is a single component configured to retract all the spherical locking elements into their respective receptacles.  
     
     
         21 . The method of  claim 18 , wherein the release cage is comprised of a plurality of components, each configured to retract one or more spherical locking elements into their respective receptacles.