Page 172 - Well Control for Completions and Interventions

164 Well Control for Completions and Interventions

Figure 4.16 Cutaway view of a Cameron “U” ram preventer. This is the most widely
used of all the ram preventer types available.

Figure 4.17 Simplified diagram of a ram preventer.

shutting in the well was needed. This led to the development of hydrauli-
cally operated ram preventers. Modern ram preventers normally close
more quickly than annular preventers as they require less hydraulic fluid.
The API RP 53 stipulates a closure time of 30 seconds for ram BOP clo-
sure (land and platform) and 45 seconds for subsea applications. Most will
easily beat this. As well as being able to shut the well in much more
quickly than a manually operated system, hydraulics have the obvious
benefit of remote operation. There is no need to expose the drill crew to
the risks associated with closing in the well manually.
Fig. 4.17 is a simplified illustration showing the normal configuration
of hydraulic chamber and hydraulic piston used in most ram type BOPs.
Pressure applied to the opening or closing chamber is used to move the
piston, opening or closing the preventer.
When rams are closed, hydraulic pressure acts on the surface area of
the operating piston. Well pressure acts on the surface area of the ram
shaft in opposition to the opening force. Since the piston area is larger
than the shaft area, closure force provided by the hydraulic pressure will
be proportionally higher than the opening force from well pressure. The